This document is a reference manual for the LLVM assembly language. LLVM is a Static Single Assignment (SSA) based representation that provides type safety, low-level operations, flexibility, and the capability of representing 'all' high-level languages cleanly. It is the common code representation used throughout all phases of the LLVM compilation strategy.
The LLVM code representation is designed to be used in three different forms: as an in-memory compiler IR, as an on-disk bitcode representation (suitable for fast loading by a Just-In-Time compiler), and as a human readable assembly language representation. This allows LLVM to provide a powerful intermediate representation for efficient compiler transformations and analysis, while providing a natural means to debug and visualize the transformations. The three different forms of LLVM are all equivalent. This document describes the human readable representation and notation.
The LLVM representation aims to be light-weight and low-level while being expressive, typed, and extensible at the same time. It aims to be a "universal IR" of sorts, by being at a low enough level that high-level ideas may be cleanly mapped to it (similar to how microprocessors are "universal IR's", allowing many source languages to be mapped to them). By providing type information, LLVM can be used as the target of optimizations: for example, through pointer analysis, it can be proven that a C automatic variable is never accessed outside of the current function... allowing it to be promoted to a simple SSA value instead of a memory location.
It is important to note that this document describes 'well formed' LLVM assembly language. There is a difference between what the parser accepts and what is considered 'well formed'. For example, the following instruction is syntactically okay, but not well formed:
%x = add i32 1, %x
...because the definition of %x does not dominate all of its uses. The LLVM infrastructure provides a verification pass that may be used to verify that an LLVM module is well formed. This pass is automatically run by the parser after parsing input assembly and by the optimizer before it outputs bitcode. The violations pointed out by the verifier pass indicate bugs in transformation passes or input to the parser.
LLVM identifiers come in two basic types: global and local. Global identifiers (functions, global variables) begin with the @ character. Local identifiers (register names, types) begin with the % character. Additionally, there are three different formats for identifiers, for different purposes:
LLVM requires that values start with a prefix for two reasons: Compilers don't need to worry about name clashes with reserved words, and the set of reserved words may be expanded in the future without penalty. Additionally, unnamed identifiers allow a compiler to quickly come up with a temporary variable without having to avoid symbol table conflicts.
Reserved words in LLVM are very similar to reserved words in other languages. There are keywords for different opcodes ('add', 'bitcast', 'ret', etc...), for primitive type names ('void', 'i32', etc...), and others. These reserved words cannot conflict with variable names, because none of them start with a prefix character ('%' or '@').
Here is an example of LLVM code to multiply the integer variable '%X' by 8:
The easy way:
%result = mul i32 %X, 8
After strength reduction:
%result = shl i32 %X, i8 3
And the hard way:
This last way of multiplying %X by 8 illustrates several important lexical features of LLVM:
...and it also shows a convention that we follow in this document. When demonstrating instructions, we will follow an instruction with a comment that defines the type and name of value produced. Comments are shown in italic text.
LLVM programs are composed of "Module"s, each of which is a translation unit of the input programs. Each module consists of functions, global variables, and symbol table entries. Modules may be combined together with the LLVM linker, which merges function (and global variable) definitions, resolves forward declarations, and merges symbol table entries. Here is an example of the "hello world" module:
; Declare the string constant as a global constant... @.LC0 = internal constant [13 x i8] c"hello world\0A\00" ; [13 x i8]* ; External declaration of the puts function declare i32 @puts(i8 *) ; i32(i8 *)* ; Definition of main function define i32 @main() { ; i32()* ; Convert [13 x i8]* to i8 *... %cast210 = getelementptr [13 x i8]* @.LC0, i64 0, i64 0 ; i8 * ; Call puts function to write out the string to stdout... call i32 @puts(i8 * %cast210) ; i32 ret i32 0
}
This example is made up of a global variable named ".LC0", an external declaration of the "puts" function, and a function definition for "main".
In general, a module is made up of a list of global values, where both functions and global variables are global values. Global values are represented by a pointer to a memory location (in this case, a pointer to an array of char, and a pointer to a function), and have one of the following linkage types.
All Global Variables and Functions have one of the following types of linkage:
The next two types of linkage are targeted for Microsoft Windows platform only. They are designed to support importing (exporting) symbols from (to) DLLs (Dynamic Link Libraries).
__imp_
and the function or variable name.
__imp_
and the function or variable
name.
For example, since the ".LC0" variable is defined to be internal, if another module defined a ".LC0" variable and was linked with this one, one of the two would be renamed, preventing a collision. Since "main" and "puts" are external (i.e., lacking any linkage declarations), they are accessible outside of the current module.
It is illegal for a function declaration to have any linkage type other than "externally visible", dllimport or extern_weak.
Aliases can have only external, internal, weak or weak_odr linkages.
LLVM functions, calls and invokes can all have an optional calling convention specified for the call. The calling convention of any pair of dynamic caller/callee must match, or the behavior of the program is undefined. The following calling conventions are supported by LLVM, and more may be added in the future:
More calling conventions can be added/defined on an as-needed basis, to support pascal conventions or any other well-known target-independent convention.
All Global Variables and Functions have one of the following visibility styles:
LLVM IR allows you to specify name aliases for certain types. This can make it easier to read the IR and make the IR more condensed (particularly when recursive types are involved). An example of a name specification is:
%mytype = type { %mytype*, i32 }
You may give a name to any type except "void". Type name aliases may be used anywhere a type is expected with the syntax "%mytype".
Note that type names are aliases for the structural type that they indicate, and that you can therefore specify multiple names for the same type. This often leads to confusing behavior when dumping out a .ll file. Since LLVM IR uses structural typing, the name is not part of the type. When printing out LLVM IR, the printer will pick one name to render all types of a particular shape. This means that if you have code where two different source types end up having the same LLVM type, that the dumper will sometimes print the "wrong" or unexpected type. This is an important design point and isn't going to change.
Global variables define regions of memory allocated at compilation time instead of run-time. Global variables may optionally be initialized, may have an explicit section to be placed in, and may have an optional explicit alignment specified. A variable may be defined as "thread_local", which means that it will not be shared by threads (each thread will have a separated copy of the variable). A variable may be defined as a global "constant," which indicates that the contents of the variable will never be modified (enabling better optimization, allowing the global data to be placed in the read-only section of an executable, etc). Note that variables that need runtime initialization cannot be marked "constant" as there is a store to the variable.
LLVM explicitly allows declarations of global variables to be marked constant, even if the final definition of the global is not. This capability can be used to enable slightly better optimization of the program, but requires the language definition to guarantee that optimizations based on the 'constantness' are valid for the translation units that do not include the definition.
As SSA values, global variables define pointer values that are in scope (i.e. they dominate) all basic blocks in the program. Global variables always define a pointer to their "content" type because they describe a region of memory, and all memory objects in LLVM are accessed through pointers.
A global variable may be declared to reside in a target-specifc numbered address space. For targets that support them, address spaces may affect how optimizations are performed and/or what target instructions are used to access the variable. The default address space is zero. The address space qualifier must precede any other attributes.
LLVM allows an explicit section to be specified for globals. If the target supports it, it will emit globals to the section specified.
An explicit alignment may be specified for a global. If not present, or if the alignment is set to zero, the alignment of the global is set by the target to whatever it feels convenient. If an explicit alignment is specified, the global is forced to have at least that much alignment. All alignments must be a power of 2.
For example, the following defines a global in a numbered address space with an initializer, section, and alignment:
@G = addrspace(5) constant float 1.0, section "foo", align 4
LLVM function definitions consist of the "define" keyord, an optional linkage type, an optional visibility style, an optional calling convention, a return type, an optional parameter attribute for the return type, a function name, a (possibly empty) argument list (each with optional parameter attributes), optional function attributes, an optional section, an optional alignment, an optional garbage collector name, an opening curly brace, a list of basic blocks, and a closing curly brace. LLVM function declarations consist of the "declare" keyword, an optional linkage type, an optional visibility style, an optional calling convention, a return type, an optional parameter attribute for the return type, a function name, a possibly empty list of arguments, an optional alignment, and an optional garbage collector name.
A function definition contains a list of basic blocks, forming the CFG (Control Flow Graph) for the function. Each basic block may optionally start with a label (giving the basic block a symbol table entry), contains a list of instructions, and ends with a terminator instruction (such as a branch or function return).
The first basic block in a function is special in two ways: it is immediately executed on entrance to the function, and it is not allowed to have predecessor basic blocks (i.e. there can not be any branches to the entry block of a function). Because the block can have no predecessors, it also cannot have any PHI nodes.
LLVM allows an explicit section to be specified for functions. If the target supports it, it will emit functions to the section specified.
An explicit alignment may be specified for a function. If not present, or if the alignment is set to zero, the alignment of the function is set by the target to whatever it feels convenient. If an explicit alignment is specified, the function is forced to have at least that much alignment. All alignments must be a power of 2.
Aliases act as "second name" for the aliasee value (which can be either function, global variable, another alias or bitcast of global value). Aliases may have an optional linkage type, and an optional visibility style.
@<Name> = alias [Linkage] [Visibility] <AliaseeTy> @<Aliasee>
The return type and each parameter of a function type may have a set of parameter attributes associated with them. Parameter attributes are used to communicate additional information about the result or parameters of a function. Parameter attributes are considered to be part of the function, not of the function type, so functions with different parameter attributes can have the same function type.
Parameter attributes are simple keywords that follow the type specified. If multiple parameter attributes are needed, they are space separated. For example:
declare i32 @printf(i8* noalias nocapture, ...) declare i32 @atoi(i8 zeroext) declare signext i8 @returns_signed_char()
Note that any attributes for the function result (nounwind, readonly) come immediately after the argument list.
Currently, only the following parameter attributes are defined:
Each function may specify a garbage collector name, which is simply a string.
define void @f() gc "name" { ...
The compiler declares the supported values of name. Specifying a collector which will cause the compiler to alter its output in order to support the named garbage collection algorithm.
Function attributes are set to communicate additional information about a function. Function attributes are considered to be part of the function, not of the function type, so functions with different parameter attributes can have the same function type.
Function attributes are simple keywords that follow the type specified. If multiple attributes are needed, they are space separated. For example:
define void @f() noinline { ... } define void @f() alwaysinline { ... } define void @f() alwaysinline optsize { ... } define void @f() optsize
If a function that has an ssp attribute is inlined into a function that doesn't have an ssp attribute, then the resulting function will have an ssp attribute.
If a function that has an sspreq attribute is inlined into a function that doesn't have an sspreq attribute or which has an ssp attribute, then the resulting function will have an sspreq attribute.
Modules may contain "module-level inline asm" blocks, which corresponds to the GCC "file scope inline asm" blocks. These blocks are internally concatenated by LLVM and treated as a single unit, but may be separated in the .ll file if desired. The syntax is very simple:
module asm "inline asm code goes here" module asm "more can go here"
The strings can contain any character by escaping non-printable characters. The escape sequence used is simply "\xx" where "xx" is the two digit hex code for the number.
The inline asm code is simply printed to the machine code .s file when assembly code is generated.
A module may specify a target specific data layout string that specifies how data is to be laid out in memory. The syntax for the data layout is simply:
target datalayout = "layout specification"
The layout specification consists of a list of specifications separated by the minus sign character ('-'). Each specification starts with a letter and may include other information after the letter to define some aspect of the data layout. The specifications accepted are as follows:
When constructing the data layout for a given target, LLVM starts with a default set of specifications which are then (possibly) overriden by the specifications in the datalayout keyword. The default specifications are given in this list:
When LLVM is determining the alignment for a given type, it uses the following rules:
The LLVM type system is one of the most important features of the intermediate representation. Being typed enables a number of optimizations to be performed on the intermediate representation directly, without having to do extra analyses on the side before the transformation. A strong type system makes it easier to read the generated code and enables novel analyses and transformations that are not feasible to perform on normal three address code representations.
The types fall into a few useful classifications:
| Classification | Types |
|---|---|
| integer | i1, i2, i3, ... i8, ... i16, ... i32, ... i64, ... |
| floating point | float, double, x86_fp80, fp128, ppc_fp128 |
| first class | integer, floating point, pointer, vector, structure, array, label. |
| primitive | label, void, floating point. |
| derived | integer, array, function, pointer, structure, packed structure, vector, opaque. |
The first class types are perhaps the most important. Values of these types are the only ones which can be produced by instructions, passed as arguments, or used as operands to instructions.
The primitive types are the fundamental building blocks of the LLVM system.
| Type | Description |
|---|---|
| float | 32-bit floating point value |
| double | 64-bit floating point value |
| fp128 | 128-bit floating point value (112-bit mantissa) |
| x86_fp80 | 80-bit floating point value (X87) |
| ppc_fp128 | 128-bit floating point value (two 64-bits) |
The void type does not represent any value and has no size.
void
The label type represents code labels.
label
The real power in LLVM comes from the derived types in the system. This is what allows a programmer to represent arrays, functions, pointers, and other useful types. Note that these derived types may be recursive: For example, it is possible to have a two dimensional array.
The integer type is a very simple derived type that simply specifies an arbitrary bit width for the integer type desired. Any bit width from 1 bit to 2^23-1 (about 8 million) can be specified.
iN
The number of bits the integer will occupy is specified by the N value.
| i1 | a single-bit integer. |
| i32 | a 32-bit integer. |
| i1942652 | a really big integer of over 1 million bits. |
Note that the code generator does not yet support large integer types to be used as function return types. The specific limit on how large a return type the code generator can currently handle is target-dependent; currently it's often 64 bits for 32-bit targets and 128 bits for 64-bit targets.
The array type is a very simple derived type that arranges elements sequentially in memory. The array type requires a size (number of elements) and an underlying data type.
[<# elements> x <elementtype>]
The number of elements is a constant integer value; elementtype may be any type with a size.
| [40 x i32] | Array of 40 32-bit integer values. |
| [41 x i32] | Array of 41 32-bit integer values. |
| [4 x i8] | Array of 4 8-bit integer values. |
Here are some examples of multidimensional arrays:
| [3 x [4 x i32]] | 3x4 array of 32-bit integer values. |
| [12 x [10 x float]] | 12x10 array of single precision floating point values. |
| [2 x [3 x [4 x i16]]] | 2x3x4 array of 16-bit integer values. |
Note that 'variable sized arrays' can be implemented in LLVM with a zero length array. Normally, accesses past the end of an array are undefined in LLVM (e.g. it is illegal to access the 5th element of a 3 element array). As a special case, however, zero length arrays are recognized to be variable length. This allows implementation of 'pascal style arrays' with the LLVM type "{ i32, [0 x float]}", for example.
Note that the code generator does not yet support large aggregate types to be used as function return types. The specific limit on how large an aggregate return type the code generator can currently handle is target-dependent, and also dependent on the aggregate element types.
The function type can be thought of as a function signature. It consists of a return type and a list of formal parameter types. The return type of a function type is a scalar type, a void type, or a struct type. If the return type is a struct type then all struct elements must be of first class types, and the struct must have at least one element.
<returntype list> (<parameter list>)
...where '<parameter list>' is a comma-separated list of type specifiers. Optionally, the parameter list may include a type ..., which indicates that the function takes a variable number of arguments. Variable argument functions can access their arguments with the variable argument handling intrinsic functions. '<returntype list>' is a comma-separated list of first class type specifiers.
| i32 (i32) | function taking an i32, returning an i32 |
| float (i16 signext, i32 *) * | Pointer to a function that takes an i16 that should be sign extended and a pointer to i32, returning float. |
| i32 (i8*, ...) | A vararg function that takes at least one pointer to i8 (char in C), which returns an integer. This is the signature for printf in LLVM. |
| {i32, i32} (i32) | A function taking an i32, returning two i32 values as an aggregate of type { i32, i32 } |
The structure type is used to represent a collection of data members together in memory. The packing of the field types is defined to match the ABI of the underlying processor. The elements of a structure may be any type that has a size.
Structures are accessed using 'load and 'store' by getting a pointer to a field with the 'getelementptr' instruction.
{ <type list> }
| { i32, i32, i32 } | A triple of three i32 values |
| { float, i32 (i32) * } | A pair, where the first element is a float and the second element is a pointer to a function that takes an i32, returning an i32. |
Note that the code generator does not yet support large aggregate types to be used as function return types. The specific limit on how large an aggregate return type the code generator can currently handle is target-dependent, and also dependent on the aggregate element types.
The packed structure type is used to represent a collection of data members together in memory. There is no padding between fields. Further, the alignment of a packed structure is 1 byte. The elements of a packed structure may be any type that has a size.
Structures are accessed using 'load and 'store' by getting a pointer to a field with the 'getelementptr' instruction.
< { <type list> } >
| < { i32, i32, i32 } > | A triple of three i32 values |
| < { float, i32 (i32)* } > | A pair, where the first element is a float and the second element is a pointer to a function that takes an i32, returning an i32. |
As in many languages, the pointer type represents a pointer or reference to another object, which must live in memory. Pointer types may have an optional address space attribute defining the target-specific numbered address space where the pointed-to object resides. The default address space is zero.
Note that LLVM does not permit pointers to void (void*) nor does it permit pointers to labels (label*). Use i8* instead.
<type> *
| [4 x i32]* | A pointer to array of four i32 values. |
| i32 (i32 *) * | A pointer to a function that takes an i32*, returning an i32. |
| i32 addrspace(5)* | A pointer to an i32 value that resides in address space #5. |
A vector type is a simple derived type that represents a vector of elements. Vector types are used when multiple primitive data are operated in parallel using a single instruction (SIMD). A vector type requires a size (number of elements) and an underlying primitive data type. Vectors must have a power of two length (1, 2, 4, 8, 16 ...). Vector types are considered first class.
< <# elements> x <elementtype> >
The number of elements is a constant integer value; elementtype may be any integer or floating point type.
| <4 x i32> | Vector of 4 32-bit integer values. |
| <8 x float> | Vector of 8 32-bit floating-point values. |
| <2 x i64> | Vector of 2 64-bit integer values. |
Note that the code generator does not yet support large vector types to be used as function return types. The specific limit on how large a vector return type codegen can currently handle is target-dependent; currently it's often a few times longer than a hardware vector register.
Opaque types are used to represent unknown types in the system. This corresponds (for example) to the C notion of a forward declared structure type. In LLVM, opaque types can eventually be resolved to any type (not just a structure type).
opaque
| opaque | An opaque type. |
An "up reference" allows you to refer to a lexically enclosing type without requiring it to have a name. For instance, a structure declaration may contain a pointer to any of the types it is lexically a member of. Example of up references (with their equivalent as named type declarations) include:
{ \2 * } %x = type { %x* } { \2 }* %y = type { %y }* \1* %z = type %z*
An up reference is needed by the asmprinter for printing out cyclic types when there is no declared name for a type in the cycle. Because the asmprinter does not want to print out an infinite type string, it needs a syntax to handle recursive types that have no names (all names are optional in llvm IR).
\<level>
The level is the count of the lexical type that is being referred to.
| \1* | Self-referential pointer. |
| { { \3*, i8 }, i32 } | Recursive structure where the upref refers to the out-most structure. |
LLVM has several different basic types of constants. This section describes them all and their syntax.
The one non-intuitive notation for constants is the hexadecimal form of floating point constants. For example, the form 'double 0x432ff973cafa8000' is equivalent to (but harder to read than) 'double 4.5e+15'. The only time hexadecimal floating point constants are required (and the only time that they are generated by the disassembler) is when a floating point constant must be emitted but it cannot be represented as a decimal floating point number in a reasonable number of digits. For example, NaN's, infinities, and other special values are represented in their IEEE hexadecimal format so that assembly and disassembly do not cause any bits to change in the constants.
When using the hexadecimal form, constants of types float and double are represented using the 16-digit form shown above (which matches the IEEE754 representation for double); float values must, however, be exactly representable as IEE754 single precision. Hexadecimal format is always used for long double, and there are three forms of long double. The 80-bit format used by x86 is represented as 0xK followed by 20 hexadecimal digits. The 128-bit format used by PowerPC (two adjacent doubles) is represented by 0xM followed by 32 hexadecimal digits. The IEEE 128-bit format is represented by 0xL followed by 32 hexadecimal digits; no currently supported target uses this format. Long doubles will only work if they match the long double format on your target. All hexadecimal formats are big-endian (sign bit at the left).
Complex constants are a (potentially recursive) combination of simple constants and smaller complex constants.
The addresses of global variables and functions are always implicitly valid (link-time) constants. These constants are explicitly referenced when the identifier for the global is used and always have pointer type. For example, the following is a legal LLVM file:
@X = global i32 17 @Y = global i32 42 @Z = global [2 x i32*] [ i32* @X, i32* @Y ]
The string 'undef' is recognized as a type-less constant that has no specific value. Undefined values may be of any type and be used anywhere a constant is permitted.
Undefined values indicate to the compiler that the program is well defined no matter what value is used, giving the compiler more freedom to optimize.
Constant expressions are used to allow expressions involving other constants to be used as constants. Constant expressions may be of any first class type and may involve any LLVM operation that does not have side effects (e.g. load and call are not supported). The following is the syntax for constant expressions:
Embedded metadata provides a way to attach arbitrary data to the instruction stream without affecting the behaviour of the program. There are two metadata primitives, strings and nodes. All metadata has the type of an empty struct and is identified in syntax by a preceding exclamation point ('!').
A metadata string is a string surrounded by double quotes. It can contain any character by escaping non-printable characters with "\xx" where "xx" is the two digit hex code. For example: "!"test\00"".
Metadata nodes are represented with notation similar to structure constants (a comma separated list of elements, surrounded by braces and preceeded by an exclamation point). For example: "!{ { } !"test\00", i32 10}".
Optimizations may rely on metadata to provide additional information about the program that isn't available in the instructions, or that isn't easily computable. Similarly, the code generator may expect a certain metadata format to be used to express debugging information.
LLVM supports inline assembler expressions (as opposed to Module-Level Inline Assembly) through the use of a special value. This value represents the inline assembler as a string (containing the instructions to emit), a list of operand constraints (stored as a string), and a flag that indicates whether or not the inline asm expression has side effects. An example inline assembler expression is:
i32 (i32) asm "bswap $0", "=r,r"
Inline assembler expressions may only be used as the callee operand of a call instruction. Thus, typically we have:
%X = call i32 asm "bswap $0", "=r,r"(i32 %Y)
Inline asms with side effects not visible in the constraint list must be marked as having side effects. This is done through the use of the 'sideeffect' keyword, like so:
call void asm sideeffect "eieio", ""()
TODO: The format of the asm and constraints string still need to be documented here. Constraints on what can be done (e.g. duplication, moving, etc need to be documented). This is probably best done by reference to another document that covers inline asm from a holistic perspective.
The LLVM instruction set consists of several different classifications of instructions: terminator instructions, binary instructions, bitwise binary instructions, memory instructions, and other instructions.
As mentioned previously, every basic block in a program ends with a "Terminator" instruction, which indicates which block should be executed after the current block is finished. These terminator instructions typically yield a 'void' value: they produce control flow, not values (the one exception being the 'invoke' instruction).
There are six different terminator instructions: the 'ret' instruction, the 'br' instruction, the 'switch' instruction, the 'invoke' instruction, the 'unwind' instruction, and the 'unreachable' instruction.
ret <type> <value> ; Return a value from a non-void function ret void ; Return from void function
The 'ret' instruction is used to return control flow (and optionally a value) from a function back to the caller.
There are two forms of the 'ret' instruction: one that returns a value and then causes control flow, and one that just causes control flow to occur.
The 'ret' instruction optionally accepts a single argument, the return value. The type of the return value must be a 'first class' type.
A function is not well formed if it it has a non-void return type and contains a 'ret' instruction with no return value or a return value with a type that does not match its type, or if it has a void return type and contains a 'ret' instruction with a return value.
When the 'ret' instruction is executed, control flow returns back to the calling function's context. If the caller is a "call" instruction, execution continues at the instruction after the call. If the caller was an "invoke" instruction, execution continues at the beginning of the "normal" destination block. If the instruction returns a value, that value shall set the call or invoke instruction's return value.
ret i32 5 ; Return an integer value of 5 ret void ; Return from a void function ret { i32, i8 } { i32 4, i8 2 } ; Return a struct of values 4 and 2
Note that the code generator does not yet fully support large return values. The specific sizes that are currently supported are dependent on the target. For integers, on 32-bit targets the limit is often 64 bits, and on 64-bit targets the limit is often 128 bits. For aggregate types, the current limits are dependent on the element types; for example targets are often limited to 2 total integer elements and 2 total floating-point elements.
br i1 <cond>, label <iftrue>, label <iffalse>
br label <dest> ; Unconditional branch
The 'br' instruction is used to cause control flow to transfer to a different basic block in the current function. There are two forms of this instruction, corresponding to a conditional branch and an unconditional branch.
The conditional branch form of the 'br' instruction takes a single 'i1' value and two 'label' values. The unconditional form of the 'br' instruction takes a single 'label' value as a target.
Upon execution of a conditional 'br' instruction, the 'i1' argument is evaluated. If the value is true, control flows to the 'iftrue' label argument. If "cond" is false, control flows to the 'iffalse' label argument.
Test:
%cond = icmp eq, i32 %a, %b
br i1 %cond, label %IfEqual, label %IfUnequal
IfEqual:
ret i32 1
IfUnequal:
ret i32 0
switch <intty> <value>, label <defaultdest> [ <intty> <val>, label <dest> ... ]
The 'switch' instruction is used to transfer control flow to one of several different places. It is a generalization of the 'br' instruction, allowing a branch to occur to one of many possible destinations.
The 'switch' instruction uses three parameters: an integer comparison value 'value', a default 'label' destination, and an array of pairs of comparison value constants and 'label's. The table is not allowed to contain duplicate constant entries.
The switch instruction specifies a table of values and destinations. When the 'switch' instruction is executed, this table is searched for the given value. If the value is found, control flow is transfered to the corresponding destination; otherwise, control flow is transfered to the default destination.
Depending on properties of the target machine and the particular switch instruction, this instruction may be code generated in different ways. For example, it could be generated as a series of chained conditional branches or with a lookup table.
; Emulate a conditional br instruction %Val = zext i1 %value to i32 switch i32 %Val, label %truedest [ i32 0, label %falsedest ] ; Emulate an unconditional br instruction switch i32 0, label %dest [ ] ; Implement a jump table: switch i32 %val, label %otherwise [ i32 0, label %onzero i32 1, label %onone i32 2, label %ontwo ]
<result> = invoke [cconv] [ret attrs] <ptr to function ty> <function ptr val>(<function args>) [fn attrs] to label <normal label> unwind label <exception label>
The 'invoke' instruction causes control to transfer to a specified function, with the possibility of control flow transfer to either the 'normal' label or the 'exception' label. If the callee function returns with the "ret" instruction, control flow will return to the "normal" label. If the callee (or any indirect callees) returns with the "unwind" instruction, control is interrupted and continued at the dynamically nearest "exception" label.
This instruction requires several arguments:
This instruction is designed to operate as a standard 'call' instruction in most regards. The primary difference is that it establishes an association with a label, which is used by the runtime library to unwind the stack.
This instruction is used in languages with destructors to ensure that proper cleanup is performed in the case of either a longjmp or a thrown exception. Additionally, this is important for implementation of 'catch' clauses in high-level languages that support them.
%retval = invoke i32 @Test(i32 15) to label %Continue unwind label %TestCleanup ; {i32}:retval set %retval = invoke coldcc i32 %Testfnptr(i32 15) to label %Continue unwind label %TestCleanup ; {i32}:retval set
unwind
The 'unwind' instruction unwinds the stack, continuing control flow at the first callee in the dynamic call stack which used an invoke instruction to perform the call. This is primarily used to implement exception handling.
The 'unwind' instruction causes execution of the current function to immediately halt. The dynamic call stack is then searched for the first invoke instruction on the call stack. Once found, execution continues at the "exceptional" destination block specified by the invoke instruction. If there is no invoke instruction in the dynamic call chain, undefined behavior results.
unreachable
The 'unreachable' instruction has no defined semantics. This instruction is used to inform the optimizer that a particular portion of the code is not reachable. This can be used to indicate that the code after a no-return function cannot be reached, and other facts.
The 'unreachable' instruction has no defined semantics.
Binary operators are used to do most of the computation in a program. They require two operands of the same type, execute an operation on them, and produce a single value. The operands might represent multiple data, as is the case with the vector data type. The result value has the same type as its operands.
There are several different binary operators:
<result> = add <ty> <op1>, <op2> ; yields {ty}:result
The 'add' instruction returns the sum of its two operands.
The two arguments to the 'add' instruction must be integer, floating point, or vector values. Both arguments must have identical types.
The value produced is the integer or floating point sum of the two operands.
If an integer sum has unsigned overflow, the result returned is the mathematical result modulo 2n, where n is the bit width of the result.
Because LLVM integers use a two's complement representation, this instruction is appropriate for both signed and unsigned integers.
<result> = add i32 4, %var ; yields {i32}:result = 4 + %var
<result> = sub <ty> <op1>, <op2> ; yields {ty}:result
The 'sub' instruction returns the difference of its two operands.
Note that the 'sub' instruction is used to represent the 'neg' instruction present in most other intermediate representations.
The two arguments to the 'sub' instruction must be integer, floating point, or vector values. Both arguments must have identical types.
The value produced is the integer or floating point difference of the two operands.
If an integer difference has unsigned overflow, the result returned is the mathematical result modulo 2n, where n is the bit width of the result.
Because LLVM integers use a two's complement representation, this instruction is appropriate for both signed and unsigned integers.
<result> = sub i32 4, %var ; yields {i32}:result = 4 - %var <result> = sub i32 0, %val ; yields {i32}:result = -%var
<result> = mul <ty> <op1>, <op2> ; yields {ty}:result
The 'mul' instruction returns the product of its two operands.
The two arguments to the 'mul' instruction must be integer, floating point, or vector values. Both arguments must have identical types.
The value produced is the integer or floating point product of the two operands.
If the result of an integer multiplication has unsigned overflow, the result returned is the mathematical result modulo 2n, where n is the bit width of the result.
Because LLVM integers use a two's complement representation, and the result is the same width as the operands, this instruction returns the correct result for both signed and unsigned integers. If a full product (e.g. i32xi32->i64) is needed, the operands should be sign-extended or zero-extended as appropriate to the width of the full product.
<result> = mul i32 4, %var ; yields {i32}:result = 4 * %var
<result> = udiv <ty> <op1>, <op2> ; yields {ty}:result
The 'udiv' instruction returns the quotient of its two operands.
The two arguments to the 'udiv' instruction must be integer or vector of integer values. Both arguments must have identical types.
The value produced is the unsigned integer quotient of the two operands.
Note that unsigned integer division and signed integer division are distinct operations; for signed integer division, use 'sdiv'.
Division by zero leads to undefined behavior.
<result> = udiv i32 4, %var ; yields {i32}:result = 4 / %var
<result> = sdiv <ty> <op1>, <op2> ; yields {ty}:result
The 'sdiv' instruction returns the quotient of its two operands.
The two arguments to the 'sdiv' instruction must be integer or vector of integer values. Both arguments must have identical types.
The value produced is the signed integer quotient of the two operands rounded towards zero.
Note that signed integer division and unsigned integer division are distinct operations; for unsigned integer division, use 'udiv'.
Division by zero leads to undefined behavior. Overflow also leads to undefined behavior; this is a rare case, but can occur, for example, by doing a 32-bit division of -2147483648 by -1.
<result> = sdiv i32 4, %var ; yields {i32}:result = 4 / %var
<result> = fdiv <ty> <op1>, <op2> ; yields {ty}:result
The 'fdiv' instruction returns the quotient of its two operands.
The two arguments to the 'fdiv' instruction must be floating point or vector of floating point values. Both arguments must have identical types.
The value produced is the floating point quotient of the two operands.
<result> = fdiv float 4.0, %var ; yields {float}:result = 4.0 / %var
<result> = urem <ty> <op1>, <op2> ; yields {ty}:result
The 'urem' instruction returns the remainder from the unsigned division of its two arguments.
The two arguments to the 'urem' instruction must be integer or vector of integer values. Both arguments must have identical types.
This instruction returns the unsigned integer remainder of a division. This instruction always performs an unsigned division to get the remainder.
Note that unsigned integer remainder and signed integer remainder are distinct operations; for signed integer remainder, use 'srem'.
Taking the remainder of a division by zero leads to undefined behavior.
<result> = urem i32 4, %var ; yields {i32}:result = 4 % %var
<result> = srem <ty> <op1>, <op2> ; yields {ty}:result
The 'srem' instruction returns the remainder from the signed division of its two operands. This instruction can also take vector versions of the values in which case the elements must be integers.
The two arguments to the 'srem' instruction must be integer or vector of integer values. Both arguments must have identical types.
This instruction returns the remainder of a division (where the result has the same sign as the dividend, op1), not the modulo operator (where the result has the same sign as the divisor, op2) of a value. For more information about the difference, see The Math Forum. For a table of how this is implemented in various languages, please see Wikipedia: modulo operation.
Note that signed integer remainder and unsigned integer remainder are distinct operations; for unsigned integer remainder, use 'urem'.
Taking the remainder of a division by zero leads to undefined behavior. Overflow also leads to undefined behavior; this is a rare case, but can occur, for example, by taking the remainder of a 32-bit division of -2147483648 by -1. (The remainder doesn't actually overflow, but this rule lets srem be implemented using instructions that return both the result of the division and the remainder.)
<result> = srem i32 4, %var ; yields {i32}:result = 4 % %var
<result> = frem <ty> <op1>, <op2> ; yields {ty}:result
The 'frem' instruction returns the remainder from the division of its two operands.
The two arguments to the 'frem' instruction must be floating point or vector of floating point values. Both arguments must have identical types.
This instruction returns the remainder of a division. The remainder has the same sign as the dividend.
<result> = frem float 4.0, %var ; yields {float}:result = 4.0 % %var
Bitwise binary operators are used to do various forms of bit-twiddling in a program. They are generally very efficient instructions and can commonly be strength reduced from other instructions. They require two operands of the same type, execute an operation on them, and produce a single value. The resulting value is the same type as its operands.
<result> = shl <ty> <op1>, <op2> ; yields {ty}:result
The 'shl' instruction returns the first operand shifted to the left a specified number of bits.
Both arguments to the 'shl' instruction must be the same integer or vector of integer type. 'op2' is treated as an unsigned value.
The value produced is op1 * 2op2 mod 2n, where n is the width of the result. If op2 is (statically or dynamically) negative or equal to or larger than the number of bits in op1, the result is undefined. If the arguments are vectors, each vector element of op1 is shifted by the corresponding shift amount in op2.
<result> = shl i32 4, %var ; yields {i32}: 4 << %var <result> = shl i32 4, 2 ; yields {i32}: 16 <result> = shl i32 1, 10 ; yields {i32}: 1024 <result> = shl i32 1, 32 ; undefined <result> = shl <2 x i32> < i32 1, i32 1>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 2, i32 4>
<result> = lshr <ty> <op1>, <op2> ; yields {ty}:result
The 'lshr' instruction (logical shift right) returns the first operand shifted to the right a specified number of bits with zero fill.
Both arguments to the 'lshr' instruction must be the same integer or vector of integer type. 'op2' is treated as an unsigned value.
This instruction always performs a logical shift right operation. The most significant bits of the result will be filled with zero bits after the shift. If op2 is (statically or dynamically) equal to or larger than the number of bits in op1, the result is undefined. If the arguments are vectors, each vector element of op1 is shifted by the corresponding shift amount in op2.
<result> = lshr i32 4, 1 ; yields {i32}:result = 2 <result> = lshr i32 4, 2 ; yields {i32}:result = 1 <result> = lshr i8 4, 3 ; yields {i8}:result = 0 <result> = lshr i8 -2, 1 ; yields {i8}:result = 0x7FFFFFFF <result> = lshr i32 1, 32 ; undefined <result> = lshr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 2> ; yields: result=<2 x i32> < i32 0x7FFFFFFF, i32 1>
<result> = ashr <ty> <op1>, <op2> ; yields {ty}:result
The 'ashr' instruction (arithmetic shift right) returns the first operand shifted to the right a specified number of bits with sign extension.
Both arguments to the 'ashr' instruction must be the same integer or vector of integer type. 'op2' is treated as an unsigned value.
This instruction always performs an arithmetic shift right operation, The most significant bits of the result will be filled with the sign bit of op1. If op2 is (statically or dynamically) equal to or larger than the number of bits in op1, the result is undefined. If the arguments are vectors, each vector element of op1 is shifted by the corresponding shift amount in op2.
<result> = ashr i32 4, 1 ; yields {i32}:result = 2 <result> = ashr i32 4, 2 ; yields {i32}:result = 1 <result> = ashr i8 4, 3 ; yields {i8}:result = 0 <result> = ashr i8 -2, 1 ; yields {i8}:result = -1 <result> = ashr i32 1, 32 ; undefined <result> = ashr <2 x i32> < i32 -2, i32 4>, < i32 1, i32 3> ; yields: result=<2 x i32> < i32 -1, i32 0>
<result> = and <ty> <op1>, <op2> ; yields {ty}:result
The 'and' instruction returns the bitwise logical and of its two operands.
The two arguments to the 'and' instruction must be integer or vector of integer values. Both arguments must have identical types.
The truth table used for the 'and' instruction is:
| In0 | In1 | Out |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
<result> = and i32 4, %var ; yields {i32}:result = 4 & %var <result> = and i32 15, 40 ; yields {i32}:result = 8 <result> = and i32 4, 8 ; yields {i32}:result = 0
<result> = or <ty> <op1>, <op2> ; yields {ty}:result
The 'or' instruction returns the bitwise logical inclusive or of its two operands.
The two arguments to the 'or' instruction must be integer or vector of integer values. Both arguments must have identical types.
The truth table used for the 'or' instruction is:
| In0 | In1 | Out |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
<result> = or i32 4, %var ; yields {i32}:result = 4 | %var <result> = or i32 15, 40 ; yields {i32}:result = 47 <result> = or i32 4, 8 ; yields {i32}:result = 12
<result> = xor <ty> <op1>, <op2> ; yields {ty}:result
The 'xor' instruction returns the bitwise logical exclusive or of its two operands. The xor is used to implement the "one's complement" operation, which is the "~" operator in C.
The two arguments to the 'xor' instruction must be integer or vector of integer values. Both arguments must have identical types.
The truth table used for the 'xor' instruction is:
| In0 | In1 | Out |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
<result> = xor i32 4, %var ; yields {i32}:result = 4 ^ %var <result> = xor i32 15, 40 ; yields {i32}:result = 39 <result> = xor i32 4, 8 ; yields {i32}:result = 12 <result> = xor i32 %V, -1 ; yields {i32}:result = ~%V
LLVM supports several instructions to represent vector operations in a target-independent manner. These instructions cover the element-access and vector-specific operations needed to process vectors effectively. While LLVM does directly support these vector operations, many sophisticated algorithms will want to use target-specific intrinsics to take full advantage of a specific target.
<result> = extractelement <n x <ty>> <val>, i32 <idx> ; yields <ty>
The 'extractelement' instruction extracts a single scalar element from a vector at a specified index.
The first operand of an 'extractelement' instruction is a value of vector type. The second operand is an index indicating the position from which to extract the element. The index may be a variable.
The result is a scalar of the same type as the element type of val. Its value is the value at position idx of val. If idx exceeds the length of val, the results are undefined.
%result = extractelement <4 x i32> %vec, i32 0 ; yields i32
<result> = insertelement <n x <ty>> <val>, <ty> <elt>, i32 <idx> ; yields <n x <ty>>
The 'insertelement' instruction inserts a scalar element into a vector at a specified index.
The first operand of an 'insertelement' instruction is a value of vector type. The second operand is a scalar value whose type must equal the element type of the first operand. The third operand is an index indicating the position at which to insert the value. The index may be a variable.
The result is a vector of the same type as val. Its element values are those of val except at position idx, where it gets the value elt. If idx exceeds the length of val, the results are undefined.
%result = insertelement <4 x i32> %vec, i32 1, i32 0 ; yields <4 x i32>
<result> = shufflevector <n x <ty>> <v1>, <n x <ty>> <v2>, <m x i32> <mask> ; yields <m x <ty>>
The 'shufflevector' instruction constructs a permutation of elements from two input vectors, returning a vector with the same element type as the input and length that is the same as the shuffle mask.
The first two operands of a 'shufflevector' instruction are vectors with types that match each other. The third argument is a shuffle mask whose element type is always 'i32'. The result of the instruction is a vector whose length is the same as the shuffle mask and whose element type is the same as the element type of the first two operands.
The shuffle mask operand is required to be a constant vector with either constant integer or undef values.
The elements of the two input vectors are numbered from left to right across both of the vectors. The shuffle mask operand specifies, for each element of the result vector, which element of the two input vectors the result element gets. The element selector may be undef (meaning "don't care") and the second operand may be undef if performing a shuffle from only one vector.
%result = shufflevector <4 x i32> %v1, <4 x i32> %v2, <4 x i32> <i32 0, i32 4, i32 1, i32 5> ; yields <4 x i32> %result = shufflevector <4 x i32> %v1, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> - Identity shuffle. %result = shufflevector <8 x i32> %v1, <8 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3> ; yields <4 x i32> %result = shufflevector <4 x i32> %v1, <4 x i32> %v2, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 > ; yields <8 x i32>
LLVM supports several instructions for working with aggregate values.
<result> = extractvalue <aggregate type> <val>, <idx>{, <idx>}*
The 'extractvalue' instruction extracts the value of a struct field or array element from an aggregate value.
The first operand of an 'extractvalue' instruction is a value of struct or array type. The operands are constant indices to specify which value to extract in a similar manner as indices in a 'getelementptr' instruction.
The result is the value at the position in the aggregate specified by the index operands.
%result = extractvalue {i32, float} %agg, 0 ; yields i32
<result> = insertvalue <aggregate type> <val>, <ty> <val>, <idx> ; yields <n x <ty>>
The 'insertvalue' instruction inserts a value into a struct field or array element in an aggregate.
The first operand of an 'insertvalue' instruction is a value of struct or array type. The second operand is a first-class value to insert. The following operands are constant indices indicating the position at which to insert the value in a similar manner as indices in a 'getelementptr' instruction. The value to insert must have the same type as the value identified by the indices.
The result is an aggregate of the same type as val. Its value is that of val except that the value at the position specified by the indices is that of elt.
%result = insertvalue {i32, float} %agg, i32 1, 0 ; yields {i32, float}
A key design point of an SSA-based representation is how it represents memory. In LLVM, no memory locations are in SSA form, which makes things very simple. This section describes how to read, write, allocate, and free memory in LLVM.
<result> = malloc <type>[, i32 <NumElements>][, align <alignment>] ; yields {type*}:result
The 'malloc' instruction allocates memory from the system heap and returns a pointer to it. The object is always allocated in the generic address space (address space zero).
The 'malloc' instruction allocates sizeof(<type>)*NumElements bytes of memory from the operating system and returns a pointer of the appropriate type to the program. If "NumElements" is specified, it is the number of elements allocated, otherwise "NumElements" is defaulted to be one. If a constant alignment is specified, the value result of the allocation is guaranteed to be aligned to at least that boundary. If not specified, or if zero, the target can choose to align the allocation on any convenient boundary.
'type' must be a sized type.
Memory is allocated using the system "malloc" function, and a pointer is returned. The result of a zero byte allocation is undefined. The result is null if there is insufficient memory available.
%array = malloc [4 x i8] ; yields {[%4 x i8]*}:array %size = add i32 2, 2 ; yields {i32}:size = i32 4 %array1 = malloc i8, i32 4 ; yields {i8*}:array1 %array2 = malloc [12 x i8], i32 %size ; yields {[12 x i8]*}:array2 %array3 = malloc i32, i32 4, align 1024 ; yields {i32*}:array3 %array4 = malloc i32, align 1024 ; yields {i32*}:array4
Note that the code generator does not yet respect the alignment value.
free <type> <value> ; yields {void}
The 'free' instruction returns memory back to the unused memory heap to be reallocated in the future.
'value' shall be a pointer value that points to a value that was allocated with the 'malloc' instruction.
Access to the memory pointed to by the pointer is no longer defined after this instruction executes. If the pointer is null, the operation is a noop.
%array = malloc [4 x i8] ; yields {[4 x i8]*}:array free [4 x i8]* %array
<result> = alloca <type>[, i32 <NumElements>][, align <alignment>] ; yields {type*}:result
The 'alloca' instruction allocates memory on the stack frame of the currently executing function, to be automatically released when this function returns to its caller. The object is always allocated in the generic address space (address space zero).
The 'alloca' instruction allocates sizeof(<type>)*NumElements bytes of memory on the runtime stack, returning a pointer of the appropriate type to the program. If "NumElements" is specified, it is the number of elements allocated, otherwise "NumElements" is defaulted to be one. If a constant alignment is specified, the value result of the allocation is guaranteed to be aligned to at least that boundary. If not specified, or if zero, the target can choose to align the allocation on any convenient boundary.
'type' may be any sized type.
Memory is allocated; a pointer is returned. The operation is undefiend if there is insufficient stack space for the allocation. 'alloca'd memory is automatically released when the function returns. The 'alloca' instruction is commonly used to represent automatic variables that must have an address available. When the function returns (either with the ret or unwind instructions), the memory is reclaimed. Allocating zero bytes is legal, but the result is undefined.
%ptr = alloca i32 ; yields {i32*}:ptr %ptr = alloca i32, i32 4 ; yields {i32*}:ptr %ptr = alloca i32, i32 4, align 1024 ; yields {i32*}:ptr %ptr = alloca i32, align 1024 ; yields {i32*}:ptr
<result> = load <ty>* <pointer>[, align <alignment>]
<result> = volatile load <ty>* <pointer>[, align <alignment>]
The 'load' instruction is used to read from memory.
The argument to the 'load' instruction specifies the memory address from which to load. The pointer must point to a first class type. If the load is marked as volatile, then the optimizer is not allowed to modify the number or order of execution of this load with other volatile load and store instructions.
The optional constant "align" argument specifies the alignment of the operation (that is, the alignment of the memory address). A value of 0 or an omitted "align" argument means that the operation has the preferential alignment for the target. It is the responsibility of the code emitter to ensure that the alignment information is correct. Overestimating the alignment results in an undefined behavior. Underestimating the alignment may produce less efficient code. An alignment of 1 is always safe.
The location of memory pointed to is loaded. If the value being loaded is of scalar type then the number of bytes read does not exceed the minimum number of bytes needed to hold all bits of the type. For example, loading an i24 reads at most three bytes. When loading a value of a type like i20 with a size that is not an integral number of bytes, the result is undefined if the value was not originally written using a store of the same type.
%ptr = alloca i32 ; yields {i32*}:ptr store i32 3, i32* %ptr ; yields {void} %val = load i32* %ptr ; yields {i32}:val = i32 3
store <ty> <value>, <ty>* <pointer>[, align <alignment>] ; yields {void} volatile store <ty> <value>, <ty>* <pointer>[, align <alignment>] ; yields {void}
The 'store' instruction is used to write to memory.
There are two arguments to the 'store' instruction: a value to store and an address at which to store it. The type of the '<pointer>' operand must be a pointer to the first class type of the '<value>' operand. If the store is marked as volatile, then the optimizer is not allowed to modify the number or order of execution of this store with other volatile load and store instructions.
The optional constant "align" argument specifies the alignment of the operation (that is, the alignment of the memory address). A value of 0 or an omitted "align" argument means that the operation has the preferential alignment for the target. It is the responsibility of the code emitter to ensure that the alignment information is correct. Overestimating the alignment results in an undefined behavior. Underestimating the alignment may produce less efficient code. An alignment of 1 is always safe.
The contents of memory are updated to contain '<value>' at the location specified by the '<pointer>' operand. If '<value>' is of scalar type then the number of bytes written does not exceed the minimum number of bytes needed to hold all bits of the type. For example, storing an i24 writes at most three bytes. When writing a value of a type like i20 with a size that is not an integral number of bytes, it is unspecified what happens to the extra bits that do not belong to the type, but they will typically be overwritten.
%ptr = alloca i32 ; yields {i32*}:ptr store i32 3, i32* %ptr ; yields {void} %val = load i32* %ptr ; yields {i32}:val = i32 3
<result> = getelementptr <pty>* <ptrval>{, <ty> <idx>}*
The 'getelementptr' instruction is used to get the address of a subelement of an aggregate data structure. It performs address calculation only and does not access memory.
The first argument is always a pointer, and forms the basis of the calculation. The remaining arguments are indices, that indicate which of the elements of the aggregate object are indexed. The interpretation of each index is dependent on the type being indexed into. The first index always indexes the pointer value given as the first argument, the second index indexes a value of the type pointed to (not necessarily the value directly pointed to, since the first index can be non-zero), etc. The first type indexed into must be a pointer value, subsequent types can be arrays, vectors and structs. Note that subsequent types being indexed into can never be pointers, since that would require loading the pointer before continuing calculation.
The type of each index argument depends on the type it is indexing into. When indexing into a (packed) structure, only i32 integer constants are allowed. When indexing into an array, pointer or vector, only integers of 32 or 64 bits are allowed (also non-constants). 32-bit values will be sign extended to 64-bits if required.
For example, let's consider a C code fragment and how it gets compiled to LLVM:
struct RT { char A; int B[10][20]; char C; }; struct ST { int X; double Y; struct RT Z; }; int *foo(struct ST *s) { return &s[1].Z.B[5][13]; }
The LLVM code generated by the GCC frontend is:
%RT = type { i8 , [10 x [20 x i32]], i8 } %ST = type { i32, double, %RT } define i32* %foo(%ST* %s) { entry: %reg = getelementptr %ST* %s, i32 1, i32 2, i32 1, i32 5, i32 13 ret i32* %reg }
In the example above, the first index is indexing into the '%ST*' type, which is a pointer, yielding a '%ST' = '{ i32, double, %RT }' type, a structure. The second index indexes into the third element of the structure, yielding a '%RT' = '{ i8 , [10 x [20 x i32]], i8 }' type, another structure. The third index indexes into the second element of the structure, yielding a '[10 x [20 x i32]]' type, an array. The two dimensions of the array are subscripted into, yielding an 'i32' type. The 'getelementptr' instruction returns a pointer to this element, thus computing a value of 'i32*' type.
Note that it is perfectly legal to index partially through a structure, returning a pointer to an inner element. Because of this, the LLVM code for the given testcase is equivalent to:
define i32* %foo(%ST* %s) { %t1 = getelementptr %ST* %s, i32 1 ; yields %ST*:%t1 %t2 = getelementptr %ST* %t1, i32 0, i32 2 ; yields %RT*:%t2 %t3 = getelementptr %RT* %t2, i32 0, i32 1 ; yields [10 x [20 x i32]]*:%t3 %t4 = getelementptr [10 x [20 x i32]]* %t3, i32 0, i32 5 ; yields [20 x i32]*:%t4 %t5 = getelementptr [20 x i32]* %t4, i32 0, i32 13 ; yields i32*:%t5 ret i32* %t5 }
Note that it is undefined to access an array out of bounds: array and pointer indexes must always be within the defined bounds of the array type when accessed with an instruction that dereferences the pointer (e.g. a load or store instruction). The one exception for this rule is zero length arrays. These arrays are defined to be accessible as variable length arrays, which requires access beyond the zero'th element.
The getelementptr instruction is often confusing. For some more insight into how it works, see the getelementptr FAQ.
; yields [12 x i8]*:aptr %aptr = getelementptr {i32, [12 x i8]}* %saptr, i64 0, i32 1 ; yields i8*:vptr %vptr = getelementptr {i32, <2 x i8>}* %svptr, i64 0, i32 1, i32 1 ; yields i8*:eptr %eptr = getelementptr [12 x i8]* %aptr, i64 0, i32 1
The instructions in this category are the conversion instructions (casting) which all take a single operand and a type. They perform various bit conversions on the operand.
<result> = trunc <ty> <value> to <ty2> ; yields ty2
The 'trunc' instruction truncates its operand to the type ty2.
The 'trunc' instruction takes a value to trunc, which must be an integer type, and a type that specifies the size and type of the result, which must be an integer type. The bit size of value must be larger than the bit size of ty2. Equal sized types are not allowed.
The 'trunc' instruction truncates the high order bits in value and converts the remaining bits to ty2. Since the source size must be larger than the destination size, trunc cannot be a no-op cast. It will always truncate bits.
%X = trunc i32 257 to i8 ; yields i8:1 %Y = trunc i32 123 to i1 ; yields i1:true %Y = trunc i32 122 to i1 ; yields i1:false
<result> = zext <ty> <value> to <ty2> ; yields ty2
The 'zext' instruction zero extends its operand to type ty2.
The 'zext' instruction takes a value to cast, which must be of integer type, and a type to cast it to, which must also be of integer type. The bit size of the value must be smaller than the bit size of the destination type, ty2.
The zext fills the high order bits of the value with zero bits until it reaches the size of the destination type, ty2.
When zero extending from i1, the result will always be either 0 or 1.
%X = zext i32 257 to i64 ; yields i64:257 %Y = zext i1 true to i32 ; yields i32:1
<result> = sext <ty> <value> to <ty2> ; yields ty2
The 'sext' sign extends value to the type ty2.
The 'sext' instruction takes a value to cast, which must be of integer type, and a type to cast it to, which must also be of integer type. The bit size of the value must be smaller than the bit size of the destination type, ty2.
The 'sext' instruction performs a sign extension by copying the sign bit (highest order bit) of the value until it reaches the bit size of the type ty2.
When sign extending from i1, the extension always results in -1 or 0.
%X = sext i8 -1 to i16 ; yields i16 :65535 %Y = sext i1 true to i32 ; yields i32:-1
<result> = fptrunc <ty> <value> to <ty2> ; yields ty2
The 'fptrunc' instruction truncates value to type ty2.
The 'fptrunc' instruction takes a floating point value to cast and a floating point type to cast it to. The size of value must be larger than the size of ty2. This implies that fptrunc cannot be used to make a no-op cast.
The 'fptrunc' instruction truncates a value from a larger floating point type to a smaller floating point type. If the value cannot fit within the destination type, ty2, then the results are undefined.
%X = fptrunc double 123.0 to float ; yields float:123.0 %Y = fptrunc double 1.0E+300 to float ; yields undefined
<result> = fpext <ty> <value> to <ty2> ; yields ty2
The 'fpext' extends a floating point value to a larger floating point value.
The 'fpext' instruction takes a floating point value to cast, and a floating point type to cast it to. The source type must be smaller than the destination type.
The 'fpext' instruction extends the value from a smaller floating point type to a larger floating point type. The fpext cannot be used to make a no-op cast because it always changes bits. Use bitcast to make a no-op cast for a floating point cast.
%X = fpext float 3.1415 to double ; yields double:3.1415 %Y = fpext float 1.0 to float ; yields float:1.0 (no-op)
<result> = fptoui <ty> <value> to <ty2> ; yields ty2
The 'fptoui' converts a floating point value to its unsigned integer equivalent of type ty2.
The 'fptoui' instruction takes a value to cast, which must be a scalar or vector floating point value, and a type to cast it to ty2, which must be an integer type. If ty is a vector floating point type, ty2 must be a vector integer type with the same number of elements as ty
The 'fptoui' instruction converts its floating point operand into the nearest (rounding towards zero) unsigned integer value. If the value cannot fit in ty2, the results are undefined.
%X = fptoui double 123.0 to i32 ; yields i32:123 %Y = fptoui float 1.0E+300 to i1 ; yields undefined:1 %X = fptoui float 1.04E+17 to i8 ; yields undefined:1
<result> = fptosi <ty> <value> to <ty2> ; yields ty2
The 'fptosi' instruction converts floating point value to type ty2.
The 'fptosi' instruction takes a value to cast, which must be a scalar or vector floating point value, and a type to cast it to ty2, which must be an integer type. If ty is a vector floating point type, ty2 must be a vector integer type with the same number of elements as ty
The 'fptosi' instruction converts its floating point operand into the nearest (rounding towards zero) signed integer value. If the value cannot fit in ty2, the results are undefined.
%X = fptosi double -123.0 to i32 ; yields i32:-123 %Y = fptosi float 1.0E-247 to i1 ; yields undefined:1 %X = fptosi float 1.04E+17 to i8 ; yields undefined:1
<result> = uitofp <ty> <value> to <ty2> ; yields ty2
The 'uitofp' instruction regards value as an unsigned integer and converts that value to the ty2 type.
The 'uitofp' instruction takes a value to cast, which must be a scalar or vector integer value, and a type to cast it to ty2, which must be an floating point type. If ty is a vector integer type, ty2 must be a vector floating point type with the same number of elements as ty
The 'uitofp' instruction interprets its operand as an unsigned integer quantity and converts it to the corresponding floating point value. If the value cannot fit in the floating point value, the results are undefined.
%X = uitofp i32 257 to float ; yields float:257.0 %Y = uitofp i8 -1 to double ; yields double:255.0
<result> = sitofp <ty> <value> to <ty2> ; yields ty2
The 'sitofp' instruction regards value as a signed integer and converts that value to the ty2 type.
The 'sitofp' instruction takes a value to cast, which must be a scalar or vector integer value, and a type to cast it to ty2, which must be an floating point type. If ty is a vector integer type, ty2 must be a vector floating point type with the same number of elements as ty
The 'sitofp' instruction interprets its operand as a signed integer quantity and converts it to the corresponding floating point value. If the value cannot fit in the floating point value, the results are undefined.
%X = sitofp i32 257 to float ; yields float:257.0 %Y = sitofp i8 -1 to double ; yields double:-1.0
<result> = ptrtoint <ty> <value> to <ty2> ; yields ty2
The 'ptrtoint' instruction converts the pointer value to the integer type ty2.
The 'ptrtoint' instruction takes a value to cast, which must be a pointer value, and a type to cast it to ty2, which must be an integer type.
The 'ptrtoint' instruction converts value to integer type ty2 by interpreting the pointer value as an integer and either truncating or zero extending that value to the size of the integer type. If value is smaller than ty2 then a zero extension is done. If value is larger than ty2 then a truncation is done. If they are the same size, then nothing is done (no-op cast) other than a type change.
%X = ptrtoint i32* %X to i8 ; yields truncation on 32-bit architecture %Y = ptrtoint i32* %x to i64 ; yields zero extension on 32-bit architecture
<result> = inttoptr <ty> <value> to <ty2> ; yields ty2
The 'inttoptr' instruction converts an integer value to a pointer type, ty2.
The 'inttoptr' instruction takes an integer value to cast, and a type to cast it to, which must be a pointer type.
The 'inttoptr' instruction converts value to type ty2 by applying either a zero extension or a truncation depending on the size of the integer value. If value is larger than the size of a pointer then a truncation is done. If value is smaller than the size of a pointer then a zero extension is done. If they are the same size, nothing is done (no-op cast).
%X = inttoptr i32 255 to i32* ; yields zero extension on 64-bit architecture %X = inttoptr i32 255 to i32* ; yields no-op on 32-bit architecture %Y = inttoptr i64 0 to i32* ; yields truncation on 32-bit architecture
<result> = bitcast <ty> <value> to <ty2> ; yields ty2
The 'bitcast' instruction converts value to type ty2 without changing any bits.
The 'bitcast' instruction takes a value to cast, which must be a non-aggregate first class value, and a type to cast it to, which must also be a non-aggregate first class type. The bit sizes of value and the destination type, ty2, must be identical. If the source type is a pointer, the destination type must also be a pointer. This instruction supports bitwise conversion of vectors to integers and to vectors of other types (as long as they have the same size).
The 'bitcast' instruction converts value to type ty2. It is always a no-op cast because no bits change with this conversion. The conversion is done as if the value had been stored to memory and read back as type ty2. Pointer types may only be converted to other pointer types with this instruction. To convert pointers to other types, use the inttoptr or ptrtoint instructions first.
%X = bitcast i8 255 to i8 ; yields i8 :-1 %Y = bitcast i32* %x to sint* ; yields sint*:%x %Z = bitcast <2 x int> %V to i64; ; yields i64: %V
The instructions in this category are the "miscellaneous" instructions, which defy better classification.
<result> = icmp <cond> <ty> <op1>, <op2> ; yields {i1} or {<N x i1>}:result
The 'icmp' instruction returns a boolean value or a vector of boolean values based on comparison of its two integer, integer vector, or pointer operands.
The 'icmp' instruction takes three operands. The first operand is the condition code indicating the kind of comparison to perform. It is not a value, just a keyword. The possible condition code are:
The remaining two arguments must be integer or pointer or integer vector typed. They must also be identical types.
The 'icmp' compares op1 and op2 according to the condition code given as cond. The comparison performed always yields either an i1 or vector of i1 result, as follows:
If the operands are pointer typed, the pointer values are compared as if they were integers.
If the operands are integer vectors, then they are compared element by element. The result is an i1 vector with the same number of elements as the values being compared. Otherwise, the result is an i1.
<result> = icmp eq i32 4, 5 ; yields: result=false <result> = icmp ne float* %X, %X ; yields: result=false <result> = icmp ult i16 4, 5 ; yields: result=true <result> = icmp sgt i16 4, 5 ; yields: result=false <result> = icmp ule i16 -4, 5 ; yields: result=false <result> = icmp sge i16 4, 5 ; yields: result=false
Note that the code generator does not yet support vector types with the icmp instruction.
<result> = fcmp <cond> <ty> <op1>, <op2> ; yields {i1} or {<N x i1>}:result
The 'fcmp' instruction returns a boolean value or vector of boolean values based on comparison of its operands.
If the operands are floating point scalars, then the result type is a boolean (i1).
If the operands are floating point vectors, then the result type is a vector of boolean with the same number of elements as the operands being compared.
The 'fcmp' instruction takes three operands. The first operand is the condition code indicating the kind of comparison to perform. It is not a value, just a keyword. The possible condition code are:
Ordered means that neither operand is a QNAN while unordered means that either operand may be a QNAN.
Each of val1 and val2 arguments must be either a floating point type or a vector of floating point type. They must have identical types.
The 'fcmp' instruction compares op1 and op2 according to the condition code given as cond. If the operands are vectors, then the vectors are compared element by element. Each comparison performed always yields an i1 result, as follows:
<result> = fcmp oeq float 4.0, 5.0 ; yields: result=false <result> = fcmp one float 4.0, 5.0 ; yields: result=true <result> = fcmp olt float 4.0, 5.0 ; yields: result=true <result> = fcmp ueq double 1.0, 2.0 ; yields: result=false
Note that the code generator does not yet support vector types with the fcmp instruction.
<result> = vicmp <cond> <ty> <op1>, <op2> ; yields {ty}:result
The 'vicmp' instruction returns an integer vector value based on element-wise comparison of its two integer vector operands.
The 'vicmp' instruction takes three operands. The first operand is the condition code indicating the kind of comparison to perform. It is not a value, just a keyword. The possible condition code are:
The remaining two arguments must be vector or integer typed. They must also be identical types.
The 'vicmp' instruction compares op1 and op2 according to the condition code given as cond. The comparison yields a vector of integer result, of identical type as the values being compared. The most significant bit in each element is 1 if the element-wise comparison evaluates to true, and is 0 otherwise. All other bits of the result are undefined. The condition codes are evaluated identically to the 'icmp' instruction.
<result> = vicmp eq <2 x i32> < i32 4, i32 0>, < i32 5, i32 0> ; yields: result=<2 x i32> < i32 0, i32 -1 > <result> = vicmp ult <2 x i8 > < i8 1, i8 2>, < i8 2, i8 2 > ; yields: result=<2 x i8> < i8 -1, i8 0 >
<result> = vfcmp <cond> <ty> <op1>, <op2>
The 'vfcmp' instruction returns an integer vector value based on element-wise comparison of its two floating point vector operands. The output elements have the same width as the input elements.
The 'vfcmp' instruction takes three operands. The first operand is the condition code indicating the kind of comparison to perform. It is not a value, just a keyword. The possible condition code are:
The remaining two arguments must be vector of floating point typed. They must also be identical types.
The 'vfcmp' instruction compares op1 and op2 according to the condition code given as cond. The comparison yields a vector of integer result, with an identical number of elements as the values being compared, and each element having identical with to the width of the floating point elements. The most significant bit in each element is 1 if the element-wise comparison evaluates to true, and is 0 otherwise. All other bits of the result are undefined. The condition codes are evaluated identically to the 'fcmp' instruction.
; yields: result=<2 x i32> < i32 0, i32 -1 > <result> = vfcmp oeq <2 x float> < float 4, float 0 >, < float 5, float 0 > ; yields: result=<2 x i64> < i64 -1, i64 0 > <result> = vfcmp ult <2 x double> < double 1, double 2 >, < double 2, double 2>
<result> = phi <ty> [ <val0>, <label0>], ...
The 'phi' instruction is used to implement the φ node in the SSA graph representing the function.
The type of the incoming values is specified with the first type field. After this, the 'phi' instruction takes a list of pairs as arguments, with one pair for each predecessor basic block of the current block. Only values of first class type may be used as the value arguments to the PHI node. Only labels may be used as the label arguments.
There must be no non-phi instructions between the start of a basic block and the PHI instructions: i.e. PHI instructions must be first in a basic block.
At runtime, the 'phi' instruction logically takes on the value specified by the pair corresponding to the predecessor basic block that executed just prior to the current block.
Loop: ; Infinite loop that counts from 0 on up... %indvar = phi i32 [ 0, %LoopHeader ], [ %nextindvar, %Loop ] %nextindvar = add i32 %indvar, 1 br label %Loop
<result> = select selty <cond>, <ty> <val1>, <ty> <val2> ; yields ty selty is either i1 or {<N x i1>}
The 'select' instruction is used to choose one value based on a condition, without branching.
The 'select' instruction requires an 'i1' value or a vector of 'i1' values indicating the condition, and two values of the same first class type. If the val1/val2 are vectors and the condition is a scalar, then entire vectors are selected, not individual elements.
If the condition is an i1 and it evaluates to 1, the instruction returns the first value argument; otherwise, it returns the second value argument.
If the condition is a vector of i1, then the value arguments must be vectors of the same size, and the selection is done element by element.
%X = select i1 true, i8 17, i8 42 ; yields i8:17
Note that the code generator does not yet support conditions with vector type.
<result> = [tail] call [cconv] [ret attrs] <ty> [<fnty>*] <fnptrval>(<function args>) [fn attrs]
The 'call' instruction represents a simple function call.
This instruction requires several arguments:
The optional "tail" marker indicates whether the callee function accesses any allocas or varargs in the caller. If the "tail" marker is present, the function call is eligible for tail call optimization. Note that calls may be marked "tail" even if they do not occur before a ret instruction.
The optional "cconv" marker indicates which calling convention the call should use. If none is specified, the call defaults to using C calling conventions.
The optional Parameter Attributes list for return values. Only 'zeroext', 'signext', and 'inreg' attributes are valid here.
'ty': the type of the call instruction itself which is also the type of the return value. Functions that return no value are marked void.
'fnty': shall be the signature of the pointer to function value being invoked. The argument types must match the types implied by this signature. This type can be omitted if the function is not varargs and if the function type does not return a pointer to a function.
'fnptrval': An LLVM value containing a pointer to a function to be invoked. In most cases, this is a direct function invocation, but indirect calls are just as possible, calling an arbitrary pointer to function value.
'function args': argument list whose types match the function signature argument types. All arguments must be of first class type. If the function signature indicates the function accepts a variable number of arguments, the extra arguments can be specified.
The optional function attributes list. Only 'noreturn', 'nounwind', 'readonly' and 'readnone' attributes are valid here.
The 'call' instruction is used to cause control flow to transfer to a specified function, with its incoming arguments bound to the specified values. Upon a 'ret' instruction in the called function, control flow continues with the instruction after the function call, and the return value of the function is bound to the result argument.
%retval = call i32 @test(i32 %argc) call i32 (i8 *, ...)* @printf(i8 * %msg, i32 12, i8 42) ; yields i32 %X = tail call i32 @foo() ; yields i32 %Y = tail call fastcc i32 @foo() ; yields i32 call void %foo(i8 97 signext) %struct.A = type { i32, i8 } %r = call %struct.A @foo() ; yields { 32, i8 } %gr = extractvalue %struct.A %r, 0 ; yields i32 %gr1 = extractvalue %struct.A %r, 1 ; yields i8 %Z = call void @foo() noreturn ; indicates that %foo never returns normally %ZZ = call zeroext i32 @bar() ; Return value is %zero extended
<resultval> = va_arg <va_list*> <arglist>, <argty>
The 'va_arg' instruction is used to access arguments passed through the "variable argument" area of a function call. It is used to implement the va_arg macro in C.
This instruction takes a va_list* value and the type of the argument. It returns a value of the specified argument type and increments the va_list to point to the next argument. The actual type of va_list is target specific.
The 'va_arg' instruction loads an argument of the specified type from the specified va_list and causes the va_list to point to the next argument. For more information, see the variable argument handling Intrinsic Functions.
It is legal for this instruction to be called in a function which does not take a variable number of arguments, for example, the vfprintf function.
va_arg is an LLVM instruction instead of an intrinsic function because it takes a type as an argument.
See the variable argument processing section.
Note that the code generator does not yet fully support va_arg on many targets. Also, it does not currently support va_arg with aggregate types on any target.
LLVM supports the notion of an "intrinsic function". These functions have well known names and semantics and are required to follow certain restrictions. Overall, these intrinsics represent an extension mechanism for the LLVM language that does not require changing all of the transformations in LLVM when adding to the language (or the bitcode reader/writer, the parser, etc...).
Intrinsic function names must all start with an "llvm." prefix. This prefix is reserved in LLVM for intrinsic names; thus, function names may not begin with this prefix. Intrinsic functions must always be external functions: you cannot define the body of intrinsic functions. Intrinsic functions may only be used in call or invoke instructions: it is illegal to take the address of an intrinsic function. Additionally, because intrinsic functions are part of the LLVM language, it is required if any are added that they be documented here.
Some intrinsic functions can be overloaded, i.e., the intrinsic represents a family of functions that perform the same operation but on different data types. Because LLVM can represent over 8 million different integer types, overloading is used commonly to allow an intrinsic function to operate on any integer type. One or more of the argument types or the result type can be overloaded to accept any integer type. Argument types may also be defined as exactly matching a previous argument's type or the result type. This allows an intrinsic function which accepts multiple arguments, but needs all of them to be of the same type, to only be overloaded with respect to a single argument or the result.
Overloaded intrinsics will have the names of its overloaded argument types encoded into its function name, each preceded by a period. Only those types which are overloaded result in a name suffix. Arguments whose type is matched against another type do not. For example, the llvm.ctpop function can take an integer of any width and returns an integer of exactly the same integer width. This leads to a family of functions such as i8 @llvm.ctpop.i8(i8 %val) and i29 @llvm.ctpop.i29(i29 %val). Only one type, the return type, is overloaded, and only one type suffix is required. Because the argument's type is matched against the return type, it does not require its own name suffix.
To learn how to add an intrinsic function, please see the Extending LLVM Guide.
Variable argument support is defined in LLVM with the va_arg instruction and these three intrinsic functions. These functions are related to the similarly named macros defined in the <stdarg.h> header file.
All of these functions operate on arguments that use a target-specific value type "va_list". The LLVM assembly language reference manual does not define what this type is, so all transformations should be prepared to handle these functions regardless of the type used.
This example shows how the va_arg instruction and the variable argument handling intrinsic functions are used.
define i32 @test(i32 %X, ...) { ; Initialize variable argument processing %ap = alloca i8* %ap2 = bitcast i8** %ap to i8* call void @llvm.va_start(i8* %ap2) ; Read a single integer argument %tmp = va_arg i8** %ap, i32 ; Demonstrate usage of llvm.va_copy and llvm.va_end %aq = alloca i8* %aq2 = bitcast i8** %aq to i8* call void @llvm.va_copy(i8* %aq2, i8* %ap2) call void @llvm.va_end(i8* %aq2) ; Stop processing of arguments. call void @llvm.va_end(i8* %ap2) ret i32 %tmp } declare void @llvm.va_start(i8*) declare void @llvm.va_copy(i8*, i8*) declare void @llvm.va_end(i8*)
declare void %llvm.va_start(i8* <arglist>)
The 'llvm.va_start' intrinsic initializes *<arglist> for subsequent use by va_arg.
The argument is a pointer to a va_list element to initialize.
The 'llvm.va_start' intrinsic works just like the va_start macro available in C. In a target-dependent way, it initializes the va_list element to which the argument points, so that the next call to va_arg will produce the first variable argument passed to the function. Unlike the C va_start macro, this intrinsic does not need to know the last argument of the function as the compiler can figure that out.
declare void @llvm.va_end(i8* <arglist>)
The 'llvm.va_end' intrinsic destroys *<arglist>, which has been initialized previously with llvm.va_start or llvm.va_copy.
The argument is a pointer to a va_list to destroy.
The 'llvm.va_end' intrinsic works just like the va_end macro available in C. In a target-dependent way, it destroys the va_list element to which the argument points. Calls to llvm.va_start and llvm.va_copy must be matched exactly with calls to llvm.va_end.
declare void @llvm.va_copy(i8* <destarglist>, i8* <srcarglist>)
The 'llvm.va_copy' intrinsic copies the current argument position from the source argument list to the destination argument list.
The first argument is a pointer to a va_list element to initialize. The second argument is a pointer to a va_list element to copy from.
The 'llvm.va_copy' intrinsic works just like the va_copy macro available in C. In a target-dependent way, it copies the source va_list element into the destination va_list element. This intrinsic is necessary because the llvm.va_start intrinsic may be arbitrarily complex and require, for example, memory allocation.
LLVM support for Accurate Garbage Collection (GC) requires the implementation and generation of these intrinsics. These intrinsics allow identification of GC roots on the stack, as well as garbage collector implementations that require read and write barriers.  For more details, see Accurate Garbage Collection with LLVM.
The garbage collection intrinsics only operate on objects in the generic address space (address space zero).
declare void @llvm.gcroot(i8** %ptrloc, i8* %metadata)
The 'llvm.gcroot' intrinsic declares the existence of a GC root to the code generator, and allows some metadata to be associated with it.
The first argument specifies the address of a stack object that contains the root pointer. The second pointer (which must be either a constant or a global value address) contains the meta-data to be associated with the root.
At runtime, a call to this intrinsic stores a null pointer into the "ptrloc" location. At compile-time, the code generator generates information to allow the runtime to find the pointer at GC safe points. The 'llvm.gcroot' intrinsic may only be used in a function which specifies a GC algorithm.
declare i8* @llvm.gcread(i8* %ObjPtr, i8** %Ptr)
The 'llvm.gcread' intrinsic identifies reads of references from heap locations, allowing garbage collector implementations that require read barriers.
The second argument is the address to read from, which should be an address allocated from the garbage collector. The first object is a pointer to the start of the referenced object, if needed by the language runtime (otherwise null).
The 'llvm.gcread' intrinsic has the same semantics as a load instruction, but may be replaced with substantially more complex code by the garbage collector runtime, as needed. The 'llvm.gcread' intrinsic may only be used in a function which specifies a GC algorithm.
declare void @llvm.gcwrite(i8* %P1, i8* %Obj, i8** %P2)
The 'llvm.gcwrite' intrinsic identifies writes of references to heap locations, allowing garbage collector implementations that require write barriers (such as generational or reference counting collectors).
The first argument is the reference to store, the second is the start of the object to store it to, and the third is the address of the field of Obj to store to. If the runtime does not require a pointer to the object, Obj may be null.
The 'llvm.gcwrite' intrinsic has the same semantics as a store instruction, but may be replaced with substantially more complex code by the garbage collector runtime, as needed. The 'llvm.gcwrite' intrinsic may only be used in a function which specifies a GC algorithm.
These intrinsics are provided by LLVM to expose special features that may only be implemented with code generator support.
declare i8 *@llvm.returnaddress(i32 <level>)
The 'llvm.returnaddress' intrinsic attempts to compute a target-specific value indicating the return address of the current function or one of its callers.
The argument to this intrinsic indicates which function to return the address for. Zero indicates the calling function, one indicates its caller, etc. The argument is required to be a constant integer value.
The 'llvm.returnaddress' intrinsic either returns a pointer indicating the return address of the specified call frame, or zero if it cannot be identified. The value returned by this intrinsic is likely to be incorrect or 0 for arguments other than zero, so it should only be used for debugging purposes.
Note that calling this intrinsic does not prevent function inlining or other aggressive transformations, so the value returned may not be that of the obvious source-language caller.
declare i8 *@llvm.frameaddress(i32 <level>)
The 'llvm.frameaddress' intrinsic attempts to return the target-specific frame pointer value for the specified stack frame.
The argument to this intrinsic indicates which function to return the frame pointer for. Zero indicates the calling function, one indicates its caller, etc. The argument is required to be a constant integer value.
The 'llvm.frameaddress' intrinsic either returns a pointer indicating the frame address of the specified call frame, or zero if it cannot be identified. The value returned by this intrinsic is likely to be incorrect or 0 for arguments other than zero, so it should only be used for debugging purposes.
Note that calling this intrinsic does not prevent function inlining or other aggressive transformations, so the value returned may not be that of the obvious source-language caller.
declare i8 *@llvm.stacksave()
The 'llvm.stacksave' intrinsic is used to remember the current state of the function stack, for use with llvm.stackrestore. This is useful for implementing language features like scoped automatic variable sized arrays in C99.
This intrinsic returns a opaque pointer value that can be passed to llvm.stackrestore. When an llvm.stackrestore intrinsic is executed with a value saved from llvm.stacksave, it effectively restores the state of the stack to the state it was in when the llvm.stacksave intrinsic executed. In practice, this pops any alloca blocks from the stack that were allocated after the llvm.stacksave was executed.
declare void @llvm.stackrestore(i8 * %ptr)
The 'llvm.stackrestore' intrinsic is used to restore the state of the function stack to the state it was in when the corresponding llvm.stacksave intrinsic executed. This is useful for implementing language features like scoped automatic variable sized arrays in C99.
See the description for llvm.stacksave.
declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>)
The 'llvm.prefetch' intrinsic is a hint to the code generator to insert a prefetch instruction if supported; otherwise, it is a noop. Prefetches have no effect on the behavior of the program but can change its performance characteristics.
address is the address to be prefetched, rw is the specifier determining if the fetch should be for a read (0) or write (1), and locality is a temporal locality specifier ranging from (0) - no locality, to (3) - extremely local keep in cache. The rw and locality arguments must be constant integers.
This intrinsic does not modify the behavior of the program. In particular, prefetches cannot trap and do not produce a value. On targets that support this intrinsic, the prefetch can provide hints to the processor cache for better performance.
declare void @llvm.pcmarker(i32 <id>)
The 'llvm.pcmarker' intrinsic is a method to export a Program Counter (PC) in a region of code to simulators and other tools. The method is target specific, but it is expected that the marker will use exported symbols to transmit the PC of the marker. The marker makes no guarantees that it will remain with any specific instruction after optimizations. It is possible that the presence of a marker will inhibit optimizations. The intended use is to be inserted after optimizations to allow correlations of simulation runs.
id is a numerical id identifying the marker.
This intrinsic does not modify the behavior of the program. Backends that do not support this intrinisic may ignore it.
declare i64 @llvm.readcyclecounter( )
The 'llvm.readcyclecounter' intrinsic provides access to the cycle counter register (or similar low latency, high accuracy clocks) on those targets that support it. On X86, it should map to RDTSC. On Alpha, it should map to RPCC. As the backing counters overflow quickly (on the order of 9 seconds on alpha), this should only be used for small timings.
When directly supported, reading the cycle counter should not modify any memory. Implementations are allowed to either return a application specific value or a system wide value. On backends without support, this is lowered to a constant 0.
LLVM provides intrinsics for a few important standard C library functions. These intrinsics allow source-language front-ends to pass information about the alignment of the pointer arguments to the code generator, providing opportunity for more efficient code generation.
This is an overloaded intrinsic. You can use llvm.memcpy on any integer bit width. Not all targets support all bit widths however.
declare void @llvm.memcpy.i8(i8 * <dest>, i8 * <src>, i8 <len>, i32 <align>) declare void @llvm.memcpy.i16(i8 * <dest>, i8 * <src>, i16 <len>, i32 <align>) declare void @llvm.memcpy.i32(i8 * <dest>, i8 * <src>, i32 <len>, i32 <align>) declare void @llvm.memcpy.i64(i8 * <dest>, i8 * <src>, i64 <len>, i32 <align>)
The 'llvm.memcpy.*' intrinsics copy a block of memory from the source location to the destination location.
Note that, unlike the standard libc function, the llvm.memcpy.* intrinsics do not return a value, and takes an extra alignment argument.
The first argument is a pointer to the destination, the second is a pointer to the source. The third argument is an integer argument specifying the number of bytes to copy, and the fourth argument is the alignment of the source and destination locations.
If the call to this intrinisic has an alignment value that is not 0 or 1, then the caller guarantees that both the source and destination pointers are aligned to that boundary.
The 'llvm.memcpy.*' intrinsics copy a block of memory from the source location to the destination location, which are not allowed to overlap. It copies "len" bytes of memory over. If the argument is known to be aligned to some boundary, this can be specified as the fourth argument, otherwise it should be set to 0 or 1.
This is an overloaded intrinsic. You can use llvm.memmove on any integer bit width. Not all targets support all bit widths however.
declare void @llvm.memmove.i8(i8 * <dest>, i8 * <src>, i8 <len>, i32 <align>) declare void @llvm.memmove.i16(i8 * <dest>, i8 * <src>, i16 <len>, i32 <align>) declare void @llvm.memmove.i32(i8 * <dest>, i8 * <src>, i32 <len>, i32 <align>) declare void @llvm.memmove.i64(i8 * <dest>, i8 * <src>, i64 <len>, i32 <align>)
The 'llvm.memmove.*' intrinsics move a block of memory from the source location to the destination location. It is similar to the 'llvm.memcpy' intrinsic but allows the two memory locations to overlap.
Note that, unlike the standard libc function, the llvm.memmove.* intrinsics do not return a value, and takes an extra alignment argument.
The first argument is a pointer to the destination, the second is a pointer to the source. The third argument is an integer argument specifying the number of bytes to copy, and the fourth argument is the alignment of the source and destination locations.
If the call to this intrinisic has an alignment value that is not 0 or 1, then the caller guarantees that the source and destination pointers are aligned to that boundary.
The 'llvm.memmove.*' intrinsics copy a block of memory from the source location to the destination location, which may overlap. It copies "len" bytes of memory over. If the argument is known to be aligned to some boundary, this can be specified as the fourth argument, otherwise it should be set to 0 or 1.
This is an overloaded intrinsic. You can use llvm.memset on any integer bit width. Not all targets support all bit widths however.
declare void @llvm.memset.i8(i8 * <dest>, i8 <val>, i8 <len>, i32 <align>) declare void @llvm.memset.i16(i8 * <dest>, i8 <val>, i16 <len>, i32 <align>) declare void @llvm.memset.i32(i8 * <dest>, i8 <val>, i32 <len>, i32 <align>) declare void @llvm.memset.i64(i8 * <dest>, i8 <val>, i64 <len>, i32 <align>)
The 'llvm.memset.*' intrinsics fill a block of memory with a particular byte value.
Note that, unlike the standard libc function, the llvm.memset intrinsic does not return a value, and takes an extra alignment argument.
The first argument is a pointer to the destination to fill, the second is the byte value to fill it with, the third argument is an integer argument specifying the number of bytes to fill, and the fourth argument is the known alignment of destination location.
If the call to this intrinisic has an alignment value that is not 0 or 1, then the caller guarantees that the destination pointer is aligned to that boundary.
The 'llvm.memset.*' intrinsics fill "len" bytes of memory starting at the destination location. If the argument is known to be aligned to some boundary, this can be specified as the fourth argument, otherwise it should be set to 0 or 1.
This is an overloaded intrinsic. You can use llvm.sqrt on any floating point or vector of floating point type. Not all targets support all types however.
declare float @llvm.sqrt.f32(float %Val) declare double @llvm.sqrt.f64(double %Val) declare x86_fp80 @llvm.sqrt.f80(x86_fp80 %Val) declare fp128 @llvm.sqrt.f128(fp128 %Val) declare ppc_fp128 @llvm.sqrt.ppcf128(ppc_fp128 %Val)
The 'llvm.sqrt' intrinsics return the sqrt of the specified operand, returning the same value as the libm 'sqrt' functions would. Unlike sqrt in libm, however, llvm.sqrt has undefined behavior for negative numbers other than -0.0 (which allows for better optimization, because there is no need to worry about errno being set). llvm.sqrt(-0.0) is defined to return -0.0 like IEEE sqrt.
The argument and return value are floating point numbers of the same type.
This function returns the sqrt of the specified operand if it is a nonnegative floating point number.
This is an overloaded intrinsic. You can use llvm.powi on any floating point or vector of floating point type. Not all targets support all types however.
declare float @llvm.powi.f32(float %Val, i32 %power) declare double @llvm.powi.f64(double %Val, i32 %power) declare x86_fp80 @llvm.powi.f80(x86_fp80 %Val, i32 %power) declare fp128 @llvm.powi.f128(fp128 %Val, i32 %power) declare ppc_fp128 @llvm.powi.ppcf128(ppc_fp128 %Val, i32 %power)
The 'llvm.powi.*' intrinsics return the first operand raised to the specified (positive or negative) power. The order of evaluation of multiplications is not defined. When a vector of floating point type is used, the second argument remains a scalar integer value.
The second argument is an integer power, and the first is a value to raise to that power.
This function returns the first value raised to the second power with an unspecified sequence of rounding operations.
This is an overloaded intrinsic. You can use llvm.sin on any floating point or vector of floating point type. Not all targets support all types however.
declare float @llvm.sin.f32(float %Val) declare double @llvm.sin.f64(double %Val) declare x86_fp80 @llvm.sin.f80(x86_fp80 %Val) declare fp128 @llvm.sin.f128(fp128 %Val) declare ppc_fp128 @llvm.sin.ppcf128(ppc_fp128 %Val)
The 'llvm.sin.*' intrinsics return the sine of the operand.
The argument and return value are floating point numbers of the same type.
This function returns the sine of the specified operand, returning the same values as the libm sin functions would, and handles error conditions in the same way.
This is an overloaded intrinsic. You can use llvm.cos on any floating point or vector of floating point type. Not all targets support all types however.
declare float @llvm.cos.f32(float %Val) declare double @llvm.cos.f64(double %Val) declare x86_fp80 @llvm.cos.f80(x86_fp80 %Val) declare fp128 @llvm.cos.f128(fp128 %Val) declare ppc_fp128 @llvm.cos.ppcf128(ppc_fp128 %Val)
The 'llvm.cos.*' intrinsics return the cosine of the operand.
The argument and return value are floating point numbers of the same type.
This function returns the cosine of the specified operand, returning the same values as the libm cos functions would, and handles error conditions in the same way.
This is an overloaded intrinsic. You can use llvm.pow on any floating point or vector of floating point type. Not all targets support all types however.
declare float @llvm.pow.f32(float %Val, float %Power) declare double @llvm.pow.f64(double %Val, double %Power) declare x86_fp80 @llvm.pow.f80(x86_fp80 %Val, x86_fp80 %Power) declare fp128 @llvm.pow.f128(fp128 %Val, fp128 %Power) declare ppc_fp128 @llvm.pow.ppcf128(ppc_fp128 %Val, ppc_fp128 Power)
The 'llvm.pow.*' intrinsics return the first operand raised to the specified (positive or negative) power.
The second argument is a floating point power, and the first is a value to raise to that power.
This function returns the first value raised to the second power, returning the same values as the libm pow functions would, and handles error conditions in the same way.
LLVM provides intrinsics for a few important bit manipulation operations. These allow efficient code generation for some algorithms.
This is an overloaded intrinsic function. You can use bswap on any integer type that is an even number of bytes (i.e. BitWidth % 16 == 0).
declare i16 @llvm.bswap.i16(i16 <id>) declare i32 @llvm.bswap.i32(i32 <id>) declare i64 @llvm.bswap.i64(i64 <id>)
The 'llvm.bswap' family of intrinsics is used to byte swap integer values with an even number of bytes (positive multiple of 16 bits). These are useful for performing operations on data that is not in the target's native byte order.
The llvm.bswap.i16 intrinsic returns an i16 value that has the high and low byte of the input i16 swapped. Similarly, the llvm.bswap.i32 intrinsic returns an i32 value that has the four bytes of the input i32 swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the returned i32 will have its bytes in 3, 2, 1, 0 order. The llvm.bswap.i48, llvm.bswap.i64 and other intrinsics extend this concept to additional even-byte lengths (6 bytes, 8 bytes and more, respectively).
This is an overloaded intrinsic. You can use llvm.ctpop on any integer bit width. Not all targets support all bit widths however.
declare i8 @llvm.ctpop.i8(i8 <src>) declare i16 @llvm.ctpop.i16(i16 <src>) declare i32 @llvm.ctpop.i32(i32 <src>) declare i64 @llvm.ctpop.i64(i64 <src>) declare i256 @llvm.ctpop.i256(i256 <src>)
The 'llvm.ctpop' family of intrinsics counts the number of bits set in a value.
The only argument is the value to be counted. The argument may be of any integer type. The return type must match the argument type.
The 'llvm.ctpop' intrinsic counts the 1's in a variable.
This is an overloaded intrinsic. You can use llvm.ctlz on any integer bit width. Not all targets support all bit widths however.
declare i8 @llvm.ctlz.i8 (i8 <src>) declare i16 @llvm.ctlz.i16(i16 <src>) declare i32 @llvm.ctlz.i32(i32 <src>) declare i64 @llvm.ctlz.i64(i64 <src>) declare i256 @llvm.ctlz.i256(i256 <src>)
The 'llvm.ctlz' family of intrinsic functions counts the number of leading zeros in a variable.
The only argument is the value to be counted. The argument may be of any integer type. The return type must match the argument type.
The 'llvm.ctlz' intrinsic counts the leading (most significant) zeros in a variable. If the src == 0 then the result is the size in bits of the type of src. For example, llvm.ctlz(i32 2) = 30.
This is an overloaded intrinsic. You can use llvm.cttz on any integer bit width. Not all targets support all bit widths however.
declare i8 @llvm.cttz.i8 (i8 <src>) declare i16 @llvm.cttz.i16(i16 <src>) declare i32 @llvm.cttz.i32(i32 <src>) declare i64 @llvm.cttz.i64(i64 <src>) declare i256 @llvm.cttz.i256(i256 <src>)
The 'llvm.cttz' family of intrinsic functions counts the number of trailing zeros.
The only argument is the value to be counted. The argument may be of any integer type. The return type must match the argument type.
The 'llvm.cttz' intrinsic counts the trailing (least significant) zeros in a variable. If the src == 0 then the result is the size in bits of the type of src. For example, llvm.cttz(2) = 1.
This is an overloaded intrinsic. You can use llvm.part.select on any integer bit width.
declare i17 @llvm.part.select.i17 (i17 %val, i32 %loBit, i32 %hiBit) declare i29 @llvm.part.select.i29 (i29 %val, i32 %loBit, i32 %hiBit)
The 'llvm.part.select' family of intrinsic functions selects a range of bits from an integer value and returns them in the same bit width as the original value.
The first argument, %val and the result may be integer types of any bit width but they must have the same bit width. The second and third arguments must be i32 type since they specify only a bit index.
The operation of the 'llvm.part.select' intrinsic has two modes of operation: forwards and reverse. If %loBit is greater than %hiBits then the intrinsic operates in reverse mode. Otherwise it operates in forward mode.
In forward mode, this intrinsic is the equivalent of shifting %val right by %loBit bits and then ANDing it with a mask with only the %hiBit - %loBit bits set, as follows:
In reverse mode, a similar computation is made except that the bits are returned in the reverse order. So, for example, if X has the value i16 0x0ACF<PHONE_NUMBER>11) and we apply part.select(i16 X, 8, 3) to it, we get back the value i16 0x0026<PHONE_NUMBER>10).
This is an overloaded intrinsic. You can use llvm.part.set on any integer bit width.
declare i17 @llvm.part.set.i17.i9 (i17 %val, i9 %repl, i32 %lo, i32 %hi) declare i29 @llvm.part.set.i29.i9 (i29 %val, i9 %repl, i32 %lo, i32 %hi)
The 'llvm.part.set' family of intrinsic functions replaces a range of bits in an integer value with another integer value. It returns the integer with the replaced bits.
The first argument, %val, and the result may be integer types of any bit width, but they must have the same bit width. %val is the value whose bits will be replaced. The second argument, %repl may be an integer of any bit width. The third and fourth arguments must be i32 type since they specify only a bit index.
The operation of the 'llvm.part.set' intrinsic has two modes of operation: forwards and reverse. If %lo is greater than %hi then the intrinsic operates in reverse mode. Otherwise it operates in forward mode.
For both modes, the %repl value is prepared for use by either truncating it down to the size of the replacement area or zero extending it up to that size.
In forward mode, the bits between %lo and %hi (inclusive) are replaced with corresponding bits from %repl. That is the 0th bit in %repl replaces the %loth bit in %val and etc. up to the %hith bit.
In reverse mode, a similar computation is made except that the bits are reversed. That is, the 0th bit in %repl replaces the %hi bit in %val and etc. down to the %loth bit.
llvm.part.set(0xFFFF, 0, 4, 7) -> 0xFF0F llvm.part.set(0xFFFF, 0, 7, 4) -> 0xFF0F llvm.part.set(0xFFFF, 1, 7, 4) -> 0xFF8F llvm.part.set(0xFFFF, F, 8, 3) -> 0xFFE7 llvm.part.set(0xFFFF, 0, 3, 8) -> 0xFE07
LLVM provides intrinsics for some arithmetic with overflow operations.
This is an overloaded intrinsic. You can use llvm.sadd.with.overflow on any integer bit width.
declare {i16, i1} @llvm.sadd.with.overflow.i16(i16 %a, i16 %b) declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) declare {i64, i1} @llvm.sadd.with.overflow.i64(i64 %a, i64 %b)
The 'llvm.sadd.with.overflow' family of intrinsic functions perform a signed addition of the two arguments, and indicate whether an overflow occurred during the signed summation.
The arguments (%a and %b) and the first element of the result structure may be of integer types of any bit width, but they must have the same bit width. The second element of the result structure must be of type i1. %a and %b are the two values that will undergo signed addition.
The 'llvm.sadd.with.overflow' family of intrinsic functions perform a signed addition of the two variables. They return a structure — the first element of which is the signed summation, and the second element of which is a bit specifying if the signed summation resulted in an overflow.
%res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b) %sum = extractvalue {i32, i1} %res, 0 %obit = extractvalue {i32, i1} %res, 1 br i1 %obit, label %overflow, label %normal
This is an overloaded intrinsic. You can use llvm.uadd.with.overflow on any integer bit width.
declare {i16, i1} @llvm.uadd.with.overflow.i16(i16 %a, i16 %b) declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b) declare {i64, i1} @llvm.uadd.with.overflow.i64(i64 %a, i64 %b)
The 'llvm.uadd.with.overflow' family of intrinsic functions perform an unsigned addition of the two arguments, and indicate whether a carry occurred during the unsigned summation.
The arguments (%a and %b) and the first element of the result structure may be of integer types of any bit width, but they must have the same bit width. The second element of the result structure must be of type i1. %a and %b are the two values that will undergo unsigned addition.
The 'llvm.uadd.with.overflow' family of intrinsic functions perform an unsigned addition of the two arguments. They return a structure — the first element of which is the sum, and the second element of which is a bit specifying if the unsigned summation resulted in a carry.
%res = call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b) %sum = extractvalue {i32, i1} %res, 0 %obit = extractvalue {i32, i1} %res, 1 br i1 %obit, label %carry, label %normal
This is an overloaded intrinsic. You can use llvm.ssub.with.overflow on any integer bit width.
declare {i16, i1} @llvm.ssub.with.overflow.i16(i16 %a, i16 %b) declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b) declare {i64, i1} @llvm.ssub.with.overflow.i64(i64 %a, i64 %b)
The 'llvm.ssub.with.overflow' family of intrinsic functions perform a signed subtraction of the two arguments, and indicate whether an overflow occurred during the signed subtraction.
The arguments (%a and %b) and the first element of the result structure may be of integer types of any bit width, but they must have the same bit width. The second element of the result structure must be of type i1. %a and %b are the two values that will undergo signed subtraction.
The 'llvm.ssub.with.overflow' family of intrinsic functions perform a signed subtraction of the two arguments. They return a structure — the first element of which is the subtraction, and the second element of which is a bit specifying if the signed subtraction resulted in an overflow.
%res = call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b) %sum = extractvalue {i32, i1} %res, 0 %obit = extractvalue {i32, i1} %res, 1 br i1 %obit, label %overflow, label %normal
This is an overloaded intrinsic. You can use llvm.usub.with.overflow on any integer bit width.
declare {i16, i1} @llvm.usub.with.overflow.i16(i16 %a, i16 %b) declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b) declare {i64, i1} @llvm.usub.with.overflow.i64(i64 %a, i64 %b)
The 'llvm.usub.with.overflow' family of intrinsic functions perform an unsigned subtraction of the two arguments, and indicate whether an overflow occurred during the unsigned subtraction.
The arguments (%a and %b) and the first element of the result structure may be of integer types of any bit width, but they must have the same bit width. The second element of the result structure must be of type i1. %a and %b are the two values that will undergo unsigned subtraction.
The 'llvm.usub.with.overflow' family of intrinsic functions perform an unsigned subtraction of the two arguments. They return a structure — the first element of which is the subtraction, and the second element of which is a bit specifying if the unsigned subtraction resulted in an overflow.
%res = call {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b) %sum = extractvalue {i32, i1} %res, 0 %obit = extractvalue {i32, i1} %res, 1 br i1 %obit, label %overflow, label %normal
This is an overloaded intrinsic. You can use llvm.smul.with.overflow on any integer bit width.
declare {i16, i1} @llvm.smul.with.overflow.i16(i16 %a, i16 %b) declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b) declare {i64, i1} @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
The 'llvm.smul.with.overflow' family of intrinsic functions perform a signed multiplication of the two arguments, and indicate whether an overflow occurred during the signed multiplication.
The arguments (%a and %b) and the first element of the result structure may be of integer types of any bit width, but they must have the same bit width. The second element of the result structure must be of type i1. %a and %b are the two values that will undergo signed multiplication.
The 'llvm.smul.with.overflow' family of intrinsic functions perform a signed multiplication of the two arguments. They return a structure — the first element of which is the multiplication, and the second element of which is a bit specifying if the signed multiplication resulted in an overflow.
%res = call {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b) %sum = extractvalue {i32, i1} %res, 0 %obit = extractvalue {i32, i1} %res, 1 br i1 %obit, label %overflow, label %normal
This is an overloaded intrinsic. You can use llvm.umul.with.overflow on any integer bit width.
declare {i16, i1} @llvm.umul.with.overflow.i16(i16 %a, i16 %b) declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b) declare {i64, i1} @llvm.umul.with.overflow.i64(i64 %a, i64 %b)
Warning: 'llvm.umul.with.overflow' is badly broken. It is actively being fixed, but it should not currently be used!
The 'llvm.umul.with.overflow' family of intrinsic functions perform a unsigned multiplication of the two arguments, and indicate whether an overflow occurred during the unsigned multiplication.
The arguments (%a and %b) and the first element of the result structure may be of integer types of any bit width, but they must have the same bit width. The second element of the result structure must be of type i1. %a and %b are the two values that will undergo unsigned multiplication.
The 'llvm.umul.with.overflow' family of intrinsic functions perform an unsigned multiplication of the two arguments. They return a structure — the first element of which is the multiplication, and the second element of which is a bit specifying if the unsigned multiplication resulted in an overflow.
%res = call {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b) %sum = extractvalue {i32, i1} %res, 0 %obit = extractvalue {i32, i1} %res, 1 br i1 %obit, label %overflow, label %normal
The LLVM debugger intrinsics (which all start with llvm.dbg. prefix), are described in the LLVM Source Level Debugging document.
The LLVM exception handling intrinsics (which all start with llvm.eh. prefix), are described in the LLVM Exception Handling document.
This intrinsic makes it possible to excise one parameter, marked with the nest attribute, from a function. The result is a callable function pointer lacking the nest parameter - the caller does not need to provide a value for it. Instead, the value to use is stored in advance in a "trampoline", a block of memory usually allocated on the stack, which also contains code to splice the nest value into the argument list. This is used to implement the GCC nested function address extension.
For example, if the function is i32 f(i8* nest %c, i32 %x, i32 %y) then the resulting function pointer has signature i32 (i32, i32)*. It can be created as follows:
%tramp = alloca [10 x i8], align 4 ; size and alignment only correct for X86 %tramp1 = getelementptr [10 x i8]* %tramp, i32 0, i32 0 %p = call i8* @llvm.init.trampoline( i8* %tramp1, i8* bitcast (i32 (i8* nest , i32, i32)* @f to i8*), i8* %nval ) %fp = bitcast i8* %p to i32 (i32, i32)*
The call %val = call i32 %fp( i32 %x, i32 %y ) is then equivalent to %val = call i32 %f( i8* %nval, i32 %x, i32 %y ).
declare i8* @llvm.init.trampoline(i8* <tramp>, i8* <func>, i8* <nval>)
This fills the memory pointed to by tramp with code and returns a function pointer suitable for executing it.
The llvm.init.trampoline intrinsic takes three arguments, all pointers. The tramp argument must point to a sufficiently large and sufficiently aligned block of memory; this memory is written to by the intrinsic. Note that the size and the alignment are target-specific - LLVM currently provides no portable way of determining them, so a front-end that generates this intrinsic needs to have some target-specific knowledge. The func argument must hold a function bitcast to an i8*.
The block of memory pointed to by tramp is filled with target dependent code, turning it into a function. A pointer to this function is returned, but needs to be bitcast to an appropriate function pointer type before being called. The new function's signature is the same as that of func with any arguments marked with the nest attribute removed. At most one such nest argument is allowed, and it must be of pointer type. Calling the new function is equivalent to calling func with the same argument list, but with nval used for the missing nest argument. If, after calling llvm.init.trampoline, the memory pointed to by tramp is modified, then the effect of any later call to the returned function pointer is undefined.
These intrinsic functions expand the "universal IR" of LLVM to represent hardware constructs for atomic operations and memory synchronization. This provides an interface to the hardware, not an interface to the programmer. It is aimed at a low enough level to allow any programming models or APIs (Application Programming Interfaces) which need atomic behaviors to map cleanly onto it. It is also modeled primarily on hardware behavior. Just as hardware provides a "universal IR" for source languages, it also provides a starting point for developing a "universal" atomic operation and synchronization IR.
These do not form an API such as high-level threading libraries, software transaction memory systems, atomic primitives, and intrinsic functions as found in BSD, GNU libc, atomic_ops, APR, and other system and application libraries. The hardware interface provided by LLVM should allow a clean implementation of all of these APIs and parallel programming models. No one model or paradigm should be selected above others unless the hardware itself ubiquitously does so.
declare void @llvm.memory.barrier( i1 <ll>, i1 <ls>, i1 <sl>, i1 <ss>, i1 <device> )
The llvm.memory.barrier intrinsic guarantees ordering between specific pairs of memory access types.
The llvm.memory.barrier intrinsic requires five boolean arguments. The first four arguments enables a specific barrier as listed below. The fith argument specifies that the barrier applies to io or device or uncached memory.
This intrinsic causes the system to enforce some ordering constraints upon the loads and stores of the program. This barrier does not indicate when any events will occur, it only enforces an order in which they occur. For any of the specified pairs of load and store operations (f.ex. load-load, or store-load), all of the first operations preceding the barrier will complete before any of the second operations succeeding the barrier begin. Specifically the semantics for each pairing is as follows:
These semantics are applied with a logical "and" behavior when more than one is enabled in a single memory barrier intrinsic.
Backends may implement stronger barriers than those requested when they do not support as fine grained a barrier as requested. Some architectures do not need all types of barriers and on such architectures, these become noops.
%ptr = malloc i32 store i32 4, %ptr %result1 = load i32* %ptr ; yields {i32}:result1 = 4 call void @llvm.memory.barrier( i1 false, i1 true, i1 false, i1 false ) ; guarantee the above finishes store i32 8, %ptr ; before this begins
This is an overloaded intrinsic. You can use llvm.atomic.cmp.swap on any integer bit width and for different address spaces. Not all targets support all bit widths however.
declare i8 @llvm.atomic.cmp.swap.i8.p0i8( i8* <ptr>, i8 <cmp>, i8 <val> ) declare i16 @llvm.atomic.cmp.swap.i16.p0i16( i16* <ptr>, i16 <cmp>, i16 <val> ) declare i32 @llvm.atomic.cmp.swap.i32.p0i32( i32* <ptr>, i32 <cmp>, i32 <val> ) declare i64 @llvm.atomic.cmp.swap.i64.p0i64( i64* <ptr>, i64 <cmp>, i64 <val> )
This loads a value in memory and compares it to a given value. If they are equal, it stores a new value into the memory.
The llvm.atomic.cmp.swap intrinsic takes three arguments. The result as well as both cmp and val must be integer values with the same bit width. The ptr argument must be a pointer to a value of this integer type. While any bit width integer may be used, targets may only lower representations they support in hardware.
This entire intrinsic must be executed atomically. It first loads the value in memory pointed to by ptr and compares it with the value cmp. If they are equal, val is stored into the memory. The loaded value is yielded in all cases. This provides the equivalent of an atomic compare-and-swap operation within the SSA framework.
%ptr = malloc i32 store i32 4, %ptr %val1 = add i32 4, 4 %result1 = call i32 @llvm.atomic.cmp.swap.i32.p0i32( i32* %ptr, i32 4, %val1 ) ; yields {i32}:result1 = 4 %stored1 = icmp eq i32 %result1, 4 ; yields {i1}:stored1 = true %memval1 = load i32* %ptr ; yields {i32}:memval1 = 8 %val2 = add i32 1, 1 %result2 = call i32 @llvm.atomic.cmp.swap.i32.p0i32( i32* %ptr, i32 5, %val2 ) ; yields {i32}:result2 = 8 %stored2 = icmp eq i32 %result2, 5 ; yields {i1}:stored2 = false %memval2 = load i32* %ptr ; yields {i32}:memval2 = 8
This is an overloaded intrinsic. You can use llvm.atomic.swap on any integer bit width. Not all targets support all bit widths however.
declare i8 @llvm.atomic.swap.i8.p0i8( i8* <ptr>, i8 <val> ) declare i16 @llvm.atomic.swap.i16.p0i16( i16* <ptr>, i16 <val> ) declare i32 @llvm.atomic.swap.i32.p0i32( i32* <ptr>, i32 <val> ) declare i64 @llvm.atomic.swap.i64.p0i64( i64* <ptr>, i64 <val> )
This intrinsic loads the value stored in memory at ptr and yields the value from memory. It then stores the value in val in the memory at ptr.
The llvm.atomic.swap intrinsic takes two arguments. Both the val argument and the result must be integers of the same bit width. The first argument, ptr, must be a pointer to a value of this integer type. The targets may only lower integer representations they support.
This intrinsic loads the value pointed to by ptr, yields it, and stores val back into ptr atomically. This provides the equivalent of an atomic swap operation within the SSA framework.