3.2. Values

Values are what a module mostly consists of.


An undefined value (mapping to LLVM’s “undef”).

class llvmlite.ir.Constant(typ, constant)

A literal value. typ is the type of the represented value (a Type instance). constant is the Python value to be represented. Which Python types are allowed for constant depends on typ:

  • All types accept Undefined, and turn it into LLVM’s “undef”.
  • All types accept None, and turn it into LLVM’s “zeroinitializer”.
  • IntType accepts any Python integer or boolean.
  • FloatType and DoubleType accept any Python real number.
  • Aggregate types (i.e. array and structure types) accept a sequence of Python values corresponding to the type’s element types.
  • In addition, ArrayType also accepts a single bytearray instance to initialize the array from a string of bytes. This is useful for character constants.
classmethod literal_struct(elements)

An alternate constructor for constant structs. elements is a sequence of values (Constant or otherwise). A constant struct containing the elems in order is returned


You cannot define constant functions. Use a function declaration instead.

class llvmlite.ir.Value

The base class for non-literal values.

class llvmlite.ir.MetaDataString(module, value)

A string literal for use in metadata. module is the module the metadata belongs to. value is a Python string.

class llvmlite.ir.MDValue

A metadata node. To create an instance, call Module.add_metadata().

class llvmlite.ir.NamedMetaData

A named metadata. To create an instance, call Module.add_named_metadata(). Named metadata has the following method:


Append the given piece of metadata to the collection of operands referred to by the NamedMetaData. md can be either a MetaDataString or a MDValue.

class llvmlite.ir.Argument

One of a function’s arguments. Arguments have the following method:


Add an argument attribute to this argument. attr is a Python string.

class llvmlite.ir.Block

A basic block. You shouldn’t instantiate or mutate this type directly; instead, call the helper methods on Function and IRBuilder.

Basic blocks have the following methods and attributes:

replace(old, new)

Replace the instruction old with the other instruction new in this block’s list of instructions. All uses of old in the whole function are also patched. old and new are Instruction objects.


The function this block is defined in.


Whether this block ends with a terminator instruction.


The block’s terminator instruction, if any. Otherwise None.

class llvmlite.ir.BlockAddress

A constant representing an address of a basic block.

Block address constants have the following attributes:


The function the basic block is defined in.


The basic block. Must be a part of function.

3.2.1. Global values

Global values are values accessible using a module-wide name.

class llvmlite.ir.GlobalValue

The base class for global values. Global values have the following writable attribute:


A Python string describing the linkage behaviour of the global value (e.g. whether it is visible from other modules). Default is the empty string, meaning “external”.

class llvmlite.ir.GlobalVariable(module, typ, name, addrspace=0)

A global variable. module is where the variable will be defined. typ is the variable’s type. name is the variable’s name (a Python string). addrspace is an optional address space to store the variable in.

typ cannot be a function type. To declare a global function, use Function.

The returned Value’s actual type is a pointer to typ. To read (respectively write) the variable’s contents, you need to load() from (respectively store() to) the returned Value.

Global variables have the following writable attributes:


If true, the variable is declared a constant, i.e. its contents cannot be ever modified. Default is False.


If true, the address of the variable is deemed insignificant, i.e. it will be merged with other variables which have the same initializer. Default is False.


The variable’s initialization value (probably a Constant of type typ). Default is None, meaning the variable is uninitialized.

class llvmlite.ir.Function(module, typ, name)

A global function. module is where the function will be defined. typ is the function’s type (a FunctionType instance). name is the function’s name (a Python string).

If a global function has any basic blocks, it is a function definition. Otherwise, it is a function declaration.

Functions have the following methods and attributes:


Append a basic block to this function’s body. If name is non empty, it names the block’s entry label.

A new Block is returned.

insert_basic_block(before, name='')

Similar to append_basic_block(), but inserts it before the basic block before in the function’s list of basic blocks.


The function’s arguments as a tuple of Argument instances.


A set of function attributes. Each optional attribute is a Python string. By default this is empty. Use the add() method to add an attribute:

fnty = ir.FunctionType(ir.DoubleType(), (ir.DoubleType(),))
fn = Function(module, fnty, "sqrt")

The function’s calling convention (a Python string). Default is the empty string.


Whether the global function is a declaration (True) or a definition (False).

3.2.2. Instructions

Every instruction is also a value: it has a name (the recipient’s name), a well-defined type, and can be used as an operand in other instructions or in literals.

Instruction types should usually not be instantiated directly. Instead, use the helper methods on the IRBuilder class.

class llvmlite.ir.Instruction

The base class for all instructions. Instructions have the following method and attributes:

set_metadata(name, node)

Add an instruction-specific metadata named name pointing to the given metadata node (a MDValue).


The function this instruction is part of.


The module this instruction’s function is defined in.

class llvmlite.ir.PredictableInstr

The class of instructions for which we can specificy the probabilities of different outcomes (e.g. a switch or a conditional branch). Predictable instructions have the following method:


Set the weights of the instruction’s possible outcomes. weights is a sequence of positive integers, each corresponding to a different outcome and specifying its relative probability compared to other outcomes (the greater, the likelier).

class llvmlite.ir.SwitchInstr

A switch instruction. Switch instructions have the following method:

add_case(val, block)

Add a case to the switch instruction. val should be a Constant or a Python value compatible with the switch instruction’s operand type. block is a Block to jump to if, and only if, val and the switch operand compare equal.

class llvmlite.ir.IndirectBranch

An indirect branch instruction. Indirect branch instructions have the following method:

add_destination(value, block)

Add an outgoing edge. The indirect branch instruction must refer to every basic block it can transfer control to.

class llvmlite.ir.PhiInstr

A phi instruction. Phi instructions have the following method:

add_incoming(value, block)

Add an incoming edge. Whenever transfer is controlled from block (a Block), the phi instruction takes the given value.

class llvmlite.ir.LandingPad

A landing pad. Landing pads have the following method:

add_clause(value, block)

Add a catch or filter clause. Create catch clauses using CatchClause, and filter clauses using FilterClause.

3.2.3. Landing pad clauses

Landing pads have the following classes associated with them:

class llvmlite.ir.CatchClause(value)

A catch clause. Instructs the personality function to compare the in-flight exception typeinfo with value, which should have type IntType(8).as_pointer().as_pointer().

class llvmlite.ir.FilterClause(value)

A filter clause. Instructs the personality function to check inclusion of the the in-flight exception typeinfo in value, which should have type ArrayType(IntType(8).as_pointer().as_pointer(), ...).