1. Abstract
2. Introduction
3. Identifiers
4. Type System
   1. Primitive Types
      1. Type Classifications
   2. Derived Types
      1. Array Type
      2. Function Type
      3. Pointer Type
      4. Structure Type
      5. Packed Type
5. High Level Structure
   1. Module Structure
   2. Function Structure
6. Instruction Reference
   1. Terminator Instructions
      1. 'ret' Instruction
      2. 'br' Instruction
      3. 'switch' Instruction
      4. 'invoke' Instruction
   2. Unary Operations
      1. 'not' Instruction
   3. Binary Operations
      1. 'add' Instruction
      2. 'sub' Instruction
      3. 'mul' Instruction
      4. 'div' Instruction
      5. 'rem' Instruction
      6. 'setcc' Instructions
   4. Bitwise Binary Operations
      1. 'and' Instruction
      2. 'or' Instruction
      3. 'xor' Instruction
      4. 'shl' Instruction
      5. 'shr' Instruction
   5. Memory Access Operations
      1. 'malloc' Instruction
      2. 'free' Instruction
      3. 'alloca' Instruction
      4. 'getelementptr' Instruction
      5. 'load' Instruction
      6. 'store' Instruction
   6. Other Operations
      1. 'cast .. to' Instruction
      2. 'call' Instruction
      3. 'icall' Instruction
      4. 'phi' Instruction
   7. Builtin Functions
7. TODO List
   1. Exception Handling Instructions
   2. Synchronization Instructions
8. Possible Extensions
   1. 'tailcall' Instruction
   2. Global Variables
   3. Explicit Parrellelism
9. Related Work

Abstract

This document describes the LLVM assembly language. LLVM is an SSA based representation that is a useful midlevel IR, providing type safety, low level operations, flexibility, and the capability to represent 'all' high level languages cleanly.

The LLVM code representation is designed to be used in three different forms: as an in-memory compiler IR, as an on-disk bytecode representation, suitable for fast loading by a dynamic 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 a light weight and low level while being expressive, type safe, 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 safety, 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 int 1, %x

...because only a phi node may refer to itself. The LLVM api provides a verification pass (created by the createVerifierPass function) 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 bytecode. Often, violations pointed out by the verifier pass indicate bugs in transformation passes.

Describe the typesetting conventions here.

LLVM uses three different forms of identifiers, for different purposes:
1. Numeric constants are represented as you would expect: 12, -3 123.421, etc.
2. Named values are represented as a string of characters with a '%' prefix. For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual regular expression used is '%[a-zA-Z$._][a-zA-Z$._0-9]*'.
3. Unnamed values are represented as an unsigned numeric value with a '%' prefix. For example, %12, %2, %44.

LLVM requires the values start with a '%' sign 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', 'cast', 'ret', etc...), for primitive type names ('void', 'uint', etc...), and others. These reserved words cannot conflict with variable names, because none of them start with a '%' character.

Here is an example of LLVM code to multiply the integer variable '%X' by 8:

The easy way:

  %result = mul int %X, 8

After strength reduction:

  %result = shl int %X, ubyte 3

And the hard way:

  add int %X, %X           ; yields {int}:%0
  add int %0, %0           ; yields {int}:%1
  %result = add int %1, %1

This last way of multiplying %X by 8 illustrates several important lexical features of LLVM:
1. Comments are delimited with a ';' and go until the end of line.
2. Unnamed temporaries are created when the result of a computation is not assigned to a named value.
3. Unnamed temporaries are numbered sequentially

...and it also show 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.

The LLVM type system is critical to the overall usefulness of the language and runtime. Being strongly typed enables a number of optimizations to be performed on the IR 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 assembly language form for the type system was heavily influenced by the type problems in the C language¹.

The primitive types are the fundemental building blocks of the LLVM system. The current set of primitive types are as follows:

void No value ubyte Unsigned 8 bit value ushort Unsigned 16 bit value uint Unsigned 32 bit value ulong Unsigned 64 bit value float 32 bit floating point value label Branch destination

bool True or False value sbyte Signed 8 bit value short Signed 16 bit value int Signed 32 bit value long Signed 64 bit value double 64 bit floating point value

Overview:

The structure type is used to represent a collection of data members together in memory. Although the runtime is allowed to lay out the data members any way that it would like, they are guaranteed to be "close" to each other.

Structures are accessed using 'load and 'store' by getting a pointer to a field with the 'getelementptr' instruction.

Syntax:

  { <type list> }

Examples:

{ int, int, int }	: a triple of three int values
{ float, int (int *) * }	: A pair, where the first element is a float and the second element is a pointer to a function that takes an int, returning an int.

As was mentioned previously, every basic block in a program ends with a "Terminator" instruction. All of these terminator instructions yield a 'void' value: they produce control flow, not values.

There are four different terminator instructions: the 'ret' instruction, the 'br' instruction, the 'switch' instruction, and the 'invoke' instruction.

Syntax:

  ret <type> <value>       ; Return a value from a non-void function
  ret void                 ; Return from void function

Overview:

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' instructruction: one that returns a value and then causes control flow, and one that just causes control flow to occur.

Arguments:

The 'ret' instruction may return any 'first class' type. Notice that a function is not well formed if there exists a 'ret' instruction inside of the function that returns a value that does not match the return type of the function.

Semantics:

When the 'ret' instruction is executed, control flow returns back to the calling function's context. If the instruction returns a value, that value shall be propogated into the calling function's data space.

Example:

  ret int 5                       ; Return an integer value of 5
  ret void                        ; Return from a void function

Syntax:

  br bool <cond>, label <iftrue>, label <iffalse>
  br label <dest>          ; Unconditional branch

Overview:

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.

Arguments:

The conditional branch form of the 'br' instruction takes a single 'bool' value and two 'label' values. The unconditional form of the 'br' instruction takes a single 'label' value as a target.

Semantics:

Upon execution of a conditional 'br' instruction, the 'bool' 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.

Example:

Test:
  %cond = seteq int %a, %b
  br bool %cond, label %IfEqual, label %IfUnequal
IfEqual:
  ret bool true
IfUnequal:
  ret bool false

Syntax:

  ; Definitions for lookup indirect branch
  %switchtype = type [<anysize> x { uint, label }]

  ; Lookup indirect branch
  switch uint <value>, label <defaultdest>, %switchtype <switchtable>

  ; Indexed indirect branch
  switch uint <idxvalue>, label <defaultdest>, [<anysize> x label] <desttable>

Overview:

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' statement supports two different styles of indirect branching: lookup branching and indexed branching. Lookup branching is generally useful if the values to switch on are spread far appart, where index branching is useful if the values to switch on are generally dense.

The two different forms of the 'switch' statement are simple hints to the underlying virtual machine implementation. For example, a virtual machine may choose to implement a small indirect branch table as a series of predicated comparisons: if it is faster for the target architecture.

Arguments:

The lookup form of the 'switch' instruction uses three parameters: a 'uint' comparison value 'value', a default 'label' destination, and an array of pairs of comparison value constants and 'label's. The sized array must be a constant value.

The indexed form of the 'switch' instruction uses three parameters: an 'uint' index value, a default 'label' and a sized array of 'label's. The 'dests' array must be a constant array.

Semantics:

The lookup style switch statement 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, the corresponding destination is branched to.

The index branch form simply looks up a label element directly in a table and branches to it.

In either case, the compiler knows the static size of the array, because it is provided as part of the constant values type.

Example:

  ; Emulate a conditional br instruction
  %Val = cast bool %value to uint
  switch uint %Val, label %truedest, [1 x label] [label %falsedest ]

  ; Emulate an unconditional br instruction
  switch uint 0, label %dest, [ 0 x label] [ ]

  ; Implement a jump table using the constant pool:
  void "testmeth"(int %arg0)
    %switchdests = [3 x label] [ label %onzero, label %onone, label %ontwo ]
  begin
  ...
    switch uint %val, label %otherwise, [3 x label] %switchdests...
  ...
  end

  ; Implement the equivilent jump table directly:
  switch uint %val, label %otherwise, [3 x label] [ label %onzero, 
                                                    label %onone, 
                                                    label %ontwo ]

Syntax:

  <result> = invoke <ptr to function ty> %<function ptr val>(<function args>)
                 to label <normal label> except label <exception label>

Overview:

The 'invoke' instruction is used to cause control flow to transfer to a specified function, with the possibility of control flow transfer to either the 'normal label' label or the 'exception label'. The 'call' instruction is closely related, but guarantees that control flow either never returns from the called function, or that it returns to the instruction succeeding the 'call' instruction.

Arguments:

This instruction requires several arguments:
1. 'ptr to function ty': shall be the signature of the pointer to function value being invoked. In most cases, this is a direct method invocation, but indirect invoke's are just as possible, branching off an arbitrary pointer to function value.

2. 'function ptr val': An LLVM value containing a pointer to a function to be invoked.
3. 'function args': argument list whose types match the function signature argument types.
4. 'normal label': the label reached when the called function executes a 'ret' instruction.
5. 'exception label': the label reached when an exception is thrown.

Semantics:

This instruction is designed to operate as a standard 'call' instruction in most regards. The primary difference is that it assiciates a label with the function invocation that may be accessed via the runtime library provided by the execution environment. 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.

For a more comprehensive explanation of this instruction look in the llvm/docs/2001-05-18-ExceptionHandling.txt document.

Example:

  %retval = invoke int %Test(int 15)
              to label %Continue except label %TestCleanup     ; {int}:retval set

Unary operators are used to do a simple operation to a single value.

There is only one unary operator: the 'not' instruction.

Syntax:

  <result> = not <ty> <var>       ; yields {ty}:result

Overview:

The 'not' instruction returns the logical inverse of its operand.

Arguments:

The single argument to 'not' must be of of integral type.

Semantics:

The 'not' instruction returns the logical inverse of an integral type.

  <result> = xor bool true, <var> ; yields {bool}:result

Example:

  %x = not int 1                  ; {int}:x is now equal to 0
  %x = not bool true              ; {bool}:x is now equal to false

Binary operators are used to do most of the computation in a program. They require two operands, execute an operation on them, and produce a single value. The result value of a binary operator is not neccesarily the same type as its operands.

There are several different binary operators:

Syntax:

  <result> = add <ty> <var1>, <var2>   ; yields {ty}:result

Overview:

The 'add' instruction returns the sum of its two operands.

Arguments:

The two arguments to the 'add' instruction must be either integral or floating point values. Both arguments must have identical types.

Semantics:

...

Example:

  <result> = add int 4, %var          ; yields {int}:result = 4 + %var

Syntax:

  <result> = sub <ty> <var1>, <var2>   ; yields {ty}:result

Overview:

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.

Arguments:

The two arguments to the 'sub' instruction must be either integral or floating point values. Both arguments must have identical types.

Semantics:

...

Example:

  <result> = sub int 4, %var          ; yields {int}:result = 4 - %var
  <result> = sub int 0, %val          ; yields {int}:result = -%var

Syntax:

  <result> = mul <ty> <var1>, <var2>   ; yields {ty}:result

Overview:

The 'mul' instruction returns the product of its two operands.

Arguments:

The two arguments to the 'mul' instruction must be either integral or floating point values. Both arguments must have identical types.

Semantics:

...

There is no signed vs unsigned multiplication. The appropriate action is taken based on the type of the operand.

Example:

  <result> = mul int 4, %var          ; yields {int}:result = 4 * %var

Syntax:

  <result> = div <ty> <var1>, <var2>   ; yields {ty}:result

Overview:

The 'div' instruction returns the quotient of its two operands.

Arguments:

The two arguments to the 'div' instruction must be either integral or floating point values. Both arguments must have identical types.

Semantics:

...

Example:

  <result> = div int 4, %var          ; yields {int}:result = 4 / %var

Syntax:

  <result> = rem <ty> <var1>, <var2>   ; yields {ty}:result

Overview:

The 'rem' instruction returns the remainder from the division of its two operands.

Arguments:

The two arguments to the 'rem' instruction must be either integral or floating point values. Both arguments must have identical types.

Semantics:

TODO: remainder or modulus?

...

Example:

  <result> = rem int 4, %var          ; yields {int}:result = 4 % %var

Syntax:

  <result> = seteq <ty> <var1>, <var2>   ; yields {bool}:result
  <result> = setne <ty> <var1>, <var2>   ; yields {bool}:result
  <result> = setlt <ty> <var1>, <var2>   ; yields {bool}:result
  <result> = setgt <ty> <var1>, <var2>   ; yields {bool}:result
  <result> = setle <ty> <var1>, <var2>   ; yields {bool}:result
  <result> = setge <ty> <var1>, <var2>   ; yields {bool}:result

Overview:

The 'setcc' family of instructions returns a boolean value based on a comparison of their two operands.

Arguments:

The two arguments to the 'setcc' instructions must be of first class or pointer type (it is not possible to compare 'label's, 'array's, 'structure' or 'void' values). Both arguments must have identical types.

The 'setlt', 'setgt', 'setle', and 'setge' instructions do not operate on 'bool' typed arguments.

Semantics:

The 'seteq' instruction yields a true 'bool' value if both operands are equal.
The 'setne' instruction yields a true 'bool' value if both operands are unequal.
The 'setlt' instruction yields a true 'bool' value if the first operand is less than the second operand.
The 'setgt' instruction yields a true 'bool' value if the first operand is greater than the second operand.
The 'setle' instruction yields a true 'bool' value if the first operand is less than or equal to the second operand.
The 'setge' instruction yields a true 'bool' value if the first operand is greater than or equal to the second operand.

Example:

  <result> = seteq int   4, 5        ; yields {bool}:result = false
  <result> = setne float 4, 5        ; yields {bool}:result = true
  <result> = setlt uint  4, 5        ; yields {bool}:result = true
  <result> = setgt sbyte 4, 5        ; yields {bool}:result = false
  <result> = setle sbyte 4, 5        ; yields {bool}:result = true
  <result> = setge sbyte 4, 5        ; yields {bool}:result = false

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, execute an operation on them, and produce a single value. The resulting value of the bitwise binary operators is always the same type as its first operand.

Syntax:

  <result> = and <ty> <var1>, <var2>   ; yields {ty}:result

Overview:

The 'and' instruction returns the bitwise logical and of its two operands.

Arguments:

The two arguments to the 'and' instruction must be either integral or bool values. Both arguments must have identical types.

Semantics:

...

Example:

  <result> = and int 4, %var         ; yields {int}:result = 4 & %var
  <result> = and int 15, 40          ; yields {int}:result = 8
  <result> = and int 4, 8            ; yields {int}:result = 0

Syntax:

  <result> = or <ty> <var1>, <var2>   ; yields {ty}:result

Overview:

The 'or' instruction returns the bitwise logical inclusive or of its two operands.

Arguments:

The two arguments to the 'or' instruction must be either integral or bool values. Both arguments must have identical types.

Semantics:

...

Example:

  <result> = or int 4, %var         ; yields {int}:result = 4 | %var
  <result> = or int 15, 40          ; yields {int}:result = 47
  <result> = or int 4, 8            ; yields {int}:result = 12

Syntax:

  <result> = xor <ty> <var1>, <var2>   ; yields {ty}:result

Overview:

The 'xor' instruction returns the bitwise logical exclusive or of its two operands.

Arguments:

The two arguments to the 'xor' instruction must be either integral or bool values. Both arguments must have identical types.

Semantics:

...

Example:

  <result> = xor int 4, %var         ; yields {int}:result = 4 ^ %var
  <result> = xor int 15, 40          ; yields {int}:result = 39
  <result> = xor int 4, 8            ; yields {int}:result = 12

Syntax:

  <result> = shl <ty> <var1>, ubyte <var2>   ; yields {ty}:result

Overview:

The 'shl' instruction returns the first operand shifted to the left a specified number of bits.

Arguments:

The first argument to the 'shl' instruction must be an integral type. The second argument must be an 'ubyte' type.

Semantics:

... 0 bits are shifted into the emptied bit positions...

Example:

  <result> = shl int 4, ubyte %var   ; yields {int}:result = 4 << %var
  <result> = shl int 4, ubyte 2      ; yields {int}:result = 16
  <result> = shl int 1, ubyte 10     ; yields {int}:result = 1024

Syntax:

  <result> = shr <ty> <var1>, ubyte <var2>   ; yields {ty}:result

Overview:

The 'shr' instruction returns the first operand shifted to the right a specified number of bits.

Arguments:

The first argument to the 'shr' instruction must be an integral type. The second argument must be an 'ubyte' type.

Semantics:

... if the first argument is a signed type, the most significant bit is duplicated in the newly free'd bit positions. If the first argument is unsigned, zeros shall fill the empty positions...

Example:

  <result> = shr int 4, ubyte %var   ; yields {int}:result = 4 >> %var
  <result> = shr int 4, ubyte 1      ; yields {int}:result = 2
  <result> = shr int 4, ubyte 2      ; yields {int}:result = 1
  <result> = shr int 4, ubyte 3      ; yields {int}:result = 0

Accessing memory in SSA form is, well, sticky at best. This section describes how to read and write memory in LLVM.

Syntax:

  <result> = malloc <type>, uint <NumElements>     ; yields {type*}:result
  <result> = malloc <type>                         ; yields {type*}:result

Overview:

The 'malloc' instruction allocates memory from the system heap and returns a pointer to it.

Arguments:

The 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. The second form of the instruction is a shorter version of the first instruction that defaults to allocating one element.

'type' must be a sized type

Semantics:

Memory is allocated, a pointer is returned.

Example:

  %array  = malloc [4 x ubyte ]                    ; yields {[%4 x ubyte]*}:array

  %size   = add uint 2, 2                          ; yields {uint}:size = uint 4
  %array1 = malloc ubyte, uint 4                   ; yields {ubyte*}:array1
  %array2 = malloc [12 x ubyte], uint %size        ; yields {[12 x ubyte]*}:array2

Syntax:

  free <type> <value>                              ; yields {void}

Overview:

The 'free' instruction returns memory back to the unused memory heap, to be reallocated in the future.

Arguments:

'value' shall be a pointer value that points to a value that was allocated with the 'malloc' instruction.

Semantics:

Memory is available for use after this point. The contents of the 'value' pointer are undefined after this instruction.

Example:

  %array  = malloc [4 x ubyte]                    ; yields {[4 x ubyte]*}:array
            free   [4 x ubyte]* %array

Syntax:

  <result> = getelementptr <ty>* <ptrval>{, uint <aidx>|, ubyte <sidx>}*

Overview:

The 'getelementptr' instruction is used to get the address of a subelement of an aggregate data structure. In addition to being present as an explicit instruction, the 'getelementptr' functionality is present in both the 'load' and 'store' instructions to allow more compact specification of common expressions.

Arguments:

This instruction takes a list of uint values and ubyte constants that indicate what form of addressing to perform. The actual types of the arguments provided depend on the type of the first pointer argument. The 'getelementptr' instruction is used to index down through the type levels of a structure.

TODO.

Semantics:

Example:

  %aptr = getelementptr {int, [12 x ubyte]}* %sptr, 1   ; yields {[12 x ubyte]*}:aptr
  %ub   = load [12x ubyte]* %aptr, 4                    ;yields {ubyte}:ub

Syntax:

  <result> = load <ty>* <pointer>
  <result> = load <ty>* <pointer> <index list>

Overview:

The 'load' instruction is used to read from memory.

Arguments:

There are three forms of the 'load' instruction: one for reading from a general pointer, one for reading from a pointer to an array, and one for reading from a pointer to a structure.

In the first form, '<ty>' must be a pointer to a simple type (a primitive type or another pointer).

In the second form, '<ty>' must be a pointer to an array, and a list of one or more indices is provided as indexes into the (possibly multidimensional) array. No bounds checking is performed on array reads.

In the third form, the pointer must point to a (possibly nested) structure. There shall be one ubyte argument for each level of dereferencing involved.

Semantics:

...

Examples:

  %ptr = alloca int                               ; yields {int*}:ptr
  store int 3, int* %ptr                          ; yields {void}
  %val = load int* %ptr                           ; yields {int}:val = int 3

  %array = malloc [4 x ubyte]                     ; yields {[4 x ubyte]*}:array
  store ubyte 124, [4 x ubyte]* %array, uint 4
  %val   = load [4 x ubyte]* %array, uint 4       ; yields {ubyte}:val = ubyte 124
  %val   = load {{int, float}}* %stptr, 0, 1      ; yields {float}:val

Syntax:

  store <ty> <value>, <ty>* <pointer>                   ; yields {void}
  store <ty> <value>, <ty>* <arrayptr>{, uint <idx>}+   ; yields {void}
  store <ty> <value>, <ty>* <structptr>{, ubyte <idx>}+ ; yields {void}e

Overview:

The 'store' instruction is used to write to memory.

Arguments:

There are three forms of the 'store' instruction: one for writing through a general pointer, one for writing through a pointer to a (possibly multidimensional) array, and one for writing to an element of a (potentially nested) structure.

The semantics of this instruction closely match that of the load instruction, except that memory is written to, not read from.

Semantics:

...

Example:

  %ptr = alloca int                               ; yields {int*}:ptr
  store int 3, int* %ptr                          ; yields {void}
  %val = load int* %ptr                           ; yields {int}:val = int 3

  %array = malloc [4 x ubyte]                     ; yields {[4 x ubyte]*}:array
  store ubyte 124, [4 x ubyte]* %array, uint 4
  %val   = load [4 x ubyte]* %array, uint 4       ; yields {ubyte}:val = ubyte 124
  %val   = load {{int, float}}* %stptr, 0, 1      ; yields {float}:val

The instructions in this catagory are the "miscellaneous" functions, that defy better classification.

TODO

Talk about what is considered true or false for integrals.

Syntax:

Overview:

Arguments:

Semantics:

Example:

Notice: Preliminary idea!

Builtin functions are very similar to normal functions, except they are defined by the implementation. Invocations of these functions are very similar to function invocations, except that the syntax is a little less verbose.

Builtin functions are useful to implement semi-high level ideas like a 'min' or 'max' operation that can have important properties when doing program analysis. For example:

• Some optimizations can make use of identities defined over the functions, for example a parrallelizing compiler could make use of 'min' identities to parrellelize a loop.
• Builtin functions would have polymorphic types, where normal function calls may only have a single type.
• Builtin functions would be known to not have side effects, simplifying analysis over straight function calls.
• The syntax of the builtin are cleaner than the syntax of the 'call' instruction (very minor point).
Because these invocations are explicit in the representation, the runtime can choose to implement these builtin functions any way that they want, including:
• Inlining the code directly into the invocation
• Implementing the functions in some sort of Runtime class, convert invocation to a standard function call.
• Implementing the functions in some sort of Runtime class, and perform standard inlining optimizations on it.
Note that these builtins do not use quoted identifiers: the name of the builtin effectively becomes an identifier in the language.

Example:

  ; Example of a normal function call
  %maximum = call int %maximum(int %arg1, int %arg2)   ; yields {int}:%maximum

  ; Examples of potential builtin functions
  %max = max(int %arg1, int %arg2)                     ; yields {int}:%max
  %min = min(int %arg1, int %arg2)                     ; yields {int}:%min
  %sin = sin(double %arg)                              ; yields {double}:%sin
  %cos = cos(double %arg)                              ; yields {double}:%cos

  ; Show that builtin's are polymorphic, like instructions
  %max = max(float %arg1, float %arg2)                 ; yields {float}:%max
  %cos = cos(float %arg)                               ; yields {float}:%cos

The 'maximum' vs 'max' example illustrates the difference in calling semantics between a 'call' instruction and a builtin function invocation. Notice that the 'maximum' example assumes that the function is defined local to the caller.

This list of random topics includes things that will need to be addressed before the llvm may be used to implement a java like langauge. Right now, it is pretty much useless for any language, given to unavailable of structure types

These extensions are distinct from the TODO list, as they are mostly "interesting" ideas that could be implemented in the future by someone so motivated. They are not directly required to get Java like languages working.

This could be useful. Who knows. '.net' does it, but is the optimization really worth the extra hassle? Using strong typing would make this trivial to implement and a runtime could always callback to using downconverting this to a normal 'call' instruction.

With the rise of massively parrellel architectures (like the IA64 architecture, multithreaded CPU cores, and SIMD data sets) it is becoming increasingly more important to extract all of the ILP from a code stream possible. It would be interesting to research encoding functions that can explicitly represent this. One straightforward way to do this would be to introduce a "stop" instruction that is equilivent to the IA64 stop bit.

Codesigned virtual machines.

SafeTSA

Description here

Java

Desciption here

Microsoft .net

Desciption here

GNU RTL Intermediate Representation

Desciption here

IA64 Architecture & Instruction Set

Desciption here

MMIX Instruction Set

Desciption here

"Interview With Bjarne Stroustrup"

This interview influenced the design and thought process behind LLVM in several ways, most notably the way that derived types are written in text format. See the question that starts with "you defined the C declarator syntax as an experiment that failed".

Intel MMX, MMX2, SSE, SSE2

Description here

AMD 3Dnow!, 3Dnow! 2

Desciption here

Sun VIS ISA

Desciption here

more...