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| -rw-r--r-- | doc/il.txt | 108 |
1 files changed, 108 insertions, 0 deletions
diff --git a/doc/il.txt b/doc/il.txt index bfd2867..6e058bf 100644 --- a/doc/il.txt +++ b/doc/il.txt @@ -274,6 +274,28 @@ the compiled file. They define a global symbol that contains a pointer to the function code. This pointer can be used in call instructions or stored in memory. +The type given right before the function name is the +return type of the function. All return values of this +function must have the return type. If the return +type is missing, the function cannot return any value. + +The parameter list is a comma separated list of +temporary names prefixed by types. The types are used +to correctly implement C compatibility. When an argument +has an aggregate type, is is set on entry of the +function to a pointer to the aggregate passed by the +caller. In the example below, we have to use a load +instruction to get the value of the first (and only) +member of the struct. + + type :one = { w } + + function w $getone(:one %p) { + @start + %val =w loadw %p + ret %val + } + Since global symbols are defined mutually recursive, there is no need for function declarations: A function can be referenced before its definition. @@ -304,9 +326,95 @@ can start with a sequence of <@ Phi > instructions. INST* # Regular instructions JUMP # Jump or return +All blocks have a name that is specified by a label at +their commencement. Then follows a sequence of +instructions that have "fall-through" flow. Finally +one jump terminates the block. The jump can either +transfer control to another block of the same function +or return, they are described further below. + +The first block in a function must not be the target of +any jump in the program. If this need is encountered, +the frontend can always insert an empty prelude block +at the beginning of the function. + +When one block jumps to the next block in the IL file, +it is not necessary to give the jump instruction, it +will be automatically added by the parser. For example +the start block in the example below jumps directly +to the loop block. + + function $loop() { + @start + @loop + %x =w phi @start 100, @loop %x1 + %x1 =w sub %x, 1 + jnz %x1, @loop, @end + @end + ret + } ~ Instructions ~~~~~~~~~~~~~~ +Regular instructions are described in details in sections +below. The IL uses a three-address code, which means that +one instruction computes an operation between two operands +and assigns the result to a third one. + +An instruction has both a name and a return type, this +return type is a base type that defines the size of the +instruction's result. The type of the arguments can be +unambiguously inferred using the instruction name and the +return type. For example, for all arithmetic instructions, +the type of the arguments is the same as the return type. +The two additions below are valid if `%y` is a word or a long +(because of <@ Subtyping >). + + %x =w add 0, %y + %z =w add %x, %x + +Some instructions, like comparisons and memory loads +have operand types that differ from their return types. +For instance, two floating points can be compared to give a +word result (0 if the comparison succeeds, 1 if it fails). + + %c =w cgts %a, %b + +In the example above, both operands have to have single type. +This is made explicit by the instruction suffix. + ~ Jumps ~~~~~~~ + + `bnf + JUMP := + 'jmp' @IDENT # Unconditional + | 'jnz' VAL, @IDENT, @IDENT # Conditional + | 'ret' [ VAL ] # Return + +A jump instruction ends every block and transfers the +control to another program location. The target of +a jump must never be the first block in a function. +The three kinds of jumps available are described in +the following list. + + 1. Unconditional jump. + + Simply jumps to another block of the same function. + + 2. Conditional jump. + + When its word argument is non-zero, it jumps to its + first label argument; otherwise it jumps to the other + label. The argument must be of word type, because of + subtyping a long argument can be passed, but only its + first 32 bits will be compared to 0. + + 3. Function return. + + Terminates the execution of the current function, + optionally returning a value to the caller. The value + returned must have the type given in the function + prototype. If the function prototype does not specify + a return type, no return value can be used. |