Creating and using functions

Params

gcc_jit_param

A gcc_jit_param represents a parameter to a function.

gcc_jit_param * gcc_jit_context_new_param(gcc_jit_context *ctxt, gcc_jit_location *loc, gcc_jit_type *type, const char *name)

In preparation for creating a function, create a new parameter of the given type and name.

The parameter type must be non-void.

The parameter name must be non-NULL. The call takes a copy of the underlying string, so it is valid to pass in a pointer to an on-stack buffer.

Parameters are lvalues, and thus are also rvalues (and objects), so the following upcasts are available:

gcc_jit_lvalue * gcc_jit_param_as_lvalue(gcc_jit_param *param)

Upcasting from param to lvalue.

gcc_jit_rvalue * gcc_jit_param_as_rvalue(gcc_jit_param *param)

Upcasting from param to rvalue.

gcc_jit_object * gcc_jit_param_as_object(gcc_jit_param *param)

Upcasting from param to object.

Functions

gcc_jit_function

A gcc_jit_function represents a function - either one that we’re creating ourselves, or one that we’re referencing.

gcc_jit_function * gcc_jit_context_new_function(gcc_jit_context *ctxt, gcc_jit_location *loc, enum gcc_jit_function_kind kind, gcc_jit_type *return_type, const char *name, int num_params, gcc_jit_param **params, int is_variadic)

Create a gcc_jit_function with the given name and parameters.

enum gcc_jit_function_kind

This enum controls the kind of function created, and has the following values:

GCC_JIT_FUNCTION_EXPORTED

Function is defined by the client code and visible by name outside of the JIT.

This value is required if you want to extract machine code for this function from a gcc_jit_result via gcc_jit_result_get_code().

GCC_JIT_FUNCTION_INTERNAL

Function is defined by the client code, but is invisible outside of the JIT. Analogous to a “static” function.

GCC_JIT_FUNCTION_IMPORTED

Function is not defined by the client code; we’re merely referring to it. Analogous to using an “extern” function from a header file.

GCC_JIT_FUNCTION_ALWAYS_INLINE

Function is only ever inlined into other functions, and is invisible outside of the JIT.

Analogous to prefixing with inline and adding __attribute__((always_inline))

Inlining will only occur when the optimization level is above 0; when optimization is off, this is essentially the same as GCC_JIT_FUNCTION_INTERNAL.

The parameter name must be non-NULL. The call takes a copy of the underlying string, so it is valid to pass in a pointer to an on-stack buffer.

gcc_jit_function * gcc_jit_context_get_builtin_function(gcc_jit_context *ctxt, const char *name)

Get the gcc_jit_function for the built-in function with the given name. For example:

gcc_jit_function *fn
  = gcc_jit_context_get_builtin_function (ctxt, "__builtin_memcpy");

Note

Due to technical limitations with how libgccjit interacts with the insides of GCC, not all built-in functions are supported. More precisely, not all types are supported for parameters of built-in functions from libgccjit. Attempts to get a built-in function that uses such a parameter will lead to an error being emitted within the context.

gcc_jit_object * gcc_jit_function_as_object(gcc_jit_function *func)

Upcasting from function to object.

gcc_jit_param * gcc_jit_function_get_param(gcc_jit_function *func, int index)

Get the param of the given index (0-based).

void gcc_jit_function_dump_to_dot(gcc_jit_function *func, const char *path)

Emit the function in graphviz format to the given path.

gcc_jit_lvalue * gcc_jit_function_new_local(gcc_jit_function *func, gcc_jit_location *loc, gcc_jit_type *type, const char *name)

Create a new local variable within the function, of the given type and name.

The parameter type must be non-void.

The parameter name must be non-NULL. The call takes a copy of the underlying string, so it is valid to pass in a pointer to an on-stack buffer.

Blocks

gcc_jit_block

A gcc_jit_block represents a basic block within a function i.e. a sequence of statements with a single entry point and a single exit point.

The first basic block that you create within a function will be the entrypoint.

Each basic block that you create within a function must be terminated, either with a conditional, a jump, a return, or a switch.

It’s legal to have multiple basic blocks that return within one function.

gcc_jit_block * gcc_jit_function_new_block(gcc_jit_function *func, const char *name)

Create a basic block of the given name. The name may be NULL, but providing meaningful names is often helpful when debugging: it may show up in dumps of the internal representation, and in error messages. It is copied, so the input buffer does not need to outlive the call; you can pass in a pointer to an on-stack buffer, e.g.:

for (pc = 0; pc < fn->fn_num_ops; pc++)
 {
   char buf[16];
   sprintf (buf, "instr%i", pc);
   state.op_blocks[pc] = gcc_jit_function_new_block (state.fn, buf);
 }
gcc_jit_object * gcc_jit_block_as_object(gcc_jit_block *block)

Upcast from block to object.

gcc_jit_function * gcc_jit_block_get_function(gcc_jit_block *block)

Which function is this block within?

Statements

void gcc_jit_block_add_eval(gcc_jit_block *block, gcc_jit_location *loc, gcc_jit_rvalue *rvalue)

Add evaluation of an rvalue, discarding the result (e.g. a function call that “returns” void).

This is equivalent to this C code:

(void)expression;
void gcc_jit_block_add_assignment(gcc_jit_block *block, gcc_jit_location *loc, gcc_jit_lvalue *lvalue, gcc_jit_rvalue *rvalue)

Add evaluation of an rvalue, assigning the result to the given lvalue.

This is roughly equivalent to this C code:

lvalue = rvalue;
void gcc_jit_block_add_assignment_op(gcc_jit_block *block, gcc_jit_location *loc, gcc_jit_lvalue *lvalue, enum gcc_jit_binary_op op, gcc_jit_rvalue *rvalue)

Add evaluation of an rvalue, using the result to modify an lvalue.

This is analogous to “+=” and friends:

lvalue += rvalue;
lvalue *= rvalue;
lvalue /= rvalue;

etc. For example:

/* "i++" */
gcc_jit_block_add_assignment_op (
  loop_body, NULL,
  i,
  GCC_JIT_BINARY_OP_PLUS,
  gcc_jit_context_one (ctxt, int_type));
void gcc_jit_block_add_comment(gcc_jit_block *block, gcc_jit_location *loc, const char *text)

Add a no-op textual comment to the internal representation of the code. It will be optimized away, but will be visible in the dumps seen via GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE and GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE, and thus may be of use when debugging how your project’s internal representation gets converted to the libgccjit IR.

The parameter text must be non-NULL. It is copied, so the input buffer does not need to outlive the call. For example:

char buf[100];
snprintf (buf, sizeof (buf),
          "op%i: %s",
          pc, opcode_names[op->op_opcode]);
gcc_jit_block_add_comment (block, loc, buf);
void gcc_jit_block_end_with_conditional(gcc_jit_block *block, gcc_jit_location *loc, gcc_jit_rvalue *boolval, gcc_jit_block *on_true, gcc_jit_block *on_false)

Terminate a block by adding evaluation of an rvalue, branching on the result to the appropriate successor block.

This is roughly equivalent to this C code:

if (boolval)
  goto on_true;
else
  goto on_false;

block, boolval, on_true, and on_false must be non-NULL.

void gcc_jit_block_end_with_jump(gcc_jit_block *block, gcc_jit_location *loc, gcc_jit_block *target)

Terminate a block by adding a jump to the given target block.

This is roughly equivalent to this C code:

goto target;
void gcc_jit_block_end_with_return(gcc_jit_block *block, gcc_jit_location *loc, gcc_jit_rvalue *rvalue)

Terminate a block by adding evaluation of an rvalue, returning the value.

This is roughly equivalent to this C code:

return expression;
void gcc_jit_block_end_with_void_return(gcc_jit_block *block, gcc_jit_location *loc)

Terminate a block by adding a valueless return, for use within a function with “void” return type.

This is equivalent to this C code:

return;
void gcc_jit_block_end_with_switch(gcc_jit_block *block, gcc_jit_location *loc, gcc_jit_rvalue *expr, gcc_jit_block *default_block, int num_cases, gcc_jit_case **cases)

Terminate a block by adding evalation of an rvalue, then performing a multiway branch.

This is roughly equivalent to this C code:

switch (expr)
  {
  default:
    goto default_block;

  case C0.min_value ... C0.max_value:
    goto C0.dest_block;

  case C1.min_value ... C1.max_value:
    goto C1.dest_block;

  ...etc...

  case C[N - 1].min_value ... C[N - 1].max_value:
    goto C[N - 1].dest_block;
}

block, expr, default_block and cases must all be non-NULL.

expr must be of the same integer type as all of the min_value and max_value within the cases.

num_cases must be >= 0.

The ranges of the cases must not overlap (or have duplicate values).

The API entrypoints relating to switch statements and cases:

were added in LIBGCCJIT_ABI_3; you can test for their presence using

#ifdef LIBGCCJIT_HAVE_SWITCH_STATEMENTS
gcc_jit_case

A gcc_jit_case represents a case within a switch statement, and is created within a particular gcc_jit_context using gcc_jit_context_new_case().

Each case expresses a multivalued range of integer values. You can express single-valued cases by passing in the same value for both min_value and max_value.

gcc_jit_case * gcc_jit_context_new_case(gcc_jit_context *ctxt, gcc_jit_rvalue *min_value, gcc_jit_rvalue *max_value, gcc_jit_block *dest_block)

Create a new gcc_jit_case instance for use in a switch statement. min_value and max_value must be constants of an integer type, which must match that of the expression of the switch statement.

dest_block must be within the same function as the switch statement.

gcc_jit_object * gcc_jit_case_as_object(gcc_jit_case *case_)

Upcast from a case to an object.

Here’s an example of creating a switch statement:


void
create_code (gcc_jit_context *ctxt, void *user_data)
{
  /* Let's try to inject the equivalent of:
      int
      test_switch (int x)
      {
	switch (x)
	  {
	  case 0 ... 5:
	     return 3;

	  case 25 ... 27:
	     return 4;

	  case -42 ... -17:
	     return 83;

	  case 40:
	     return 8;

	  default:
	     return 10;
	  }
      }
   */
  gcc_jit_type *t_int =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
  gcc_jit_type *return_type = t_int;
  gcc_jit_param *x =
    gcc_jit_context_new_param (ctxt, NULL, t_int, "x");
  gcc_jit_param *params[1] = {x};
  gcc_jit_function *func =
    gcc_jit_context_new_function (ctxt, NULL,
				  GCC_JIT_FUNCTION_EXPORTED,
				  return_type,
				  "test_switch",
				  1, params, 0);

  gcc_jit_block *b_initial =
    gcc_jit_function_new_block (func, "initial");

  gcc_jit_block *b_default =
    gcc_jit_function_new_block (func, "default");
  gcc_jit_block *b_case_0_5 =
    gcc_jit_function_new_block (func, "case_0_5");
  gcc_jit_block *b_case_25_27 =
    gcc_jit_function_new_block (func, "case_25_27");
  gcc_jit_block *b_case_m42_m17 =
    gcc_jit_function_new_block (func, "case_m42_m17");
  gcc_jit_block *b_case_40 =
    gcc_jit_function_new_block (func, "case_40");

  gcc_jit_case *cases[4] = {
    gcc_jit_context_new_case (
      ctxt,
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 0),
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 5),
      b_case_0_5),
    gcc_jit_context_new_case (
      ctxt,
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 25),
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 27),
      b_case_25_27),
    gcc_jit_context_new_case (
      ctxt,
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, -42),
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, -17),
      b_case_m42_m17),
    gcc_jit_context_new_case (
      ctxt,
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 40),
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 40),
      b_case_40)
  };
  gcc_jit_block_end_with_switch (
    b_initial, NULL,
    gcc_jit_param_as_rvalue (x),
    b_default,
    4, cases);

  gcc_jit_block_end_with_return (
    b_case_0_5, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 3));
  gcc_jit_block_end_with_return (
    b_case_25_27, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 4));
  gcc_jit_block_end_with_return (
    b_case_m42_m17, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 83));
  gcc_jit_block_end_with_return (
    b_case_40, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 8));
  gcc_jit_block_end_with_return (
    b_default, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 10));
}