1.3.1 Expressions: lvalues and rvalues ¶

The base class of expression is the gcc_jit_rvalue *, representing an expression that can be on the `right'-hand side of an assignment: a value that can be computed somehow, and assigned `to' a storage area (such as a variable). It has a specific gcc_jit_type *.

Anothe important class is gcc_jit_lvalue *. A gcc_jit_lvalue *. is something that can of the `left'-hand side of an assignment: a storage area (such as a variable).

In other words, every assignment can be thought of as:

LVALUE = RVALUE;

Note that gcc_jit_lvalue * is a subclass of gcc_jit_rvalue *, where in an assignment of the form:

LVALUE_A = LVALUE_B;

the LVALUE_B implies reading the current value of that storage area, assigning it into the LVALUE_A.

So far the only expressions we’ve seen are i * i:

gcc_jit_rvalue *expr =
  gcc_jit_context_new_binary_op (
    ctxt, NULL,
    GCC_JIT_BINARY_OP_MULT, int_type,
    gcc_jit_param_as_rvalue (param_i),
    gcc_jit_param_as_rvalue (param_i));

which is a gcc_jit_rvalue *, and the various function parameters: param_i and param_n, instances of gcc_jit_param *, which is a subclass of gcc_jit_lvalue * (and, in turn, of gcc_jit_rvalue *): we can both read from and write to function parameters within the body of a function.

Our new example has a couple of local variables. We create them by calling gcc_jit_function_new_local(), supplying a type and a name:

/* Build locals:  */
gcc_jit_lvalue *i =
  gcc_jit_function_new_local (func, NULL, the_type, "i");
gcc_jit_lvalue *sum =
  gcc_jit_function_new_local (func, NULL, the_type, "sum");

These are instances of gcc_jit_lvalue * - they can be read from and written to.

Note that there is no precanned way to create `and' initialize a variable like in C:

int i = 0;

Instead, having added the local to the function, we have to separately add an assignment of 0 to local_i at the beginning of the function.