Module hoist 

Finding temporaries that must be declared outside a loop.

Naga IR’s Loop statement runs its continuing block after its body, but MSL has no equivalent construct, so Writer::put_block emits the continuing block at the top of a while loop, skipped on the first iteration:

bool loop_init = true;
while(true) {
    if (!loop_init) {
        <continuing>
        if (<break_if>) { break; }
    }
    loop_init = false;
    <body>
}

Expressions emitted in body are in scope in continuing, but the temporaries holding their values are declared below the generated continuing code, so they can’t be named there. Re-evaluating such an expression in place would use the state at the end of the loop iteration, which may have changed from the state at the original position.

So when a loop has a continuing block, we declare the temporaries the continuing block needs ahead of the while loop, and have the body merely assign to them.

Functions

definitions 🔒

Return the expressions that block itself computes values for, in increasing handle order.

expressions_used 🔒

Return the expressions of function that the code generated for block and extra_roots will refer to, directly or indirectly.

fits_in_temporary 🔒

Whether a value of handle’s type can be held in a default-initialized local temporary.

is_statement_result 🔒

Whether expression is the result of a statement.