wgsl-in, glsl-in: Short circuit || and &&

[adeline-sparks]

Fixes gfx-rs/wgpu#4394.

[JCapucho]

Disclaimer: only read the glsl code yet, so this might or might not apply to the wgsl frontend

There's an issue with your implementation, you're always branching on the left expression, this is true for LogicalAnd but not for LogicalOr, the latter must only execute the right hand side if it evaluates to false.

Also you seem to be creating the following pseudocode:

if (left) {
  local = right
} else {
  local = constant
}

you could instead do:

local = left
if (left) {
  local = right
}

[adeline-sparks]

Looking at this again, I think it is translating things correctly. The tests show that for the && case, the RHS is evaluated in the accept branch of the if statement, while for the || it is evaluated in the reject branch.

I'll have a go at generating multiple assignments instead of single assignment. Would it be better to create a logical not and always leave the reject branch empty so that the generated code doesn't use an else in the || case?

[teoxoy]

Looking at this again, I think it is translating things correctly. The tests show that for the && case, the RHS is evaluated in the accept branch of the if statement, while for the || it is evaluated in the reject branch.

Tests seem correct indeed, but quite verbose (see below).

Would it be better to create a logical not and always leave the reject branch empty so that the generated code doesn't use an else in the || case?

I think so (as per @JCapucho's suggestion) because the extra assignments are redundant, we already know the var is true/false.

[cwfitzgerald]

Hello, thank you for your PR against Naga!

As part of gfx-rs/wgpu#4231, we have moved development of Naga into the wgpu repository in the Naga subfolder. We have transferred all issues, but we are unable to automatically transfer PRs.

As such, please recreate your PR against the wgpu repository. We apologize for the inconvenience this causes, but will make contributing to both projects more streamlined going forward.

We are leaving PRs open, but once they are transferred, please close the original Naga PR.