AFAIK the break N construct cannot be expressed in SPIR-V because of the structured control flow rules that says:

the only blocks in a construct that can branch outside the construct are:

• ...
• a break block for the innermost loop it is nested inside of

. +CC @dj2 and @dneto0

Hmm, suspicious. "a block branching to the construct’s merge block " satisfies some requirements, but I'll have to think it over.

The literal count is error prone. I'd rather label-name the loops, then have break label.

The translation from this more general construct requires, in general, synthesis of extra state variables to track mulit-level escape. That adds complexity to translation, and is in conflict with the developer understanding (by counting) the register pressure on an invocation.

Removing approval since it sounds like this can't translate to SPIR-V (directly).

Ok, I agree that it would require non-zero-cost translation in the general case.

SPIR-V structured control flow branching rules:

the only blocks in a construct that can branch outside the construct are
* a block branching to the construct’s merge block
* a block branching from one case construct to another, for the same OpSwitch
* a back-edge block
* a continue block for the innermost loop it is nested inside of
* a break block for the innermost loop it is nested inside of
* a return block

In particular it would be temping to write:

let a = 0;
let y = 0;
loop {
  if (y >= H) break;
  let x = 0;
  loop {
    if (x >= W) break;
    a = foo(x,y);
    if (a) break 2;
    x += 1;
  }
  y += 1;
}

However, I believe there's no valid SPIR-V zero-cost equivalent.