Stream: git-wasmtime

Topic: wasmtime / issue #401 Idea: Keep track of set condition c...

Wasmtime GitHub notifications bot (Sep 27 2021 at 17:28):

alexcrichton commented on issue #401:

Lightbeam was removed in https://github.com/bytecodealliance/wasmtime/pull/3390 as explained in RFC 14, so I'm going to close this.

Wasmtime GitHub notifications bot (Sep 27 2021 at 17:28):

alexcrichton closed issue #401:

If we kept track of what conditions were set we could get better performance on the idiom:

for (int i = something; i != 0; i--) {
  // ...
}

Instead of emitting a cmp after the dec, we can work out that we already have the zero flag set from the dec and just emit a jnz. Currently there's no way to abstract over different instructions and get metadata for them, so this would be very complicated to implement without a new assembler.

EDIT: Keeping track of what instructions mutate which condition codes would allow us to implement CraneStation/lightbeam#16 in a way that only spills the "condition" if we're about to emit an instruction that would invalidate it.

Last updated: Dec 13 2025 at 19:03 UTC