Stream: git-wasmtime

Topic: wasmtime / PR #7654 Cranelift: More simplification opts f...

Wasmtime GitHub notifications bot (Dec 07 2023 at 18:15):

scottmcm opened PR #7654 from scottmcm:normalize-add-sub-const to bytecodealliance:main:

This PR came out of me seeing that the opt patterns were written out to handle both

(!x) + 1 == !(x) - (-1) == ineg(x)

and thus being sad that every pattern including (iadd _ 1) needed to be written again for (isub _ -1).

So this takes a look at more opt patterns around iadd and isub:

• Various combinations with ineg, like x + -y == -y + x == -(y - x) == x - y
• Avoiding subtract-a-"negative"-constant, so (isub x 255_u8) becomes (iadd x 1_u8) (but (isub x 1) is left alone)
• And removing now-unnecessary patterns in arithmetic.isle and bitops.isle, like I did in #7599

I originally had x + -1 → x - 1 as well, but that regressed codegen with addressing modes -- something that had been in one x64 LEA ended up being a LEA and a SUB. So there's an interesting question about whether to turn all (isub x CONST) into (iadd x CONST), but that felt like something that would need a zulip conversation, and thus it's not included in this hopefully-simpler PR.

Wasmtime GitHub notifications bot (Dec 07 2023 at 18:15):

scottmcm requested abrown for a review on PR #7654.

Wasmtime GitHub notifications bot (Dec 07 2023 at 18:15):

scottmcm requested wasmtime-compiler-reviewers for a review on PR #7654.

Wasmtime GitHub notifications bot (Dec 07 2023 at 19:44):

github-actions[bot] commented on PR #7654:

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cc @cfallin, @fitzgen

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Wasmtime GitHub notifications bot (Dec 07 2023 at 22:45):

alexcrichton submitted PR review:

Thanks!

Wasmtime GitHub notifications bot (Dec 07 2023 at 23:20):

alexcrichton merged PR #7654.

Last updated: Dec 06 2025 at 06:05 UTC