cranelift(aarch64): lower bare ctz/clz boolean tests via tst/cmp+Cond#13336
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cranelift(aarch64): lower bare ctz/clz boolean tests via tst/cmp+Cond#13336ggreif wants to merge 2 commits into
ctz/clz boolean tests via tst/cmp+Cond#13336ggreif wants to merge 2 commits into
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Follow-up to bytecodealliance#13332. That PR added egraph rules collapsing `(eq (ctz X) 0)` / `(ne (ctz X) 0)` / clz analogues to direct LSB / sign-bit tests — but only when the comparison is mediated by an explicit `icmp`. The wasm front-end translates `wasm if (ctz X)` to `brif (ireduce.i32 (ctz.i64 X))` directly (no `icmp`), so the egraph rules don't fire on the wasm-natural shape. This commit closes the gap by specialising `is_nonzero` in the x64 backend — the helper that all `brif`/`select`/`trapif` lowerings funnel through. Four rules: `ctz`/`clz` × bare/`ireduce`-wrapped. The `ireduce` variant catches the wasm front-end's `i32.wrap_i64` over a 64-bit `ctz`/`clz` — a no-op on values in [0, bitwidth]. Test deltas (tests/disas/ctz-clz-bool-condition.wat): if_ctz_bare_i32: 5 insns -> 2 (testl $1, %edx; je) if_ctz_bare_i64: 5 insns -> 2 (testq $1, %rdx; je) if_clz_bare_i32: 7 insns -> 2 (testl %edx, %edx; jns) The icmp-mediated cases (collapsed by bytecodealliance#13332's egraph rules) are unchanged. The numeric-comparison negative test stays untouched. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
aarch64 analogue of the x64 follow-up. Specialises `is_nonzero (ctz X)` and `is_nonzero (clz X)` (plus their `ireduce`-wrapped variants) so the wasm-natural `brif (ireduce.i32 (ctz.i64 X))` shape lowers to a single bit-test instead of `rbit; clz; cmp; b.cond`. ctz: `tst Xn, #1` + `Cond.Eq` — branches when LSB is clear. clz: `cmp Xn, #0` + `Cond.Pl` — branches when sign bit is clear. Test deltas (tests/disas/aarch64-ctz-clz-bool-condition.wat): if_ctz_bare_i32: `tst w4, #1; b.eq` if_ctz_bare_i64: `tst x4, #1; b.eq` if_clz_bare_i32: `cmp w4, #0; b.pl` Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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ctz/clz boolean tests via tst/cmp+Cond
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aarch64 analogue of #13334; egraph counterpart in #13332.
Same shape as the x64 follow-up: specialise
is_nonzero (ctz X)/is_nonzero (clz X)(and theirireduce-wrapped variants) incranelift/codegen/src/isa/aarch64/inst.isle, so the wasm-naturalbrif (ireduce.i32 (ctz.i64 X))shape lowers to a single bit-test instead ofrbit; clz; cmp; b.cond.aarch64-specific instructions used:
ctz:tst Xn, #1(logical AND with immediate, flags only) +Cond.Eq— branches when LSB is clear.clz:cmp Xn, #0+Cond.Pl— branches when sign bit (N flag) is clear, i.e. X is signed-non-negative.Test deltas (
tests/disas/aarch64-ctz-clz-bool-condition.wat, newly added):if_ctz_bare_i32rbit + clz + ...)tst w4, #1; b.eq)if_ctz_bare_i64tst x4, #1; b.eq)if_clz_bare_i32clz + ...)cmp w4, #0; b.pl)Negative test (
(ctz X) == 4) correctly untouched. Same motivation as #13334 — closes the gap for non-Rust wasm frontends like Motoko'smoc.riscv64 and s390x to follow.