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cmd/compile: optimize BSRQ with nonzero input

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Same as BSFQ, if the input is known to be nonzero we don't need a CMOV
to correct for the weird all-zero behavior of the BSRQ instruction.

Fixes #51964

Change-Id: Ic1d14fdf3e7e698ff2f47efecfd761d8a036012a
Reviewed-on: https://go-review.googlesource.com/c/go/+/396034
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Keith Randall 2022-03-26 10:03:06 -07:00
parent 56400fc706
commit 7d3b64a2e3
2 changed files with 24 additions and 1 deletions
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2
src/cmd/compile/internal/ssa/gen/AMD64.rules
View File

@ -2073,7 +2073,7 @@
(CMPXCHGLlock [off1+off2] {sym} ptr old new_ mem)
// We don't need the conditional move if we know the arg of BSF is not zero.
(CMOVQEQ x _ (Select1 (BSFQ (ORQconst [c] _)))) && c != 0 => x
(CMOVQEQ x _ (Select1 (BS(F|R)Q (ORQconst [c] _)))) && c != 0 => x
// Extension is unnecessary for trailing zeros.
(BSFQ (ORQconst <t> [1<<8] (MOVBQZX x))) => (BSFQ (ORQconst <t> [1<<8] x))
(BSFQ (ORQconst <t> [1<<16] (MOVWQZX x))) => (BSFQ (ORQconst <t> [1<<16] x))

23
src/cmd/compile/internal/ssa/rewriteAMD64.go
View File

@ -5191,6 +5191,29 @@ func rewriteValueAMD64_OpAMD64CMOVQEQ(v *Value) bool {
v.copyOf(x)
return true
}
// match: (CMOVQEQ x _ (Select1 (BSRQ (ORQconst [c] _))))
// cond: c != 0
// result: x
for {
x := v_0
if v_2.Op != OpSelect1 {
break
}
v_2_0 := v_2.Args[0]
if v_2_0.Op != OpAMD64BSRQ {
break
}
v_2_0_0 := v_2_0.Args[0]
if v_2_0_0.Op != OpAMD64ORQconst {
break
}
c := auxIntToInt32(v_2_0_0.AuxInt)
if !(c != 0) {
break
}
v.copyOf(x)
return true
}
return false
}
func rewriteValueAMD64_OpAMD64CMOVQGE(v *Value) bool {