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cmd/compile: fold double negate on arm64

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Fixes #48467

Change-Id: I52305dbf561ee3eee6c1f053e555a3a6ec1ab892
Reviewed-on: https://go-review.googlesource.com/c/go/+/350910
Trust: Keith Randall <khr@golang.org>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
This commit is contained in:
Keith Randall 2021-09-19 09:23:37 -07:00
parent 83b36ffb10
commit 315dbd10c9
3 changed files with 19 additions and 0 deletions
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1
src/cmd/compile/internal/ssa/gen/ARM64.rules
View file

@ -1363,6 +1363,7 @@
(XOR x (MVN y)) => (EON x y)
(OR x (MVN y)) => (ORN x y)
(MVN (XOR x y)) => (EON x y)
(NEG (NEG x)) => x
(CSEL [cc] (MOVDconst [-1]) (MOVDconst [0]) flag) => (CSETM [cc] flag)
(CSEL [cc] (MOVDconst [0]) (MOVDconst [-1]) flag) => (CSETM [arm64Negate(cc)] flag)

10
src/cmd/compile/internal/ssa/rewriteARM64.go
View file

@ -15691,6 +15691,16 @@ func rewriteValueARM64_OpARM64NEG(v *Value) bool {
v.AddArg2(x, y)
return true
}
// match: (NEG (NEG x))
// result: x
for {
if v_0.Op != OpARM64NEG {
break
}
x := v_0.Args[0]
v.copyOf(x)
return true
}
// match: (NEG (MOVDconst [c]))
// result: (MOVDconst [-c])
for {

8
test/codegen/bits.go
View file

@ -6,6 +6,8 @@
package codegen
import "math/bits"
/************************************
* 64-bit instructions
************************************/
@ -355,3 +357,9 @@ func issue44228b(a []int32, i int) bool {
// amd64: "BTL", -"SHL"
return a[i>>5]&(1<<(i&31)) != 0
}
func issue48467(x, y uint64) uint64 {
// arm64: -"NEG"
d, borrow := bits.Sub64(x, y, 0)
return x - d&(-borrow)
}