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cmd/compile: rewrite Rsh to RshU if arguments are proved positive

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Fixes #76332

Change-Id: I9044025d5dc599531c7f88ed2870bcf3d8b0acbd
Reviewed-on: https://go-review.googlesource.com/c/go/+/721206
Reviewed-by: Mark Freeman <markfreeman@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Jorropo 2025-11-18 01:42:37 +01:00 • committed by Gopher Robot
parent 3820f94c1d
commit ec92bc6d63
3 changed files with 43 additions and 20 deletions
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43
src/cmd/compile/internal/ssa/prove.go
View file

@ -2664,14 +2664,30 @@ var mostNegativeDividend = map[Op]int64{
OpMod64: -1 << 63,
}
var unsignedOp = map[Op]Op{
OpDiv8: OpDiv8u,
OpDiv16: OpDiv16u,
OpDiv32: OpDiv32u,
OpDiv64: OpDiv64u,
OpMod8: OpMod8u,
OpMod16: OpMod16u,
OpMod32: OpMod32u,
OpMod64: OpMod64u,
OpDiv8: OpDiv8u,
OpDiv16: OpDiv16u,
OpDiv32: OpDiv32u,
OpDiv64: OpDiv64u,
OpMod8: OpMod8u,
OpMod16: OpMod16u,
OpMod32: OpMod32u,
OpMod64: OpMod64u,
OpRsh8x8: OpRsh8Ux8,
OpRsh8x16: OpRsh8Ux16,
OpRsh8x32: OpRsh8Ux32,
OpRsh8x64: OpRsh8Ux64,
OpRsh16x8: OpRsh16Ux8,
OpRsh16x16: OpRsh16Ux16,
OpRsh16x32: OpRsh16Ux32,
OpRsh16x64: OpRsh16Ux64,
OpRsh32x8: OpRsh32Ux8,
OpRsh32x16: OpRsh32Ux16,
OpRsh32x32: OpRsh32Ux32,
OpRsh32x64: OpRsh32Ux64,
OpRsh64x8: OpRsh64Ux8,
OpRsh64x16: OpRsh64Ux16,
OpRsh64x32: OpRsh64Ux32,
OpRsh64x64: OpRsh64Ux64,
}
var bytesizeToConst = [...]Op{
@ -2758,8 +2774,15 @@ func simplifyBlock(sdom SparseTree, ft *factsTable, b *Block) {
case OpRsh8x8, OpRsh8x16, OpRsh8x32, OpRsh8x64,
OpRsh16x8, OpRsh16x16, OpRsh16x32, OpRsh16x64,
OpRsh32x8, OpRsh32x16, OpRsh32x32, OpRsh32x64,
OpRsh64x8, OpRsh64x16, OpRsh64x32, OpRsh64x64,
OpLsh8x8, OpLsh8x16, OpLsh8x32, OpLsh8x64,
OpRsh64x8, OpRsh64x16, OpRsh64x32, OpRsh64x64:
if ft.isNonNegative(v.Args[0]) {
if b.Func.pass.debug > 0 {
b.Func.Warnl(v.Pos, "Proved %v is unsigned", v.Op)
}
v.Op = unsignedOp[v.Op]
}
fallthrough
case OpLsh8x8, OpLsh8x16, OpLsh8x32, OpLsh8x64,
OpLsh16x8, OpLsh16x16, OpLsh16x32, OpLsh16x64,
OpLsh32x8, OpLsh32x16, OpLsh32x32, OpLsh32x64,
OpLsh64x8, OpLsh64x16, OpLsh64x32, OpLsh64x64,

6
test/prove.go
View file

@ -253,7 +253,7 @@ func f9(a, b bool) int {
func f10(a string) int {
n := len(a)
b := a[:n>>1] // ERROR "Proved IsSliceInBounds$"
b := a[:n>>1] // ERROR "(Proved IsSliceInBounds|Proved Rsh64x64 is unsigned)$"
// We optimize comparisons with small constant strings (see cmd/compile/internal/gc/walk.go),
// so this string literal must be long.
if b == "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" {
@ -1086,7 +1086,7 @@ func issue57077(s []int) (left, right []int) {
}
func issue76332(s []int) (left, right []int) {
middle := len(s) >> 1
middle := len(s) >> 1 // ERROR "Proved Rsh64x64 is unsigned$"
left = s[:middle] // ERROR "Proved IsSliceInBounds$"
right = s[middle:] // ERROR "Proved IsSliceInBounds$"
return
@ -2564,7 +2564,7 @@ func rightshift(v *[256]int) int {
}
}
for i := range 1024 { // ERROR "Induction"
if v[i>>2] == 0 { // ERROR "Proved IsInBounds"
if v[i>>2] == 0 { // ERROR "(Proved IsInBounds|Proved Rsh64x64 is unsigned)"
return i
}
}

14
test/prove_constant_folding.go
View file

@ -30,10 +30,10 @@ func f0u(x uint) int {
}
if x < 1000 {
return int(x)>>31 // ERROR "Proved.+is constant 0$"
return int(x) >> 31 // ERROR "(Proved.+is constant 0|Proved Rsh[0-9]+x[0-9]+ is unsigned)$"
}
if x := int32(x); x < -1000 {
return int(x>>31) // ERROR "Proved.+is constant -1$"
return int(x >> 31) // ERROR "Proved.+is constant -1$"
}
return int(x) + 1
@ -45,35 +45,35 @@ func sh64(n int64) int64 {
if n < 0 {
return n
}
return n >> 63 // ERROR "Proved .+ is constant 0$"
return n >> 63 // ERROR "(Proved .+ is constant 0|Proved Rsh[0-9]+x[0-9]+ is unsigned)$"
}
func sh32(n int32) int32 {
if n < 0 {
return n
}
return n >> 31 // ERROR "Proved .+ is constant 0$"
return n >> 31 // ERROR "(Proved .+ is constant 0|Proved Rsh[0-9]+x[0-9]+ is unsigned)$"
}
func sh32x64(n int32) int32 {
if n < 0 {
return n
}
return n >> uint64(31) // ERROR "Proved .+ is constant 0$"
return n >> uint64(31) // ERROR "(Proved .+ is constant 0|Proved Rsh[0-9]+x[0-9]+ is unsigned)$"
}
func sh32x64n(n int32) int32 {
if n >= 0 {
return 0
}
return n >> 31// ERROR "Proved .+ is constant -1$"
return n >> 31 // ERROR "Proved .+ is constant -1$"
}
func sh16(n int16) int16 {
if n < 0 {
return n
}
return n >> 15 // ERROR "Proved .+ is constant 0$"
return n >> 15 // ERROR "(Proved .+ is constant 0|Proved Rsh[0-9]+x[0-9]+ is unsigned)$"
}
func sh64noopt(n int64) int64 {