From: Jorropo <jorropo.pgm@gmail.com>
Date: Tue, 18 Nov 2025 00:33:40 +0000 (+0100)
Subject: cmd/compile: propagate unsigned relations for Rsh if arguments are positive
X-Git-Tag: go1.26rc1~204
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=3820f94c1d081921494ada1da64b4fab21ae1a48;p=gostls13.git

cmd/compile: propagate unsigned relations for Rsh if arguments are positive

Updates #76332

Change-Id: Ifaa4d12897138d88d56b9d4e530c53dcee70bd58
Reviewed-on: https://go-review.googlesource.com/c/go/+/721205
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Mark Freeman <markfreeman@google.com>
Reviewed-by: Keith Randall <khr@google.com>
---

diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go
index 4ffab848ba..f6175a3bd7 100644
--- a/src/cmd/compile/internal/ssa/prove.go
+++ b/src/cmd/compile/internal/ssa/prove.go
@@ -2474,9 +2474,18 @@ func addLocalFacts(ft *factsTable, b *Block) {
 			//ft.update(b, v, v.Args[0], unsigned, gt|eq)
 			//ft.update(b, v, v.Args[1], unsigned, gt|eq)
 		case OpDiv64, OpDiv32, OpDiv16, OpDiv8:
-			if ft.isNonNegative(v.Args[0]) && ft.isNonNegative(v.Args[1]) {
-				ft.update(b, v, v.Args[0], unsigned, lt|eq)
+			if !ft.isNonNegative(v.Args[1]) {
+				break
 			}
+			fallthrough
+		case OpRsh8x64, OpRsh8x32, OpRsh8x16, OpRsh8x8,
+			OpRsh16x64, OpRsh16x32, OpRsh16x16, OpRsh16x8,
+			OpRsh32x64, OpRsh32x32, OpRsh32x16, OpRsh32x8,
+			OpRsh64x64, OpRsh64x32, OpRsh64x16, OpRsh64x8:
+			if !ft.isNonNegative(v.Args[0]) {
+				break
+			}
+			fallthrough
 		case OpDiv64u, OpDiv32u, OpDiv16u, OpDiv8u,
 			OpRsh8Ux64, OpRsh8Ux32, OpRsh8Ux16, OpRsh8Ux8,
 			OpRsh16Ux64, OpRsh16Ux32, OpRsh16Ux16, OpRsh16Ux8,
@@ -2491,12 +2500,17 @@ func addLocalFacts(ft *factsTable, b *Block) {
 				zl := ft.limits[z.ID]
 				var uminDivisor uint64
 				switch v.Op {
-				case OpDiv64u, OpDiv32u, OpDiv16u, OpDiv8u:
+				case OpDiv64u, OpDiv32u, OpDiv16u, OpDiv8u,
+					OpDiv64, OpDiv32, OpDiv16, OpDiv8:
 					uminDivisor = zl.umin
 				case OpRsh8Ux64, OpRsh8Ux32, OpRsh8Ux16, OpRsh8Ux8,
 					OpRsh16Ux64, OpRsh16Ux32, OpRsh16Ux16, OpRsh16Ux8,
 					OpRsh32Ux64, OpRsh32Ux32, OpRsh32Ux16, OpRsh32Ux8,
-					OpRsh64Ux64, OpRsh64Ux32, OpRsh64Ux16, OpRsh64Ux8:
+					OpRsh64Ux64, OpRsh64Ux32, OpRsh64Ux16, OpRsh64Ux8,
+					OpRsh8x64, OpRsh8x32, OpRsh8x16, OpRsh8x8,
+					OpRsh16x64, OpRsh16x32, OpRsh16x16, OpRsh16x8,
+					OpRsh32x64, OpRsh32x32, OpRsh32x16, OpRsh32x8,
+					OpRsh64x64, OpRsh64x32, OpRsh64x16, OpRsh64x8:
 					uminDivisor = 1 << zl.umin
 				default:
 					panic("unreachable")
diff --git a/test/prove.go b/test/prove.go
index 1f893938e3..38181b5fa5 100644
--- a/test/prove.go
+++ b/test/prove.go
@@ -253,9 +253,10 @@ func f9(a, b bool) int {
 
 func f10(a string) int {
 	n := len(a)
+	b := a[:n>>1] // ERROR "Proved IsSliceInBounds$"
 	// We optimize comparisons with small constant strings (see cmd/compile/internal/gc/walk.go),
 	// so this string literal must be long.
-	if a[:n>>1] == "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" {
+	if b == "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" {
 		return 0
 	}
 	return 1
@@ -1084,6 +1085,13 @@ func issue57077(s []int) (left, right []int) {
 	return
 }
 
+func issue76332(s []int) (left, right []int) {
+	middle := len(s) >> 1
+	left = s[:middle]     // ERROR "Proved IsSliceInBounds$"
+	right = s[middle:]    // ERROR "Proved IsSliceInBounds$"
+	return
+}
+
 func issue51622(b []byte) int {
 	if len(b) >= 3 && b[len(b)-3] == '#' { // ERROR "Proved IsInBounds$"
 		return len(b)