[release-branch.go1.26] cmd/compile: avoid folding 64-bit integers into 32-bit constants

Folding a 64-bit integer into a 32-bit constant may result in a negative
integer if the value exceeds math.MaxInt32 (the maximum value of a 32-
bit signed integer). This negative value will be sign-extended to 64
bits at runtime, leading to unexpected results when used in bitwise
AND/OR operations.

Fixes #77618

Change-Id: Idb081a3c20c28bddddcc8eff1225d62123b37a2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/745581
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
(cherry picked from commit 3c8b5e673816c733f13a38b1ed1f53d7d49ea084)
Reviewed-on: https://go-review.googlesource.com/c/go/+/745840
Reviewed-by: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>

3 files changed, 48 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/ssa/_gen/AMD64.rules b/src/cmd/compile/internal/ssa/_gen/AMD64.rules
index b49e85b53c..956077d392 100644
--- a/src/cmd/compile/internal/ssa/_gen/AMD64.rules
+++ b/src/cmd/compile/internal/ssa/_gen/AMD64.rules
@@ -1578,7 +1578,8 @@
 
 (MOVBload [off] {sym} (SB) _) && symIsRO(sym) => (MOVLconst [int32(read8(sym, int64(off)))])
 (MOVWload [off] {sym} (SB) _) && symIsRO(sym) => (MOVLconst [int32(read16(sym, int64(off), config.ctxt.Arch.ByteOrder))])
-(MOVLload [off] {sym} (SB) _) && symIsRO(sym) => (MOVLconst [int32(read32(sym, int64(off), config.ctxt.Arch.ByteOrder))])
+(MOVLload <t> [off] {sym} (SB) _) && symIsRO(sym) && is32BitInt(t) => (MOVLconst [int32(read32(sym, int64(off), config.ctxt.Arch.ByteOrder))])
+(MOVLload <t> [off] {sym} (SB) _) && symIsRO(sym) && is64BitInt(t) => (MOVQconst [int64(read32(sym, int64(off), config.ctxt.Arch.ByteOrder))])
 (MOVQload [off] {sym} (SB) _) && symIsRO(sym) => (MOVQconst [int64(read64(sym, int64(off), config.ctxt.Arch.ByteOrder))])
 (MOVBQSXload [off] {sym} (SB) _) && symIsRO(sym) => (MOVQconst [int64(int8(read8(sym, int64(off))))])
 (MOVWQSXload [off] {sym} (SB) _) && symIsRO(sym) => (MOVQconst [int64(int16(read16(sym, int64(off), config.ctxt.Arch.ByteOrder)))])
diff --git a/src/cmd/compile/internal/ssa/rewriteAMD64.go b/src/cmd/compile/internal/ssa/rewriteAMD64.go
index b1b1c84046..d005b15a57 100644
--- a/src/cmd/compile/internal/ssa/rewriteAMD64.go
+++ b/src/cmd/compile/internal/ssa/rewriteAMD64.go
@@ -16399,19 +16399,34 @@ func rewriteValueAMD64_OpAMD64MOVLload(v *Value) bool {
 		v.AddArg(val)
 		return true
 	}
-	// match: (MOVLload [off] {sym} (SB) _)
-	// cond: symIsRO(sym)
+	// match: (MOVLload <t> [off] {sym} (SB) _)
+	// cond: symIsRO(sym) && is32BitInt(t)
 	// result: (MOVLconst [int32(read32(sym, int64(off), config.ctxt.Arch.ByteOrder))])
 	for {
+		t := v.Type
 		off := auxIntToInt32(v.AuxInt)
 		sym := auxToSym(v.Aux)
-		if v_0.Op != OpSB || !(symIsRO(sym)) {
+		if v_0.Op != OpSB || !(symIsRO(sym) && is32BitInt(t)) {
 			break
 		}
 		v.reset(OpAMD64MOVLconst)
 		v.AuxInt = int32ToAuxInt(int32(read32(sym, int64(off), config.ctxt.Arch.ByteOrder)))
 		return true
 	}
+	// match: (MOVLload <t> [off] {sym} (SB) _)
+	// cond: symIsRO(sym) && is64BitInt(t)
+	// result: (MOVQconst [int64(read32(sym, int64(off), config.ctxt.Arch.ByteOrder))])
+	for {
+		t := v.Type
+		off := auxIntToInt32(v.AuxInt)
+		sym := auxToSym(v.Aux)
+		if v_0.Op != OpSB || !(symIsRO(sym) && is64BitInt(t)) {
+			break
+		}
+		v.reset(OpAMD64MOVQconst)
+		v.AuxInt = int64ToAuxInt(int64(read32(sym, int64(off), config.ctxt.Arch.ByteOrder)))
+		return true
+	}
 	return false
 }
 func rewriteValueAMD64_OpAMD64MOVLstore(v *Value) bool {
diff --git a/test/fixedbugs/issue77613.go b/test/fixedbugs/issue77613.go
new file mode 100644
index 0000000000..df71ed48e9
--- /dev/null
+++ b/test/fixedbugs/issue77613.go
@@ -0,0 +1,28 @@
+// run
+
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"strings"
+)
+
+func main() {
+	str1 := "你好世界"
+	if !strings.HasSuffix(str1, "世界") {
+		panic(1)
+	}
+
+	str2 := "こんにちは"
+	if !strings.HasSuffix(str2, "ちは") {
+		panic(2)
+	}
+
+	str3 := "спасибо"
+	if !strings.HasSuffix(str3, "ибо") {
+		panic(3)
+	}
+}