[release-branch.go1.18] cmd/compile: fix conditional select rule

ARM64 maintains booleans in the low byte of registers. Upper parts
of that register are junk.
This rule is using all 32 bits of a boolean-containing register, which
is wrong. Change the rule to only look at the low bit.

Fixes #57211

Change-Id: Ibbef86b2be859df3d06d993db00e1231c481c428
Reviewed-on: https://go-review.googlesource.com/c/go/+/456556
Auto-Submit: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/456558
Reviewed-by: Than McIntosh <thanm@google.com>

3 files changed, 45 insertions, 5 deletions

diff --git a/src/cmd/compile/internal/ssa/gen/ARM64.rules b/src/cmd/compile/internal/ssa/gen/ARM64.rules
index 09e70ad13be..ad999600789 100644
--- a/src/cmd/compile/internal/ssa/gen/ARM64.rules
+++ b/src/cmd/compile/internal/ssa/gen/ARM64.rules
@@ -316,9 +316,9 @@
 (FCMPD x (FMOVDconst [0])) => (FCMPD0 x)
 (FCMPD (FMOVDconst [0]) x) => (InvertFlags (FCMPD0 x))
 
-// CSEL needs a flag-generating argument. Synthesize a CMPW if necessary.
+// CSEL needs a flag-generating argument. Synthesize a TSTW if necessary.
 (CondSelect x y boolval) && flagArg(boolval) != nil => (CSEL [boolval.Op] x y flagArg(boolval))
-(CondSelect x y boolval) && flagArg(boolval) == nil => (CSEL [OpARM64NotEqual] x y (CMPWconst [0] boolval))
+(CondSelect x y boolval) && flagArg(boolval) == nil => (CSEL [OpARM64NotEqual] x y (TSTWconst [1] boolval))
 
 (OffPtr [off] ptr:(SP)) && is32Bit(off) => (MOVDaddr [int32(off)] ptr)
 (OffPtr [off] ptr) => (ADDconst [off] ptr)
diff --git a/src/cmd/compile/internal/ssa/rewriteARM64.go b/src/cmd/compile/internal/ssa/rewriteARM64.go
index 1ee25c2eee9..ad1052f88d7 100644
--- a/src/cmd/compile/internal/ssa/rewriteARM64.go
+++ b/src/cmd/compile/internal/ssa/rewriteARM64.go
@@ -23409,7 +23409,7 @@ func rewriteValueARM64_OpCondSelect(v *Value) bool {
 	}
 	// match: (CondSelect x y boolval)
 	// cond: flagArg(boolval) == nil
-	// result: (CSEL [OpARM64NotEqual] x y (CMPWconst [0] boolval))
+	// result: (CSEL [OpARM64NotEqual] x y (TSTWconst [1] boolval))
 	for {
 		x := v_0
 		y := v_1
@@ -23419,8 +23419,8 @@ func rewriteValueARM64_OpCondSelect(v *Value) bool {
 		}
 		v.reset(OpARM64CSEL)
 		v.AuxInt = opToAuxInt(OpARM64NotEqual)
-		v0 := b.NewValue0(v.Pos, OpARM64CMPWconst, types.TypeFlags)
-		v0.AuxInt = int32ToAuxInt(0)
+		v0 := b.NewValue0(v.Pos, OpARM64TSTWconst, types.TypeFlags)
+		v0.AuxInt = int32ToAuxInt(1)
 		v0.AddArg(boolval)
 		v.AddArg3(x, y, v0)
 		return true
diff --git a/test/fixedbugs/issue57184.go b/test/fixedbugs/issue57184.go
new file mode 100644
index 00000000000..1384b50be87
--- /dev/null
+++ b/test/fixedbugs/issue57184.go
@@ -0,0 +1,40 @@
+// run
+
+// Copyright 2022 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 (
+	"log"
+	"reflect"
+	"sort"
+)
+
+func main() {
+	const length = 257
+	x := make([]int64, length)
+	for i := 0; i < length; i++ {
+		x[i] = int64(i) * 27644437 % int64(length)
+	}
+
+	isLessStatic := func(i, j int) bool {
+		return x[i] < x[j]
+	}
+
+	isLessReflect := reflect.MakeFunc(reflect.TypeOf(isLessStatic), func(args []reflect.Value) []reflect.Value {
+		i := args[0].Int()
+		j := args[1].Int()
+		b := x[i] < x[j]
+		return []reflect.Value{reflect.ValueOf(b)}
+	}).Interface().(func(i, j int) bool)
+
+	sort.SliceStable(x, isLessReflect)
+
+	for i := 0; i < length-1; i++ {
+		if x[i] >= x[i+1] {
+			log.Fatalf("not sorted! (length=%v, idx=%v)\n%v\n", length, i, x)
+		}
+	}
+}