cmd/compile/internal/ssa: fix endless compile loop on AMD64

We currently rewrite
(TESTQ (MOVQconst [c] x)) into (TESTQconst [c] x)
and (TESTQconst [-1] x) into (TESTQ x x)
if x is a (MOVQconst [-1]) we will be stuck in the endless rewrite loop.
Don't perform the rewrite in such cases.

Fixes #25006

Change-Id: I77f561ba2605fc104f1e5d5c57f32e9d67a2c000
Reviewed-on: https://go-review.googlesource.com/108879
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -1443,10 +1443,10 @@
 (CMPLconst x [0]) -> (TESTL x x)
 (CMPWconst x [0]) -> (TESTW x x)
 (CMPBconst x [0]) -> (TESTB x x)
-(TESTQconst [-1] x) -> (TESTQ x x)
+(TESTQconst [-1] x) && x.Op != OpAMD64MOVQconst -> (TESTQ x x)
-(TESTLconst [-1] x) -> (TESTL x x)
+(TESTLconst [-1] x) && x.Op != OpAMD64MOVLconst -> (TESTL x x)
-(TESTWconst [-1] x) -> (TESTW x x)
+(TESTWconst [-1] x) && x.Op != OpAMD64MOVLconst -> (TESTW x x)
-(TESTBconst [-1] x) -> (TESTB x x)
+(TESTBconst [-1] x) && x.Op != OpAMD64MOVLconst -> (TESTB x x)
 
 // Combining byte loads into larger (unaligned) loads.
 // There are many ways these combinations could occur.  This is

src/cmd/compile/internal/ssa/rewriteAMD64.go

@@ -49732,13 +49732,16 @@ func rewriteValueAMD64_OpAMD64TESTB_0(v *Value) bool {
 }
 func rewriteValueAMD64_OpAMD64TESTBconst_0(v *Value) bool {
 	// match: (TESTBconst [-1] x)
-	// cond:
+	// cond: x.Op != OpAMD64MOVLconst
 	// result: (TESTB x x)
 	for {
 		if v.AuxInt != -1 {
 			break
 		}
 		x := v.Args[0]
+		if !(x.Op != OpAMD64MOVLconst) {
+			break
+		}
 		v.reset(OpAMD64TESTB)
 		v.AddArg(x)
 		v.AddArg(x)
@@ -49841,13 +49844,16 @@ func rewriteValueAMD64_OpAMD64TESTL_0(v *Value) bool {
 }
 func rewriteValueAMD64_OpAMD64TESTLconst_0(v *Value) bool {
 	// match: (TESTLconst [-1] x)
-	// cond:
+	// cond: x.Op != OpAMD64MOVLconst
 	// result: (TESTL x x)
 	for {
 		if v.AuxInt != -1 {
 			break
 		}
 		x := v.Args[0]
+		if !(x.Op != OpAMD64MOVLconst) {
+			break
+		}
 		v.reset(OpAMD64TESTL)
 		v.AddArg(x)
 		v.AddArg(x)
@@ -49956,13 +49962,16 @@ func rewriteValueAMD64_OpAMD64TESTQ_0(v *Value) bool {
 }
 func rewriteValueAMD64_OpAMD64TESTQconst_0(v *Value) bool {
 	// match: (TESTQconst [-1] x)
-	// cond:
+	// cond: x.Op != OpAMD64MOVQconst
 	// result: (TESTQ x x)
 	for {
 		if v.AuxInt != -1 {
 			break
 		}
 		x := v.Args[0]
+		if !(x.Op != OpAMD64MOVQconst) {
+			break
+		}
 		v.reset(OpAMD64TESTQ)
 		v.AddArg(x)
 		v.AddArg(x)
@@ -50065,13 +50074,16 @@ func rewriteValueAMD64_OpAMD64TESTW_0(v *Value) bool {
 }
 func rewriteValueAMD64_OpAMD64TESTWconst_0(v *Value) bool {
 	// match: (TESTWconst [-1] x)
-	// cond:
+	// cond: x.Op != OpAMD64MOVLconst
 	// result: (TESTW x x)
 	for {
 		if v.AuxInt != -1 {
 			break
 		}
 		x := v.Args[0]
+		if !(x.Op != OpAMD64MOVLconst) {
+			break
+		}
 		v.reset(OpAMD64TESTW)
 		v.AddArg(x)
 		v.AddArg(x)

test/fixedbugs/issue25006.go

@@ -0,0 +1,30 @@
+// compile
+
+// Copyright 2018 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 p
+
+func spin() {
+	var i int
+	var b bool
+
+	switch 1 {
+	case 0:
+		i = 1
+	}
+	switch 1 {
+	case i:
+	default:
+		i = 1
+		b = !b && (b && !b) && b
+	}
+	switch false {
+	case false:
+		i = 3 + -i
+		switch 0 {
+		case 1 - i:
+		}
+	}
+}