cmd/compile: mark LAA and LAAG as clobbering flags on s390x

The atomic add instructions modify the condition code and so need to
be marked as clobbering flags.

Fixes #24449.

Change-Id: Ic69c8d775fbdbfb2a56c5e0cfca7a49c0d7f6897
Reviewed-on: https://go-review.googlesource.com/101455
Run-TryBot: Michael Munday <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: mundaym

src/cmd/compile/internal/ssa/gen/S390XOps.go

@@ -491,8 +491,8 @@ func init() {
 		// Atomic adds.
 		// *(arg0+auxint+aux) += arg1.  arg2=mem.
 		// Returns a tuple of <old contents of *(arg0+auxint+aux), memory>.
-		{name: "LAA", argLength: 3, reg: gpstorelaa, asm: "LAA", typ: "(UInt32,Mem)", aux: "SymOff", faultOnNilArg0: true, hasSideEffects: true, symEffect: "RdWr"},
-		{name: "LAAG", argLength: 3, reg: gpstorelaa, asm: "LAAG", typ: "(UInt64,Mem)", aux: "SymOff", faultOnNilArg0: true, hasSideEffects: true, symEffect: "RdWr"},
+		{name: "LAA", argLength: 3, reg: gpstorelaa, asm: "LAA", typ: "(UInt32,Mem)", aux: "SymOff", clobberFlags: true, faultOnNilArg0: true, hasSideEffects: true, symEffect: "RdWr"},
+		{name: "LAAG", argLength: 3, reg: gpstorelaa, asm: "LAAG", typ: "(UInt64,Mem)", aux: "SymOff", clobberFlags: true, faultOnNilArg0: true, hasSideEffects: true, symEffect: "RdWr"},
 		{name: "AddTupleFirst32", argLength: 2}, // arg1=tuple <x,y>.  Returns <x+arg0,y>.
 		{name: "AddTupleFirst64", argLength: 2}, // arg1=tuple <x,y>.  Returns <x+arg0,y>.
 

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

@@ -0,0 +1,62 @@
+// run
+
+// 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 main
+
+import (
+	"sync/atomic"
+)
+
+var cnt32 int32
+
+//go:noinline
+func test32(a, b []int) bool {
+	// Try to generate flag value, issue atomic
+	// adds and then re-use the flag value to see if
+	// the atomic add has clobbered them.
+	atomic.AddInt32(&cnt32, 1)
+	if len(a) == len(b) {
+		atomic.AddInt32(&cnt32, 2)
+	}
+	atomic.AddInt32(&cnt32, 4)
+	if len(a) >= len(b) {
+		atomic.AddInt32(&cnt32, 8)
+	}
+	if len(a) <= len(b) {
+		atomic.AddInt32(&cnt32, 16)
+	}
+	return atomic.LoadInt32(&cnt32) == 31
+}
+
+var cnt64 int64
+
+//go:noinline
+func test64(a, b []int) bool {
+	// Try to generate flag value, issue atomic
+	// adds and then re-use the flag value to see if
+	// the atomic add has clobbered them.
+	atomic.AddInt64(&cnt64, 1)
+	if len(a) == len(b) {
+		atomic.AddInt64(&cnt64, 2)
+	}
+	atomic.AddInt64(&cnt64, 4)
+	if len(a) >= len(b) {
+		atomic.AddInt64(&cnt64, 8)
+	}
+	if len(a) <= len(b) {
+		atomic.AddInt64(&cnt64, 16)
+	}
+	return atomic.LoadInt64(&cnt64) == 31
+}
+
+func main() {
+	if !test32([]int{}, []int{}) {
+		panic("test32")
+	}
+	if !test64([]int{}, []int{}) {
+		panic("test64")
+	}
+}