cmd/compile/internal/ssa: intrinsify atomic.Xchg8 on amd64

For #68578

Change-Id: Ia9580579bfc4709945bfcf6ec3803d5d11812187
Reviewed-on: https://go-review.googlesource.com/c/go/+/606901
Reviewed-by: Mauri de Souza Meneguzzo <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Martin Möhrmann <[email protected]>
Auto-Submit: Rhys Hiltner <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: rhysh

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

@@ -563,6 +563,7 @@
 (AtomicStorePtrNoWB ptr val mem) => (Select1 (XCHGQ <types.NewTuple(typ.BytePtr,types.TypeMem)> val ptr mem))
 
 // Atomic exchanges.
+(AtomicExchange8 ptr val mem) => (XCHGB val ptr mem)
 (AtomicExchange32 ptr val mem) => (XCHGL val ptr mem)
 (AtomicExchange64 ptr val mem) => (XCHGQ val ptr mem)
 

src/cmd/compile/internal/ssa/_gen/genericOps.go

@@ -604,6 +604,7 @@ var genericOps = []opData{
 	{name: "AtomicStorePtrNoWB", argLength: 3, typ: "Mem", hasSideEffects: true},               // Store arg1 to *arg0.  arg2=memory.  Returns memory.
 	{name: "AtomicStoreRel32", argLength: 3, typ: "Mem", hasSideEffects: true},                 // Store arg1 to *arg0.  arg2=memory.  Lock release, returns memory.
 	{name: "AtomicStoreRel64", argLength: 3, typ: "Mem", hasSideEffects: true},                 // Store arg1 to *arg0.  arg2=memory.  Lock release, returns memory.
+	{name: "AtomicExchange8", argLength: 3, typ: "(UInt8,Mem)", hasSideEffects: true},          // Store arg1 to *arg0.  arg2=memory.  Returns old contents of *arg0 and new memory.
 	{name: "AtomicExchange32", argLength: 3, typ: "(UInt32,Mem)", hasSideEffects: true},        // Store arg1 to *arg0.  arg2=memory.  Returns old contents of *arg0 and new memory.
 	{name: "AtomicExchange64", argLength: 3, typ: "(UInt64,Mem)", hasSideEffects: true},        // Store arg1 to *arg0.  arg2=memory.  Returns old contents of *arg0 and new memory.
 	{name: "AtomicAdd32", argLength: 3, typ: "(UInt32,Mem)", hasSideEffects: true},             // Do *arg0 += arg1.  arg2=memory.  Returns sum and new memory.

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

@@ -296,6 +296,13 @@ func initIntrinsics(cfg *intrinsicBuildConfig) {
 		},
 		sys.PPC64)
 
+	addF("internal/runtime/atomic", "Xchg8",
+		func(s *state, n *ir.CallExpr, args []*ssa.Value) *ssa.Value {
+			v := s.newValue3(ssa.OpAtomicExchange8, types.NewTuple(types.Types[types.TUINT8], types.TypeMem), args[0], args[1], s.mem())
+			s.vars[memVar] = s.newValue1(ssa.OpSelect1, types.TypeMem, v)
+			return s.newValue1(ssa.OpSelect0, types.Types[types.TUINT8], v)
+		},
+		sys.AMD64)
 	addF("internal/runtime/atomic", "Xchg",
 		func(s *state, n *ir.CallExpr, args []*ssa.Value) *ssa.Value {
 			v := s.newValue3(ssa.OpAtomicExchange32, types.NewTuple(types.Types[types.TUINT32], types.TypeMem), args[0], args[1], s.mem())

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

@@ -84,6 +84,7 @@ var wantIntrinsics = map[testIntrinsicKey]struct{}{
 	{"amd64", "internal/runtime/atomic", "Xadduintptr"}:        struct{}{},
 	{"amd64", "internal/runtime/atomic", "Xchg"}:               struct{}{},
 	{"amd64", "internal/runtime/atomic", "Xchg64"}:             struct{}{},
+	{"amd64", "internal/runtime/atomic", "Xchg8"}:              struct{}{},
 	{"amd64", "internal/runtime/atomic", "Xchgint32"}:          struct{}{},
 	{"amd64", "internal/runtime/atomic", "Xchgint64"}:          struct{}{},
 	{"amd64", "internal/runtime/atomic", "Xchguintptr"}:        struct{}{},