[dev.ssa] cmd/compile: fix write barriers for SSA

The old write barriers used _nostore versions, which
don't work for Ian's cgo checker.  Instead, we adopt the
same write barrier pattern as the default compiler.

It's a bit trickier to code up but should be more efficient.

Change-Id: I6696c3656cf179e28f800b0e096b7259bd5f3bb7
Reviewed-on: https://go-review.googlesource.com/18941
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

misc/cgo/errors/ptr.go

@@ -134,7 +134,6 @@ var ptrTests = []ptrTest{
 		body:    `parg := [1]**C.char{&hello[0]}; C.f(&parg[0])`,
 		fail:    true,
 	},
-	/*
 	{
 		// Storing a Go pointer into C memory should fail.
 		name: "barrier",
@@ -238,7 +237,6 @@ var ptrTests = []ptrTest{
                           func GoFn() *byte { return (*byte)(C.malloc(1)) }`,
 		body: `C.GoFn()`,
 	},
-	*/
 }
 
 func main() {

src/cmd/compile/internal/gc/builtin.go

@@ -117,7 +117,6 @@ const runtimeimport = "" +
 	"func @\"\".writebarrierfat1110 (@\"\".dst·1 *any, _ uintptr, @\"\".src·3 any)\n" +
 	"func @\"\".writebarrierfat1111 (@\"\".dst·1 *any, _ uintptr, @\"\".src·3 any)\n" +
 	"func @\"\".typedmemmove (@\"\".typ·1 *byte, @\"\".dst·2 *any, @\"\".src·3 *any)\n" +
-	"func @\"\".typedmemmove_nostore (@\"\".typ·1 *byte, @\"\".dst·2 *any)\n" +
 	"func @\"\".typedslicecopy (@\"\".typ·2 *byte, @\"\".dst·3 any, @\"\".src·4 any) (? int)\n" +
 	"func @\"\".selectnbsend (@\"\".chanType·2 *byte, @\"\".hchan·3 chan<- any, @\"\".elem·4 *any) (? bool)\n" +
 	"func @\"\".selectnbrecv (@\"\".chanType·2 *byte, @\"\".elem·3 *any, @\"\".hchan·4 <-chan any) (? bool)\n" +

src/cmd/compile/internal/gc/builtin/runtime.go

@@ -151,7 +151,6 @@ func writebarrierfat1111(dst *any, _ uintptr, src any)
 
 // *byte is really *runtime.Type
 func typedmemmove(typ *byte, dst *any, src *any)
-func typedmemmove_nostore(typ *byte, dst *any)
 func typedslicecopy(typ *byte, dst any, src any) int
 
 func selectnbsend(chanType *byte, hchan chan<- any, elem *any) bool

src/cmd/compile/internal/gc/go.go

@@ -868,6 +868,7 @@ var throwreturn *Node
 
 var growslice *Node
 
-var typedmemmove_nostore *Node
+var writebarrierptr *Node
+var typedmemmove *Node
 
 var panicdottype *Node

src/cmd/compile/internal/gc/pgen.go

@@ -353,7 +353,8 @@ func compile(fn *Node) {
 		panicdivide = Sysfunc("panicdivide")
 		throwreturn = Sysfunc("throwreturn")
 		growslice = Sysfunc("growslice")
-		typedmemmove_nostore = Sysfunc("typedmemmove_nostore")
+		writebarrierptr = Sysfunc("writebarrierptr")
+		typedmemmove = Sysfunc("typedmemmove")
 		panicdottype = Sysfunc("panicdottype")
 	}
 

src/runtime/mbarrier.go

@@ -197,14 +197,6 @@ func typedmemmove(typ *_type, dst, src unsafe.Pointer) {
 	heapBitsBulkBarrier(uintptr(dst), typ.size)
 }
 
-//go:nosplit
-func typedmemmove_nostore(typ *_type, dst unsafe.Pointer) {
-	if typ.kind&kindNoPointers != 0 {
-		return
-	}
-	heapBitsBulkBarrier(uintptr(dst), typ.size)
-}
-
 //go:linkname reflect_typedmemmove reflect.typedmemmove
 func reflect_typedmemmove(typ *_type, dst, src unsafe.Pointer) {
 	typedmemmove(typ, dst, src)