cmd/compile: report typedslicecopy write barriers

Most write barrier calls are inserted by SSA, but copy and append are
lowered to runtime.typedslicecopy during walk. Fix these to set
Func.WBPos and emit the "write barrier" warning, as done for the write
barriers inserted by SSA. As part of this, we refactor setting WBPos
and emitting this warning into the frontend so it can be shared by
both walk and SSA.

Change-Id: I5fe9997d9bdb55e03e01dd58aee28908c35f606b
Reviewed-on: https://go-review.googlesource.com/73411
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -136,11 +136,6 @@ func buildssa(fn *Node, worker int) *ssa.Func {
 	if fn.Func.Pragma&Nosplit != 0 {
 		s.f.NoSplit = true
 	}
-	defer func() {
-		if s.f.WBPos.IsKnown() {
-			fn.Func.WBPos = s.f.WBPos
-		}
-	}()
 	s.exitCode = fn.Func.Exit
 	s.panics = map[funcLine]*ssa.Block{}
 
@@ -5180,10 +5175,6 @@ func (e *ssafn) Debug_checknil() bool {
 	return Debug_checknil != 0
 }
 
-func (e *ssafn) Debug_wb() bool {
-	return Debug_wb != 0
-}
-
 func (e *ssafn) UseWriteBarrier() bool {
 	return use_writebarrier
 }
@@ -5205,6 +5196,10 @@ func (e *ssafn) Syslook(name string) *obj.LSym {
 	return nil
 }
 
+func (e *ssafn) SetWBPos(pos src.XPos) {
+	e.curfn.Func.setWBPos(pos)
+}
+
 func (n *Node) Typ() *types.Type {
 	return n.Type
 }

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

@@ -427,7 +427,7 @@ type Func struct {
 	Label int32 // largest auto-generated label in this function
 
 	Endlineno src.XPos
-	WBPos     src.XPos // position of first write barrier
+	WBPos     src.XPos // position of first write barrier; see SetWBPos
 
 	Pragma syntax.Pragma // go:xxx function annotations
 
@@ -484,6 +484,15 @@ func (f *Func) SetHasDefer(b bool)            { f.flags.set(funcHasDefer, b) }
 func (f *Func) SetNilCheckDisabled(b bool)    { f.flags.set(funcNilCheckDisabled, b) }
 func (f *Func) SetInlinabilityChecked(b bool) { f.flags.set(funcInlinabilityChecked, b) }
 
+func (f *Func) setWBPos(pos src.XPos) {
+	if Debug_wb != 0 {
+		Warnl(pos, "write barrier")
+	}
+	if !f.WBPos.IsKnown() {
+		f.WBPos = pos
+	}
+}
+
 type Op uint8
 
 // Node ops.

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

@@ -2955,6 +2955,7 @@ func appendslice(n *Node, init *Nodes) *Node {
 		nptr1.SetSliceBounds(nod(OLEN, l1, nil), nil, nil)
 		nptr1.Etype = 1
 		nptr2 := l2
+		Curfn.Func.setWBPos(n.Pos)
 		fn := syslook("typedslicecopy")
 		fn = substArgTypes(fn, l1.Type, l2.Type)
 		var ln Nodes
@@ -3117,6 +3118,7 @@ func walkappend(n *Node, init *Nodes, dst *Node) *Node {
 //
 func copyany(n *Node, init *Nodes, runtimecall bool) *Node {
 	if types.Haspointers(n.Left.Type.Elem()) {
+		Curfn.Func.setWBPos(n.Pos)
 		fn := writebarrierfn("typedslicecopy", n.Left.Type, n.Right.Type)
 		return mkcall1(fn, n.Type, init, typename(n.Left.Type.Elem()), n.Left, n.Right)
 	}

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

@@ -88,7 +88,6 @@ type Logger interface {
 
 	// Forwards the Debug flags from gc
 	Debug_checknil() bool
-	Debug_wb() bool
 }
 
 type Frontend interface {
@@ -131,6 +130,10 @@ type Frontend interface {
 
 	// UseWriteBarrier returns whether write barrier is enabled
 	UseWriteBarrier() bool
+
+	// SetWBPos indicates that a write barrier has been inserted
+	// in this function at position pos.
+	SetWBPos(pos src.XPos)
 }
 
 // interface used to hold a *gc.Node (a stack variable).

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

@@ -125,6 +125,8 @@ func (d DummyFrontend) Syslook(s string) *obj.LSym {
 func (DummyFrontend) UseWriteBarrier() bool {
 	return true // only writebarrier_test cares
 }
+func (DummyFrontend) SetWBPos(pos src.XPos) {
+}
 
 func (d DummyFrontend) Logf(msg string, args ...interface{}) { d.t.Logf(msg, args...) }
 func (d DummyFrontend) Log() bool                            { return true }
@@ -132,7 +134,6 @@ func (d DummyFrontend) Log() bool                            { return true }
 func (d DummyFrontend) Fatalf(_ src.XPos, msg string, args ...interface{}) { d.t.Fatalf(msg, args...) }
 func (d DummyFrontend) Warnl(_ src.XPos, msg string, args ...interface{})  { d.t.Logf(msg, args...) }
 func (d DummyFrontend) Debug_checknil() bool                               { return false }
-func (d DummyFrontend) Debug_wb() bool                                     { return false }
 
 var dummyTypes Types
 

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

@@ -44,8 +44,6 @@ type Func struct {
 	scheduled bool // Values in Blocks are in final order
 	NoSplit   bool // true if function is marked as nosplit.  Used by schedule check pass.
 
-	WBPos src.XPos // line number of first write barrier
-
 	// when register allocation is done, maps value ids to locations
 	RegAlloc []Location
 

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

@@ -226,12 +226,7 @@ func writebarrier(f *Func) {
 
 			if fn != nil {
 				// Note that we set up a writebarrier function call.
-				if !f.WBPos.IsKnown() {
+				f.fe.SetWBPos(pos)
-					f.WBPos = pos
-				}
-				if f.fe.Debug_wb() {
-					f.Warnl(pos, "write barrier")
-				}
 			}
 		}