[release-branch.go1.15] cmd/compile: don't allow go:notinheap on the heap or stack

Right now we just prevent such types from being on the heap. This CL
makes it so they cannot appear on the stack either. The distinction
between heap and stack is pretty vague at the language level (e.g. it
is affected by -N), and we don't need the flexibility anyway.

Once go:notinheap types cannot be in either place, we don't need to
consider pointers to such types to be pointers, at least according to
the garbage collector and stack copying. (This is the big win of this
CL, in my opinion.)

The distinction between HasPointers and HasHeapPointer no longer
exists. There is only HasPointers.

This CL is cleanup before possible use of go:notinheap to fix #40954.

Update #13386

Change-Id: Ibd895aadf001c0385078a6d4809c3f374991231a
Reviewed-on: https://go-review.googlesource.com/c/go/+/255320
Trust: Keith Randall <khr@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

16 files changed, 53 insertions, 66 deletions

diff --git a/src/cmd/compile/internal/gc/escape.go b/src/cmd/compile/internal/gc/escape.go
index ddf89f6159..d5cca4a38b 100644
--- a/src/cmd/compile/internal/gc/escape.go
+++ b/src/cmd/compile/internal/gc/escape.go
@@ -1029,6 +1029,9 @@ func (e *Escape) newLoc(n *Node, transient bool) *EscLocation {
 	if e.curfn == nil {
 		Fatalf("e.curfn isn't set")
 	}
+	if n != nil && n.Type != nil && n.Type.NotInHeap() {
+		yyerrorl(n.Pos, "%v is go:notinheap; stack allocation disallowed", n.Type)
+	}
 
 	n = canonicalNode(n)
 	loc := &EscLocation{
diff --git a/src/cmd/compile/internal/gc/pgen_test.go b/src/cmd/compile/internal/gc/pgen_test.go
index 41f0808a1c..b1db29825c 100644
--- a/src/cmd/compile/internal/gc/pgen_test.go
+++ b/src/cmd/compile/internal/gc/pgen_test.go
@@ -20,7 +20,7 @@ func typeWithoutPointers() *types.Type {
 
 func typeWithPointers() *types.Type {
 	t := types.New(TSTRUCT)
-	f := &types.Field{Type: types.New(TPTR)}
+	f := &types.Field{Type: types.NewPtr(types.New(TINT))}
 	t.SetFields([]*types.Field{f})
 	return t
 }
@@ -181,14 +181,6 @@ func TestStackvarSort(t *testing.T) {
 		nodeWithClass(Node{Type: &types.Type{}, Sym: &types.Sym{Name: "xyz"}}, PAUTO),
 		nodeWithClass(Node{Type: typeWithoutPointers(), Sym: &types.Sym{}}, PAUTO),
 	}
-	// haspointers updates Type.Haspointers as a side effect, so
-	// exercise this function on all inputs so that reflect.DeepEqual
-	// doesn't produce false positives.
-	for i := range want {
-		want[i].Type.HasPointers()
-		inp[i].Type.HasPointers()
-	}
-
 	sort.Sort(byStackVar(inp))
 	if !reflect.DeepEqual(want, inp) {
 		t.Error("sort failed")
diff --git a/src/cmd/compile/internal/gc/plive.go b/src/cmd/compile/internal/gc/plive.go
index 4681d8ea72..09e5487f60 100644
--- a/src/cmd/compile/internal/gc/plive.go
+++ b/src/cmd/compile/internal/gc/plive.go
@@ -436,7 +436,7 @@ func (lv *Liveness) regEffects(v *ssa.Value) (uevar, kill liveRegMask) {
 		case ssa.LocalSlot:
 			return mask
 		case *ssa.Register:
-			if ptrOnly && !v.Type.HasHeapPointer() {
+			if ptrOnly && !v.Type.HasPointers() {
 				return mask
 			}
 			regs[0] = loc
@@ -451,7 +451,7 @@ func (lv *Liveness) regEffects(v *ssa.Value) (uevar, kill liveRegMask) {
 				if loc1 == nil {
 					continue
 				}
-				if ptrOnly && !v.Type.FieldType(i).HasHeapPointer() {
+				if ptrOnly && !v.Type.FieldType(i).HasPointers() {
 					continue
 				}
 				regs[nreg] = loc1.(*ssa.Register)
@@ -568,13 +568,13 @@ func onebitwalktype1(t *types.Type, off int64, bv bvec) {
 	if t.Align > 0 && off&int64(t.Align-1) != 0 {
 		Fatalf("onebitwalktype1: invalid initial alignment: type %v has alignment %d, but offset is %v", t, t.Align, off)
 	}
+	if !t.HasPointers() {
+		// Note: this case ensures that pointers to go:notinheap types
+		// are not considered pointers by garbage collection and stack copying.
+		return
+	}
 
 	switch t.Etype {
-	case TINT8, TUINT8, TINT16, TUINT16,
-		TINT32, TUINT32, TINT64, TUINT64,
-		TINT, TUINT, TUINTPTR, TBOOL,
-		TFLOAT32, TFLOAT64, TCOMPLEX64, TCOMPLEX128:
-
 	case TPTR, TUNSAFEPTR, TFUNC, TCHAN, TMAP:
 		if off&int64(Widthptr-1) != 0 {
 			Fatalf("onebitwalktype1: invalid alignment, %v", t)
diff --git a/src/cmd/compile/internal/gc/range.go b/src/cmd/compile/internal/gc/range.go
index d78a5f0d8d..5434b0167a 100644
--- a/src/cmd/compile/internal/gc/range.go
+++ b/src/cmd/compile/internal/gc/range.go
@@ -586,7 +586,7 @@ func arrayClear(n, v1, v2, a *Node) bool {
 	n.Nbody.Append(nod(OAS, hn, tmp))
 
 	var fn *Node
-	if a.Type.Elem().HasHeapPointer() {
+	if a.Type.Elem().HasPointers() {
 		// memclrHasPointers(hp, hn)
 		Curfn.Func.setWBPos(stmt.Pos)
 		fn = mkcall("memclrHasPointers", nil, nil, hp, hn)
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 9291301f36..8dd1277705 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -1151,6 +1151,9 @@ opswitch:
 		}
 
 	case ONEW:
+		if n.Type.Elem().NotInHeap() {
+			yyerror("%v is go:notinheap; heap allocation disallowed", n.Type.Elem())
+		}
 		if n.Esc == EscNone {
 			if n.Type.Elem().Width >= maxImplicitStackVarSize {
 				Fatalf("large ONEW with EscNone: %v", n)
@@ -1319,6 +1322,9 @@ opswitch:
 			l = r
 		}
 		t := n.Type
+		if t.Elem().NotInHeap() {
+			yyerror("%v is go:notinheap; heap allocation disallowed", t.Elem())
+		}
 		if n.Esc == EscNone {
 			if !isSmallMakeSlice(n) {
 				Fatalf("non-small OMAKESLICE with EscNone: %v", n)
@@ -1360,10 +1366,6 @@ opswitch:
 			// When len and cap can fit into int, use makeslice instead of
 			// makeslice64, which is faster and shorter on 32 bit platforms.
 
-			if t.Elem().NotInHeap() {
-				yyerror("%v is go:notinheap; heap allocation disallowed", t.Elem())
-			}
-
 			len, cap := l, r
 
 			fnname := "makeslice64"
@@ -1398,7 +1400,7 @@ opswitch:
 
 		t := n.Type
 		if t.Elem().NotInHeap() {
-			Fatalf("%v is go:notinheap; heap allocation disallowed", t.Elem())
+			yyerror("%v is go:notinheap; heap allocation disallowed", t.Elem())
 		}
 
 		length := conv(n.Left, types.Types[TINT])
@@ -2002,9 +2004,6 @@ func walkprint(nn *Node, init *Nodes) *Node {
 }
 
 func callnew(t *types.Type) *Node {
-	if t.NotInHeap() {
-		yyerror("%v is go:notinheap; heap allocation disallowed", t)
-	}
 	dowidth(t)
 	n := nod(ONEWOBJ, typename(t), nil)
 	n.Type = types.NewPtr(t)
@@ -2579,7 +2578,7 @@ func mapfast(t *types.Type) int {
 	}
 	switch algtype(t.Key()) {
 	case AMEM32:
-		if !t.Key().HasHeapPointer() {
+		if !t.Key().HasPointers() {
 			return mapfast32
 		}
 		if Widthptr == 4 {
@@ -2587,7 +2586,7 @@ func mapfast(t *types.Type) int {
 		}
 		Fatalf("small pointer %v", t.Key())
 	case AMEM64:
-		if !t.Key().HasHeapPointer() {
+		if !t.Key().HasPointers() {
 			return mapfast64
 		}
 		if Widthptr == 8 {
@@ -2734,7 +2733,7 @@ func appendslice(n *Node, init *Nodes) *Node {
 	nodes.Append(nod(OAS, s, nt))
 
 	var ncopy *Node
-	if elemtype.HasHeapPointer() {
+	if elemtype.HasPointers() {
 		// copy(s[len(l1):], l2)
 		nptr1 := nod(OSLICE, s, nil)
 		nptr1.Type = s.Type
@@ -3072,7 +3071,7 @@ func walkappend(n *Node, init *Nodes, dst *Node) *Node {
 // Also works if b is a string.
 //
 func copyany(n *Node, init *Nodes, runtimecall bool) *Node {
-	if n.Left.Type.Elem().HasHeapPointer() {
+	if n.Left.Type.Elem().HasPointers() {
 		Curfn.Func.setWBPos(n.Pos)
 		fn := writebarrierfn("typedslicecopy", n.Left.Type.Elem(), n.Right.Type.Elem())
 		n.Left = cheapexpr(n.Left, init)
diff --git a/src/cmd/compile/internal/ssa/decompose.go b/src/cmd/compile/internal/ssa/decompose.go
index c59ec4c77d..6e72e3825c 100644
--- a/src/cmd/compile/internal/ssa/decompose.go
+++ b/src/cmd/compile/internal/ssa/decompose.go
@@ -139,7 +139,7 @@ func decomposeStringPhi(v *Value) {
 
 func decomposeSlicePhi(v *Value) {
 	types := &v.Block.Func.Config.Types
-	ptrType := types.BytePtr
+	ptrType := v.Type.Elem().PtrTo()
 	lenType := types.Int
 
 	ptr := v.Block.NewValue0(v.Pos, OpPhi, ptrType)
diff --git a/src/cmd/compile/internal/ssa/gen/dec.rules b/src/cmd/compile/internal/ssa/gen/dec.rules
index 3fd2be409f..4c677f8418 100644
--- a/src/cmd/compile/internal/ssa/gen/dec.rules
+++ b/src/cmd/compile/internal/ssa/gen/dec.rules
@@ -66,14 +66,14 @@
     (Load <typ.Int>
       (OffPtr <typ.IntPtr> [2*config.PtrSize] ptr)
       mem))
-(Store dst (SliceMake ptr len cap) mem) =>
+(Store {t} dst (SliceMake ptr len cap) mem) =>
   (Store {typ.Int}
     (OffPtr <typ.IntPtr> [2*config.PtrSize] dst)
     cap
     (Store {typ.Int}
       (OffPtr <typ.IntPtr> [config.PtrSize] dst)
       len
-      (Store {typ.BytePtr} dst ptr mem)))
+      (Store {t.Elem().PtrTo()} dst ptr mem)))
 
 // interface ops
 (ITab (IMake itab _)) => itab
diff --git a/src/cmd/compile/internal/ssa/nilcheck.go b/src/cmd/compile/internal/ssa/nilcheck.go
index 6b24371ac7..d1bad529e7 100644
--- a/src/cmd/compile/internal/ssa/nilcheck.go
+++ b/src/cmd/compile/internal/ssa/nilcheck.go
@@ -235,7 +235,7 @@ func nilcheckelim2(f *Func) {
 				continue
 			}
 			if v.Type.IsMemory() || v.Type.IsTuple() && v.Type.FieldType(1).IsMemory() {
-				if v.Op == OpVarKill || v.Op == OpVarLive || (v.Op == OpVarDef && !v.Aux.(GCNode).Typ().HasHeapPointer()) {
+				if v.Op == OpVarKill || v.Op == OpVarLive || (v.Op == OpVarDef && !v.Aux.(GCNode).Typ().HasPointers()) {
 					// These ops don't really change memory.
 					continue
 					// Note: OpVarDef requires that the defined variable not have pointers.
diff --git a/src/cmd/compile/internal/ssa/rewritedec.go b/src/cmd/compile/internal/ssa/rewritedec.go
index cef781ffaa..e0fa9768d9 100644
--- a/src/cmd/compile/internal/ssa/rewritedec.go
+++ b/src/cmd/compile/internal/ssa/rewritedec.go
@@ -328,9 +328,10 @@ func rewriteValuedec_OpStore(v *Value) bool {
 		v.AddArg3(v0, len, v1)
 		return true
 	}
-	// match: (Store dst (SliceMake ptr len cap) mem)
-	// result: (Store {typ.Int} (OffPtr <typ.IntPtr> [2*config.PtrSize] dst) cap (Store {typ.Int} (OffPtr <typ.IntPtr> [config.PtrSize] dst) len (Store {typ.BytePtr} dst ptr mem)))
+	// match: (Store {t} dst (SliceMake ptr len cap) mem)
+	// result: (Store {typ.Int} (OffPtr <typ.IntPtr> [2*config.PtrSize] dst) cap (Store {typ.Int} (OffPtr <typ.IntPtr> [config.PtrSize] dst) len (Store {t.Elem().PtrTo()} dst ptr mem)))
 	for {
+		t := auxToType(v.Aux)
 		dst := v_0
 		if v_1.Op != OpSliceMake {
 			break
@@ -350,7 +351,7 @@ func rewriteValuedec_OpStore(v *Value) bool {
 		v2.AuxInt = int64ToAuxInt(config.PtrSize)
 		v2.AddArg(dst)
 		v3 := b.NewValue0(v.Pos, OpStore, types.TypeMem)
-		v3.Aux = typeToAux(typ.BytePtr)
+		v3.Aux = typeToAux(t.Elem().PtrTo())
 		v3.AddArg3(dst, ptr, mem)
 		v1.AddArg3(v2, len, v3)
 		v.AddArg3(v0, cap, v1)
diff --git a/src/cmd/compile/internal/ssa/writebarrier.go b/src/cmd/compile/internal/ssa/writebarrier.go
index c7fb059475..214798a1ab 100644
--- a/src/cmd/compile/internal/ssa/writebarrier.go
+++ b/src/cmd/compile/internal/ssa/writebarrier.go
@@ -31,7 +31,7 @@ func needwb(v *Value, zeroes map[ID]ZeroRegion) bool {
 	if !ok {
 		v.Fatalf("store aux is not a type: %s", v.LongString())
 	}
-	if !t.HasHeapPointer() {
+	if !t.HasPointers() {
 		return false
 	}
 	if IsStackAddr(v.Args[0]) {
diff --git a/src/cmd/compile/internal/types/type.go b/src/cmd/compile/internal/types/type.go
index 9c51b00f84..7d9becfa00 100644
--- a/src/cmd/compile/internal/types/type.go
+++ b/src/cmd/compile/internal/types/type.go
@@ -1397,14 +1397,9 @@ func (t *Type) IsUntyped() bool {
 	return false
 }
 
-// TODO(austin): We probably only need HasHeapPointer. See
-// golang.org/cl/73412 for discussion.
-
+// HasPointers reports whether t contains a heap pointer.
+// Note that this function ignores pointers to go:notinheap types.
 func (t *Type) HasPointers() bool {
-	return t.hasPointers1(false)
-}
-
-func (t *Type) hasPointers1(ignoreNotInHeap bool) bool {
 	switch t.Etype {
 	case TINT, TUINT, TINT8, TUINT8, TINT16, TUINT16, TINT32, TUINT32, TINT64,
 		TUINT64, TUINTPTR, TFLOAT32, TFLOAT64, TCOMPLEX64, TCOMPLEX128, TBOOL, TSSA:
@@ -1414,34 +1409,27 @@ func (t *Type) hasPointers1(ignoreNotInHeap bool) bool {
 		if t.NumElem() == 0 { // empty array has no pointers
 			return false
 		}
-		return t.Elem().hasPointers1(ignoreNotInHeap)
+		return t.Elem().HasPointers()
 
 	case TSTRUCT:
 		for _, t1 := range t.Fields().Slice() {
-			if t1.Type.hasPointers1(ignoreNotInHeap) {
+			if t1.Type.HasPointers() {
 				return true
 			}
 		}
 		return false
 
 	case TPTR, TSLICE:
-		return !(ignoreNotInHeap && t.Elem().NotInHeap())
+		return !t.Elem().NotInHeap()
 
 	case TTUPLE:
 		ttup := t.Extra.(*Tuple)
-		return ttup.first.hasPointers1(ignoreNotInHeap) || ttup.second.hasPointers1(ignoreNotInHeap)
+		return ttup.first.HasPointers() || ttup.second.HasPointers()
 	}
 
 	return true
 }
 
-// HasHeapPointer reports whether t contains a heap pointer.
-// This is used for write barrier insertion, so it ignores
-// pointers to go:notinheap types.
-func (t *Type) HasHeapPointer() bool {
-	return t.hasPointers1(true)
-}
-
 func (t *Type) Symbol() *obj.LSym {
 	return TypeLinkSym(t)
 }
diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go
index e43813bcc4..b268d5a058 100644
--- a/src/runtime/export_test.go
+++ b/src/runtime/export_test.go
@@ -986,9 +986,8 @@ func MapHashCheck(m interface{}, k interface{}) (uintptr, uintptr) {
 }
 
 func MSpanCountAlloc(bits []byte) int {
-	s := mspan{
-		nelems:     uintptr(len(bits) * 8),
-		gcmarkBits: (*gcBits)(unsafe.Pointer(&bits[0])),
-	}
+	s := (*mspan)(mheap_.spanalloc.alloc())
+	s.nelems = uintptr(len(bits) * 8)
+	s.gcmarkBits = (*gcBits)(unsafe.Pointer(&bits[0]))
 	return s.countAlloc()
 }
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index fe988c46d9..b2fbcd4105 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -937,7 +937,8 @@ func scanstack(gp *g, gcw *gcWork) {
 		x := state.head
 		state.head = x.next
 		if stackTraceDebug {
-			for _, obj := range x.obj[:x.nobj] {
+			for i := 0; i < x.nobj; i++ {
+				obj := &x.obj[i]
 				if obj.typ == nil { // reachable
 					continue
 				}
diff --git a/src/runtime/mgcstack.go b/src/runtime/mgcstack.go
index 211d882fa6..8eb941a328 100644
--- a/src/runtime/mgcstack.go
+++ b/src/runtime/mgcstack.go
@@ -167,8 +167,6 @@ func (obj *stackObject) setType(typ *_type) {
 
 // A stackScanState keeps track of the state used during the GC walk
 // of a goroutine.
-//
-//go:notinheap
 type stackScanState struct {
 	cache pcvalueCache
 
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 0d0cac240b..814364aa42 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -918,8 +918,6 @@ type _defer struct {
 // handling during stack growth: because they are pointer-typed and
 // _panic values only live on the stack, regular stack pointer
 // adjustment takes care of them.
-//
-//go:notinheap
 type _panic struct {
 	argp      unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
 	arg       interface{}    // argument to panic
diff --git a/test/notinheap2.go b/test/notinheap2.go
index 944f2993ab..de1e6db1d3 100644
--- a/test/notinheap2.go
+++ b/test/notinheap2.go
@@ -13,12 +13,14 @@ type nih struct {
 	next *nih
 }
 
-// Globals and stack variables are okay.
+// Global variables are okay.
 
 var x nih
 
+// Stack variables are not okay.
+
 func f() {
-	var y nih
+	var y nih // ERROR "nih is go:notinheap; stack allocation disallowed"
 	x = y
 }
 
@@ -26,11 +28,17 @@ func f() {
 
 var y *nih
 var z []nih
+var w []nih
+var n int
 
 func g() {
 	y = new(nih)       // ERROR "heap allocation disallowed"
 	z = make([]nih, 1) // ERROR "heap allocation disallowed"
 	z = append(z, x)   // ERROR "heap allocation disallowed"
+	// Test for special case of OMAKESLICECOPY
+	x := make([]nih, n) // ERROR "heap allocation disallowed"
+	copy(x, z)
+	z = x
 }
 
 // Writes don't produce write barriers.