[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 <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>

Author: randall77

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{

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")

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)

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)

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)
@@ -2579,15 +2578,15 @@ 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 {
 			return mapfast32ptr
 		}
 		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)

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)

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

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.

src/cmd/compile/internal/ssa/rewritedec.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]) {

src/cmd/compile/internal/ssa/writebarrier.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)
 }

src/cmd/compile/internal/types/type.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()
 }

src/runtime/export_test.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
 				}

src/runtime/mgcmark.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
 

src/runtime/mgcstack.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

src/runtime/runtime2.go

@@ -13,24 +13,32 @@ 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
 }
 
 // Heap allocation is not okay.
 
 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.