cmd/compile: remove go:notinheap pragma

Updates #46731

Change-Id: I247fa9c7ca97feb9053665da7ff56e7f5b571f74
Reviewed-on: https://go-review.googlesource.com/c/go/+/422815
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Joedian Reid <joedian@golang.org>

src/cmd/compile/internal/ir/node.go

@@ -454,9 +454,6 @@ const (
 	Nowritebarrierrec  // error on write barrier in this or recursive callees
 	Yeswritebarrierrec // cancels Nowritebarrierrec in this function and callees
 
-	// Runtime and cgo type pragmas
-	NotInHeap // values of this type must not be heap allocated
-
 	// Go command pragmas
 	GoBuildPragma
 

src/cmd/compile/internal/noder/decl.go

@@ -212,33 +212,9 @@ func (g *irgen) typeDecl(out *ir.Nodes, decl *syntax.TypeDecl) {
 		ntyp.SetVargen()
 	}
 
-	pragmas := g.pragmaFlags(decl.Pragma, typePragmas)
+	pragmas := g.pragmaFlags(decl.Pragma, 0)
 	name.SetPragma(pragmas) // TODO(mdempsky): Is this still needed?
 
-	if pragmas&ir.NotInHeap != 0 {
-		ntyp.SetNotInHeap(true)
-	}
-
-	// We need to use g.typeExpr(decl.Type) here to ensure that for
-	// chained, defined-type declarations like:
-	//
-	//	type T U
-	//
-	//	//go:notinheap
-	//	type U struct { … }
-	//
-	// we mark both T and U as NotInHeap. If we instead used just
-	// g.typ(otyp.Underlying()), then we'd instead set T's underlying
-	// type directly to the struct type (which is not marked NotInHeap)
-	// and fail to mark T as NotInHeap.
-	//
-	// Also, we rely here on Type.SetUnderlying allowing passing a
-	// defined type and handling forward references like from T to U
-	// above. Contrast with go/types's Named.SetUnderlying, which
-	// disallows this.
-	//
-	// [mdempsky: Subtleties like these are why I always vehemently
-	// object to new type pragmas.]
 	ntyp.SetUnderlying(g.typeExpr(decl.Type))
 
 	tparams := otyp.(*types2.Named).TypeParams()

src/cmd/compile/internal/noder/lex.go

@@ -36,8 +36,6 @@ const (
 		ir.Nowritebarrier |
 		ir.Nowritebarrierrec |
 		ir.Yeswritebarrierrec
-
-	typePragmas = ir.NotInHeap
 )
 
 func pragmaFlag(verb string) ir.PragmaFlag {
@@ -77,8 +75,6 @@ func pragmaFlag(verb string) ir.PragmaFlag {
 		return ir.UintptrEscapes | ir.UintptrKeepAlive // implies UintptrKeepAlive
 	case "go:registerparams": // TODO(register args) remove after register abi is working
 		return ir.RegisterParams
-	case "go:notinheap":
-		return ir.NotInHeap
 	}
 	return 0
 }

src/cmd/compile/internal/noder/noder.go

@@ -344,9 +344,6 @@ func (p *noder) pragma(pos syntax.Pos, blankLine bool, text string, old syntax.P
 		if flag == 0 && !allowedStdPragmas[verb] && base.Flag.Std {
 			p.error(syntax.Error{Pos: pos, Msg: fmt.Sprintf("//%s is not allowed in the standard library", verb)})
 		}
-		if flag == ir.NotInHeap && *base.Flag.LowerP != "runtime/internal/sys" {
-			p.error(syntax.Error{Pos: pos, Msg: "//go:notinheap only allowed in runtime/internal/sys"})
-		}
 		pragma.Flag |= flag
 		pragma.Pos = append(pragma.Pos, pragmaPos{flag, pos})
 	}

src/cmd/compile/internal/noder/reader.go

@@ -1096,9 +1096,6 @@ func (r *reader) typeExt(name *ir.Name) {
 	}
 
 	name.SetPragma(r.pragmaFlag())
-	if name.Pragma()&ir.NotInHeap != 0 {
-		typ.SetNotInHeap(true)
-	}
 
 	typecheck.SetBaseTypeIndex(typ, r.Int64(), r.Int64())
 }
@@ -2440,16 +2437,6 @@ func (r *reader) expr() (res ir.Node) {
 		// TODO(mdempsky): Stop constructing expressions of untyped type.
 		x = typecheck.DefaultLit(x, typ)
 
-		if op, why := typecheck.Convertop(x.Op() == ir.OLITERAL, x.Type(), typ); op == ir.OXXX {
-			// types2 ensured that x is convertable to typ under standard Go
-			// semantics, but cmd/compile also disallows some conversions
-			// involving //go:notinheap.
-			//
-			// TODO(mdempsky): This can be removed after #46731 is implemented.
-			base.ErrorfAt(pos, "cannot convert %L to type %v%v", x, typ, why)
-			base.ErrorExit() // harsh, but prevents constructing invalid IR
-		}
-
 		ce := ir.NewConvExpr(pos, ir.OCONV, typ, x)
 		ce.TypeWord, ce.SrcRType = typeWord, srcRType
 		if implicit {

src/cmd/compile/internal/noder/writer.go

@@ -2355,7 +2355,7 @@ func (c *declCollector) Visit(n syntax.Node) syntax.Visitor {
 		if n.Alias {
 			pw.checkPragmas(n.Pragma, 0, false)
 		} else {
-			pw.checkPragmas(n.Pragma, typePragmas, false)
+			pw.checkPragmas(n.Pragma, 0, false)
 
 			// Assign a unique ID to function-scoped defined types.
 			if c.withinFunc {

src/cmd/compile/internal/typebits/typebits.go

@@ -18,7 +18,7 @@ func Set(t *types.Type, off int64, bv bitvec.BitVec) {
 		base.Fatalf("typebits.Set: invalid initial alignment: type %v has alignment %d, but offset is %v", t, uint8(t.Alignment()), off)
 	}
 	if !t.HasPointers() {
-		// Note: this case ensures that pointers to go:notinheap types
+		// Note: this case ensures that pointers to not-in-heap types
 		// are not considered pointers by garbage collection and stack copying.
 		return
 	}

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

@@ -901,7 +901,7 @@ func tcUnsafeSlice(n *ir.BinaryExpr) *ir.BinaryExpr {
 		base.Errorf("first argument to unsafe.Slice must be pointer; have %L", t)
 	} else if t.Elem().NotInHeap() {
 		// TODO(mdempsky): This can be relaxed, but should only affect the
-		// Go runtime itself. End users should only see //go:notinheap
+		// Go runtime itself. End users should only see not-in-heap
 		// types due to incomplete C structs in cgo, and those types don't
 		// have a meaningful size anyway.
 		base.Errorf("unsafe.Slice of incomplete (or unallocatable) type not allowed")

src/cmd/compile/internal/typecheck/subr.go

@@ -471,15 +471,15 @@ func Convertop(srcConstant bool, src, dst *types.Type) (ir.Op, string) {
 		return ir.OXXX, ""
 	}
 
-	// Conversions from regular to go:notinheap are not allowed
+	// Conversions from regular to not-in-heap are not allowed
 	// (unless it's unsafe.Pointer). These are runtime-specific
 	// rules.
-	// (a) Disallow (*T) to (*U) where T is go:notinheap but U isn't.
+	// (a) Disallow (*T) to (*U) where T is not-in-heap but U isn't.
 	if src.IsPtr() && dst.IsPtr() && dst.Elem().NotInHeap() && !src.Elem().NotInHeap() {
 		why := fmt.Sprintf(":\n\t%v is incomplete (or unallocatable), but %v is not", dst.Elem(), src.Elem())
 		return ir.OXXX, why
 	}
-	// (b) Disallow string to []T where T is go:notinheap.
+	// (b) Disallow string to []T where T is not-in-heap.
 	if src.IsString() && dst.IsSlice() && dst.Elem().NotInHeap() && (dst.Elem().Kind() == types.ByteType.Kind() || dst.Elem().Kind() == types.RuneType.Kind()) {
 		why := fmt.Sprintf(":\n\t%v is incomplete (or unallocatable)", dst.Elem())
 		return ir.OXXX, why