[dev.regabi] cmd/compile: address some ir TODOs

Previously, ODOTTYPE/ODOTTYPE2 were forced to reuse some available
Node fields for storing pointers to runtime type descriptors. This
resulted in awkward field types for TypeAssertExpr and AddrExpr.

This CL gives TypeAssertExpr proper fields for the runtime type
descriptors, and also tightens the field types as
possible/appropriate.

Passes toolstash -cmp.

Change-Id: I521ee7a1462affc5459de33a0de6c68a7d6416ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/280637
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

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

@@ -109,7 +109,7 @@ func NewAddStringExpr(pos src.XPos, list []Node) *AddStringExpr {
 type AddrExpr struct {
 	miniExpr
 	X     Node
-	Alloc Node // preallocated storage if any
+	Alloc *Name // preallocated storage if any
 }
 
 func NewAddrExpr(pos src.XPos, x Node) *AddrExpr {
@@ -660,8 +660,13 @@ func (n *StarExpr) SetOTYPE(t *types.Type) {
 type TypeAssertExpr struct {
 	miniExpr
 	X     Node
-	Ntype Node  // TODO: Should be Ntype, but reused as address of type structure
+	Ntype Ntype
-	Itab  Nodes // Itab[0] is itab
+
+	// Runtime type information provided by walkDotType.
+	// Caution: These aren't always populated; see walkDotType.
+	SrcType *AddrExpr // *runtime._type for X's type
+	DstType *AddrExpr // *runtime._type for Type
+	Itab    *AddrExpr // *runtime.itab for Type implementing X's type
 }
 
 func NewTypeAssertExpr(pos src.XPos, x Node, typ Ntype) *TypeAssertExpr {

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

@@ -32,13 +32,11 @@ func (n *AddrExpr) doChildren(do func(Node) error) error {
 	var err error
 	err = maybeDoList(n.init, err, do)
 	err = maybeDo(n.X, err, do)
-	err = maybeDo(n.Alloc, err, do)
 	return err
 }
 func (n *AddrExpr) editChildren(edit func(Node) Node) {
 	editList(n.init, edit)
 	n.X = maybeEdit(n.X, edit)
-	n.Alloc = maybeEdit(n.Alloc, edit)
 }
 
 func (n *ArrayType) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
@@ -954,7 +952,6 @@ func (n *TypeAssertExpr) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
 func (n *TypeAssertExpr) copy() Node {
 	c := *n
 	c.init = c.init.Copy()
-	c.Itab = c.Itab.Copy()
 	return &c
 }
 func (n *TypeAssertExpr) doChildren(do func(Node) error) error {
@@ -962,14 +959,12 @@ func (n *TypeAssertExpr) doChildren(do func(Node) error) error {
 	err = maybeDoList(n.init, err, do)
 	err = maybeDo(n.X, err, do)
 	err = maybeDo(n.Ntype, err, do)
-	err = maybeDoList(n.Itab, err, do)
 	return err
 }
 func (n *TypeAssertExpr) editChildren(edit func(Node) Node) {
 	editList(n.init, edit)
 	n.X = maybeEdit(n.X, edit)
-	n.Ntype = maybeEdit(n.Ntype, edit)
+	n.Ntype = toNtype(maybeEdit(n.Ntype, edit))
-	editList(n.Itab, edit)
 }
 
 func (n *TypeSwitchGuard) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }

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

@@ -5979,7 +5979,7 @@ func (s *state) floatToUint(cvttab *f2uCvtTab, n ir.Node, x *ssa.Value, ft, tt *
 // If commaok is false, resok will be nil.
 func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Value) {
 	iface := s.expr(n.X)        // input interface
-	target := s.expr(n.Ntype) // target type
+	target := s.expr(n.DstType) // target type
 	byteptr := s.f.Config.Types.BytePtr
 
 	if n.Type().IsInterface() {
@@ -6086,7 +6086,7 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 		targetITab = target
 	} else {
 		// Looking for pointer to itab for target type and source interface.
-		targetITab = s.expr(n.Itab[0])
+		targetITab = s.expr(n.Itab)
 	}
 
 	var tmp ir.Node     // temporary for use with large types
@@ -6113,7 +6113,7 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 	if !commaok {
 		// on failure, panic by calling panicdottype
 		s.startBlock(bFail)
-		taddr := s.expr(n.Ntype.(*ir.AddrExpr).Alloc)
+		taddr := s.expr(n.SrcType)
 		if n.X.Type().IsEmptyInterface() {
 			s.rtcall(ir.Syms.PanicdottypeE, false, nil, itab, target, taddr)
 		} else {

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

@@ -649,7 +649,7 @@ func tcDotType(n *ir.TypeAssertExpr) ir.Node {
 	}
 
 	if n.Ntype != nil {
-		n.Ntype = typecheck(n.Ntype, ctxType)
+		n.Ntype = typecheckNtype(n.Ntype)
 		n.SetType(n.Ntype.Type())
 		n.Ntype = nil
 		if n.Type() == nil {

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

@@ -639,12 +639,13 @@ func walkDot(n *ir.SelectorExpr, init *ir.Nodes) ir.Node {
 func walkDotType(n *ir.TypeAssertExpr, init *ir.Nodes) ir.Node {
 	n.X = walkExpr(n.X, init)
 	// Set up interface type addresses for back end.
-	n.Ntype = reflectdata.TypePtr(n.Type())
+
+	n.DstType = reflectdata.TypePtr(n.Type())
 	if n.Op() == ir.ODOTTYPE {
-		n.Ntype.(*ir.AddrExpr).Alloc = reflectdata.TypePtr(n.X.Type())
+		n.SrcType = reflectdata.TypePtr(n.X.Type())
 	}
 	if !n.Type().IsInterface() && !n.X.Type().IsEmptyInterface() {
-		n.Itab = []ir.Node{reflectdata.ITabAddr(n.Type(), n.X.Type())}
+		n.Itab = reflectdata.ITabAddr(n.Type(), n.X.Type())
 	}
 	return n
 }