cmd/compile: construct typename in walk instead of SSA conversion

This eliminates references to lineno and
other globals from ssa conversion.

Passes toolstash-check.

Updates #15756

Change-Id: I9792074fab0036b42f454b79139d0b27db913fb5
Reviewed-on: https://go-review.googlesource.com/38721
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -2156,9 +2156,7 @@ func (s *state) append(n *Node, inplace bool) *ssa.Value {
 
 	// Call growslice
 	s.startBlock(grow)
-	sym := s.lookupSymbol(n, &ssa.ExternSymbol{Typ: Types[TUINTPTR], Sym: Linksym(typenamesym(n.Type.Elem()))})
-	taddr := s.newValue1A(ssa.OpAddr, Types[TUINTPTR], sym, s.sb)
-
+	taddr := s.expr(n.Left)
 	r := s.rtcall(growslice, true, []*Type{pt, Types[TINT], Types[TINT]}, taddr, p, l, c, nl)
 
 	if inplace {
@@ -3970,8 +3968,7 @@ func (s *state) floatToUint(cvttab *f2uCvtTab, n *Node, x *ssa.Value, ft, tt *Ty
 // If commaok is false, resok will be nil.
 func (s *state) dottype(n *Node, commaok bool) (res, resok *ssa.Value) {
 	iface := s.expr(n.Left)   // input interface
-	lineno = n.Pos                     // for typename call
-	target := s.expr(typename(n.Type)) // target type
+	target := s.expr(n.Right) // target type
 	byteptr := s.f.Config.Types.BytePtr
 
 	if n.Type.IsInterface() {
@@ -4105,8 +4102,7 @@ func (s *state) dottype(n *Node, commaok bool) (res, resok *ssa.Value) {
 	if !commaok {
 		// on failure, panic by calling panicdottype
 		s.startBlock(bFail)
-		sym := s.lookupSymbol(n, &ssa.ExternSymbol{Typ: byteptr, Sym: Linksym(typenamesym(n.Left.Type))})
-		taddr := s.newValue1A(ssa.OpAddr, byteptr, sym, s.sb)
+		taddr := s.expr(n.Right.Right)
 		if n.Left.Type.IsEmptyInterface() {
 			s.rtcall(panicdottypeE, false, nil, itab, target, taddr)
 		} else {

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

@@ -1980,6 +1980,15 @@ func liststmt(l []*Node) *Node {
 	return n
 }
 
+func (l Nodes) asblock() *Node {
+	n := nod(OBLOCK, nil, nil)
+	n.List = l
+	if l.Len() != 0 {
+		n.Pos = l.First().Pos
+	}
+	return n
+}
+
 func ngotype(n *Node) *Sym {
 	if n.Type != nil {
 		return typenamesym(n.Type)

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

@@ -4,7 +4,9 @@
 
 package gc
 
-import "sort"
+import (
+	"sort"
+)
 
 const (
 	// expression switch
@@ -825,16 +827,16 @@ func (s *typeSwitch) walk(sw *Node) {
 // case body if the variable is of type t.
 func (s *typeSwitch) typeone(t *Node) *Node {
 	var name *Node
-	var init []*Node
+	var init Nodes
 	if t.Rlist.Len() == 0 {
 		name = nblank
 		nblank = typecheck(nblank, Erv|Easgn)
 	} else {
 		name = t.Rlist.First()
-		init = []*Node{nod(ODCL, name, nil)}
+		init.Append(nod(ODCL, name, nil))
 		a := nod(OAS, name, nil)
 		a = typecheck(a, Etop)
-		init = append(init, a)
+		init.Append(a)
 	}
 
 	a := nod(OAS2, nil, nil)
@@ -843,13 +845,15 @@ func (s *typeSwitch) typeone(t *Node) *Node {
 	b.Type = t.Left.Type // interface.(type)
 	a.Rlist.Set1(b)
 	a = typecheck(a, Etop)
-	init = append(init, a)
+	a = walkexpr(a, &init)
+	init.Append(a)
 
 	c := nod(OIF, nil, nil)
 	c.Left = s.okname
 	c.Nbody.Set1(t.Right) // if ok { goto l }
 
-	return liststmt(append(init, c))
+	init.Append(c)
+	return init.asblock()
 }
 
 // walkCases generates an AST implementing the cases in cc.

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

@@ -382,7 +382,7 @@ const (
 	OADDSTR          // +{List} (string addition, list elements are strings)
 	OADDR            // &Left
 	OANDAND          // Left && Right
-	OAPPEND          // append(List)
+	OAPPEND          // append(List); after walk, Left may contain elem type descriptor
 	OARRAYBYTESTR    // Type(Left) (Type is string, Left is a []byte)
 	OARRAYBYTESTRTMP // Type(Left) (Type is string, Left is a []byte, ephemeral)
 	OARRAYRUNESTR    // Type(Left) (Type is string, Left is a []rune)
@@ -430,8 +430,8 @@ const (
 	ODOTMETH   // Left.Sym (Left is non-interface, Right is method name)
 	ODOTINTER  // Left.Sym (Left is interface, Right is method name)
 	OXDOT      // Left.Sym (before rewrite to one of the preceding)
-	ODOTTYPE   // Left.Right or Left.Type (.Right during parsing, .Type once resolved)
-	ODOTTYPE2  // Left.Right or Left.Type (.Right during parsing, .Type once resolved; on rhs of OAS2DOTTYPE)
+	ODOTTYPE   // Left.Right or Left.Type (.Right during parsing, .Type once resolved); after walk, .Right contains address of interface type descriptor and .Right.Right contains address of concrete type descriptor
+	ODOTTYPE2  // Left.Right or Left.Type (.Right during parsing, .Type once resolved; on rhs of OAS2DOTTYPE); after walk, .Right contains address of interface type descriptor
 	OEQ        // Left == Right
 	ONE        // Left != Right
 	OLT        // Left < Right

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

@@ -504,7 +504,7 @@ opswitch:
 		// TODO(mdempsky): Just return n; see discussion on CL 38655.
 
 	case ONOT, OMINUS, OPLUS, OCOM, OREAL, OIMAG, ODOTMETH, ODOTINTER,
-		OIND, OSPTR, OITAB, OIDATA, ODOTTYPE, ODOTTYPE2, OADDR:
+		OIND, OSPTR, OITAB, OIDATA, OADDR:
 		n.Left = walkexpr(n.Left, init)
 
 	case OEFACE, OAND, OSUB, OMUL, OLT, OLE, OGE, OGT, OADD, OOR, OXOR:
@@ -515,6 +515,14 @@ opswitch:
 		usefield(n)
 		n.Left = walkexpr(n.Left, init)
 
+	case ODOTTYPE, ODOTTYPE2:
+		n.Left = walkexpr(n.Left, init)
+		// Set up interface type addresses for back end.
+		n.Right = typename(n.Type)
+		if n.Op == ODOTTYPE {
+			n.Right.Right = typename(n.Left.Type)
+		}
+
 	case ODOTPTR:
 		usefield(n)
 		if n.Op == ODOTPTR && n.Left.Type.Elem().Width == 0 {
@@ -706,6 +714,8 @@ opswitch:
 			if r.Op == OAPPEND {
 				// Left in place for back end.
 				// Do not add a new write barrier.
+				// Set up address of type for back end.
+				r.Left = typename(r.Type.Elem())
 				break opswitch
 			}
 			// Otherwise, lowered for race detector.
@@ -839,8 +849,7 @@ opswitch:
 
 	case OAS2DOTTYPE:
 		walkexprlistsafe(n.List.Slice(), init)
-		e := n.Rlist.First() // i.(T)
-		e.Left = walkexpr(e.Left, init)
+		n.Rlist.SetFirst(walkexpr(n.Rlist.First(), init))
 
 	case OCONVIFACE:
 		n.Left = walkexpr(n.Left, init)