cmd/compile: simplify noding const declarations

By grouping all the logic into constDecl, we're able to get rid of the
lastconst and lasttype globals, and simplify the logic slightly. Still
clunky, but much easier to reason about.

Change-Id: I446696c31084b3bfc1fd5d3651655a81ddd159ab
Reviewed-on: https://go-review.googlesource.com/36023
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -286,47 +286,6 @@ func variter(vl []*Node, t *Node, el []*Node) []*Node {
 	return init
 }
 
-// declare constants from grammar
-// new_name_list [[type] = expr_list]
-func constiter(vl []*Node, t *Node, cl []*Node, iotaVal int64) []*Node {
-	var lno src.XPos // default is to leave line number alone in listtreecopy
-	if len(cl) == 0 {
-		if t != nil {
-			yyerror("const declaration cannot have type without expression")
-		}
-		cl = lastconst
-		t = lasttype
-		lno = vl[0].Pos
-	} else {
-		lastconst = cl
-		lasttype = t
-	}
-
-	var vv []*Node
-	for i, v := range vl {
-		if i >= len(cl) {
-			yyerror("missing value in const declaration")
-			break
-		}
-
-		c := treecopy(cl[i], lno)
-
-		v.Op = OLITERAL
-		declare(v, dclcontext)
-
-		v.Name.Param.Ntype = t
-		v.Name.Defn = c
-		v.SetIota(iotaVal)
-
-		vv = append(vv, nod(ODCLCONST, v, nil))
-	}
-
-	if len(cl) > len(vl) {
-		yyerror("extra expression in const declaration")
-	}
-	return vv
-}
-
 // newname returns a new ONAME Node associated with symbol s.
 func newname(s *Sym) *Node {
 	if s == nil {

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

@@ -223,10 +223,6 @@ var dclcontext Class // PEXTERN/PAUTO
 
 var statuniqgen int // name generator for static temps
 
-var lastconst []*Node
-
-var lasttype *Node
-
 var Maxarg int64
 
 var Stksize int64 // stack size for current frame

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

@@ -117,9 +117,7 @@ func (p *noder) node() {
 }
 
 func (p *noder) decls(decls []syntax.Decl) (l []*Node) {
-	var lastConstGroup *syntax.Group
-	var lastConstRHS []*Node
-	var iotaVal int64
+	var cs constState
 
 	for _, decl := range decls {
 		p.lineno(decl)
@@ -131,23 +129,7 @@ func (p *noder) decls(decls []syntax.Decl) (l []*Node) {
 			l = append(l, p.varDecl(decl)...)
 
 		case *syntax.ConstDecl:
-			// Tricky to handle golang.org/issue/15550 correctly.
-
-			if decl.Group == nil || decl.Group != lastConstGroup {
-				iotaVal = 0
-				lastConstRHS = nil
-			}
-
-			lastconst = lastConstRHS
-
-			l = append(l, p.constDecl(decl, iotaVal)...)
-
-			lastConstRHS = lastconst
-			lastconst = nil
-
-			iotaVal++
-
-			lastConstGroup = decl.Group
+			l = append(l, p.constDecl(decl, &cs)...)
 
 		case *syntax.TypeDecl:
 			l = append(l, p.typeDecl(decl))
@@ -222,16 +204,62 @@ func (p *noder) varDecl(decl *syntax.VarDecl) []*Node {
 	return variter(names, typ, exprs)
 }
 
-func (p *noder) constDecl(decl *syntax.ConstDecl, iotaVal int64) []*Node {
+type constState struct {
+	group  *syntax.Group
+	typ    *Node
+	values []*Node
+	iota   int64
+}
+
+func (p *noder) constDecl(decl *syntax.ConstDecl, cs *constState) []*Node {
+	if decl.Group == nil || decl.Group != cs.group {
+		*cs = constState{
+			group: decl.Group,
+		}
+	}
+
 	names := p.declNames(decl.NameList)
 	typ := p.typeExprOrNil(decl.Type)
 
-	var exprs []*Node
+	var values []*Node
 	if decl.Values != nil {
-		exprs = p.exprList(decl.Values)
+		values = p.exprList(decl.Values)
+		cs.typ, cs.values = typ, values
+	} else {
+		if typ != nil {
+			yyerror("const declaration cannot have type without expression")
+		}
+		typ, values = cs.typ, cs.values
+	}
+
+	var nn []*Node
+	for i, n := range names {
+		if i >= len(values) {
+			yyerror("missing value in const declaration")
+			break
+		}
+		v := values[i]
+		if decl.Values == nil {
+			v = treecopy(v, n.Pos)
 		}
 
-	return constiter(names, typ, exprs, iotaVal)
+		n.Op = OLITERAL
+		declare(n, dclcontext)
+
+		n.Name.Param.Ntype = typ
+		n.Name.Defn = v
+		n.SetIota(cs.iota)
+
+		nn = append(nn, p.nod(decl, ODCLCONST, n, nil))
+	}
+
+	if len(values) > len(names) {
+		yyerror("extra expression in const declaration")
+	}
+
+	cs.iota++
+
+	return nn
 }
 
 func (p *noder) typeDecl(decl *syntax.TypeDecl) *Node {