cmd/compile: remove some more gotos in gc

Split typecheckrange into two, separating the bigger chunk of code that
takes care of the range expression. It had to sometimes exit early,
which was done via a goto in the larger func. This lets us simplify many
declarations and the flow of the code. While at it, also replace the
toomany int with a bool.

In the case of walkselect, split it into two funcs too since using a
defer for all the trailing work would be a bit much. It also lets us
simplify the declarations and the flow of the code, since now
walkselectcases has a narrower scope and straightforward signature.

Also replace the gotos in typecheckaste with a lineno defer.

Passes toolstash -cmp on std cmd.

Change-Id: Iacfaa0a34c987c44f180a792c473558785cf6823
Reviewed-on: https://go-review.googlesource.com/72374
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -13,14 +13,6 @@ import (
 
 // range
 func typecheckrange(n *Node) {
-	var toomany bool
-	var why string
-	var t1 *types.Type
-	var t2 *types.Type
-	var v1 *Node
-	var v2 *Node
-	var ls []*Node
-
 	// Typechecking order is important here:
 	// 0. first typecheck range expression (slice/map/chan),
 	//	it is evaluated only once and so logically it is not part of the loop.
@@ -30,15 +22,31 @@ func typecheckrange(n *Node) {
 	// 2. decldepth++ to denote loop body.
 	// 3. typecheck body.
 	// 4. decldepth--.
+	typecheckrangeExpr(n)
+
+	// second half of dance, the first half being typecheckrangeExpr
+	n.SetTypecheck(1)
+	ls := n.List.Slice()
+	for i1, n1 := range ls {
+		if n1.Typecheck() == 0 {
+			ls[i1] = typecheck(ls[i1], Erv|Easgn)
+		}
+	}
+
+	decldepth++
+	typecheckslice(n.Nbody.Slice(), Etop)
+	decldepth--
+}
 
+func typecheckrangeExpr(n *Node) {
 	n.Right = typecheck(n.Right, Erv)
 
 	t := n.Right.Type
 	if t == nil {
-		goto out
+		return
 	}
 	// delicate little dance.  see typecheckas2
-	ls = n.List.Slice()
+	ls := n.List.Slice()
 	for i1, n1 := range ls {
 		if n1.Name == nil || n1.Name.Defn != n {
 			ls[i1] = typecheck(ls[i1], Erv|Easgn)
@@ -50,11 +58,12 @@ func typecheckrange(n *Node) {
 	}
 	n.Type = t
 
-	toomany = false
+	var t1, t2 *types.Type
+	toomany := false
 	switch t.Etype {
 	default:
 		yyerrorl(n.Pos, "cannot range over %L", n.Right)
-		goto out
+		return
 
 	case TARRAY, TSLICE:
 		t1 = types.Types[TINT]
@@ -67,7 +76,7 @@ func typecheckrange(n *Node) {
 	case TCHAN:
 		if !t.ChanDir().CanRecv() {
 			yyerrorl(n.Pos, "invalid operation: range %v (receive from send-only type %v)", n.Right, n.Right.Type)
-			goto out
+			return
 		}
 
 		t1 = t.Elem()
@@ -85,11 +94,10 @@ func typecheckrange(n *Node) {
 		yyerrorl(n.Pos, "too many variables in range")
 	}
 
-	v1 = nil
+	var v1, v2 *Node
 	if n.List.Len() != 0 {
 		v1 = n.List.First()
 	}
-	v2 = nil
 	if n.List.Len() > 1 {
 		v2 = n.List.Second()
 	}
@@ -105,6 +113,7 @@ func typecheckrange(n *Node) {
 		v2 = nil
 	}
 
+	var why string
 	if v1 != nil {
 		if v1.Name != nil && v1.Name.Defn == n {
 			v1.Type = t1
@@ -122,20 +131,6 @@ func typecheckrange(n *Node) {
 		}
 		checkassign(n, v2)
 	}
-
-	// second half of dance
-out:
-	n.SetTypecheck(1)
-	ls = n.List.Slice()
-	for i1, n1 := range ls {
-		if n1.Typecheck() == 0 {
-			ls[i1] = typecheck(ls[i1], Erv|Easgn)
-		}
-	}
-
-	decldepth++
-	typecheckslice(n.Nbody.Slice(), Etop)
-	decldepth--
 }
 
 func cheapComputableIndex(width int64) bool {

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

@@ -78,35 +78,41 @@ func typecheckselect(sel *Node) {
 		typecheckslice(ncase.Nbody.Slice(), Etop)
 	}
 
-	sel.Xoffset = int64(sel.List.Len())
 	lineno = lno
 }
 
 func walkselect(sel *Node) {
-	if sel.List.Len() == 0 && sel.Xoffset != 0 {
-		Fatalf("double walkselect") // already rewrote
+	lno := setlineno(sel)
+	if sel.Nbody.Len() != 0 {
+		Fatalf("double walkselect")
 	}
 
-	lno := setlineno(sel)
-	i := sel.List.Len()
+	init := sel.Ninit.Slice()
+	sel.Ninit.Set(nil)
+
+	init = append(init, walkselectcases(&sel.List)...)
+	sel.List.Set(nil)
+
+	sel.Nbody.Set(init)
+	walkstmtlist(sel.Nbody.Slice())
+
+	lineno = lno
+}
+
+func walkselectcases(cases *Nodes) []*Node {
+	n := cases.Len()
+	sellineno := lineno
 
 	// optimization: zero-case select
-	var init []*Node
-	var r *Node
-	var n *Node
-	var var_ *Node
-	var selv *Node
-	var chosen *Node
-	if i == 0 {
-		sel.Nbody.Set1(mkcall("block", nil, nil))
-		goto out
+	if n == 0 {
+		return []*Node{mkcall("block", nil, nil)}
 	}
 
 	// optimization: one-case select: single op.
 	// TODO(rsc): Reenable optimization once order.go can handle it.
 	// golang.org/issue/7672.
-	if i == 1 {
-		cas := sel.List.First()
+	if n == 1 {
+		cas := cases.First()
 		setlineno(cas)
 		l := cas.Ninit.Slice()
 		if cas.Left != nil { // not default:
@@ -161,15 +167,14 @@ func walkselect(sel *Node) {
 
 		l = append(l, cas.Nbody.Slice()...)
 		l = append(l, nod(OBREAK, nil, nil))
-		sel.Nbody.Set(l)
-		goto out
+		return l
 	}
 
 	// convert case value arguments to addresses.
 	// this rewrite is used by both the general code and the next optimization.
-	for _, cas := range sel.List.Slice() {
+	for _, cas := range cases.Slice() {
 		setlineno(cas)
-		n = cas.Left
+		n := cas.Left
 		if n == nil {
 			continue
 		}
@@ -197,15 +202,15 @@ func walkselect(sel *Node) {
 	}
 
 	// optimization: two-case select but one is default: single non-blocking op.
-	if i == 2 && (sel.List.First().Left == nil || sel.List.Second().Left == nil) {
+	if n == 2 && (cases.First().Left == nil || cases.Second().Left == nil) {
 		var cas *Node
 		var dflt *Node
-		if sel.List.First().Left == nil {
-			cas = sel.List.Second()
-			dflt = sel.List.First()
+		if cases.First().Left == nil {
+			cas = cases.Second()
+			dflt = cases.First()
 		} else {
-			dflt = sel.List.Second()
-			cas = sel.List.First()
+			dflt = cases.Second()
+			cas = cases.First()
 		}
 
 		n := cas.Left
@@ -239,26 +244,24 @@ func walkselect(sel *Node) {
 		r.Left = typecheck(r.Left, Erv)
 		r.Nbody.Set(cas.Nbody.Slice())
 		r.Rlist.Set(append(dflt.Ninit.Slice(), dflt.Nbody.Slice()...))
-		sel.Nbody.Set2(r, nod(OBREAK, nil, nil))
-		goto out
+		return []*Node{r, nod(OBREAK, nil, nil)}
 	}
 
-	init = sel.Ninit.Slice()
-	sel.Ninit.Set(nil)
+	var init []*Node
 
 	// generate sel-struct
-	setlineno(sel)
-	selv = temp(selecttype(sel.Xoffset))
-	r = nod(OAS, selv, nil)
+	lineno = sellineno
+	selv := temp(selecttype(int64(n)))
+	r := nod(OAS, selv, nil)
 	r = typecheck(r, Etop)
 	init = append(init, r)
-	var_ = conv(conv(nod(OADDR, selv, nil), types.Types[TUNSAFEPTR]), types.NewPtr(types.Types[TUINT8]))
-	r = mkcall("newselect", nil, nil, var_, nodintconst(selv.Type.Width), nodintconst(sel.Xoffset))
+	var_ := conv(conv(nod(OADDR, selv, nil), types.Types[TUNSAFEPTR]), types.NewPtr(types.Types[TUINT8]))
+	r = mkcall("newselect", nil, nil, var_, nodintconst(selv.Type.Width), nodintconst(int64(n)))
 	r = typecheck(r, Etop)
 	init = append(init, r)
 
 	// register cases
-	for _, cas := range sel.List.Slice() {
+	for _, cas := range cases.Slice() {
 		setlineno(cas)
 
 		init = append(init, cas.Ninit.Slice()...)
@@ -290,8 +293,8 @@ func walkselect(sel *Node) {
 	}
 
 	// run the select
-	setlineno(sel)
-	chosen = temp(types.Types[TINT])
+	lineno = sellineno
+	chosen := temp(types.Types[TINT])
 	r = nod(OAS, chosen, mkcall("selectgo", types.Types[TINT], nil, var_))
 	r = typecheck(r, Etop)
 	init = append(init, r)
@@ -300,7 +303,7 @@ func walkselect(sel *Node) {
 	init = append(init, nod(OVARKILL, selv, nil))
 
 	// dispatch cases
-	for i, cas := range sel.List.Slice() {
+	for i, cas := range cases.Slice() {
 		setlineno(cas)
 
 		cond := nod(OEQ, chosen, nodintconst(int64(i)))
@@ -312,12 +315,7 @@ func walkselect(sel *Node) {
 		init = append(init, r)
 	}
 
-	sel.Nbody.Set(init)
-
-out:
-	sel.List.Set(nil)
-	walkstmtlist(sel.Nbody.Slice())
-	lineno = lno
+	return init
 }
 
 // Keep in sync with src/runtime/select.go.

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

@@ -2547,18 +2547,18 @@ func hasddd(t *types.Type) bool {
 // typecheck assignment: type list = expression list
 func typecheckaste(op Op, call *Node, isddd bool, tstruct *types.Type, nl Nodes, desc func() string) {
 	var t *types.Type
-	var n *Node
 	var n1 int
 	var n2 int
 	var i int
 
 	lno := lineno
+	defer func() { lineno = lno }()
 
 	if tstruct.Broke() {
-		goto out
+		return
 	}
 
-	n = nil
+	var n *Node
 	if nl.Len() == 1 {
 		n = nl.First()
 		if n.Type != nil && n.Type.IsFuncArgStruct() {
@@ -2587,7 +2587,7 @@ func typecheckaste(op Op, call *Node, isddd bool, tstruct *types.Type, nl Nodes,
 							}
 						}
 					}
-					goto out
+					return
 				}
 
 				if i >= len(rfs) {
@@ -2606,7 +2606,7 @@ func typecheckaste(op Op, call *Node, isddd bool, tstruct *types.Type, nl Nodes,
 			if len(rfs) > len(lfs) {
 				goto toomany
 			}
-			goto out
+			return
 		}
 	}
 
@@ -2650,7 +2650,7 @@ func typecheckaste(op Op, call *Node, isddd bool, tstruct *types.Type, nl Nodes,
 				if n.Type != nil {
 					nl.SetIndex(i, assignconvfn(n, t, desc))
 				}
-				goto out
+				return
 			}
 
 			for ; i < nl.Len(); i++ {
@@ -2660,8 +2660,7 @@ func typecheckaste(op Op, call *Node, isddd bool, tstruct *types.Type, nl Nodes,
 					nl.SetIndex(i, assignconvfn(n, t.Elem(), desc))
 				}
 			}
-
-			goto out
+			return
 		}
 
 		if i >= nl.Len() {
@@ -2685,9 +2684,6 @@ func typecheckaste(op Op, call *Node, isddd bool, tstruct *types.Type, nl Nodes,
 			yyerror("invalid use of ... in %v", op)
 		}
 	}
-
-out:
-	lineno = lno
 	return
 
 notenough:
@@ -2709,8 +2705,7 @@ notenough:
 			n.SetDiag(true)
 		}
 	}
-
-	goto out
+	return
 
 toomany:
 	details := errorDetails(nl, tstruct, isddd)
@@ -2719,7 +2714,6 @@ toomany:
 	} else {
 		yyerror("too many arguments to %v%s", op, details)
 	}
-	goto out
 }
 
 func errorDetails(nl Nodes, tstruct *types.Type, isddd bool) string {