cmd/compile: allow inlining of functions that declare a const

Consider functions with an ODCLCONST for inlining and modify exprfmt to
ignore those nodes when exporting. Don't add symbols to the export list
if there is no definition.  This occurs when OLITERAL symbols are looked
up via Pkglookup for non-exported symbols.

Fixes #7655

Change-Id: I1de827850f4c69e58107447314fe7433e378e069
Reviewed-on: https://go-review.googlesource.com/20773
Run-TryBot: Todd Neal <todd@tneal.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -984,7 +984,7 @@ func (p *exporter) node(n *Node) {
 	case OBREAK, OCONTINUE, OGOTO, OFALL, OXFALL:
 		p.nodesOrNil(n.Left, nil)
 
-	case OEMPTY:
+	case OEMPTY, ODCLCONST:
 		// nothing to do
 
 	case OLABEL:

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

@@ -751,7 +751,7 @@ func (p *importer) node() *Node {
 	case OBREAK, OCONTINUE, OGOTO, OFALL, OXFALL:
 		n.Left, _ = p.nodesOrNil()
 
-	case OEMPTY:
+	case OEMPTY, ODCLCONST:
 		// nothing to do
 
 	case OLABEL:

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

@@ -176,7 +176,7 @@ func reexportdep(n *Node) {
 		fallthrough
 
 	case OTYPE:
-		if n.Sym != nil && !exportedsym(n.Sym) {
+		if n.Sym != nil && n.Sym.Def != nil && !exportedsym(n.Sym) {
 			if Debug['E'] != 0 {
 				fmt.Printf("reexport literal/type %v\n", n.Sym)
 			}
@@ -331,7 +331,7 @@ func dumpexporttype(t *Type) {
 			if Debug['l'] < 2 {
 				typecheckinl(f.Type.Nname)
 			}
-			exportf("\tfunc %v %v %v { %v }\n", Tconv(f.Type.Recvs(), FmtSharp), Sconv(f.Sym, FmtShort|FmtByte|FmtSharp), Tconv(f.Type, FmtShort|FmtSharp), Hconv(f.Type.Nname.Func.Inl, FmtSharp))
+			exportf("\tfunc %v %v %v { %v }\n", Tconv(f.Type.Recvs(), FmtSharp), Sconv(f.Sym, FmtShort|FmtByte|FmtSharp), Tconv(f.Type, FmtShort|FmtSharp), Hconv(f.Type.Nname.Func.Inl, FmtSharp|FmtBody))
 			reexportdeplist(f.Type.Nname.Func.Inl)
 		} else {
 			exportf("\tfunc %v %v %v\n", Tconv(f.Type.Recvs(), FmtSharp), Sconv(f.Sym, FmtShort|FmtByte|FmtSharp), Tconv(f.Type, FmtShort|FmtSharp))

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

@@ -1413,6 +1413,13 @@ func exprfmt(n *Node, prec int) string {
 		f += fmt.Sprintf(" %v ", Oconv(Op(n.Etype), FmtSharp))
 		f += exprfmt(n.Right, nprec+1)
 		return f
+
+	case ODCLCONST:
+		// if exporting, DCLCONST should just be removed as its usage
+		// has already been replaced with literals
+		if fmtbody {
+			return ""
+		}
 	}
 
 	return fmt.Sprintf("<node %v>", Oconv(n.Op, 0))

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

@@ -217,8 +217,7 @@ func ishairy(n *Node, budget *int) bool {
 		OSWITCH,
 		OPROC,
 		ODEFER,
-		ODCLTYPE,  // can't print yet
+		ODCLTYPE, // can't print yet
-		ODCLCONST, // can't print yet
 		ORETJMP:
 		return true
 	}

test/inline.go

@@ -31,3 +31,8 @@ func g(x int) int {
 func h(x int) int { // ERROR "can inline h"
 	return x + 2
 }
+
+func i(x int) int { // ERROR "can inline i"
+	const y = 2
+	return x + y
+}