cmd/compile: remove ignored bool from exported ODCL nodes

This shortens the export format by 1 byte for each exported ODCL
node in inlined function bodies.

Maintain backward compatibility by updating format version and
continue to accept older format.

Change-Id: I549bb3ade90bc0f146decf8016d5c9c3f14eb293
Reviewed-on: https://go-review.googlesource.com/27999
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -158,7 +158,7 @@ const debugFormat = false // default: false
 const forceObjFileStability = true
 
 // Current export format version. Increase with each format change.
-const exportVersion = 1
+const exportVersion = 2
 
 // exportInlined enables the export of inlined function bodies and related
 // dependencies. The compiler should work w/o any loss of functionality with
@@ -1418,17 +1418,7 @@ func (p *exporter) stmt(n *Node) {
 	switch op := n.Op; op {
 	case ODCL:
 		p.op(ODCL)
-		switch n.Left.Class {
-		case PPARAM, PPARAMOUT, PAUTO, PAUTOHEAP:
-			// TODO(gri) when is this not PAUTO?
-			// Also, originally this didn't look like
-			// the default case. Investigate.
-			fallthrough
-		default:
-			// TODO(gri) Can we ever reach here?
-			p.bool(false)
 		p.sym(n.Left)
-		}
 		p.typ(n.Left.Type)
 
 	// case ODCLFIELD:

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

@@ -86,10 +86,10 @@ func Import(in *bufio.Reader) {
 
 	// read version specific flags - extend as necessary
 	switch p.version {
-	// case 2:
+	// case 3:
 	// 	...
 	//	fallthrough
-	case 1:
+	case 2, 1:
 		p.debugFormat = p.rawStringln(p.rawByte()) == "debug"
 		p.trackAllTypes = p.bool()
 		p.posInfoFormat = p.bool()
@@ -1000,14 +1000,14 @@ func (p *importer) node() *Node {
 	// --------------------------------------------------------------------
 	// statements
 	case ODCL:
-		var lhs *Node
-		if p.bool() {
-			lhs = p.expr()
-		} else {
-			lhs = dclname(p.sym())
-		}
-		// TODO(gri) avoid list created here!
-		return liststmt(variter([]*Node{lhs}, typenod(p.typ()), nil))
+		if p.version < 2 {
+			// versions 0 and 1 exported a bool here but it
+			// was always false - simply ignore in this case
+			p.bool()
+		}
+		lhs := dclname(p.sym())
+		typ := typenod(p.typ())
+		return liststmt(variter([]*Node{lhs}, typ, nil)) // TODO(gri) avoid list creation
 
 	// case ODCLFIELD:
 	//	unimplemented

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

@@ -3,7 +3,7 @@
 package gc
 
 const runtimeimport = "" +
-	"version 1\n\n\x00\x00\x01\rruntime\x00\t\x11newobject\x00\x02\x17\"\vt" +
+	"version 2\n\n\x00\x00\x01\rruntime\x00\t\x11newobject\x00\x02\x17\"\vt" +
 	"yp·2\x00\x00\x01\x17:\x00\t\x13panicindex\x00\x00\x00\t\x13panicslice\x00\x00" +
 	"\x00\t\x15panicdivide\x00\x00\x00\t\x15throwreturn\x00\x00\x00\t\x11throw" +
 	"init\x00\x00\x00\t\x11panicwrap\x00\x05 \x00 \x00 \x00\x00\t\rgopanic\x00\x01\x1b\x00" +
@@ -106,6 +106,6 @@ const runtimeimport = "" +
 	"b\x16\x98\x03\x00b\x00\v\xf8\x01\v\x00\x01\x00\n$$\n"
 
 const unsafeimport = "" +
-	"version 1\n\n\x00\x00\x01\vunsafe\x00\x05\r\rPointer\x00\x16\x00\t\x0fOff" +
+	"version 2\n\n\x00\x00\x01\vunsafe\x00\x05\r\rPointer\x00\x16\x00\t\x0fOff" +
 	"setof\x00\x01:\x00\x01\x16\x00\t\vSizeof\x00\x01:\x00\x01\x16\x00\t\rAlignof\x00\x01:\x00" +
 	"\x01\x16\x00\v\b\v\x00\x01\x00\n$$\n"

src/go/internal/gcimporter/bimport.go

@@ -93,10 +93,10 @@ func BImportData(imports map[string]*types.Package, data []byte, path string) (_
 
 	// read version specific flags - extend as necessary
 	switch p.version {
-	// case 2:
+	// case 3:
 	// 	...
 	//	fallthrough
-	case 1:
+	case 2, 1:
 		p.debugFormat = p.rawStringln(p.rawByte()) == "debug"
 		p.trackAllTypes = p.int() != 0
 		p.posInfoFormat = p.int() != 0