cmd/compile: call missing popdcl in various genxxx functions

Not calling popdcl doesn't have an impact on generated code but
the result is a growing (rather than empty) stack of symbols,
possibly causing more data to remain alive than necessary.

Also: minor cleanups.

Change-Id: Ic4fdbcd8843637d69ab1aa15e896a7e6339bc990
Reviewed-on: https://go-review.googlesource.com/20554Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Robert Griesemer <gri@golang.org>

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

@@ -280,6 +280,8 @@ func genhash(sym *Sym, t *Type) {
 	typecheck(&fn, Etop)
 	typechecklist(fn.Nbody.Slice(), Etop)
 	Curfn = nil
+	popdcl()
+	testdclstack()
 
 	// Disable safemode while compiling this code: the code we
 	// generate internally can refer to unsafe.Pointer.
@@ -472,6 +474,8 @@ func geneq(sym *Sym, t *Type) {
 	typecheck(&fn, Etop)
 	typechecklist(fn.Nbody.Slice(), Etop)
 	Curfn = nil
+	popdcl()
+	testdclstack()
 
 	// Disable safemode while compiling this code: the code we
 	// generate internally can refer to unsafe.Pointer.

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

@@ -76,9 +76,10 @@ type Sym struct {
 	Pkg        *Pkg
 	Name       string // variable name
 	Def        *Node  // definition: ONAME OTYPE OPACK or OLITERAL
-	Label      *Label // corresponding label (ephemeral)
 	Block      int32  // blocknumber to catch redeclaration
 	Lastlineno int32  // last declaration for diagnostic
+
+	Label   *Label // corresponding label (ephemeral)
 	Origpkg *Pkg   // original package for . import
 	Lsym    *obj.LSym
 	Fsym    *Sym // funcsym

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

@@ -2142,8 +2142,8 @@ func (p *parser) structdcl() []*Node {
 		typ := p.ntype()
 		tag := p.oliteral()
 
-		if l := fields; len(l) == 0 || l[0].Sym.Name == "?" {
-			// ? symbol, during import (list1(nil) == nil)
+		if len(fields) == 0 || fields[0].Sym.Name == "?" {
+			// ? symbol, during import
 			n := typ
 			if n.Op == OIND {
 				n = n.Left

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

@@ -2030,6 +2030,8 @@ func genwrapper(rcvr *Type, method *Type, newnam *Sym, iface int) {
 
 	funcbody(fn)
 	Curfn = fn
+	popdcl()
+	testdclstack()
 
 	// wrappers where T is anonymous (struct or interface) can be duplicated.
 	if rcvr.Etype == TSTRUCT || rcvr.Etype == TINTER || Isptr[rcvr.Etype] && rcvr.Type.Etype == TSTRUCT {