cmd/internal/obj: drop Addr's Gotype field

The Gotype field is only used for ATYPE instructions. Instead of
specially storing the Go type symbol in From.Gotype, just store it in
To.Sym like any other 2-argument instruction would.

Modest reduction in allocations:

name       old alloc/op    new alloc/op    delta
Template      42.0MB ± 0%     41.8MB ± 0%  -0.40%         (p=0.000 n=9+10)
Unicode       34.3MB ± 0%     34.1MB ± 0%  -0.48%         (p=0.000 n=9+10)
GoTypes        122MB ± 0%      122MB ± 0%  -0.14%         (p=0.000 n=9+10)
Compiler       518MB ± 0%      518MB ± 0%  -0.04%         (p=0.000 n=9+10)

Passes toolstash -cmp.

Change-Id: I0e603266b5d7d4e405106a26369e22773a0d3a91
Reviewed-on: https://go-review.googlesource.com/31850
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -425,7 +425,9 @@ func compile(fn *Node) {
 			fallthrough
 		case PPARAM, PPARAMOUT:
 			p := Gins(obj.ATYPE, n, nil)
-			p.From.Gotype = Linksym(ngotype(n))
+			p.To.Type = obj.TYPE_MEM
+			p.To.Name = obj.NAME_EXTERN
+			p.To.Sym = Linksym(ngotype(n))
 		}
 	}
 

src/cmd/internal/obj/link.go

@@ -160,7 +160,6 @@ type Addr struct {
 	Class  int8
 	Offset int64
 	Sym    *LSym
-	Gotype *LSym
 
 	// argument value:
 	//	for TYPE_SCONST, a string

src/cmd/internal/obj/plist.go

@@ -69,7 +69,7 @@ func flushplist(ctxt *Link, freeProgs bool) {
 				a.Asym = p.From.Sym
 				a.Aoffset = int32(p.From.Offset)
 				a.Name = int16(p.From.Name)
-				a.Gotype = p.From.Gotype
+				a.Gotype = p.To.Sym
 				a.Link = curtext.Autom
 				curtext.Autom = a
 				continue

src/cmd/internal/obj/sizeof_test.go

@@ -22,9 +22,9 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Addr{}, 44, 72},
+		{Addr{}, 40, 64},
 		{LSym{}, 80, 136},
-		{Prog{}, 152, 240},
+		{Prog{}, 144, 224},
 	}
 
 	for _, tt := range tests {

src/cmd/internal/obj/util.go

@@ -240,9 +240,6 @@ func Dconv(p *Prog, a *Addr) string {
 		if a.Index != REG_NONE {
 			str += fmt.Sprintf("(%v*%d)", Rconv(int(a.Index)), int(a.Scale))
 		}
-		if p != nil && p.As == ATYPE && a.Gotype != nil {
-			str += fmt.Sprintf("%s", a.Gotype.Name)
-		}
 
 	case TYPE_CONST:
 		if a.Reg != 0 {