cmd/compile: optimize loads from abi.Type.{Size_,PtrBytes,Kind_}

With the previous CL in place, we can now pretty easily optimize a few
more loads from abi.Type. I've done Size_, PtrBytes, and Kind_, which
are easily calculated.

Among std/cmd, this rule fires a number of times:

     75 abi.Type field Kind_
     50 abi.PtrType field Elem
     14 abi.Type field Hash
      4 abi.Type field Size_
      2 abi.Type field PtrBytes

The other ones that show up when compiling std/cmd are TFlag and GCData,
but these are not trivially calculated. Doing TFlag would probably be a
decent help given it's often used in things like switches where
statically knowing the kind could eliminate a bunch of dead code.

Change-Id: Ic7fd2113fa7479af914d06916edbca60cc71819f
Reviewed-on: https://go-review.googlesource.com/c/go/+/701298
Reviewed-by: Mark Freeman <markfreeman@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/internal/reflectdata/reflect.go

@@ -414,6 +414,10 @@ var kinds = []abi.Kind{
 	types.TUNSAFEPTR:  abi.UnsafePointer,
 }
 
+func ABIKindOfType(t *types.Type) abi.Kind {
+	return kinds[t.Kind()]
+}
+
 var (
 	memhashvarlen  *obj.LSym
 	memequalvarlen *obj.LSym
@@ -512,8 +516,7 @@ func dcommontype(c rttype.Cursor, t *types.Type) {
 	c.Field("Align_").WriteUint8(uint8(t.Alignment()))
 	c.Field("FieldAlign_").WriteUint8(uint8(t.Alignment()))
 
-	kind := kinds[t.Kind()]
+	c.Field("Kind_").WriteUint8(uint8(ABIKindOfType(t)))
-	c.Field("Kind_").WriteUint8(uint8(kind))
 
 	c.Field("Equal").WritePtr(eqfunc)
 	c.Field("GCData").WritePtr(gcsym)

src/cmd/compile/internal/ssa/rewrite.go

@@ -2005,7 +2005,7 @@ func isFixedLoad(v *Value, sym Sym, off int64) bool {
 		for _, f := range rttype.Type.Fields() {
 			if f.Offset == off && copyCompatibleType(v.Type, f.Type) {
 				switch f.Sym.Name {
-				case "Hash":
+				case "Size_", "PtrBytes", "Hash", "Kind_":
 					return true
 				default:
 					// fmt.Println("unknown field", f.Sym.Name)
@@ -2061,13 +2061,30 @@ func rewriteFixedLoad(v *Value, sym Sym, sb *Value, off int64) *Value {
 
 		t := (*lsym.Extra).(*obj.TypeInfo).Type.(*types.Type)
 
+		ptrSizedOpConst := OpConst64
+		if f.Config.PtrSize == 4 {
+			ptrSizedOpConst = OpConst32
+		}
+
 		for _, f := range rttype.Type.Fields() {
 			if f.Offset == off && copyCompatibleType(v.Type, f.Type) {
 				switch f.Sym.Name {
+				case "Size_":
+					v.reset(ptrSizedOpConst)
+					v.AuxInt = int64(t.Size())
+					return v
+				case "PtrBytes":
+					v.reset(ptrSizedOpConst)
+					v.AuxInt = int64(types.PtrDataSize(t))
+					return v
 				case "Hash":
 					v.reset(OpConst32)
 					v.AuxInt = int64(types.TypeHash(t))
 					return v
+				case "Kind_":
+					v.reset(OpConst8)
+					v.AuxInt = int64(reflectdata.ABIKindOfType(t))
+					return v
 				default:
 					base.Fatalf("unknown field %s for fixedLoad of %s at offset %d", f.Sym.Name, lsym.Name, off)
 				}