reflect: shorten value to 3 words

scalar is no longer needed, now that
interfaces always hold pointers.

Comparing best of 5 with TurboBoost turned off,
on a 2012 Retina MacBook Pro Core i5.
Still not completely confident in these numbers,
but the gob and template improvements seem real.

benchmark                       old ns/op   new ns/op   delta
BenchmarkBinaryTree17           3819892491  3803008185  -0.44%
BenchmarkFannkuch11             3623876405  3611776426  -0.33%
BenchmarkFmtFprintfEmpty        119         118         -0.84%
BenchmarkFmtFprintfString       294         292         -0.68%
BenchmarkFmtFprintfInt          310         304         -1.94%
BenchmarkFmtFprintfIntInt       513         507         -1.17%
BenchmarkFmtFprintfPrefixedInt  427         426         -0.23%
BenchmarkFmtFprintfFloat        562         554         -1.42%
BenchmarkFmtManyArgs            1873        1832        -2.19%
BenchmarkGobDecode              15824504    14746565    -6.81%
BenchmarkGobEncode              14347378    14208743    -0.97%
BenchmarkGzip                   537229271   537973492   +0.14%
BenchmarkGunzip                 134996775   135406149   +0.30%
BenchmarkHTTPClientServer       119065      116937      -1.79%
BenchmarkJSONEncode             29134359    28928099    -0.71%
BenchmarkJSONDecode             106867289   105770161   -1.03%
BenchmarkMandelbrot200          5798475     5791433     -0.12%
BenchmarkGoParse                5299169     5379201     +1.51%
BenchmarkRegexpMatchEasy0_32    195         195         +0.00%
BenchmarkRegexpMatchEasy0_1K    477         477         +0.00%
BenchmarkRegexpMatchEasy1_32    170         170         +0.00%
BenchmarkRegexpMatchEasy1_1K    1412        1397        -1.06%
BenchmarkRegexpMatchMedium_32   336         337         +0.30%
BenchmarkRegexpMatchMedium_1K   109025      108977      -0.04%
BenchmarkRegexpMatchHard_32     5854        5856        +0.03%
BenchmarkRegexpMatchHard_1K     184914      184748      -0.09%
BenchmarkRevcomp                829233526   836598734   +0.89%
BenchmarkTemplate               142055312   137016166   -3.55%
BenchmarkTimeParse              598         597         -0.17%
BenchmarkTimeFormat             564         568         +0.71%

Fixes #7425.

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews, iant, khr
https://golang.org/cl/158890043

src/reflect/makefunc.go

@@ -60,7 +60,7 @@ func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value {
 
 	impl := &makeFuncImpl{code: code, stack: stack, typ: ftyp, fn: fn}
 
-	return Value{t, unsafe.Pointer(impl), 0, flag(Func) << flagKindShift}
+	return Value{t, unsafe.Pointer(impl), flag(Func) << flagKindShift}
 }
 
 // makeFuncStub is an assembly function that is the code half of
@@ -92,7 +92,7 @@ func makeMethodValue(op string, v Value) Value {
 	// Ignoring the flagMethod bit, v describes the receiver, not the method type.
 	fl := v.flag & (flagRO | flagAddr | flagIndir)
 	fl |= flag(v.typ.Kind()) << flagKindShift
-	rcvr := Value{v.typ, v.ptr, v.scalar, fl}
+	rcvr := Value{v.typ, v.ptr, fl}
 
 	// v.Type returns the actual type of the method value.
 	funcType := v.Type().(*rtype)
@@ -118,7 +118,7 @@ func makeMethodValue(op string, v Value) Value {
 	// but we want Interface() and other operations to fail early.
 	methodReceiver(op, fv.rcvr, fv.method)
 
-	return Value{funcType, unsafe.Pointer(fv), 0, v.flag&flagRO | flag(Func)<<flagKindShift}
+	return Value{funcType, unsafe.Pointer(fv), v.flag&flagRO | flag(Func)<<flagKindShift}
 }
 
 // methodValueCall is an assembly function that is the code half of

src/reflect/type.go

@@ -498,7 +498,7 @@ func (t *uncommonType) Method(i int) (m Method) {
 	mt := p.typ
 	m.Type = mt
 	fn := unsafe.Pointer(&p.tfn)
-	m.Func = Value{mt, fn, 0, fl}
+	m.Func = Value{mt, fn, fl}
 	m.Index = i
 	return
 }
@@ -1805,7 +1805,7 @@ func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uin
 		// Reflect uses the "interface" calling convention for
 		// methods, where receivers take one word of argument
 		// space no matter how big they actually are.
-		if !isDirectIface(rcvr) {
+		if ifaceIndir(rcvr) {
 			// we pass a pointer to the receiver.
 			gc.append(bitsPointer)
 			stack.append2(bitsPointer)
@@ -1862,9 +1862,9 @@ func funcLayout(t *rtype, rcvr *rtype) (frametype *rtype, argSize, retOffset uin
 	return x, argSize, retOffset, stack
 }
 
-// isDirectIface reports whether t is stored directly in an interface value.
-func isDirectIface(t *rtype) bool {
-	return t.kind&kindDirectIface != 0
+// ifaceIndir reports whether t is stored indirectly in an interface value.
+func ifaceIndir(t *rtype) bool {
+	return t.kind&kindDirectIface == 0
 }
 
 // Layout matches runtime.BitVector (well enough).