reflect: fix FieldByNameFunc

The existing algorithm did not properly propagate the type
count from one level to the next, and as a consequence it
missed collisions.

Properly propagate multiplicity (count) information to the
next level.

benchmark                old ns/op    new ns/op    delta
BenchmarkFieldByName1          182          180   -1.10%
BenchmarkFieldByName2         6273         6183   -1.43%
BenchmarkFieldByName3        49267        46784   -5.04%

Fixes #4355.

R=rsc
CC=golang-dev
https://golang.org/cl/6821094

src/pkg/reflect/all_test.go

@@ -1694,6 +1694,20 @@ type S13 struct {
 	S8
 }
 
+// The X in S15.S11.S1 and S16.S11.S1 annihilate.
+type S14 struct {
+	S15
+	S16
+}
+
+type S15 struct {
+	S11
+}
+
+type S16 struct {
+	S11
+}
+
 var fieldTests = []FTest{
 	{struct{}{}, "", nil, 0},
 	{struct{}{}, "Foo", nil, 0},
@@ -1719,6 +1733,7 @@ var fieldTests = []FTest{
 	{S5{}, "Y", []int{2, 0, 1}, 0},
 	{S10{}, "X", nil, 0},
 	{S10{}, "Y", []int{2, 0, 0, 1}, 0},
+	{S14{}, "X", nil, 0},
 }
 
 func TestFieldByIndex(t *testing.T) {

src/pkg/reflect/type.go

@@ -913,19 +913,22 @@ func (t *structType) FieldByNameFunc(match func(string) bool) (result StructFiel
 
 				// Queue embedded struct fields for processing with next level,
 				// but only if we haven't seen a match yet at this level and only
-				// if the embedded types haven't alredy been queued.
+				// if the embedded types haven't already been queued.
 				if ok || ntyp == nil || ntyp.Kind() != Struct {
 					continue
 				}
 				styp := (*structType)(unsafe.Pointer(ntyp))
 				if nextCount[styp] > 0 {
-					nextCount[styp]++
+					nextCount[styp] = 2 // exact multiple doesn't matter
 					continue
 				}
 				if nextCount == nil {
 					nextCount = map[*structType]int{}
 				}
 				nextCount[styp] = 1
+				if count[t] > 1 {
+					nextCount[styp] = 2 // exact multiple doesn't matter
+				}
 				var index []int
 				index = append(index, scan.index...)
 				index = append(index, i)