cmd/gc: don't call memequal twice in generated type.eq routines

The first call is pointless. It appears to simply be a mistake.

benchmark                  old ns/op     new ns/op     delta
BenchmarkComplexAlgMap     90.7          76.1          -16.10%

Change-Id: Id0194c9f09cea8b68f17b2ac751a8e3240e47f19
Reviewed-on: https://go-review.googlesource.com/5284Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/internal/gc/subr.go

@@ -2848,7 +2848,6 @@ func eqmem(p *Node, q *Node, field *Node, size int64) *Node {
 	}
 
 	nif := Nod(OIF, nil, nil)
-	nif.Ninit = list(nif.Ninit, call)
 	nif.Ntest = Nod(ONOT, call, nil)
 	r := Nod(ORETURN, nil, nil)
 	r.List = list(r.List, Nodbool(false))

src/runtime/mapspeed_test.go

@@ -307,3 +307,22 @@ func BenchmarkSmallKeyMap(b *testing.B) {
 		_ = m[5]
 	}
 }
+
+type ComplexAlgKey struct {
+	a, b, c int64
+	_       int
+	d       int32
+	_       int
+	e       string
+	_       int
+	f, g, h int64
+}
+
+func BenchmarkComplexAlgMap(b *testing.B) {
+	m := make(map[ComplexAlgKey]bool)
+	var k ComplexAlgKey
+	m[k] = true
+	for i := 0; i < b.N; i++ {
+		_ = m[k]
+	}
+}