runtime: use better hash for non-empty interface

The implementation 'return 0' results in too many collisions.

LGTM=khr
R=golang-codereviews, adonovan, khr
CC=golang-codereviews, iant, khr, r
https://golang.org/cl/125720044

src/pkg/runtime/alg.go

@@ -111,7 +111,22 @@ func nohash(a unsafe.Pointer, s uintptr, h uintptr) uintptr {
 func interhash(a *interface {
 	f()
 }, s uintptr, h uintptr) uintptr {
-	return 0
+	tab := (*iface)(unsafe.Pointer(a)).tab
+	if tab == nil {
+		return h
+	}
+	t := tab._type
+	fn := goalg(t.alg).hash
+	if **(**uintptr)(unsafe.Pointer(&fn)) == nohashcode {
+		// calling nohash will panic too,
+		// but we can print a better error.
+		panic(errorString("hash of unhashable type " + *t._string))
+	}
+	if uintptr(t.size) <= ptrSize {
+		return c1 * fn(unsafe.Pointer(&(*eface)(unsafe.Pointer(a)).data), uintptr(t.size), h^c0)
+	} else {
+		return c1 * fn((*eface)(unsafe.Pointer(a)).data, uintptr(t.size), h^c0)
+	}
 }
 
 func nilinterhash(a *interface{}, s uintptr, h uintptr) uintptr {

src/pkg/runtime/iface.goc

@@ -475,44 +475,6 @@ func assertE2E2(inter *InterfaceType, e Eface) (ret Eface, ok bool) {
 	ok = e.type != nil;
 }
 
-static uintptr
-ifacehash1(void *data, Type *t, uintptr h)
-{
-	Alg *alg;
-	uintptr size;
-	Eface err;
-
-	if(t == nil)
-		return 0;
-
-	alg = t->alg;
-	size = t->size;
-	if(alg->hash->fn == (void(*)())runtime·nohash) {
-		// calling nohash will panic too,
-		// but we can print a better error.
-		runtime·newErrorString(runtime·catstring(runtime·gostringnocopy((byte*)"hash of unhashable type "), *t->string), &err);
-		runtime·panic(err);
-	}
-	if(size <= sizeof(data))
-		return ((uintptr(*)(void**,uintptr,uintptr))alg->hash)(&data, size, h);
-	else
-		return ((uintptr(*)(void*,uintptr,uintptr))alg->hash)(data, size, h);
-}
-
-uintptr
-runtime·ifacehash(Iface a, uintptr h)
-{
-	if(a.tab == nil)
-		return h;
-	return ifacehash1(a.data, a.tab->type, h);
-}
-
-uintptr
-runtime·efacehash(Eface a, uintptr h)
-{
-	return ifacehash1(a.data, a.type, h);
-}
-
 static bool
 ifaceeq1(void *data1, void *data2, Type *t)
 {

src/pkg/runtime/runtime.h

@@ -651,19 +651,19 @@ enum {
 };
 void	runtime·hashinit(void);
 
-uintptr	runtime·memhash(void*, uintptr, uintptr);
-uintptr	runtime·nohash(void*, uintptr, uintptr);
-uintptr	runtime·strhash(void*, uintptr, uintptr);
-uintptr	runtime·interhash(void*, uintptr, uintptr);
-uintptr	runtime·nilinterhash(void*, uintptr, uintptr);
-uintptr	runtime·f32hash(void*, uintptr, uintptr);
-uintptr	runtime·f64hash(void*, uintptr, uintptr);
-uintptr	runtime·c64hash(void*, uintptr, uintptr);
-uintptr	runtime·c128hash(void*, uintptr, uintptr);
-uintptr	runtime·aeshash(void*, uintptr, uintptr);
-uintptr	runtime·aeshash32(void*, uintptr, uintptr);
-uintptr	runtime·aeshash64(void*, uintptr, uintptr);
-uintptr	runtime·aeshashstr(void*, uintptr, uintptr);
+void	runtime·memhash(void*, uintptr, uintptr, uintptr);
+void	runtime·nohash(void*, uintptr, uintptr, uintptr);
+void	runtime·strhash(void*, uintptr, uintptr, uintptr);
+void	runtime·interhash(void*, uintptr, uintptr, uintptr);
+void	runtime·nilinterhash(void*, uintptr, uintptr, uintptr);
+void	runtime·f32hash(void*, uintptr, uintptr, uintptr);
+void	runtime·f64hash(void*, uintptr, uintptr, uintptr);
+void	runtime·c64hash(void*, uintptr, uintptr, uintptr);
+void	runtime·c128hash(void*, uintptr, uintptr, uintptr);
+void	runtime·aeshash(void*, uintptr, uintptr, uintptr);
+void	runtime·aeshash32(void*, uintptr, uintptr, uintptr);
+void	runtime·aeshash64(void*, uintptr, uintptr, uintptr);
+void	runtime·aeshashstr(void*, uintptr, uintptr, uintptr);
 
 void	runtime·memequal(bool*, uintptr, void*, void*);
 void	runtime·noequal(bool*, uintptr, void*, void*);
@@ -876,8 +876,6 @@ void	runtime·mallocinit(void);
 void	runtime·chaninit(void);
 bool	runtime·ifaceeq_c(Iface, Iface);
 bool	runtime·efaceeq_c(Eface, Eface);
-uintptr	runtime·ifacehash(Iface, uintptr);
-uintptr	runtime·efacehash(Eface, uintptr);
 void*	runtime·malloc(uintptr size);
 void	runtime·runpanic(Panic*);
 uintptr	runtime·getcallersp(void*);