runtime, gc: call interface conversion routines by reference.

Part of getting rid of vararg C calls.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/23310043

src/cmd/gc/builtin.c

@@ -42,8 +42,8 @@ char *runtimeimport =
 	"func @\"\".typ2Itab (@\"\".typ·2 *byte, @\"\".typ2·3 *byte, @\"\".cache·4 **byte) (@\"\".ret·1 *byte)\n"
 	"func @\"\".convI2E (@\"\".elem·2 any) (@\"\".ret·1 any)\n"
 	"func @\"\".convI2I (@\"\".typ·2 *byte, @\"\".elem·3 any) (@\"\".ret·1 any)\n"
-	"func @\"\".convT2E (@\"\".typ·2 *byte, @\"\".elem·3 any) (@\"\".ret·1 any)\n"
-	"func @\"\".convT2I (@\"\".typ·2 *byte, @\"\".typ2·3 *byte, @\"\".cache·4 **byte, @\"\".elem·5 any) (@\"\".ret·1 any)\n"
+	"func @\"\".convT2E (@\"\".typ·2 *byte, @\"\".elem·3 *any) (@\"\".ret·1 any)\n"
+	"func @\"\".convT2I (@\"\".typ·2 *byte, @\"\".typ2·3 *byte, @\"\".cache·4 **byte, @\"\".elem·5 *any) (@\"\".ret·1 any)\n"
 	"func @\"\".assertE2E (@\"\".typ·2 *byte, @\"\".iface·3 any) (@\"\".ret·1 any)\n"
 	"func @\"\".assertE2E2 (@\"\".typ·3 *byte, @\"\".iface·4 any) (@\"\".ret·1 any, @\"\".ok·2 bool)\n"
 	"func @\"\".assertE2I (@\"\".typ·2 *byte, @\"\".iface·3 any) (@\"\".ret·1 any)\n"

src/cmd/gc/runtime.go

@@ -58,8 +58,8 @@ func slicestringcopy(to any, fr any) int
 func typ2Itab(typ *byte, typ2 *byte, cache **byte) (ret *byte)
 func convI2E(elem any) (ret any)
 func convI2I(typ *byte, elem any) (ret any)
-func convT2E(typ *byte, elem any) (ret any)
-func convT2I(typ *byte, typ2 *byte, cache **byte, elem any) (ret any)
+func convT2E(typ *byte, elem *any) (ret any)
+func convT2I(typ *byte, typ2 *byte, cache **byte, elem *any) (ret any)
 
 // interface type assertions  x.(T)
 func assertE2E(typ *byte, iface any) (ret any)

src/cmd/gc/walk.c

@@ -898,7 +898,20 @@ walkexpr(Node **np, NodeList **init)
 				goto ret;
 			}
 		}
-		ll = list(ll, n->left);
+		if(isinter(n->left->type)) {
+			ll = list(ll, n->left);
+		} else {
+			// regular types are passed by reference to avoid C vararg calls
+			if(islvalue(n->left)) {
+				ll = list(ll, nod(OADDR, n->left, N));
+			} else {
+				var = temp(n->left->type);
+				n1 = nod(OAS, var, n->left);
+				typecheck(&n1, Etop);
+				*init = list(*init, n1);
+				ll = list(ll, nod(OADDR, var, N));
+			}
+		}
 		argtype(fn, n->left->type);
 		argtype(fn, n->type);
 		dowidth(fn->type);

src/pkg/runtime/iface.c

@@ -183,42 +183,31 @@ runtime·typ2Itab(Type *t, InterfaceType *inter, Itab **cache, Itab *ret)
 	FLUSH(&ret);
 }
 
-// func convT2I(typ *byte, typ2 *byte, cache **byte, elem any) (ret any)
+// func convT2I(typ *byte, typ2 *byte, cache **byte, elem *any) (ret any)
 #pragma textflag NOSPLIT
 void
-runtime·convT2I(Type *t, InterfaceType *inter, Itab **cache, ...)
+runtime·convT2I(Type *t, InterfaceType *inter, Itab **cache, byte *elem, Iface ret)
 {
-	byte *elem;
-	Iface *ret;
 	Itab *tab;
-	int32 wid;
 
-	elem = (byte*)(&cache+1);
-	wid = t->size;
-	ret = (Iface*)(elem + ROUND(wid, Structrnd));
 	tab = runtime·atomicloadp(cache);
 	if(!tab) {
 		tab = itab(inter, t, 0);
 		runtime·atomicstorep(cache, tab);
 	}
-	ret->tab = tab;
-	copyin(t, elem, &ret->data);
+	ret.tab = tab;
+	copyin(t, elem, &ret.data);
+	FLUSH(&ret);
 }
 
-// func convT2E(typ *byte, elem any) (ret any)
+// func convT2E(typ *byte, elem *any) (ret any)
 #pragma textflag NOSPLIT
 void
-runtime·convT2E(Type *t, ...)
+runtime·convT2E(Type *t, byte *elem, Eface ret)
 {
-	byte *elem;
-	Eface *ret;
-	int32 wid;
-
-	elem = (byte*)(&t+1);
-	wid = t->size;
-	ret = (Eface*)(elem + ROUND(wid, Structrnd));
-	ret->type = t;
-	copyin(t, elem, &ret->data);
+	ret.type = t;
+	copyin(t, elem, &ret.data);
+	FLUSH(&ret);
 }
 
 static void assertI2Tret(Type *t, Iface i, byte *ret);