gc, runtime: copy([]byte, string)

R=ken2
CC=golang-dev
https://golang.org/cl/2741041

src/cmd/gc/builtin.c.boot

@@ -33,6 +33,7 @@ char *runtimeimport =
 	"func \"\".stringiter (? string, ? int) int\n"
 	"func \"\".stringiter2 (? string, ? int) (retk int, retv int)\n"
 	"func \"\".slicecopy (to any, fr any, wid uint32) int\n"
+	"func \"\".slicestringcopy (to any, fr any) int\n"
 	"func \"\".convI2E (elem any) any\n"
 	"func \"\".convI2I (typ *uint8, elem any) any\n"
 	"func \"\".convT2E (typ *uint8, elem any) any\n"

src/cmd/gc/runtime.go

@@ -48,6 +48,7 @@ func stringtosliceint(string) []int
 func stringiter(string, int) int
 func stringiter2(string, int) (retk int, retv int)
 func slicecopy(to any, fr any, wid uint32) int
+func slicestringcopy(to any, fr any) int
 
 // interface conversions
 func convI2E(elem any) (ret any)

src/cmd/gc/typecheck.c

@@ -926,13 +926,18 @@ reswitch:
 			goto error;
 		defaultlit(&n->left, T);
 		defaultlit(&n->right, T);
+		
+		// copy([]byte, string)
+		if(isslice(n->left->type) && n->left->type->type == types[TUINT8] && n->right->type->etype == TSTRING)
+			goto ret;
+
 		if(!isslice(n->left->type) || !isslice(n->right->type)) {
 			if(!isslice(n->left->type) && !isslice(n->right->type))
 				yyerror("arguments to copy must be slices; have %lT, %lT", n->left->type, n->right->type);
 			else if(!isslice(n->left->type))
 				yyerror("first argument to copy should be slice; have %lT", n->left->type);
 			else
-				yyerror("second argument to copy should be slice; have %lT", n->right->type);
+				yyerror("second argument to copy should be slice or string; have %lT", n->right->type);
 			goto error;
 		}
 		if(!eqtype(n->left->type->type, n->right->type->type)) {

src/cmd/gc/walk.c

@@ -1261,7 +1261,10 @@ walkexpr(Node **np, NodeList **init)
 		goto ret;
 
 	case OCOPY:
-		fn = syslook("slicecopy", 1);
+		if(n->right->type->etype == TSTRING)
+			fn = syslook("slicestringcopy", 1);
+		else
+			fn = syslook("slicecopy", 1);
 		argtype(fn, n->left->type);
 		argtype(fn, n->right->type);
 		n = mkcall1(fn, n->type, init,

src/pkg/runtime/slice.c

@@ -217,6 +217,24 @@ out:
 	}
 }
 
+void
+·slicestringcopy(Slice to, String fm, int32 ret)
+{
+	if(fm.len == 0 || to.len == 0) {
+		ret = 0;
+		goto out;
+	}
+	
+	ret = fm.len;
+	if(to.len < ret)
+		ret = to.len;
+	
+	memmove(to.array, fm.str, ret);
+
+out:
+	FLUSH(&ret);
+}
+
 void
 ·printslice(Slice a)
 {