gc: generalize dst = append(src,...) inlining to arbitrary src and dst arguments.

R=rsc
CC=golang-dev
https://golang.org/cl/4517057

src/cmd/gc/builtin.c.boot

@@ -22,7 +22,6 @@ char *runtimeimport =
 	"func \"\".printsp ()\n"
 	"func \"\".goprintf ()\n"
 	"func \"\".concatstring ()\n"
-	"func \"\".append ()\n"
 	"func \"\".appendslice (typ *uint8, x any, y []any) any\n"
 	"func \"\".cmpstring (? string, ? string) int\n"
 	"func \"\".slicestring (? string, ? int, ? int) string\n"

src/cmd/gc/walk.c

@@ -20,7 +20,6 @@ static	NodeList*	reorder3(NodeList*);
 static	Node*	addstr(Node*, NodeList**);
 static	Node*	appendslice(Node*, NodeList**);
 static	Node*	append(Node*, NodeList**);
-static	int	oasappend(Node**, NodeList**);
 
 static	NodeList*	walkdefstack;
 
@@ -811,9 +810,6 @@ walkexpr(Node **np, NodeList **init)
 		if(oaslit(n, init))
 			goto ret;
 
-		if (oasappend(&n, init))
-			goto ret;
-
 		walkexpr(&n->right, init);
 		if(n->left != N && n->right != N) {
 			r = convas(nod(OAS, n->left, n->right), init);
@@ -2381,41 +2377,10 @@ appendslice(Node *n, NodeList **init)
 	return mkcall1(f, n->type, init, typename(n->type), n->list->n, n->list->next->n);
 }
 
-static Node*
-append(Node *n, NodeList **init)
-{
-	int i, j;
-	Node *f, *r;
-	NodeList *in, *args;
-
-	j = count(n->list) - 1;
-	f = syslook("append", 1);
-	f->type = T;
-	f->ntype = nod(OTFUNC, N, N);
-	in = list1(nod(ODCLFIELD, N, typenod(ptrto(types[TUINT8]))));	// type
-	in = list(in, nod(ODCLFIELD, N, typenod(types[TINT])));	// count
-	in = list(in, nod(ODCLFIELD, N, typenod(n->type)));	// slice
-	for(i=0; i<j; i++)
-		in = list(in, nod(ODCLFIELD, N, typenod(n->type->type)));
-	f->ntype->list = in;
-	f->ntype->rlist = list1(nod(ODCLFIELD, N, typenod(n->type)));
-	
-	args = list1(typename(n->type));
-	args = list(args, nodintconst(j));
-	args = concat(args, n->list);
-	
-	r = nod(OCALL, f, N);
-	r->list = args;
-	typecheck(&r, Erv);
-	walkexpr(&r, init);
-	r->type = n->type;
-
-	return r;
-}
-
-
-// expand s = append(s, a [, b]* ) to
+// expand append(src, a [, b]* ) to
 //
+//   init {
+//     s := src
 //     const argc = len(args) - 1
 //     if cap(s) - len(s) < argc {
 //          s = growslice(s, argc) 
@@ -2425,33 +2390,31 @@ append(Node *n, NodeList **init)
 //     s[n] = a
 //     s[n+1] = b
 //     ...
-//
-static int
-oasappend(Node **np, NodeList **init)
+//   }
+//   s
+static Node*
+append(Node *n, NodeList **init)
 {
 	NodeList *l, *a;
-	Node *n, *ns, *nn, *na, *nx, *fn;
+	Node *nsrc, *ns, *nn, *na, *nx, *fn;
 	int argc;
 
-	n = *np;
+	walkexprlistsafe(n->list, init);
 
-	// Check that it's an assignment of the form s = append(s, elem), where s is ONAME.
-	if (n->right == N || n->right->op != OAPPEND || n->right->isddd || 
-	    n->left == N || n->left->op != ONAME || n->left != n->right->list->n)
-		return 0;
-
-	ns = cheapexpr(n->left, init);
-	walkexprlistsafe(n->right->list, init);
-	argc = count(n->right->list) - 1;
+	nsrc = n->list->n;
+	argc = count(n->list) - 1;
 	if (argc < 1) {
-		n->op = OEMPTY;
-		return 1;
+		return nsrc;
 	}
 
-	na = nodintconst(argc);         // const argc
+	l = nil;
 
+	ns = nod(OXXX, N, N);             // var s
+	tempname(ns, nsrc->type);
+	l = list(l, nod(OAS, ns, nsrc));  // s = src
+
+	na = nodintconst(argc);         // const argc
 	nx = nod(OIF, N, N);            // if cap(s) - len(s) < argc
-	nx->lineno = n->lineno;
 	nx->ntest = nod(OLT, nod(OSUB, nod(OCAP, ns, N), nod(OLEN, ns, N)), na);
 
 	fn = syslook("growslice", 1);   //   growslice(<type>, old []T, n int64) (ret []T)
@@ -2462,7 +2425,7 @@ oasappend(Node **np, NodeList **init)
 					       typename(ns->type),
 					       ns,
 					       conv(na, types[TINT64]))));
-	l = list1(nx);
+	l = list(l, nx);
 
 	nn = nod(OXXX, N, N);                            // var n
 	tempname(nn, types[TINT]);
@@ -2472,7 +2435,7 @@ oasappend(Node **np, NodeList **init)
 	nx->etype = 1;  // disable bounds check
 	l = list(l, nod(OAS, ns, nx));                  // s = s[:n+argc]
 
-	for (a = n->right->list->next;  a != nil; a = a->next) {
+	for (a = n->list->next;  a != nil; a = a->next) {
 		nx = nod(OINDEX, ns, nn);               // s[n] ...
 		nx->etype = 1;  // disable bounds check
 		l = list(l, nod(OAS, nx, a->n));        // s[n] = arg
@@ -2481,8 +2444,7 @@ oasappend(Node **np, NodeList **init)
 	}
 
 	typechecklist(l, Etop);
-	*np = liststmt(l);
-
-	walkstmt(np);
-	return 1;
+	walkstmtlist(l);
+	*init = concat(*init, l);
+	return ns;
 }

src/pkg/runtime/slice.c

@@ -48,20 +48,6 @@ makeslice1(SliceType *t, int32 len, int32 cap, Slice *ret)
 		ret->array = runtime·mal(size);
 }
 
-// append(type *Type, n int, old []T, ...,) []T
-#pragma textflag 7
-void
-runtime·append(SliceType *t, int32 n, Slice old, ...)
-{
-	Slice sl;
-	Slice *ret;
-	
-	sl.len = n;
-	sl.array = (byte*)(&old+1);
-	ret = (Slice*)(sl.array + ((t->elem->size*n+sizeof(uintptr)-1) & ~(sizeof(uintptr)-1)));
-	appendslice1(t, old, sl, ret);
-}
-
 // appendslice(type *Type, x, y, []T) []T
 void
 runtime·appendslice(SliceType *t, Slice x, Slice y, Slice ret)