gc: add delete(m, x) but leave in m[x] = 0, false.

The old m[x] = 0, false syntax will be deleted
in a month or so, once people have had time to
change their code (there is a gofix in a separate CL).

R=ken2
CC=golang-dev
https://golang.org/cl/5265048

src/cmd/gc/builtin.c.boot

@@ -64,6 +64,7 @@ char *runtimeimport =
 	"func @\"\".mapassign1 (mapType *uint8, hmap map[any] any, key any, val any)\n"
 	"func @\"\".mapassign2 (mapType *uint8, hmap map[any] any, key any, val any, pres bool)\n"
 	"func @\"\".mapiterinit (mapType *uint8, hmap map[any] any, hiter *any)\n"
+	"func @\"\".mapdelete (mapType *uint8, hmap map[any] any, key any)\n"
 	"func @\"\".mapiternext (hiter *any)\n"
 	"func @\"\".mapiter1 (hiter *any) any\n"
 	"func @\"\".mapiter2 (hiter *any) (key any, val any)\n"

src/cmd/gc/go.h

@@ -425,7 +425,8 @@ enum
 	OAPPEND,
 	OARRAYBYTESTR, OARRAYRUNESTR,
 	OSTRARRAYBYTE, OSTRARRAYRUNE,
-	OAS, OAS2, OAS2MAPW, OAS2FUNC, OAS2RECV, OAS2MAPR, OAS2DOTTYPE, OASOP,
+	OAS, OAS2, OAS2MAPW, OAS2FUNC, OAS2RECV, OAS2MAPR, OAS2DOTTYPE,
+	OASOP,
 	OBAD,
 	OCALL, OCALLFUNC, OCALLMETH, OCALLINTER,
 	OCAP,
@@ -436,6 +437,7 @@ enum
 	OCONV, OCONVIFACE, OCONVNOP,
 	OCOPY,
 	ODCL, ODCLFUNC, ODCLFIELD, ODCLCONST, ODCLTYPE,
+	ODELETE,
 	ODOT, ODOTPTR, ODOTMETH, ODOTINTER, OXDOT,
 	ODOTTYPE,
 	ODOTTYPE2,

src/cmd/gc/lex.c

@@ -1624,6 +1624,7 @@ static	struct
 	"close",	LNAME,		Txxx,		OCLOSE,
 	"complex",	LNAME,		Txxx,		OCOMPLEX,
 	"copy",		LNAME,		Txxx,		OCOPY,
+	"delete",		LNAME,		Txxx,		ODELETE,
 	"imag",		LNAME,		Txxx,		OIMAG,
 	"len",		LNAME,		Txxx,		OLEN,
 	"make",		LNAME,		Txxx,		OMAKE,

src/cmd/gc/runtime.go

@@ -87,6 +87,7 @@ func mapaccess2(mapType *byte, hmap map[any]any, key any) (val any, pres bool)
 func mapassign1(mapType *byte, hmap map[any]any, key any, val any)
 func mapassign2(mapType *byte, hmap map[any]any, key any, val any, pres bool)
 func mapiterinit(mapType *byte, hmap map[any]any, hiter *any)
+func mapdelete(mapType *byte, hmap map[any]any, key any)
 func mapiternext(hiter *any)
 func mapiter1(hiter *any) (key any)
 func mapiter2(hiter *any) (key any, val any)

src/cmd/gc/subr.c

@@ -923,6 +923,7 @@ goopnames[] =
 	[OCOPY]		= "copy",
 	[ODEC]		= "--",
 	[ODEFER]	= "defer",
+	[ODELETE]	= "delete",
 	[ODIV]		= "/",
 	[OEQ]		= "==",
 	[OFALL]		= "fallthrough",

src/cmd/gc/typecheck.c

@@ -991,6 +991,31 @@ reswitch:
 		ok |= Etop;
 		goto ret;
 
+	case ODELETE:
+		args = n->list;
+		if(args == nil) {
+			yyerror("missing arguments to delete");
+			goto error;
+		}
+		if(args->next == nil) {
+			yyerror("missing second (key) argument to delete");
+			goto error;
+		}
+		if(args->next->next != nil) {
+			yyerror("too many arguments to delete");
+			goto error;
+		}
+		ok |= Etop;
+		typechecklist(args, Erv);
+		l = args->n;
+		r = args->next->n;
+		if(l->type != T && l->type->etype != TMAP) {
+			yyerror("first argument to delete must be map; have %lT", l->type);
+			goto error;
+		}
+		args->next->n = assignconv(r, l->type->down, "delete");
+		goto ret;
+
 	case OAPPEND:
 		ok |= Erv;
 		args = n->list;
@@ -2284,7 +2309,7 @@ typecheckas2(Node *n)
 {
 	int cl, cr;
 	NodeList *ll, *lr;
-	Node *l, *r;
+	Node *l, *r, *rr;
 	Iter s;
 	Type *t;
 
@@ -2325,8 +2350,14 @@ typecheckas2(Node *n)
 			goto out;
 		n->op = OAS2MAPW;
 		n->rlist->n = assignconv(r, l->type, "assignment");
-		r = n->rlist->next->n;
-		n->rlist->next->n = assignconv(r, types[TBOOL], "assignment");
+		rr = n->rlist->next->n;
+		n->rlist->next->n = assignconv(rr, types[TBOOL], "assignment");
+		if(isconst(rr, CTBOOL) && !rr->val.u.bval) {
+			n->op = ODELETE;
+			n->list = list(list1(l->left), l->right);
+			n->right = n->rlist->n;
+			n->rlist = nil;
+		}
 		goto out;
 	}
 

src/cmd/gc/walk.c

@@ -9,6 +9,7 @@
 static	Node*	walkprint(Node*, NodeList**, int);
 static	Node*	conv(Node*, Type*);
 static	Node*	mapfn(char*, Type*);
+static	Node*	mapfndel(char*, Type*);
 static	Node*	makenewvar(Type*, NodeList**, Node**);
 static	Node*	ascompatee1(int, Node*, Node*, NodeList**);
 static	NodeList*	ascompatee(int, NodeList*, NodeList*, NodeList**);
@@ -173,6 +174,7 @@ walkstmt(Node **np)
 	case OCALLINTER:
 	case OCALL:
 	case OCALLFUNC:
+	case ODELETE:
 	case OSEND:
 	case ORECV:
 	case OPRINT:
@@ -610,6 +612,21 @@ walkexpr(Node **np, NodeList **init)
 		n->op = OAS2FUNC;
 		goto as2func;
 
+	case ODELETE:
+		*init = concat(*init, n->ninit);
+		n->ninit = nil;
+		l = n->list->n;
+		r = n->list->next->n;
+		if(n->right != N) {
+			// TODO: Remove once two-element map assigment is gone.
+			l = safeexpr(l, init);
+			r = safeexpr(r, init);
+			safeexpr(n->right, init);  // cause side effects from n->right
+		}
+		t = l->type;
+		n = mkcall1(mapfndel("mapdelete", t), t->down, init, typename(t), l, r);
+		goto ret;
+
 	case OAS2MAPW:
 		// map[] = a,b - mapassign2
 		// a,b = m[i];
@@ -2254,6 +2271,20 @@ mapfn(char *name, Type *t)
 	return fn;
 }
 
+static Node*
+mapfndel(char *name, Type *t)
+{
+	Node *fn;
+
+	if(t->etype != TMAP)
+		fatal("mapfn %T", t);
+	fn = syslook(name, 1);
+	argtype(fn, t->down);
+	argtype(fn, t->type);
+	argtype(fn, t->down);
+	return fn;
+}
+
 static Node*
 addstr(Node *n, NodeList **init)
 {

src/pkg/runtime/hashmap.c

@@ -1028,6 +1028,28 @@ runtime·mapassign2(MapType *t, Hmap *h, ...)
 	}
 }
 
+// mapdelete(mapType *type, hmap *map[any]any, key any)
+#pragma textflag 7
+void
+runtime·mapdelete(MapType *t, Hmap *h, ...)
+{
+	byte *ak;
+
+	if(h == nil)
+		runtime·panicstring("deletion of entry in nil map");
+
+	ak = (byte*)&h + h->ko2;
+	runtime·mapassign(t, h, ak, nil);
+
+	if(debug) {
+		runtime·prints("mapdelete: map=");
+		runtime·printpointer(h);
+		runtime·prints("; key=");
+		h->keyalg->print(h->keysize, ak);
+		runtime·prints("\n");
+	}
+}
+
 // For reflect:
 //	func mapassign(t type h map, key, val iword, pres bool)
 // where an iword is the same word an interface value would use: