re PR c++/84281 (Heap grows indefinitely)

2018-02-12  Richard Biener  <rguenther@suse.de>

	PR c++/84281
	* constexpr.c (cxx_eval_vec_init_1): Use a RANGE_EXPR to compact
	uniform constructors and delay allocating them fully.

From-SVN: r257580

gcc/cp/ChangeLog

+2018-02-12  Richard Biener  <rguenther@suse.de>
+
+	PR c++/84281
+	* constexpr.c (cxx_eval_vec_init_1): Use a RANGE_EXPR to compact
+	uniform constructors and delay allocating them fully.
+
 2018-02-09  Jason Merrill  <jason@redhat.com>
 
 	PR c++/84036 - ICE with variadic capture.

gcc/cp/constexpr.c

@@ -2885,7 +2885,6 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init,
   unsigned HOST_WIDE_INT max = tree_to_uhwi (array_type_nelts_top (atype));
   verify_ctor_sanity (ctx, atype);
   vec<constructor_elt, va_gc> **p = &CONSTRUCTOR_ELTS (ctx->ctor);
-  vec_alloc (*p, max + 1);
   bool pre_init = false;
   unsigned HOST_WIDE_INT i;
 
@@ -2978,13 +2977,14 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init,
 	{
 	  if (new_ctx.ctor != ctx->ctor)
 	    eltinit = new_ctx.ctor;
-	  for (i = 1; i < max; ++i)
-	    {
-	      idx = build_int_cst (size_type_node, i);
-	      CONSTRUCTOR_APPEND_ELT (*p, idx, unshare_constructor (eltinit));
-	    }
+	  tree range = build2 (RANGE_EXPR, size_type_node,
+			       build_int_cst (size_type_node, 1),
+			       build_int_cst (size_type_node, max - 1));
+	  CONSTRUCTOR_APPEND_ELT (*p, range, unshare_constructor (eltinit));
 	  break;
 	}
+      else if (i == 0)
+	vec_safe_reserve (*p, max);
     }
 
   if (!*non_constant_p)