2018-03-12  Jakub Jelinek  <jakub@redhat.com>

	PR c++/84808
	* constexpr.c (find_array_ctor_elt): Don't use elt reference after
	first potential CONSTRUCTOR_ELTS reallocation.  Convert dindex to
	sizetype.  Formatting fixes.

	* g++.dg/cpp1y/constexpr-84808.C: New test.

--- gcc/cp/constexpr.c.jj	2018-03-07 22:52:02.000000000 +0100
+++ gcc/cp/constexpr.c	2018-03-12 12:39:46.890321137 +0100
@@ -2194,9 +2194,9 @@ find_array_ctor_elt (tree ary, tree dind
      that the same is true of the other elements and index directly.  */
   if (end > 0)
     {
-      tree cindex = (*elts)[end-1].index;
+      tree cindex = (*elts)[end - 1].index;
       if (TREE_CODE (cindex) == INTEGER_CST
-	  && compare_tree_int (cindex, end-1) == 0)
+	  && compare_tree_int (cindex, end - 1) == 0)
 	{
 	  if (i < end)
 	    return i;
@@ -2225,6 +2225,8 @@ find_array_ctor_elt (tree ary, tree dind
 	      constructor_elt e;
 	      tree lo = TREE_OPERAND (idx, 0);
 	      tree hi = TREE_OPERAND (idx, 1);
+	      tree value = elt.value;
+	      dindex = fold_convert (sizetype, dindex);
 	      if (tree_int_cst_lt (lo, dindex))
 		{
 		  /* There are still some lower elts; shorten the range.  */
@@ -2238,7 +2240,7 @@ find_array_ctor_elt (tree ary, tree dind
 		  /* Append the element we want to insert.  */
 		  ++middle;
 		  e.index = dindex;
-		  e.value = unshare_constructor (elt.value);
+		  e.value = unshare_constructor (value);
 		  vec_safe_insert (CONSTRUCTOR_ELTS (ary), middle, e);
 		}
 	      else
@@ -2254,8 +2256,8 @@ find_array_ctor_elt (tree ary, tree dind
 		    e.index = hi;
 		  else
 		    e.index = build2 (RANGE_EXPR, sizetype, new_lo, hi);
-		  e.value = unshare_constructor (elt.value);
-		  vec_safe_insert (CONSTRUCTOR_ELTS (ary), middle+1, e);
+		  e.value = unshare_constructor (value);
+		  vec_safe_insert (CONSTRUCTOR_ELTS (ary), middle + 1, e);
 		}
 	    }
 	  return middle;
--- gcc/testsuite/g++.dg/cpp1y/constexpr-84808.C.jj	2018-03-12 12:45:29.472374837 +0100
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-84808.C	2018-03-12 12:46:11.742381465 +0100
@@ -0,0 +1,27 @@
+// PR c++/84808
+// { dg-do compile { target c++14 } }
+
+struct A { int i; constexpr A () : i() {} };
+struct B { A a[24]; };
+
+constexpr int
+foo (int n)
+{
+  B b;
+  ++b.a[n + 20].i;
+  ++b.a[n + 18].i;
+  ++b.a[n + 16].i;
+  ++b.a[n + 14].i;
+  ++b.a[n + 12].i;
+  ++b.a[n + 10].i;
+  ++b.a[n + 8].i;
+  ++b.a[n + 6].i;
+  ++b.a[n + 4].i;
+  ++b.a[n + 2].i;
+  ++b.a[n].i;
+  return b.a[2].i + b.a[4].i + b.a[6].i + b.a[8].i + b.a[10].i
+	 + b.a[12].i + b.a[14].i + b.a[16].i + b.a[18].i + b.a[20].i + b.a[22].i;
+}
+
+constexpr int i = foo (2);
+static_assert (i == 11, "");