re PR c++/82872 (ICE in ignore_overflows on __PTRDIFF_MAX__ index)

	PR c++/82872
	* convert.c (convert_to_integer_1) <POINTER_TYPE>: Do not return the
	shared zero if the input has overflowed.

From-SVN: r255944

gcc/ChangeLog

+2017-12-21  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR c++/82872
+	* convert.c (convert_to_integer_1) <POINTER_TYPE>: Do not return the
+	shared zero if the input has overflowed.
+
 2017-12-21  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	* config/arm/driver-arm.c (arm_cpu_table): Specify dotprod

gcc/convert.c

@@ -671,7 +671,7 @@ convert_to_integer_1 (tree type, tree expr, bool dofold)
     {
     case POINTER_TYPE:
     case REFERENCE_TYPE:
-      if (integer_zerop (expr))
+      if (integer_zerop (expr) && !TREE_OVERFLOW (expr))
 	return build_int_cst (type, 0);
 
       /* Convert to an unsigned integer of the correct width first, and from

gcc/testsuite/ChangeLog

+2017-12-21  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* c-c++-common/pr82872.c: New test.
+
 2017-12-21  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/82973

gcc/testsuite/c-c++-common/pr82872.c

+/* PR c++/82872 */
+/* { dg-do compile } */
+
+#include <stddef.h>
+
+struct S { int i, a[1]; };
+
+size_t foo (void)
+{
+  return offsetof (struct S, a[__PTRDIFF_MAX__]);
+}