re PR c/86093 (volatile ignored on pointer in C)

	PR c/86093
	* c-typeck.c (pointer_diff): Cast both pointers to unqualified types
	before doing POINTER_DIFF_EXPR.

	* c-c++-common/pr86093.c: New test.

From-SVN: r261663

gcc/c/ChangeLog

+2018-06-15  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/86093
+	* c-typeck.c (pointer_diff): Cast both pointers to unqualified types
+	before doing POINTER_DIFF_EXPR.
+
 2018-06-07  Marek Polacek  <polacek@redhat.com>
 
 	PR c/85318

gcc/c/c-typeck.c

@@ -3840,7 +3840,12 @@ pointer_diff (location_t loc, tree op0, tree op1, tree *instrument_expr)
     op0 = build_binary_op (loc, MINUS_EXPR, convert (inttype, op0),
 			   convert (inttype, op1), false);
   else
-    op0 = build2_loc (loc, POINTER_DIFF_EXPR, inttype, op0, op1);
+    {
+      /* Cast away qualifiers.  */
+      op0 = convert (c_common_type (TREE_TYPE (op0), TREE_TYPE (op0)), op0);
+      op1 = convert (c_common_type (TREE_TYPE (op1), TREE_TYPE (op1)), op1);
+      op0 = build2_loc (loc, POINTER_DIFF_EXPR, inttype, op0, op1);
+    }
 
   /* This generates an error if op1 is pointer to incomplete type.  */
   if (!COMPLETE_OR_VOID_TYPE_P (TREE_TYPE (TREE_TYPE (orig_op1))))

gcc/testsuite/ChangeLog

 2018-06-15  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c/86093
+	* c-c++-common/pr86093.c: New test.
+
 	PR middle-end/85878
 	* gfortran.fortran-torture/compile/pr85878.f90: New test.
 

gcc/testsuite/c-c++-common/pr86093.c

+/* PR c/86093 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump-not "return 0;" "optimized" } } */
+
+char *volatile p;
+
+__PTRDIFF_TYPE__
+foo (void)
+{
+  return p - p;
+}