Re: [PATCH] Fold (int *)&a + 4 to a[1] using offset_int (PR middle-end/81695)

[Marek Polacek]

On Fri, Aug 04, 2017 at 11:08:49AM +0200, Richard Biener wrote:
> On Fri, Aug 4, 2017 at 10:38 AM, Marek Polacek <pola...@redhat.com> wrote:
> > We were crashing because size_binop_loc got operands of different types:
> > sizetype and ssizetype.  Richi suggested performing the computation in
> > offset_int which my patch tries to do.  Unsure about the sdiv_trunc part,
> > what do I use instead of EXACT_DIV_EXPR?
> 
> Use wi::divmod_trunc and check for a zero remainder.  If the remainder is not
> zero we may not fold.
> 
> Ok with that change.

Thanks, will commit this after the usual testing:

2017-08-04  Marek Polacek  <pola...@redhat.com>

        PR middle-end/81695
        * fold-const.c (fold_indirect_ref_1): For ((int *)&a + 4 -> a[1],
        perform the computation in offset_int.

        * gcc.dg/pr81695.c: New test.

diff --git gcc/fold-const.c gcc/fold-const.c
index ed6c289a64b..1f55bee8fc0 100644
--- gcc/fold-const.c
+++ gcc/fold-const.c
@@ -14106,14 +14106,21 @@ fold_indirect_ref_1 (location_t loc, tree type, tree 
op0)
                   && type == TREE_TYPE (op00type))
            {
              tree type_domain = TYPE_DOMAIN (op00type);
-             tree min_val = size_zero_node;
-             if (type_domain && TYPE_MIN_VALUE (type_domain))
-               min_val = TYPE_MIN_VALUE (type_domain);
-             op01 = size_binop_loc (loc, EXACT_DIV_EXPR, op01,
-                                    TYPE_SIZE_UNIT (type));
-             op01 = size_binop_loc (loc, PLUS_EXPR, op01, min_val);
-             return build4_loc (loc, ARRAY_REF, type, op00, op01,
-                                NULL_TREE, NULL_TREE);
+             tree min = TYPE_MIN_VALUE (type_domain);
+             if (min && TREE_CODE (min) == INTEGER_CST)
+               {
+                 offset_int off = wi::to_offset (op01);
+                 offset_int el_sz = wi::to_offset (TYPE_SIZE_UNIT (type));
+                 offset_int remainder;
+                 off = wi::divmod_trunc (off, el_sz, SIGNED, &remainder);
+                 if (remainder == 0)
+                   {
+                     off = off + wi::to_offset (min);
+                     op01 = wide_int_to_tree (sizetype, off);
+                     return build4_loc (loc, ARRAY_REF, type, op00, op01,
+                                        NULL_TREE, NULL_TREE);
+                   }
+               }
            }
        }
     }
diff --git gcc/testsuite/gcc.dg/pr81695.c gcc/testsuite/gcc.dg/pr81695.c
index e69de29bb2d..c3452580f1c 100644
--- gcc/testsuite/gcc.dg/pr81695.c
+++ gcc/testsuite/gcc.dg/pr81695.c
@@ -0,0 +1,11 @@
+/* PR middle-end/81695 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+int z[] = { };
+
+int
+main (void)
+{
+  __builtin_printf ("%d\n", *(z + 1));
+}

        Marek