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


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?

Bootstrapped/regtested on x86_64-linux, ok for trunk?  Testing on ppc64le
in progress.

2017-08-04  Marek Polacek  <polacek@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..64a84eb0197 100644
--- gcc/fold-const.c
+++ gcc/fold-const.c
@@ -14106,14 +14106,17 @@ 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));
+		  off = wi::sdiv_trunc (off, el_sz);
+		  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


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