re PR middle-end/46761 (-fgraphite-identity produces wrong code for array initialization arr[i] = i)

	PR middle-end/46761
	* graphite-clast-to-gimple.c (graphite_create_new_loop_guard): Prefer
	to use unadjusted UB.

testsuite:
	* gcc.dg/graphite/pr46761.c: New.

From-SVN: r167980

1 files changed, 16 insertions, 12 deletions

diff --git a/gcc/graphite-clast-to-gimple.c b/gcc/graphite-clast-to-gimple.c
index eef5ad16abd..0937fc8eb94 100644
--- a/gcc/graphite-clast-to-gimple.c
+++ b/gcc/graphite-clast-to-gimple.c
@@ -975,20 +975,24 @@ graphite_create_new_loop_guard (sese region, edge entry_edge,
 				     newivs_index, params_index);
   tree ub = clast_to_gcc_expression (type, stmt->UB, region, newivs,
 				     newivs_index, params_index);
-  tree one = POINTER_TYPE_P (type) ? size_one_node
-    : fold_convert (type, integer_one_node);
-  /* Adding +1 and using LT_EXPR helps with loop latches that have a
-     loop iteration count of "PARAMETER - 1".  For PARAMETER == 0 this becomes
-     2^{32|64}, and the condition lb <= ub is true, even if we do not want this.
-     However lb < ub + 1 is false, as expected.  */
-  tree ub_one = fold_build2 (POINTER_TYPE_P (type) ? POINTER_PLUS_EXPR
-			     : PLUS_EXPR, type, ub, one);
-
-  /* When ub + 1 wraps around, use lb <= ub.  */
-  if (integer_zerop (ub_one))
+  /* When ub is simply a constant or a parameter, use lb <= ub.  */
+  if (TREE_CODE (ub) == INTEGER_CST || TREE_CODE (ub) == SSA_NAME)
     cond_expr = fold_build2 (LE_EXPR, boolean_type_node, lb, ub);
   else
-    cond_expr = fold_build2 (LT_EXPR, boolean_type_node, lb, ub_one);
+    {
+      tree one = (POINTER_TYPE_P (type)
+		  ? size_one_node
+		  : fold_convert (type, integer_one_node));
+      /* Adding +1 and using LT_EXPR helps with loop latches that have a
+	 loop iteration count of "PARAMETER - 1".  For PARAMETER == 0 this becomes
+	 2^k-1 due to integer overflow, and the condition lb <= ub is true,
+	 even if we do not want this.  However lb < ub + 1 is false, as
+	 expected.  */
+      tree ub_one = fold_build2 (POINTER_TYPE_P (type) ? POINTER_PLUS_EXPR
+				 : PLUS_EXPR, type, ub, one);
+
+      cond_expr = fold_build2 (LT_EXPR, boolean_type_node, lb, ub_one);
+    }
 
   exit_edge = create_empty_if_region_on_edge (entry_edge, cond_expr);