http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46675
--- Comment #24 from H.J. Lu <hjl.tools at gmail dot com> 2010-11-28 21:04:10
UTC ---
Does this patch make any senses?
---
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index c195073..4bcdd07 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -10225,6 +10225,22 @@ fold_binary_loc (location_t loc,
fold_convert_loc (loc, type,
negate_expr (arg1)));
+ /* A - B -> A + (-B) if B is negative integer constant. */
+ if (TREE_CODE (arg1) == INTEGER_CST && !TYPE_UNSIGNED (type))
+ {
+ double_int di = tree_to_double_int (arg1);
+ if (double_int_negative_p (di))
+ {
+ tree unsigned_type = unsigned_type_for (type);
+ di = double_int_neg (di);
+ return fold_build2_loc (loc, PLUS_EXPR, unsigned_type,
+ fold_convert_loc (loc, unsigned_type, arg0
),
+ fold_convert_loc (loc,
+ unsigned_type,
+ double_int_to_tree (type
, di)));
+ }
+ }
+
/* Try folding difference of addresses. */
{
HOST_WIDE_INT diff;
---
