This fixes PR55863, a folding missed optimization caused by
folding -X - 1 to ~X. This makes data dependence analysis fail
for offsetted-by-1 accesses (in some cases).
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2013-01-04 Richard Biener <rguent...@suse.de>
PR middle-end/55863
* fold-const.c (split_tree): Undo -X - 1 to ~X folding for
reassociation.
* gcc.dg/fold-reassoc-2.c: New testcase.
Index: gcc/fold-const.c
===================================================================
*** gcc/fold-const.c (revision 194855)
--- gcc/fold-const.c (working copy)
*************** split_tree (tree in, enum tree_code code
*** 821,826 ****
--- 821,833 ----
if (neg_var_p)
var = negate_expr (var);
}
+ else if (TREE_CODE (in) == BIT_NOT_EXPR
+ && code == PLUS_EXPR)
+ {
+ /* -X - 1 is folded to ~X, undo that here. */
+ *minus_litp = build_one_cst (TREE_TYPE (in));
+ var = negate_expr (TREE_OPERAND (in, 0));
+ }
else if (TREE_CONSTANT (in))
*conp = in;
else
Index: gcc/testsuite/gcc.dg/fold-reassoc-2.c
===================================================================
*** gcc/testsuite/gcc.dg/fold-reassoc-2.c (revision 0)
--- gcc/testsuite/gcc.dg/fold-reassoc-2.c (working copy)
***************
*** 0 ****
--- 1,14 ----
+ /* { dg-do compile } */
+ /* { dg-options "-O -fdump-tree-original" } */
+
+ int foo (int i)
+ {
+ return (i + 2) - (i + 1);
+ }
+ int bar (int i)
+ {
+ return (i + 2) + ~i;
+ }
+
+ /* { dg-final { scan-tree-dump "return 1;" "original" } } */
+ /* { dg-final { cleanup-tree-dump "original" } } */
