This is the mail archive of the
gcc-help@gcc.gnu.org
mailing list for the GCC project.
Which pass optimizes if (x != x + 10) to if (1)?
- From: Zhenqiang Chen <zhenqiang dot chen at linaro dot org>
- To: gcc-help at gcc dot gnu dot org
- Date: Tue, 20 Mar 2012 11:08:45 +0800
- Subject: Which pass optimizes if (x != x + 10) to if (1)?
Hi,
For the following case: -O0/-O2 can optimize if (x != x + 10) to if
(1) at the beginning. But -Os can not. All options can optimize if (x
+ 10 != x) to if (1).
To reproduce it, check test.c.003t.original for the two commands.
gcc test.c -fdump-tree-all -c -O0.
gcc test.c -fdump-tree-all -c -Os.
void test (int x, unsigned int y)
{
if (x != x + 10)
;
if (x + 10 != x)
;
}
Which pass optimizes if (x != x + 10) to if (1)? Why is it not applied to -Os?
Thanks!
-Zhenqiang