Which pass optimizes if (x != x + 10) to if (1)?

[Zhenqiang Chen <zhenqiang.chen@xxxxxxxxxx>]

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