Zhenqiang Chen <zhenqiang.chen@xxxxxxxxxx> writes:
> 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?
It's not a separate pass. It's code in fold-const.c.
I don't know why -Os makes a difference here. It does seem odd. I
encourage you to investigate what is happening.
Ian
