Re: Why can't copy renaming capture this assignment?

[Richard Guenther <richard.guenther@gmail.com>]

On Sat, Mar 31, 2012 at 6:23 AM, Jiangning Liu <jiangning.liu@arm.com> wrote:
> Hi,
>
> For this small case,
>
> char garr[100];
> void f(void)
> {
>        unsigned short h, s;
>
>        s = 20;
>
>        for (h = 1; h < (s-1); h++)
>        {
>                garr[h] = 0;
>        }
> }
>
> After copyrename3, we have the following dump,
>
> f ()
> {
>  short unsigned int h;
>  int D.4066;
>
> <bb 2>:
>  D.4066_14 = 1;
>  if (D.4066_14 <= 18)
>    goto <bb 3>;
>  else
>    goto <bb 4>;
>
> <bb 3>:
>  # h_15 = PHI <h_8(3), 1(2)>
>  # D.4066_16 = PHI <D.4066_4(3), D.4066_14(2)>
>  garr[D.4066_16] = 0;
>  h_8 = h_15 + 1;
>  D.4066_4 = (int) h_8;
>  if (D.4066_4 <= 18)
>    goto <bb 3>;
>  else
>    goto <bb 4>;
>
> <bb 4>:
>  return;
>
> }
>
> copy renaming fails to capture the assignment statement "D.4066_4 = (int)
> h_8;" to trigger renaming partition coalesce.
>
> I find gimple_assign_single_p invoked by gimple_assign_ssa_name_copy_p
> always returns false, because for this statement " gs->gsbase.subcode" is
> NOP_EXPR rather than GIMPLE_SINGLE_RHS.
>
> Should subcode be correctly initialized anywhere to fix this problem?
>
> BTW, my expectation after copy renaming is like below,
>
> f ()
> {
>  int D.4679;
>
> <bb 2>:
>  D.4679_7 = 1;
>  if (D.4679_7 != 19)
>    goto <bb 3>;
>  else
>    goto <bb 4>;
>
> <bb 3>:
>  # D.4679_15 = PHI <D.4679_4(3), D.4679_7(2)>
>  # D.4679_17 = PHI <D.4679_14(3), 1(2)>
>  garr[D.4679_15] = 0;
>  D.4679_14 = D.4679_17 + 1;
>  D.4679_4 = D.4679_14;
>  if (D.4679_4 != 19)
>    goto <bb 3>;
>  else
>    goto <bb 4>;
>
> <bb 4>:
>  return;
>
> }

Err - you completely lost the fact that h was short instead of int.

Richard.

> and then PRE can finally remove that redundancy for symbol D.xxxx away.
>
> Thanks,
> -Jiangning
>
>
>
>
>