[Bug tree-optimization/38785] [4.5/4.6/4.7/4.8 Regression] huge performance regression on EEMBC bitmnp01

[hubicka at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38785



Jan Hubicka <hubicka at gcc dot gnu.org> changed:



           What    |Removed                     |Added

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                 CC|                            |vmakarov at redhat dot com



--- Comment #37 from Jan Hubicka <hubicka at gcc dot gnu.org> 2012-11-22 
09:50:52 UTC ---

Yes, agreed. It is overall problem of SSA form to assume that reg-reg copies in

PHIs will be optimized away by smart regalloc.  Moreover we assume the same for

constants.



This case is hard to fix later since the values are path sensitive...

Vladimir, I guess there is not much to do on regalloc side, right?



Why the problem do not reproduce on simplified testcase:

void

f (int i, long *a, long *b)

{

  int sum = 0;

  b[i] = 0;

#define PART(I) if (t()) sum++;

  PART (1);

  PART (2);

  PART (3);

  PART (4);

  PART (5);

  PART (6);

  tt (sum);

}

here we somehow do not consider the partial redundancies on sum...