[Bug c++/64191] [4.9/5 Regression] -march=native messes up dead code elimination in loop calling dtor

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64191

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2014-12-08
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot 
gnu.org
   Target Milestone|---                         |4.9.3
            Summary|-march=native messes up     |[4.9/5 Regression]
                   |dead code elimination in    |-march=native messes up
                   |loop calling dtor           |dead code elimination in
                   |                            |loop calling dtor
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmm, on the 4.9 branch we vectorize the clobber and cannot recover from that
(nor do we remove the loop earlier - because of that as well I guess).

void bar_dtor_loop(Bar*, unsigned int) (struct Bar * p, unsigned int n)
{
...
  <bb 6>:
  # e_13 = PHI <e_9(5), e_10(8)>
  e_10 = e_13 + 18446744073709551612;
  *e_10 ={v} {CLOBBER};
  if (p_4(D) < e_10)
    goto <bb 8>;
  else
    goto <bb 7>;

  <bb 8>:
  goto <bb 6>;

...

after vectorization:

  <bb 7>:
  # e_13 = PHI <e_9(6), e_10(14)>
  # vect_vec_iv_.19_45 = PHI <vect_cst_.17_43(6), vect_vec_iv_.19_46(14)>
  # ivtmp_11 = PHI <0(6), ivtmp_49(14)>
  vect_vec_iv_.19_46 = vect_vec_iv_.19_45 + vect_cst_.18_44;
  vect_e_10.20_48 = vect_vec_iv_.19_45 + vect_cst_.21_47;
  e_10 = e_13 + 18446744073709551612;
  ivtmp_49 = ivtmp_11 + 1;
  if (ivtmp_49 < bnd.13_20)
    goto <bb 14>;
  else
    goto <bb 10>;

...

  <bb 8>:
  # e_24 = PHI <e_26(9), e_33(11)>
  e_26 = e_24 + 18446744073709551612;
  *e_26 ={v} {CLOBBER};
  if (p_4(D) < e_26)
    goto <bb 9>;
  else
    goto <bb 12>;

works fine with GCC 4.8.