[Bug lto/65950] Loop is not vectorized with lto.

[gcp at sjeng dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65950

Gian-Carlo Pascutto  changed:

   What|Removed |Added

 CC||gcp at sjeng dot org

--- Comment #6 from Gian-Carlo Pascutto  ---
I'm seeing similar behavior in gcc-4.9.2 (debian stable) and gcc-5.3.1 (Ubuntu
16.04 prelease).

Adding -flto causes certain loops not to get vectorized, adding -fno-lto to
affected files fixes it.

Unfortunately producing a reduced testcase is not so easy, but program source
is available to gcc devs on request.

[Bug lto/65950] Loop is not vectorized with lto.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65950

Andrew Pinski  changed:

   What|Removed |Added

   Keywords||missed-optimization
 Status|UNCONFIRMED |NEW
   Last reconfirmed||2015-12-24
 Ever confirmed|0   |1

--- Comment #5 from Andrew Pinski  ---
Confirmed.

Right before the vectorizer:

Without LTO:
  :
  # k_36 = PHI 
  # ivtmp_88 = PHI <16(5), ivtmp_40(7)>
  _11 = (long unsigned int) k_36;
  _12 = _11 * 4;
  _14 = v_13(D) + _12;
  _15 = *_14;
  _16 = k_36 + -1;
  _17 = (float) _16;
  _23 = pretmp_83 + _12;
  _24 = *_23;
  _25 = _17 * _24;
  _26 = _15 + _25;
  *_14 = _26;
  k_28 = k_36 + 1;
  ivtmp_40 = ivtmp_88 - 1;
  if (ivtmp_40 != 0)
goto ;
  else
goto ;

  :
  goto ;


With LTO:

  :
  _11 = (long unsigned int) k_2;
  _12 = _11 * 4;
  _14 = v_13(D) + _12;
  _15 = *_14;
  _16 = k_2 + -1;
  _17 = (float) _16;
  _22 = *_21;
  _23 = _22 + _12;
  _24 = *_23;
  _25 = _17 * _24;
  _26 = _15 + _25;
  *_14 = _26;
  k_28 = k_2 + 1;

  :
  # k_2 = PHI 
  # ivtmp_36 = PHI <17(3), ivtmp_35(4)>
  _10 = K_9 + 16;
  ivtmp_35 = ivtmp_36 - 1;
  if (ivtmp_35 != 0)
goto ;
  else
goto ;

Notice the difference in the CFG.

[Bug lto/65950] Loop is not vectorized with lto.

[ysrumyan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65950

--- Comment #4 from Yuri Rumyantsev ysrumyan at gmail dot com ---
The function containing given loop is marked as:

foo/24 (foo) @0x7f39f4b84620
  Type: function definition analyzed
  Visibility: prevailing_def_ironly
  References: 
  Referring: 
  Read from file: /tmp/ccKAP5Mo.o
  Availability: local
  First run: 0
  Function flags: local nonfreeing_fn unlikely_executed
  Called by: main/23

[Bug lto/65950] Loop is not vectorized with lto.

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65950

--- Comment #3 from Richard Biener rguenth at gcc dot gnu.org ---
Do we eventually think the loop is cold?

[Bug lto/65950] Loop is not vectorized with lto.

[ysrumyan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65950

--- Comment #1 from Yuri Rumyantsev ysrumyan at gmail dot com ---
Created attachment 35432
  -- https://gcc.gnu.org/bugzilla/attachment.cgi?id=35432action=edit
test-case to reproduce

Must be compiled with -Ofast and -fopenmp options.

[Bug lto/65950] Loop is not vectorized with lto.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65950

--- Comment #2 from Andrew Pinski pinskia at gcc dot gnu.org ---
This vectorized for me with GCC 5.1.0 on aarch64-linux-gnu.