[Bug c/56787] New: 4.8.0 Vectorization Regression Compared to 4.7.2

[Bug c/56787] New: 4.8.0 Vectorization Regression Compared to 4.7.2

[freddie at witherden dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

             Bug #: 56787
           Summary: 4.8.0 Vectorization Regression Compared to 4.7.2
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: freddie@witherden.org


Created attachment 29754
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29754
Test case

When compiling the attached file with GCC 4.8.0 on an AVX capable system the
main loop isn't vectorized.  This is a regression compared with 4.7.2 on the
same system (where the loop is fully vectorized).

I apologize for the length of the test case -- smaller examples do not
reproduce the behaviour in question. 

Output of -save-temps:
gcc-mp-4.8 -v -save-temps -Ofast -march=native -std=c99 -S test.c 
Using built-in specs.
COLLECT_GCC=gcc-mp-4.8
Target: x86_64-apple-darwin12
Configured with: ../gcc-4.8-20130321/configure --prefix=/opt/local
--build=x86_64-apple-darwin12
--enable-languages=c,c++,objc,obj-c++,fortran,java
--libdir=/opt/local/lib/gcc48 --includedir=/opt/local/include/gcc48
--infodir=/opt/local/share/info --mandir=/opt/local/share/man
--datarootdir=/opt/local/share/gcc-4.8 --with-local-prefix=/opt/local
--with-system-zlib --disable-nls --program-suffix=-mp-4.8
--with-gxx-include-dir=/opt/local/include/gcc48/c++/ --with-gmp=/opt/local
--with-mpfr=/opt/local --with-mpc=/opt/local --with-ppl=/opt/local
--with-cloog=/opt/local --enable-cloog-backend=isl
--disable-cloog-version-check --enable-stage1-checking --disable-multilib
--enable-lto --enable-libstdcxx-time --with-as=/opt/local/bin/as
--with-ld=/opt/local/bin/ld --with-ar=/opt/local/bin/ar
--with-bugurl=https://trac.macports.org/newticket --with-pkgversion='MacPorts
gcc48 4.8-20130321_0'
Thread model: posix
gcc version 4.8.0 20130321 (prerelease) (MacPorts gcc48 4.8-20130321_0) 
COLLECT_GCC_OPTIONS='-mmacosx-version-min=10.8.3' '-v' '-save-temps' '-Ofast'
'-march=native' '-std=c99' '-S'
 /opt/local/libexec/gcc/x86_64-apple-darwin12/4.8.0/cc1 -E -quiet -v
-D__DYNAMIC__ test.c -march=corei7-avx -mcx16 -msahf -mno-movbe -maes -mpclmul
-mpopcnt -mno-abm -mno-lwp -mno-fma -mno-fma4 -mno-xop -mno-bmi -mno-bmi2
-mno-tbm -mavx -mno-avx2 -msse4.2 -msse4.1 -mno-lzcnt -mno-rtm -mno-hle
-mno-rdrnd -mno-f16c -mno-fsgsbase -mno-rdseed -mno-prfchw -mno-adx -mfxsr
-mxsave -mxsaveopt --param l1-cache-size=32 --param l1-cache-line-size=64
--param l2-cache-size=3072 -mtune=corei7-avx -fPIC -mmacosx-version-min=10.8.3
-std=c99 -Ofast -fpch-preprocess -o test.i
ignoring nonexistent directory
"/opt/local/lib/gcc48/gcc/x86_64-apple-darwin12/4.8.0/../../../../../x86_64-apple-darwin12/include"
#include "..." search starts here:
#include <...> search starts here:
 /opt/local/lib/gcc48/gcc/x86_64-apple-darwin12/4.8.0/include
 /opt/local/include
 /opt/local/lib/gcc48/gcc/x86_64-apple-darwin12/4.8.0/include-fixed
 /usr/include
 /System/Library/Frameworks
 /Library/Frameworks
End of search list.
COLLECT_GCC_OPTIONS='-mmacosx-version-min=10.8.3' '-v' '-save-temps' '-Ofast'
'-march=native' '-std=c99' '-S'
 /opt/local/libexec/gcc/x86_64-apple-darwin12/4.8.0/cc1 -fpreprocessed test.i
-march=corei7-avx -mcx16 -msahf -mno-movbe -maes -mpclmul -mpopcnt -mno-abm
-mno-lwp -mno-fma -mno-fma4 -mno-xop -mno-bmi -mno-bmi2 -mno-tbm -mavx
-mno-avx2 -msse4.2 -msse4.1 -mno-lzcnt -mno-rtm -mno-hle -mno-rdrnd -mno-f16c
-mno-fsgsbase -mno-rdseed -mno-prfchw -mno-adx -mfxsr -mxsave -mxsaveopt
--param l1-cache-size=32 --param l1-cache-line-size=64 --param
l2-cache-size=3072 -mtune=corei7-avx -fPIC -quiet -dumpbase test.c
-mmacosx-version-min=10.8.3 -auxbase test -Ofast -std=c99 -version -o test.s
GNU C (MacPorts gcc48 4.8-20130321_0) version 4.8.0 20130321 (prerelease)
(x86_64-apple-darwin12)
        compiled by GNU C version 4.8.0 20130321 (prerelease), GMP version
5.0.5, MPFR version 3.1.1-p2, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C (MacPorts gcc48 4.8-20130321_0) version 4.8.0 20130321 (prerelease)
(x86_64-apple-darwin12)
        compiled by GNU C version 4.8.0 20130321 (prerelease), GMP version
5.0.5, MPFR version 3.1.1-p2, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 6291d2010395c7dee8043d72914d31cb
COMPILER_PATH=/opt/local/libexec/gcc/x86_64-apple-darwin12/4.8.0/:/opt/local/libexec/gcc/x86_64-apple-darwin12/4.8.0/:/opt/local/libexec/gcc/x86_64-apple-darwin12/:/opt/local/lib/gcc48/gcc/x86_64-apple-darwin12/4.8.0/:/opt/local/lib/gcc48/gcc/x86_64-apple-darwin12/
LIBRARY_PATH=/opt/local/lib/gcc48/gcc/x86_64-apple-darwin12/4.8.0/:/opt/local/lib/gcc48/gcc/x86_64-apple-darwin12/4.8.0/../../../:/usr/lib/
COLLECT_GCC_OPTIONS='-mmacosx-version-min=10.8.3' '-v' '-save-temps' '-Ofast'
'-march=native' '-std=c99' '-S'

[Bug tree-optimization/56787] [4.8/4.9 Regression] Vectorization fails because of CLOBBER statements

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |missed-optimization
   Last reconfirmed|                            |2013-04-02
          Component|c                           |tree-optimization
                 CC|                            |matz at gcc dot gnu.org
     Ever Confirmed|0                           |1
            Summary|4.8.0 Vectorization         |[4.8/4.9 Regression]
                   |Regression Compared to      |Vectorization fails because
                   |4.7.2                       |of CLOBBER statements
   Target Milestone|---                         |4.8.1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> 2013-04-02 12:02:39 UTC ---
t.c:137: note: not vectorized: no vectype for stmt: u ={v} {CLOBBER};
 scalar_type: float[5]
t.c:137: note: bad data references.
t.c:137: note: ***** Re-trying analysis with vector size 16

[Bug tree-optimization/56787] [4.8/4.9 Regression] Vectorization fails because of CLOBBER statements

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-02 14:50:18 UTC ---
Somewhat reduced testcase:
inline void
bar (const float s[5], float z[3][5])
{
  float a = s[0], b = s[1], c = s[2], d = s[3], e = s[4];
  float f = 1.0f / a;
  float u = f * b, v = f * c, w = f * d;
  float p = 0.4f * (e - 0.5f * (b * u + c * v + d * w));
  z[0][3] = b * w;
  z[1][3] = c * w;
  z[2][3] = d * w + p;
}

void
foo (unsigned long n, const float *__restrict u0,
     const float *__restrict u1, const float *__restrict u2,
     const float *__restrict u3, const float *__restrict u4,
     const float *__restrict s0, const float *__restrict s1,
     const float *__restrict s2, float *__restrict t3,
     float *__restrict t4)
{
  unsigned long i;
  for (i = 0; i < n; i++)
    {
      float u[5], f[3][5];
      u[0] = u0[i]; u[1] = u1[i]; u[2] = u2[i]; u[3] = u3[i]; u[4] = u4[i];
      bar (u, f);
      t3[i] = s0[i] * f[0][3] + s1[i] * f[1][3] + s2[i] * f[2][3];
    }
}

[Bug tree-optimization/56787] [4.8/4.9 Regression] Vectorization fails because of CLOBBER statements

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
The clobbers are dead and useless btw, but we only remove clobbers from
within remove_unused_locals which doesn't run inbetween after IPA inlining
and right before RTL expansion (rightfully so).

Vectorizing without removing the clobbers requires us to honor them at least
for placement of aliasing vectorized stores / loads and also IV adjustments
in case the clobber is a MEM of an SSA name and that is loop variant
(now possible, but not on the 4.8 branch).

So the simplest solution is to discard all clobbers inside the vectorized
loop body.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.9.0
   Target Milestone|4.8.1                       |4.8.2
            Summary|[4.8/4.9 Regression]        |[4.8 Regression]
                   |Vectorization fails because |Vectorization fails because
                   |of CLOBBER statements       |of CLOBBER statements

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Tue May 28 13:36:25 2013
New Revision: 199380

URL: http://gcc.gnu.org/viewcvs?rev=199380&root=gcc&view=rev
Log:
2013-05-28  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/56787
    * tree-vect-data-refs.c (vect_analyze_data_refs): Drop clobbers
    from the list of data references.
    * tree-vect-loop.c (vect_determine_vectorization_factor): Skip
    clobbers.
    (vect_analyze_loop_operations): Likewise.
    (vect_transform_loop): Remove clobbers.

    * gcc.dg/vect/pr56787.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/vect/pr56787.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vect-data-refs.c
    trunk/gcc/tree-vect-loop.c

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[pthaugen at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

Pat Haugen <pthaugen at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pthaugen at gcc dot gnu.org

--- Comment #5 from Pat Haugen <pthaugen at gcc dot gnu.org> ---
The new testcase fails on powerpc64-linux, as can be seen in
http://gcc.gnu.org/ml/gcc-testresults/2013-06/msg00904.html.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[dje at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

David Edelsohn <dje at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dje at gcc dot gnu.org
      Known to work|4.9.0                       |

--- Comment #6 from David Edelsohn <dje at gcc dot gnu.org> ---
The patch fixed x86_64 but the new testcase fails on PPC64.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.8.2                       |4.8.3

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.8.2 has been released.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[ktkachov at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

ktkachov at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ktkachov at gcc dot gnu.org

--- Comment #8 from ktkachov at gcc dot gnu.org ---
Also fails on arm-* btw.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.9.0

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Maybe it works now.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
Author: rguenth
Date: Thu Dec  5 09:20:51 2013
New Revision: 205696

URL: http://gcc.gnu.org/viewcvs?rev=205696&root=gcc&view=rev
Log:
2013-12-05  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/56787
    * gcc.dg/vect/pr56787.c: Adjust to not require vector float
    division.

Modified:
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/vect/pr56787.c

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[ktkachov at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

--- Comment #11 from ktkachov at gcc dot gnu.org ---
(In reply to Richard Biener from comment #10)
> Maybe it works now.

PASSes on arm* now, thanks.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[pthaugen at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

--- Comment #12 from Pat Haugen <pthaugen at gcc dot gnu.org> ---
Working on PowerPC also.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
   Target Milestone|4.8.3                       |4.9.0
      Known to fail|                            |4.8.0, 4.8.3

--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> ---
The patch cannot be backported easily, not going to fix it for 4.8.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.0                       |4.9.1

--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.0 has been released

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.9.1                       |4.9.2

--- Comment #15 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 4.9.1 has been released.

[Bug tree-optimization/56787] [4.8 Regression] Vectorization fails because of CLOBBER statements

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56787

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
      Known to fail|                            |4.8.5

--- Comment #17 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed for 4.9.3.