[Bug tree-optimization/107195] New: wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu

[Bug tree-optimization/107195] New: wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu

[zhendong.su at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

            Bug ID: 107195
           Summary: wrong code with "-O1 -fno-tree-ccp" on
                    x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhendong.su at inf dot ethz.ch
  Target Milestone: ---

This doesn't fail with 12.2, so looks like a recent regression. Perhaps related
to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107172 or
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107194? 

Compiler Explorer: https://godbolt.org/z/94E6r84ra

[524] % gcctk -v
Using built-in specs.
COLLECT_GCC=gcctk
COLLECT_LTO_WRAPPER=/local/suz-local/software/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/13.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--enable-checking=yes --prefix=/local/suz-local/software/local/gcc-trunk
--enable-sanitizers --enable-languages=c,c++ --disable-werror --enable-multilib
--with-system-zlib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.0.0 20221009 (experimental) [master r13-3180-ge95e91eccd0] (GCC) 
[525] % 
[525] % gcctk -O1 small.c; ./a.out
[526] % 
[526] % gcctk -O1 -fno-tree-ccp small.c
[527] % ./a.out
Aborted
[528] % 
[528] % cat small.c
int a, b;
int main() {
  int c = 0;
  if (a)
    c = 1;
  c = 1 & (a && c) && b;
  if (a) {
    b = c;
    __builtin_abort ();
  }
  return 0;
}

[Bug tree-optimization/107195] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It worked with:
gcc version 13.0.0 20221008 (experimental)
(Compiler-Explorer-Build-gcc-705ed42a1ad950860f46c51216ff69dbe0f4857a-binutils-2.38) 

So definitely a recent regression.

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|wrong code with "-O1        |[13 Regression] wrong code
                   |-fno-tree-ccp" on           |with "-O1 -fno-tree-ccp" on
                   |x86_64-linux-gnu            |x86_64-linux-gnu
      Known to work|                            |12.2.0
   Target Milestone|---                         |13.0
           Keywords|                            |wrong-code

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It is more recent than the patch which exposed PR 107172 though.

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-10-10
           Keywords|                            |needs-reduction
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
            Version|unknown                     |13.0

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-reduction             |
                 CC|                            |aldyh at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=107194
            Summary|[13 Regression] wrong code  |[13 Regression] wrong code
                   |with "-O1 -fno-tree-ccp" on |with "-O1 -fno-tree-ccp" on
                   |x86_64-linux-gnu            |x86_64-linux-gnu since
                   |                            |r13-3090-gdf4c584c567263fd

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
Also started with r13-3090-gdf4c584c567263fd.

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

--- Comment #4 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
*** Bug 107194 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amacleod at redhat dot com

--- Comment #5 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
When solving 0 = _15 & 1, we calculate _15 as:

        [irange] int [-INF, -2][0, +INF] NONZERO 0xfffffffe

The known value of _15 is [0, 1] NONZERO 0x1 which is intersected with
the above, yielding:

        [0, 1] NONZERO 0x0

The final nonzero bits tells us the range is 0, but the range is still
[0, 1], which causes logical_combine to assume the range is not-zero,
as irange::zero_p() ignores the nonzero bits.

I think we should just normalize a nonzero mask of 0 to [0, 0] at
creation, thus avoiding all this.

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

--- Comment #6 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
Created attachment 53687
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53687&action=edit
untested patch

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Aldy Hernandez <aldyh@gcc.gnu.org>:

https://gcc.gnu.org/g:c4d15dddf6b9eacb36f535807ad2ee364af46e04

commit r13-3217-gc4d15dddf6b9eacb36f535807ad2ee364af46e04
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Mon Oct 10 20:42:10 2022 +0200

    [PR107195] Set range to zero when nonzero mask is 0.

    When solving 0 = _15 & 1, we calculate _15 as:

            [irange] int [-INF, -2][0, +INF] NONZERO 0xfffffffe

    The known value of _15 is [0, 1] NONZERO 0x1 which is intersected with
    the above, yielding:

            [0, 1] NONZERO 0x0

    This eventually gets copied to a _Bool [0, 1] NONZERO 0x0.

    This is problematic because here we have a bool which is zero, but
    returns false for irange::zero_p, since the latter does not look at
    nonzero bits.  This causes logical_combine to assume the range is
    not-zero, and all hell breaks loose.

    I think we should just normalize a nonzero mask of 0 to [0, 0] at
    creation, thus avoiding all this.

            PR tree-optimization/107195

    gcc/ChangeLog:

            * value-range.cc (irange::set_range_from_nonzero_bits): Set range
            to [0,0] when nonzero mask is 0.

    gcc/testsuite/ChangeLog:

            * gcc.dg/tree-ssa/pr107195-1.c: New test.
            * gcc.dg/tree-ssa/pr107195-2.c: New test.

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #8 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
fixed

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vsevolod.livinskiy at gmail dot co
                   |                            |m

--- Comment #9 from Martin Liška <marxin at gcc dot gnu.org> ---
*** Bug 107228 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Thomas Schwinge <tschwinge@gcc.gnu.org>:

https://gcc.gnu.org/g:436c4a210e8ff936063579dab3641632c06c8a7d

commit r13-3433-g436c4a210e8ff936063579dab3641632c06c8a7d
Author: Thomas Schwinge <thomas@codesourcery.com>
Date:   Mon Oct 17 09:10:03 2022 +0200

    Add 'gcc.dg/tree-ssa/pr107195-3.c' [PR107195]

    ... to display optimization performed as of recent
    commit r13-3217-gc4d15dddf6b9eacb36f535807ad2ee364af46e04
    "[PR107195] Set range to zero when nonzero mask is 0".

            PR tree-optimization/107195
            gcc/testsuite/
            * gcc.dg/tree-ssa/pr107195-3.c: New.

[Bug tree-optimization/107195] [13 Regression] wrong code with "-O1 -fno-tree-ccp" on x86_64-linux-gnu since r13-3090-gdf4c584c567263fd

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107195

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Thomas Schwinge <tschwinge@gcc.gnu.org>:

https://gcc.gnu.org/g:a9de836c2b22f878cff592b96e11c1b95d4d36ee

commit r13-3434-ga9de836c2b22f878cff592b96e11c1b95d4d36ee
Author: Thomas Schwinge <thomas@codesourcery.com>
Date:   Sun Oct 16 00:07:20 2022 +0200

    Restore 'libgomp.oacc-c-c++-common/nvptx-sese-1.c' SESE regions checking
[PR107195, PR107344]

    That is, adjust for optimization introduced with recent
    commit r13-3217-gc4d15dddf6b9eacb36f535807ad2ee364af46e04
    "[PR107195] Set range to zero when nonzero mask is 0", where GCC now
    understands that after 'r *= 2;', 'r & 1' will never hold here, and thus
    transforms/optimizes/"disturbs" the original code such that GCC/nvptx's
later
    "Neuter whole SESE regions" optimization no longer is applicable to it:

        UNSUPPORTED: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O0
        PASS: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2  (test
for excess errors)
        PASS: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2 
execution test
        [-PASS:-]{+FAIL:+}
libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2  
scan-nvptx-none-offload-rtl-dump mach "SESE regions:.*
[0-9]+{[0-9]+->[0-9]+(\\.[0-9]+)+}"

    Same for C++.

    It's unclear to me if this is an actual "problem", which optimization is
"more
    important", so I've filed PR107344 "GCC/nvptx SESE region optimization" to
    capture this question, and here restore what we intend to be testing (to my
    understanding) in 'libgomp.oacc-c-c++-common/nvptx-sese-1.c'.

            PR tree-optimization/107195
            PR target/107344
            libgomp/
            * testsuite/libgomp.oacc-c-c++-common/nvptx-sese-1.c: Restore SESE
            regions checking.