[Bug c/110115] New: Wrong code at -O1 on x86_64-linux-gnu

[Bug c/110115] New: Wrong code at -O1 on x86_64-linux-gnu

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

            Bug ID: 110115
           Summary: Wrong code at -O1 on x86_64-linux-gnu
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
  Target Milestone: ---

gcc at -O1 emits the wrong code. This seems to be a long latent bug.

Compiler explorer: https://godbolt.org/z/3h4TYEYjW

$ cat a.c
int a;
char b;
static int c(char *e, int f) {
  int d = 0;
  for (; d < f; d++)
    e[d] = 0;
  return d;
}
int g(char e, int f) {
  char h[20];
  int i = c(h, f);
  return i;
}
int j() {
  switch (a) {
  case 'f':
    return 0;
  default:
    return ~0;
  }
}
int main() {
  {
    char *k[3];
    int d = 0;
    for (; g(8, 15) - 15 + d < 1; d++)
      k[j()+1] = &b;
    *k[0] = -*k[0];
  }
}
$
$ gcc-tk -O0 a.c && ./a.out
$
$ gcc-tk -O1 a.c && ./a.out
Segmentation fault
$
$ gcc-tk -fsanitize=address,undefined a.c && ./a.out
$
$ gcc-tk -v
Using built-in specs.
COLLECT_GCC=gcc-tk
COLLECT_LTO_WRAPPER=/zdata/shaoli/compilers/ccbuilder-compilers/gcc-8d5f050dabbf6dd3b992c3b46661848dbcf30d9e/libexec/gcc/x86_64-pc-linux-gnu/14.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
--prefix=/zdata/shaoli/compilers/ccbuilder-compilers/gcc-8d5f050dabbf6dd3b992c3b46661848dbcf30d9e
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230523 (experimental) (GCC)
$

[Bug c/110115] Wrong code at -O1 on x86_64-linux-gnu

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Partition 0: size 24 align 16
        k       h

That is definitely wrong.

[Bug middle-end/110115] Wrong code at -O1 on x86_64-linux-gnu

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
          Component|c                           |middle-end
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=103006

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Most likely another dup of bug 103006.

[Bug middle-end/110115] Wrong code at -O1 on x86_64-linux-gnu

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=90348

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Most likely another dup of bug 103006.

Or rather PR 90348.

[Bug middle-end/110115] Wrong code at -O1 on x86_64-linux-gnu

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
And yes -fstack-reuse=none fixes the issue.

[Bug middle-end/110115] Wrong code at -O1 on x86_64-linux-gnu

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

--- Comment #5 from Shaohua Li <shaohua.li at inf dot ethz.ch> ---
I tried to bisect this case and I bisected it to r0-2686-gd119f34c952

[Bug middle-end/110115] [11/12/13/14 Regression] Wrong code at -O1 on x86_64-linux-gnu

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-12-18
      Known to fail|                            |11.1.0
            Summary|Wrong code at -O1 on        |[11/12/13/14 Regression]
                   |x86_64-linux-gnu            |Wrong code at -O1 on
                   |                            |x86_64-linux-gnu
   Target Milestone|---                         |11.5
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |10.1.0

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug middle-end/110115] [11/12/13/14 Regression] Wrong code at -O1 on x86_64-linux-gnu

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:1251d3957de04dc9b023a23c09400217e13deadb

commit r14-7274-g1251d3957de04dc9b023a23c09400217e13deadb
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jan 16 11:49:34 2024 +0100

    cfgexpand: Workaround CSE of ADDR_EXPRs in VAR_DECL partitioning [PR113372]

    The following patch adds a quick workaround to bugs in VAR_DECL
    partitioning.
    The problem is that there is no dependency between ADDR_EXPRs of local
    decls and CLOBBERs of those vars, so VN can CSE uses of ADDR_EXPRs
    (including ivopts integral variants thereof), which can break
    add_scope_conflicts discovery of what variables are actually used
    in certain region.
    E.g. we can have
      ivtmp.40_3 = (unsigned long) &MEM <unsigned long[100]> [(void *)&bitint.6
+ 8B];
    ...
      uses of ivtmp.40_3
    ...
      bitint.6 ={v} {CLOBBER(eos)};
    ...
      ivtmp.28_43 = (unsigned long) &MEM <unsigned long[100]> [(void
*)&bitint.6 + 8B];
    ...
      uses of ivtmp.28_43
    before VN (such as dom3), which the add_scope_conflicts code identifies as
2
    independent uses of bitint.6 variable (which is correct), but then VN
    determines ivtmp.28_43 is the same as ivtmp.40_3 and just uses ivtmp.40_3
    even in the second region; at that point add_scope_conflict thinks the
    bitint.6 variable is not used in that region anymore.

    The following patch does a simple single def-stmt check for such ADDR_EXPRs
    (rather than say trying to do a full propagation of what SSA_NAMEs can
    contain ADDR_EXPRs of local variables), which seems to workaround all 4
PRs.

    In addition to this patch I've used the attached one to gather statistics
    on the total size of all variable partitions in a function and seems
besides
    the new testcases nothing is really affected compared to no patch (I've
    actually just modified the patch to == OMP_SCAN instead of == ADDR_EXPR, so
    it looks the same except that it never triggers).  The comparison wasn't
    perfect because I've only gathered BITS_PER_WORD, main_input_filename (did
    some replacement of build directories and /tmp/ccXXXXXX names of LTO to
make
    it more similar between the two bootstraps/regtests), current_function_name
    and the total size of all variable partitions if any, because I didn't
    record e.g. the optimization options and so e.g. torture tests which
iterate
    over options could have different partition sizes even in one compiler when
    BITS_PER_WORD, main_input_filename and current_function_name are all equal.
    So had to write an awk script to check if the first triple in the second
    build appeared in the first one and the quadruple in the second build
    appeared in the first one too, otherwise print result and that only
    triggered in the new tests.
    Also, the cc1plus binary according to objdump -dr is identical between the
    two builds except for the ADDR_EXPR vs. OMP_SCAN constant in the two spots.

    2024-01-16  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/113372
            PR middle-end/90348
            PR middle-end/110115
            PR middle-end/111422
            * cfgexpand.cc (add_scope_conflicts_2): New function.
            (add_scope_conflicts_1): Use it.

            * gcc.dg/torture/bitint-49.c: New test.
            * gcc.c-torture/execute/pr90348.c: New test.
            * gcc.c-torture/execute/pr110115.c: New test.
            * gcc.c-torture/execute/pr111422.c: New test.

[Bug middle-end/110115] [11/12/13/14 Regression] Wrong code at -O1 on x86_64-linux-gnu

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:432708c306838fe1444da0df7d629a60468c0c73

commit r13-8383-g432708c306838fe1444da0df7d629a60468c0c73
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jan 16 11:49:34 2024 +0100

    cfgexpand: Workaround CSE of ADDR_EXPRs in VAR_DECL partitioning [PR113372]

    The following patch adds a quick workaround to bugs in VAR_DECL
    partitioning.
    The problem is that there is no dependency between ADDR_EXPRs of local
    decls and CLOBBERs of those vars, so VN can CSE uses of ADDR_EXPRs
    (including ivopts integral variants thereof), which can break
    add_scope_conflicts discovery of what variables are actually used
    in certain region.
    E.g. we can have
      ivtmp.40_3 = (unsigned long) &MEM <unsigned long[100]> [(void *)&bitint.6
+ 8B];
    ...
      uses of ivtmp.40_3
    ...
      bitint.6 ={v} {CLOBBER(eos)};
    ...
      ivtmp.28_43 = (unsigned long) &MEM <unsigned long[100]> [(void
*)&bitint.6 + 8B];
    ...
      uses of ivtmp.28_43
    before VN (such as dom3), which the add_scope_conflicts code identifies as
2
    independent uses of bitint.6 variable (which is correct), but then VN
    determines ivtmp.28_43 is the same as ivtmp.40_3 and just uses ivtmp.40_3
    even in the second region; at that point add_scope_conflict thinks the
    bitint.6 variable is not used in that region anymore.

    The following patch does a simple single def-stmt check for such ADDR_EXPRs
    (rather than say trying to do a full propagation of what SSA_NAMEs can
    contain ADDR_EXPRs of local variables), which seems to workaround all 4
PRs.

    In addition to this patch I've used the attached one to gather statistics
    on the total size of all variable partitions in a function and seems
besides
    the new testcases nothing is really affected compared to no patch (I've
    actually just modified the patch to == OMP_SCAN instead of == ADDR_EXPR, so
    it looks the same except that it never triggers).  The comparison wasn't
    perfect because I've only gathered BITS_PER_WORD, main_input_filename (did
    some replacement of build directories and /tmp/ccXXXXXX names of LTO to
make
    it more similar between the two bootstraps/regtests), current_function_name
    and the total size of all variable partitions if any, because I didn't
    record e.g. the optimization options and so e.g. torture tests which
iterate
    over options could have different partition sizes even in one compiler when
    BITS_PER_WORD, main_input_filename and current_function_name are all equal.
    So had to write an awk script to check if the first triple in the second
    build appeared in the first one and the quadruple in the second build
    appeared in the first one too, otherwise print result and that only
    triggered in the new tests.
    Also, the cc1plus binary according to objdump -dr is identical between the
    two builds except for the ADDR_EXPR vs. OMP_SCAN constant in the two spots.

    2024-01-16  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/113372
            PR middle-end/90348
            PR middle-end/110115
            PR middle-end/111422
            * cfgexpand.cc (add_scope_conflicts_2): New function.
            (add_scope_conflicts_1): Use it.

            * gcc.c-torture/execute/pr90348.c: New test.
            * gcc.c-torture/execute/pr110115.c: New test.
            * gcc.c-torture/execute/pr111422.c: New test.

    (cherry picked from commit 1251d3957de04dc9b023a23c09400217e13deadb)

[Bug middle-end/110115] [11/12 Regression] Wrong code at -O1 on x86_64-linux-gnu

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110115

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org
            Summary|[11/12/13/14 Regression]    |[11/12 Regression] Wrong
                   |Wrong code at -O1 on        |code at -O1 on
                   |x86_64-linux-gnu            |x86_64-linux-gnu

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Worked around for GCC 13.3+ and 14+.