[Bug tree-optimization/113136] New: [14 regression] ICE when building Perl

[Bug tree-optimization/113136] New: [14 regression] ICE when building Perl

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

            Bug ID: 113136
           Summary: [14 regression] ICE when building Perl
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sjames at gcc dot gnu.org
                CC: tnfchris at gcc dot gnu.org
  Target Milestone: ---

I'll file bugs for each of these I hit, and then even if they're dupes, we get
more test cases out of it, so...

Hit when building perl-5.38.

native=znver2:
```
x86_64-pc-linux-gnu-gcc -c -DPERL_CORE -O3 -pipe -march=native
-fdiagnostics-color=always -Waddress -Warray-bounds -Wfree-nonheap-object
-Wint-to-pointer-cast -Wmain -Wnonnull -Wodr -Wreturn-type
-Wsizeof-pointer-memaccess -Wstrict-aliasing -Wstring-compare -Wuninitialized
-Wvarargs -fno-strict-aliasing -DNO_PERL_RAND_SEED -fwrapv -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64 -std=c99 -O3 -pipe -march=native
-fdiagnostics-color=always -Waddress -Warray-bounds -Wfree-nonheap-object
-Wint-to-pointer-cast -Wmain -Wnonnull -Wodr -Wreturn-type
-Wsizeof-pointer-memaccess -Wstrict-aliasing -Wstring-compare -Wuninitialized
-Wvarargs -fno-strict-aliasing -Wall -Werror=pointer-arith -Werror=vla -Wextra
-Wno-long-long -Wno-declaration-after-statement -Wc++-compat -Wwrite-strings
-fPIC toke.c
toke.c: In function ‘yyl_try’:
toke.c:8984:1: error: definition in block 413 does not dominate use in block
420
 8984 | yyl_try(pTHX_ char *s)
      | ^~~~~~~
for SSA_NAME: vect__256.7602_2087 in statement:
vect__256.7602_2086 = PHI <vect__256.7602_2087(420)>
PHI argument
vect__256.7602_2087
for PHI node
vect__256.7602_2086 = PHI <vect__256.7602_2087(420)>
during GIMPLE pass: vect
toke.c:8984:1: internal compiler error: verify_ssa failed
0x55bcb952ea88 verify_ssa(bool, bool)
       
/usr/src/debug/sys-devel/gcc-14.0.0.9999/gcc-14.0.0.9999/gcc/tree-ssa.cc:1203
0x55bcb9130a9d execute_function_todo
       
/usr/src/debug/sys-devel/gcc-14.0.0.9999/gcc-14.0.0.9999/gcc/passes.cc:2095
0x55bcb9130f30 execute_todo
       
/usr/src/debug/sys-devel/gcc-14.0.0.9999/gcc-14.0.0.9999/gcc/passes.cc:2142
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://bugs.gentoo.org/> for instructions.
make: *** [makefile:260: toke.o] Error 1
```

```
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/14/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with:
/var/tmp/portage/sys-devel/gcc-14.0.0.9999/work/gcc-14.0.0.9999/configure
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr
--bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/14
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/14/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/14
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/14/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/14/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/14/include/g++-v14
--disable-silent-rules --disable-dependency-tracking
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/14/python
--enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt
--disable-werror --with-system-zlib --enable-nls --without-included-gettext
--disable-libunwind-exceptions --enable-checking=yes,extra,rtl,df
--with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 14.0.0 p,
commit 2250dc0cc8c46999ad1c1d79b9aeed9056459bb6' --with-gcc-major-version-only
--enable-libstdcxx-time --enable-lto --disable-libstdcxx-pch --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
--enable-multilib --with-multilib-list=m32,m64 --disable-fixed-point
--enable-targets=all --enable-libgomp --disable-libssp --disable-libada
--disable-cet --disable-systemtap --disable-valgrind-annotations
--disable-vtable-verify --disable-libvtv --with-zstd --without-isl
--enable-default-pie --enable-host-pie --disable-host-bind-now
--enable-default-ssp
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.0.0 20231225 (experimental)
0beeddd6b1b1cb41104c4df925323e8fc0437ba8 (Gentoo 14.0.0 p, commit
2250dc0cc8c46999ad1c1d79b9aeed9056459bb6)
```

'gcc -c ./toke.i -O3 -march=znver2' is enough to reproduce.

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #1 from Sam James <sjames at gcc dot gnu.org> ---
Created attachment 56933
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56933&action=edit
toke.i.xz

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #2 from Sam James <sjames at gcc dot gnu.org> ---
Created attachment 56935
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=56935&action=edit
reduced.i

Reduced.

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #3 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
This shouldn't have vectorized as outer-loop vectorization isn't supported. In
addition switch statements are not supported, but I guess the nested if
confused the code doing the analysis.

Will fix when back at work tomorrow.

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

Tamar Christina <tnfchris at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
   Target Milestone|---                         |14.0
   Last reconfirmed|                            |2023-12-26
           Assignee|unassigned at gcc dot gnu.org      |tnfchris at gcc dot gnu.org

--- Comment #4 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Thanks for the report and testcases.

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #5 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
hmm I seem unable to reproduce this one..

tnfchris@x86_64 ~/gcc-peak> ./install/bin/gcc  -O3 pr113136.c -c -march=znver2
pr113136.c: In function ‘yyl_try_d’:
pr113136.c:16:14: warning: comparison of distinct pointer types lacks a cast
[-Wcompare-distinct-pointer-types]
   16 |     while (s < yyl_try_d)
      |              ^
tnfchris@x86_64 ~/gcc-peak> ./install/bin/gcc  -O3 ~/toke.i  -c -march=znver2
tnfchris@x86_64 ~/gcc-peak> cat pr113136.c
enum { XSTATE } S_incline();
char PL_in_eval, PL_parser_6;
int PL_parser_1, PL_parser_0, PL_parser_7;
short PL_parser_8;
_Bool yyl_eol_needs_semicolon() {
  if (PL_parser_6 || PL_in_eval && PL_parser_7 && PL_parser_8)
    if (PL_parser_0 && PL_parser_1)
      return 0;
}
void yyl_try_d(char *s) {
retry:
  switch (*s) {
  case '\n':
    yyl_eol_needs_semicolon(&s);
    s++;
    while (s < yyl_try_d)
      if (*s++)
        S_incline();
    goto retry;
  }
}

tnfchris@x86_64 ~/gcc-peak> ./install/bin/gcc -v
Using built-in specs.
COLLECT_GCC=./install/bin/gcc
COLLECT_LTO_WRAPPER=/home/tnfchris/gcc-peak/install/libexec/gcc/x86_64-pc-linux-gnu/14.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /home/tnfchris/gcc-dsg/configure
--prefix=/home/tnfchris/gcc-peak/install --enable-checking=release :
(reconfigured) /home/tnfchris/gcc-dsg/configure
--prefix=/home/tnfchris/gcc-peak/install --enable-checking=release
--enable-languages=c,c++,fortran,lto,objc --no-create --no-recursion
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.0.0 20231227 (experimental) (GCC)

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #6 from Sam James <sjames at gcc dot gnu.org> ---
Can you try with --enable-checking=yes,rtl,extra? I can reproduce this on
godbolt too: https://godbolt.org/z/56r9ejMn5.

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #7 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Sam James from comment #6)
> Can you try with --enable-checking=yes,rtl,extra? I can reproduce this on
> godbolt too: https://godbolt.org/z/56r9ejMn5.

trying with that.. from the dump on godbolt it looks like the live value was
materialized in the wrong exit.

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #8 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Thanks, was able to reproduce with `--enable-checking=yes,rtl,extra`.

The issue seems to be that the value is unused, and we were relying on DSE
removing such statement. but with --enable-checking=yes,rtl,extra the extra
verification is done before we can remove the dead statements on these inverted
loops.

That's why it doesn't fail without and produces the right code.

So it looks like this is the same bug as
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113137 and the fix for that should
fix this.  It looks like for these inverted loops, even though none of the
values are used, I have to maintain the virtual phis.

I'll keep the two separate for now..

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #9 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Patch submitted

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

--- Comment #10 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tamar Christina <tnfchris@gcc.gnu.org>:

https://gcc.gnu.org/g:411de96dbf2bdafc7a90ebbfc63e68afd6388d29

commit r14-7195-g411de96dbf2bdafc7a90ebbfc63e68afd6388d29
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Fri Jan 12 15:25:34 2024 +0000

    middle-end: maintain LCSSA form when peeled vector iterations have virtual
operands

    This patch fixes several interconnected issues.

    1. When picking an exit we wanted to check for niter_desc.may_be_zero not
true.
       i.e. we want to pick an exit which we know will iterate at least once.
       However niter_desc.may_be_zero is not a boolean.  It is a tree that
encodes
       a boolean value.  !niter_desc.may_be_zero is just checking if we have
some
       information, not what the information is.  This leads us to pick a more
       difficult to vectorize exit more often than we should.

    2. Because we had this bug, we used to pick an alternative exit much more
ofthen
       which showed one issue, when the loop accesses memory and we "invert it"
we
       would corrupt the VUSE chain.  This is because on an peeled vector
iteration
       every exit restarts the loop (i.e. they're all early) BUT since we may
have
       performed a store, the vUSE would need to be updated.  This version
maintains
       virtual PHIs correctly in these cases.   Note that we can't simply
remove all
       of them and recreate them because we need the PHI nodes still in the
right
       order for if skip_vector.

    3. Since we're moving the stores to a safe location I don't think we
actually
       need to analyze whether the store is in range of the memref,  because if
we
       ever get there, we know that the loads must be in range, and if the
loads are
       in range and we get to the store we know the early breaks were not taken
and
       so the scalar loop would have done the VF stores too.

    4. Instead of searching for where to move stores to, they should always be
in
       exit belonging to the latch.  We can only ever delay stores and even if
we
       pick a different exit than the latch one as the main one, effects still
       happen in program order when vectorized.  If we don't move the stores to
the
       latch exit but instead to whever we pick as the "main" exit then we can
       perform incorrect memory accesses (luckily these are trapped by
verify_ssa).

    5. We only used to analyze loads inside the same BB as an early break, and
also
       we'd never analyze the ones inside the block where we'd be moving memory
       references to.  This is obviously bogus and to fix it this patch splits
apart
       the two constraints.  We first validate that all load memory references
are
       in bounds and only after that do we perform the alias checks for the
writes.
       This makes the code simpler to understand and more trivially correct.

    gcc/ChangeLog:

            PR tree-optimization/113137
            PR tree-optimization/113136
            PR tree-optimization/113172
            PR tree-optimization/113178
            * tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg):
            Maintain PHIs on inverted loops.
            (vect_do_peeling): Maintain virtual PHIs on inverted loops.
            * tree-vect-loop.cc (vec_init_loop_exit_info): Pick exit closes to
            latch.
            (vect_create_loop_vinfo): Record all conds instead of only alt
ones.

    gcc/testsuite/ChangeLog:

            PR tree-optimization/113137
            PR tree-optimization/113136
            PR tree-optimization/113172
            PR tree-optimization/113178
            * g++.dg/vect/vect-early-break_4-pr113137.cc: New test.
            * g++.dg/vect/vect-early-break_5-pr113137.cc: New test.
            * gcc.dg/vect/vect-early-break_95-pr113137.c: New test.
            * gcc.dg/vect/vect-early-break_96-pr113136.c: New test.
            * gcc.dg/vect/vect-early-break_97-pr113172.c: New test.

[Bug tree-optimization/113136] [14 regression] ICE when building Perl

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113136

Tamar Christina <tnfchris at gcc dot gnu.org> changed:

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

--- Comment #11 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Fixed. Thanks for the report and let me know if there's something still broken.