[Bug debug/106955] New: [13 Regression] '-fcompare-debug' failure w/ -std=c++20 -O1 -ftree-parallelize-loops=2 -fno-ipa-sra --param ggc-min-expand=55

[asolokha at gmx dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106955

            Bug ID: 106955
           Summary: [13 Regression] '-fcompare-debug' failure w/
                    -std=c++20 -O1 -ftree-parallelize-loops=2 -fno-ipa-sra
                    --param ggc-min-expand=55
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: compare-debug-failure
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

Created attachment 53582
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53582&action=edit
gkd diff

g++ 13.0.0 20220911 snapshot (g:0ea5e3f4542832b8da016b152695e64a2a386309) fails
-fcompare-debug check when compiling the following testcase, reduced from
test/std/containers/sequences/forwardlist/forwardlist.ops/sort.pass.cpp from
the libc++ 14.0.6 test suite, w/ -std=c++20 -O1 -ftree-parallelize-loops=2
-fno-ipa-sra --param ggc-min-expand=55:

#include <forward_list>
#include <iterator>
#include <algorithm>
#include <vector>

void
test_stable ()
{
  std::vector<int> v;

  for (int i = 0; i < 1000; ++i)
    v.push_back (i);

  for (int i = 0; i < 1000; ++i)
    v[i] = i;
}

% g++-13.0.0 -std=c++20 -O1 -fcompare-debug -ftree-parallelize-loops=2
-fno-ipa-sra --param ggc-min-expand=55 -c dfptqjrz.cpp
g++-13.0.0: error: dfptqjrz.cpp: '-fcompare-debug' failure

gkd diff attached.

Preprocessed testcase is still being reduced, currently at
06:43:08 INFO (66.7%, 468334 bytes, 7781 lines)
I'll post it here once the reducer yields something meaningful under several
kilobytes in size.