[Bug c++/110127] New: -fimplicit-constexpr leads to extremely slow and memory intensive compilation

[Bug c++/110127] New: -fimplicit-constexpr leads to extremely slow and memory intensive compilation

[fiesh at zefix dot tv]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110127

            Bug ID: 110127
           Summary: -fimplicit-constexpr leads to extremely slow and
                    memory intensive compilation
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fiesh at zefix dot tv
  Target Milestone: ---

Created attachment 55262
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55262&action=edit
Testcase for slow -fimplicit-constexpr

The attached test case behaves as follows:

% time g++ -std=c++20 -o /dev/null -c u.ii
g++ -std=c++20 -o /dev/null -c u.ii  0.07s user 0.01s system 99% cpu 0.078
total

% time g++ -std=c++20 -o /dev/null -fimplicit-constexpr -c u.ii
g++ -std=c++20 -o /dev/null -fimplicit-constexpr -c u.ii  1637.98s user 41.63s
system 99% cpu 27:59.91 total

The second run also consumes a large amount of memory in the region of 100GB.

I'm a bit stuck on how to reduce this further.

[Bug c++/110127] -fimplicit-constexpr leads to extremely slow and memory intensive compilation

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110127

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-06-05
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=109678
      Known to fail|                            |12.1.0, 12.3.0, 13.1.0
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org
      Known to work|                            |14.0

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Thanks for the bug report, confirmed with GCC 12.1,12.3, 13.1 and the 13
release branch, so not a regression.  On trunk the testcase compiles quickly
ever since r14-409-g4b8d0d4d7fd245 for PR109678.  It seems backporting that
commit to the 13 branch would fix the slowness there too.

[Bug c++/110127] -fimplicit-constexpr leads to extremely slow and memory intensive compilation

[fiesh at zefix dot tv]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110127

--- Comment #2 from fiesh at zefix dot tv ---
Thank you for feedback!

[Bug c++/110127] -fimplicit-constexpr leads to extremely slow and memory intensive compilation

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110127

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |13.3
             Status|NEW                         |RESOLVED

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13.3 after the backport r13-7713-gd3088f0ed25fe7.