[Bug other/99903] New: 32-bit x86 frontends randomly crash while reporting timing on Windows

["izbyshev at ispras dot ru" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99903

            Bug ID: 99903
           Summary: 32-bit x86 frontends randomly crash while reporting
                    timing on Windows
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: izbyshev at ispras dot ru
  Target Milestone: ---
              Host: i686-w64-mingw32
            Target: i686-w64-mingw32
             Build: i686-w64-mingw32

Created attachment 50503
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50503&action=edit
A reproducer

Running cc1 from i686-w64-mingw32-gcc[1] with timing report enabled (e.g.
without `-quiet` or with `-ftime-report`) may randomly crash on Windows.

A reproducer script is attached (tested on two Windows 10 1909 x64 machines).
The time to reproduce varied from seconds to half an hour. Running multiple cc1
to increase load appears to help, but is not required; just running a single
cc1 in a loop is enough too. The crash manifests as silent exit with code
3221225477 (0xc0000005; EXCEPTION_ACCESS_VIOLATION). Debugging showed the
following.

The eventual crash is actually a nested one. It happens at [2] while reporting
an ICE because `context->printer` is NULL (which, by itself, looks like a
separate bug).

The initial crash is triggered by `gcc_unreachable()` in
`timer::validate_phases()`[3].

#0  0x0125be91 in pp_format(pretty_printer*, text_info*) ()
#1  0x0125146b in diagnostic_report_diagnostic(diagnostic_context*,
diagnostic_info*) ()
#2  0x01251bd7 in diagnostic_impl(rich_location*, diagnostic_metadata const*,
int, char const*, char**, diagnostic_t)
    ()
#3  0x012521b8 in internal_error(char const*, ...) ()
#4  0x01528a96 in fancy_abort(char const*, int, char const*) ()
#5  0x014f9e9c in timer::validate_phases(_iobuf*) const [clone .cold] ()
#6  0x009400d3 in timer::print(_iobuf*) ()
#7  0x00942422 in toplev::~toplev() ()
#8  0x01526003 in main ()

And `gcc_unreachable()` is reached because `phase_user > total->user *
tolerance` is true. GCC doesn't print anything when run from `repro.py` because
of output buffering, but I extracted one message from memory:

Timing error: total of phase timers exceeds total time.
user    1.734723475976807094e-18 > 8.673617379884035472e-19

I couldn't reproduce this with 64-bit x86 GCC.

[1]
https://github.com/msys2/MINGW-packages/tree/5d82e17a56a3216a54dbb5924b92c96284ae5c97/mingw-w64-gcc
[2]
https://gcc.gnu.org/git?p=gcc.git;a=blob;f=gcc/diagnostic.c;h=ed52bc03d17afa2d7ac3419beb73e8f59b6f392b;hb=releases/gcc-10.2.0#l1077
[3]
https://gcc.gnu.org/git?p=gcc.git;a=blob;f=gcc/timevar.c;h=a3a882d32040db6503260ab51ee4bf338c4aa2b5;hb=releases/gcc-10.2.0#l628