https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109934
Fangrui Song <maskray at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |maskray at gcc dot gnu.org
--- Comment #8 from Fangrui Song <maskray at gcc dot gnu.org> ---
(In reply to GCC Commits from comment #6)
> The releases/gcc-13 branch has been updated by Sam James
> <sja...@gcc.gnu.org>:
>
> https://gcc.gnu.org/g:a987affa2b10cd8a0b1d244d9f010746837e031c
>
> commit r13-9114-ga987affa2b10cd8a0b1d244d9f010746837e031c
> Author: Aldy Hernandez <al...@redhat.com>
> Date: Tue May 23 12:34:45 2023 +0200
>
> Remove buggy special case in irange::invert [PR109934].
>
> This patch removes a buggy special case in irange::invert which seems
> to have been broken for a while, and probably never triggered because
> the legacy code was handled elsewhere, and the non-legacy code was
> using an int_range_max of int_range<255> which made it extremely
> likely for num_ranges == 255. However, with auto-resizing ranges,
> int_range_max will start off at 3 and can hit this bogus code in the
> unswitching code.
>
> PR tree-optimization/109934
>
> gcc/ChangeLog:
>
> * value-range.cc (irange::invert): Remove buggy special case.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/pr109934.c: New test.
>
> (cherry picked from commit 8d5f050dabbf6dd3b992c3b46661848dbcf30d9e)
This commit in releases/gcc-13 but not in 13.3.0 has resolved a miscompile I've
seen in LLVM llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp.
Worked around in
https://github.com/llvm/llvm-project/commit/6d67794d164ebeedbd287816e1541964fb5d6c99
Requires a -O3 build of llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
(CMAKE_BUILD_TYPE=Release; RelWithDebInfo uses -O2 and doesn't reproduce)
```
% ninja -C /tmp/out/custom-gcc-13 llc && /tmp/out/custom-gcc-13/bin/llc
llvm/test/CodeGen/X86/2008-08-06-RewriterBug.ll -mtriple=i686
ninja: Entering directory `/tmp/out/custom-gcc-13'
ninja: no work to do.
Unknown immediate size
UNREACHABLE executed at
/home/ray/llvm/llvm/lib/Target/X86/MCTargetDesc/X86BaseInfo.h:904!
```
I am curious when the regression started to happen.
