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From: "byteslice at airmail dot cc" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/105420] New: Bogus -Warray-bounds with
 non-compile time-constant variable
Date: Thu, 28 Apr 2022 13:21:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105420

            Bug ID: 105420
           Summary: Bogus -Warray-bounds with non-compile time-constant
                    variable
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: byteslice at airmail dot cc
  Target Milestone: ---

Created attachment 52894
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52894&action=3Dedit
Reduced example

On gcc 12.0.1 20220413 (Fedora 36 Beta), with c++ -O1 -fexpensive-optimizat=
ions
-ftree-vrp -Werror=3Darray-bounds, the attachment fails to compile, with the
following message:

<source>: In function 'void Initialize(int)':
<source>:9:53: error: array subscript -1 is below array bounds of 'int [8]'
[-Werror=3Darray-bounds]
    9 |   int phys_core =3D VirtualToPhysicalCoreMap[virt_core];
      |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
<source>:2:5: note: while referencing 'VirtualToPhysicalCoreMap'
    2 | int VirtualToPhysicalCoreMap[8];
      |     ^~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
Compiler returned: 1

virt_core does not have a compile time-constant evaluation, so this warning=
 is
bogus. The bogus warning does not appear in older versions of GCC.

Removing either -fexpensive-optimizations or -ftree-vrp allows compilation =
to
succeed.=