[Bug tree-optimization/106247] GCC12 warning in Eigen: array subscript is partly outside array bounds

["skunk at iskunk dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106247

Daniel Richard G. <skunk at iskunk dot org> changed:

           What    |Removed                     |Added
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                 CC|                            |skunk at iskunk dot org

--- Comment #4 from Daniel Richard G. <skunk at iskunk dot org> ---
I am seeing what may be the same issue in a different context.

This is occurring in a proprietary C source codebase newly being compiled with
12.1.0, and unfortunately the problem goes away if I attempt to cut it down to
a minimal test case. Nevertheless, the actual issue is quite simple, and IMO
clear-cut.

(some names edited to protect the guilty)

In file included from /usr/include/string.h:375,
                 from foo.c:7:
In function 'function3',
    inlined from 'function2' at foo.c:1206:5,
    inlined from 'function1' at foo.c:2840:7:
foo.c:415:3: error: array subscript 'union <anonymous>[1]' is partly outside
array bounds of 'unsigned char[5]' [-Werror=array-bounds]
  415 |   memset(constraints,0,sizeof(char)*NB_CONSTRAINTS);
      |   ^~~~~~
foo.c: In function 'function1':
foo.c:380:17: note: at offset 4 into object 'constraints' of size 5
  380 |   unsigned char constraints[NB_CONSTRAINTS];
      |                 ^~~~~~~~
cc1: all warnings being treated as errors


Curiously enough, I only see this issue in an i686 build. I don't get it on
x86-64. (Dropping -march=i686 does not help.)