[Bug c/109716] New: bogus stringop-overread "reading 4 bytes from a region of size 0"

[david at ixit dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109716

            Bug ID: 109716
           Summary: bogus stringop-overread "reading 4 bytes from a region
                    of size 0"
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: david at ixit dot cz
  Target Milestone: ---
              Host: x86_64
            Target: x86_64

Compiler: 12.2.0, 13.0.1 20230315 (experimental) [master r13-6680-ga9ae16db8cb]
Sources: https://gitlab.freedesktop.org/mesa/mesa/ main branch, (commit
b59935e2e77ed6ccf210103b028d671ee277a607 )
Command: CC=/usr/lib/gcc-snapshot/bin/gcc CXX=/usr/lib/gcc-snapshot/bin/g++
meson setup builddir-snapshot -D libdir=lib -D buildtype=release -D
build-tests=false -D enable-glcpp-tests=false -D libunwind=enabled -D glx=dri
-D gbm=enabled -D egl=enabled -D platforms=x11,wayland -D dri3=enabled -D
gallium-extra-hud=true -D gallium-vdpau=disabled -D gallium-omx=disabled -D
gallium-va=disabled -D gallium-xa=disabled -D gallium-nine=false -D
gallium-opencl=disabled -D gallium-rusticl=false -D llvm=enabled -D
gallium-drivers=r300,i915,iris,swrast -D vulkan-drivers=panfrost -D
video-codecs=h264dec,h264enc,h265dec,h265enc -D spirv-to-dxil=false -D
osmesa=true -D intel-clc=disabled -D imagination-srv=false
```
[1447/1646] Compiling C object
src/gallium/drivers/r300/libr300.a.p/r300_state_derived.c.o
../src/gallium/drivers/r300/r300_state_derived.c: In function
'r300_get_border_color':
../src/gallium/drivers/r300/r300_state_derived.c:676:5: warning:
'util_format_unswizzle_4f' reading 4 bytes from a region of size 0
[-Wstringop-overread]
  676 |     util_format_unswizzle_4f(border_swizzled, border, desc->swizzle);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../src/gallium/drivers/r300/r300_state_derived.c:676:5: note: referencing
argument 3 of type 'const unsigned char[4]'
In file included from ../src/compiler/nir/nir.h:43,
                 from ../src/gallium/auxiliary/draw/draw_context.h:42,
                 from ../src/gallium/drivers/r300/r300_state_derived.c:24:
../src/util/format/u_format.h:1684:6: note: in a call to function
'util_format_unswizzle_4f'
 1684 | void util_format_unswizzle_4f(float *dst, const float *src,
      |      ^~~~~~~~~~~~~~~~~~~~~~~~
```

Our project bug: https://gitlab.freedesktop.org/mesa/mesa/-/issues/8651