subobject init override

[Amol Surati <suratiamol@gmail.com>]

Hello,

[1] says

"Although any non-initialized subobjects are initialized implicitly, implicit
initialization of a subobject never overrides explicit initialization of the
same subobject if it appeared earlier in the initializer list (choose clang
to observe the correct output)".

There's a sample program attached on the website at [1] around the
statement, and the behaviour clearly differs between gcc and clang.

-----------
This difference is affecting Mesa builds with gcc, because Mesa utilizes
such subobject-init-override patterns. One such instance is within the
function blorp_params_get_clear_kernel_fs listed at [2].

The relevant parts were extracted and built into a small test program,
available at [3] (for gcc) and [4] (for clang)

gcc prints: "" ''
clang prints: "blorp" 'b'
clang does spit out warnings about -Winitializer-overrides before
allowing the compilation to succeed.

According to the cppref website, Mesa's usage is correct, and it is gcc
that's ignoring the fact that the subobject was previously *explicitly*
initialized.

The C spec says:
"The initialization shall occur in initializer list order, each initializer
provided for a particular subobject overriding any previously listed
initializer for the same subobject;170) all subobjects that are not
initialized explicitly are subject to default initialization."

Is there a way to force gcc to behave as clang does?
If not, could you please help determine who exactly is at fault here
and must receive a change/bug request, if needed?

Thank you,
Amol
-----------------------------
[1] https://en.cppreference.com/w/c/language/struct_initialization
[2] https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/intel/blorp/blorp_clear.c?ref_type=heads
[3] https://godbolt.org/z/env53Wq9M
[4] https://godbolt.org/z/8TMfbb5Ef