On Wed, 2024-06-05 at 11:06 +0530, Amol Surati via Gcc-help wrote: > Does this warrant a bug with gcc? There's already a bug report: https://gcc.gnu.org/PR63944. > On Fri, 17 May 2024 at 20:32, Amol Surati <suratiamol@xxxxxxxxx> > wrote: > > > > 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 -- Xi Ruoyao <xry111@xxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University
