[Bug c/96810] This is a case that gcc shoud not compile successfully, but gcc acts opposite.

["weiwt.fnst at cn dot fujitsu.com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96810

--- Comment #2 from Wei Wentao <weiwt.fnst at cn dot fujitsu.com> ---
> --- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
> >The standard says this is unspecified behavior, but the unspecified behavior
> >happens at runtime, so if the compiler could detect it at compile time, it
> >would need to be at most a warning (if the code is never called, there is no
> >unspecified behavior).  Generally this isn't something that can be detected at
> >compile time, e.g. the target data can be in a different function from target,
> >or there could be target exit data that unmaps it in between and makes it
> >valid, or the fact that the pointer must alias the array could be not known to
> >the compiler, etc.
> >And the testcase is rejected at runtime:
> >libgomp: Trying to map into device [0x7ffc13463cbc..0x7ffc13463d0c) object when
> > [0x7ffc13463cb0..0x7ffc13463cc0) is already mapped 



When I use clang to compile the same case, the compilation fails which is in
line with expectations and is opposite to the result of gcc. The details show
as below:

clang version 11.0.0

clang /.../llvm/build/bin/clang -fopenmp-version=50 -fopenmp
-I/.../common.deb.ompt.optional/include/ Example array_sections.2.c
Example_array_sections.2.c:19:7: error: original storage of expression in data
environment is shared but data environment do not fully contain mapped
expression storage
      A[2] = 0;
      ^
Example_array_sections.2.c:11:30: note: used here
#pragma omp target data map( A[0:4] )
                             ^~~~~~
1 error generated.