[Bug fortran/92956] 'libgomp.fortran/examples-4/async_target-2.f90' offloading compilation regression

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92956

--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #2)
> -Wstringop-overflow is a C-family only option that shouldn't be enabled for
> Fortran.  It took some effort to make it work that way […] I wouldn't be
> surprised if the problem was still unresolved in LTO builds

Well, this uses LTO – but only behind the scenes. When doing offloading (via
OpenACC or OpenMP ["omp target"]), the blocks which are to be run on the device
will be processes by a lto1 compiler for the device target (amdgcn, nvptx), see
https://gcc.gnu.org/wiki/Offloading    

> I don't see this test in my builds or on gcc-testresults and compiling it
> by hand gives the error below. […]
> Fatal Error: Cannot open module file ‘omp_lib.mod’ for reading at (1): No
> such file or directory

I think in order to reproduce Thomas' problem, I fear you need to configure the
compiler for actual offloading. (But see below.)

Still, I do not understand the error message. This file is part of libgomp and
installed along the compiler; in my case, it is in
$INSTALL/lib64/gcc/x86_64-pc-linux-gnu/10.0.0/finclude/ and should be found
automatically when calling 'gfortran'.

 * * *

Regarding a test case, I actually stumbled over a test case this afternoon
which fails without offloading. (There are 22 PASS and this one FAIL.) — I
don't know whether it is your commit, but the message looks very similar. In
any case:

FAIL: gfortran.dg/lto/pr87689 f_lto_pr87689_0.o-f_lto_pr87689_1.o link, -O2
-flto -flto-partition=1to1 -fno-use-linker-plugin

Which fails with:

In function 'MAIN__',
    inlined from 'main' at gcc/testsuite/gfortran.dg/lto/pr87689_0.f:13:0:
gcc/testsuite/gfortran.dg/lto/pr87689_0.f:10: warning: writing 1 byte into a
region of size 0 [-Wstringop-overflow=]
gcc/testsuite/gfortran.dg/lto/pr87689_0.f: In function 'main':
gcc/testsuite/gfortran.dg/lto/pr87689_0.f:7:22: note: at offset 1 to object 'c'
with size 1 declared here

The message is also bogus as one writes a single character to to a len=1
string.