[Bug c++/83046] ICE in nvptx offloading, C++ compilation of libgomp.oacc-c-c++-common/gang-static-2.c

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83046

--- Comment #4 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
(In reply to Martin Liška from comment #3)
> (In reply to Thomas Schwinge from comment #0)
> > ... starting with r254437 "Instrument function exit with
> > __builtin_unreachable in C++".

> > Obviously, that test case has a "-Wreturn-type mismatch" (which is not
> > diagnosed for C++; see reduced PR83045), and fixing that cures this nvptx
> > offloading ICE.
> 
> Can you please provide steps to reproduce this?

You'll either have to build an offloading compiler, but -- much simpler! -- I
assume it will be sufficient to resolve the issue seen in the
"-foffload=disable" case:

Configure GCC as usual, but add "--enable-offload-targets=nvptx-none=/no/where"
(to generally enable offloading, but without providing an actual nvptx
offloading compiler), build, and then run:

    $ make check-target-libgomp
RUNTESTFLAGS='--target_board=unix\{-foffload=disable\}
{c,c++}.exp=gang-static-2.c'
    [...]
    Running target unix/-foffload=disable
    Using /usr/share/dejagnu/baseboards/unix.exp as board description file for
target.
    Using /usr/share/dejagnu/config/unix.exp as generic interface file for
target.
    Using ../../../../source-gcc/libgomp/testsuite/config/default.exp as
tool-and-target-specific interface file.
    Running ../../../../source-gcc/libgomp/testsuite/libgomp.c/c.exp ...
    Running ../../../../source-gcc/libgomp/testsuite/libgomp.c++/c++.exp ...
    Running ../../../../source-gcc/libgomp/testsuite/libgomp.hsa.c/c.exp ...
    Running ../../../../source-gcc/libgomp/testsuite/libgomp.oacc-c/c.exp ...
    FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/gang-static-2.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0  -O2  execution test
    Running ../../../../source-gcc/libgomp/testsuite/libgomp.oacc-c++/c++.exp
...
    FAIL: libgomp.oacc-c++/../libgomp.oacc-c-c++-common/gang-static-2.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0  -O2  (test for excess errors)

                    === libgomp Summary ===

    # of expected passes            1
    # of unexpected failures        2
    # of unresolved testcases       1
    # of unsupported tests          4
    [...]

Compilation should either succeed (as it still does for C, and did before for
C++), or terminate with a suitable diagnostic (the issue discussed in PR83045
"-Wreturn-type regression in C++").

For "c.exp" the "execution test" FAILs: "libgomp: target function wasn't
mapped" (expected in this special configuration), but for c++.exp you'll see
compilation FAIL with "excess errors":

    /tmp/ccBzwk9H.o:(.gnu.offload_funcs+0x0): undefined reference to
`main._omp_fn.7'
    /tmp/ccBzwk9H.o:(.gnu.offload_funcs+0x8): undefined reference to
`main._omp_fn.6'
    /tmp/ccBzwk9H.o:(.gnu.offload_funcs+0x10): undefined reference to
`main._omp_fn.5'
    /tmp/ccBzwk9H.o:(.gnu.offload_funcs+0x18): undefined reference to
`main._omp_fn.4'
    /tmp/ccBzwk9H.o:(.gnu.offload_funcs+0x20): undefined reference to
`main._omp_fn.3'
    /tmp/ccBzwk9H.o:(.gnu.offload_funcs+0x28): undefined reference to
`main._omp_fn.2'
    /tmp/ccBzwk9H.o:(.gnu.offload_funcs+0x30): undefined reference to
`main._omp_fn.1'
    collect2: error: ld returned 1 exit status
    compiler exited with status 1

(I'll probably not be able to look into that myself in the next few weeks.)