[mpich-discuss] gcc 6.0 miscompiles mpich ?

[VandeVondele Joost]

Hi,

when compiling mpich-3.1.2 using gcc trunk (which will be gcc 6.0 in a couple of days/weeks), I noticed mpich gets miscompiled when building with CFLAGS='-O2 -ftree-vectorize -g' (but not with just -O2 -g or -O3 -g).

I believe that the miscompilation happens with the macro MPIDI_Request_create_sreq since a typical trace looks like:

Program received signal SIGSEGV: Segmentation fault - invalid memory reference.

Backtrace for this error:
#0  0x33ac83269f in ???
#1  0x7f3743953d69 in MPIDI_Isend_self
    at src/mpid/ch3/src/mpidi_isend_self.c:34
#2  0x7f374394dfa3 in MPID_Isend
    at src/mpid/ch3/src/mpid_isend.c:55
#3  0x7f374390793a in MPIC_Isend
    at src/mpi/coll/helper_fns.c:646
#4  0x7f37438628c5 in MPIR_Alltoall_intra
    at src/mpi/coll/alltoall.c:520
#5  0x7f374386376e in MPIR_Alltoall
    at src/mpi/coll/alltoall.c:726
#6  0x7f3743863827 in MPIR_Alltoall_impl
    at src/mpi/coll/alltoall.c:761
#7  0x7f3743863e7a in PMPI_Alltoall
    at src/mpi/coll/alltoall.c:884
#8  0x7f37424181bf in pmpi_alltoall_
    at src/binding/fortran/mpif_h/alltoallf.c:272

I don't know mpich well enough to extract a testcase, but it would be great if somebody could extract that and report to the gcc team (I'm happy to do the reporting if needed).

thanks in advance,

Joost

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