[committed][nvptx] Assert fork has at most one join in nvptx_find_par

[Tom de Vries]

Hi,

With the test-case of PR90009 we run into a SIGSEGV in nvptx_neuter_pars,
because par->join_insn and par->join_block are NULL.

Detect this problem earlier, by adding an assert in nvptx_find_par that
asserts that a fork cannot be paired with more than one join.

Build and tested on x86_64 with nvptx accelerator enabled.

Committed to trunk.

Thanks,
- Tom

[nvptx] Assert fork has at most one join in nvptx_find_par

2019-06-12  Tom de Vries  <tdevr...@suse.de>

        PR tree-optimization/90009
        * config/nvptx/nvptx.c (nvptx_find_par): Assert fork has at most join.

---
 gcc/config/nvptx/nvptx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
index a28099ac89d..1e34be18f75 100644
--- a/gcc/config/nvptx/nvptx.c
+++ b/gcc/config/nvptx/nvptx.c
@@ -3258,6 +3258,7 @@ nvptx_find_par (bb_insn_map_t *map, parallel *par, 
basic_block block)
            unsigned mask = UINTVAL (XVECEXP (PATTERN (end), 0, 0));
 
            gcc_assert (par->mask == mask);
+           gcc_assert (par->join_block == NULL);
            par->join_block = block;
            par->join_insn = end;
            if (nvptx_needs_shared_bcast (mask))