[PR65637][PATCH][1/3] Fix gcc_assert in expand_omp_for_static_chunk

[Tom de Vries <Tom_deVries@mentor.com>]

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On 15-04-15 15:10, Tom de Vries wrote:
> Hi,
>
> This patch series fixes PR65637.
>
> Currently, ssa-handling code in expand_omp_for_static_chunk is dead and not
> exercised by testing.
>
> Ssa-handling code in omp-low.c is only triggered by pass_parallelize_loops, and
> that pass doesn't specify a chunk size on the GIMPLE_OMP_FOR it constructs, so
> that only exercises the expand_omp_for_static_nochunk path.
>
> Using the attached trigger patch, we excercise the ssa-handling code in
> expand_omp_for_static_chunk. The following patch series fixes the problems in
> the ssa-handling code that we encounter.
>
> 1. Fix gcc_assert in expand_omp_for_static_chunk
> 2. Fix inner loop phi in expand_omp_for_static_chunk
> 3. Handle 2 preds for fin_bb in expand_omp_for_static_chunk
>
> The patch series has been bootstrapped and reg-tested on x86_64 together with
> attached trigger patch.
>
> I'll post the patches from the patch series individually, in response to this
> email.
>

This patch fixes a segfault in an gcc_assert in expand_omp_for_static_chunk
while compiling autopar/pr46099.c.

When compiling f1 from autopar/pr46099.c using expand_omp_for_static_chunk, we
redirect the edge (trip_update_bb -> fin_bb) to point to iter_part_bb:
...
       redirect_edge_and_branch (single_succ_edge (trip_update_bb), iter_part_bb);
...

And fin_bb is an empty block without any phis, so during the redirect we don't
store any entries in the edge_var_map:
...
(gdb) call debug_bb (fin_bb)
;; basic block 18, loop depth 0, count 0, freq 0, maybe hot
;;  prev block 21, next block 16, flags: (NEW)
;;  pred:       21 [100.0%]  (FALLTHRU)
;;              19 (FALSE_VALUE)
;;  succ:       16 [100.0%]  (FALLTHRU)
...

Consequently, head will be NULL.
...
       vec<edge_var_map> *head = redirect_edge_var_map_vector (re);
...

And because head is NULL, this assert causes a segfault:
...
   gcc_assert (gsi_end_p (psi) && i == head->length ());
...

This patch fixes that, by handling the case that head is NULL in the assert.

OK for trunk?

Thanks,
- Tom

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Fix gcc_assert in expand_omp_for_static_chunk

2015-04-15  Tom de Vries  <tom@codesourcery.com>

	PR tree-optimization/65637
	* omp-low.c (expand_omp_for_static_chunk): Fix gcc_assert for the case
	that head is NULL.

---
 gcc/omp-low.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/omp-low.c b/gcc/omp-low.c
index 80bddf0..f7b9d11 100644
--- a/gcc/omp-low.c
+++ b/gcc/omp-low.c
@@ -7274,7 +7274,7 @@ expand_omp_for_static_chunk (struct omp_region *region,
 	  locus = redirect_edge_var_map_location (vm);
 	  add_phi_arg (nphi, redirect_edge_var_map_def (vm), re, locus);
 	}
-      gcc_assert (gsi_end_p (psi) && i == head->length ());
+      gcc_assert (gsi_end_p (psi) && (head == NULL || i == head->length ()));
       redirect_edge_var_map_clear (re);
       while (1)
 	{
-- 
1.9.1