[Patch] [middle-end & nvptx] gcc/tracer.c: Don't split BB with SIMT LANE [PR95654]

[Tom de Vries]

[ cc-ing author omp support for nvptx. ]

On 9/16/20 12:39 PM, Tobias Burnus wrote:
> Hi Tom, hi Richard, hello all,
> 
> @Richard: does it look okay from the ME side?
> @Tom: Can you check which IFN_GOMP_SIMT should be
> excluded with -ftracer?
> 
> Pre-remark, I do not know much about SIMT – except that they
> only appear with nvptx and somehow relate to lanes on the
> GPU.
> 
> In any case, as the testcase libgomp.fortran/pr66199-5.f90 shows,
> if a basic block with  GOMP_SIMT_VOTE_ANY in it is duplicated,
> which happens via -ftracer for this testcase, the result is wrong.
> 
> The testcase ignores all the loop work but via "lastprivate" takes
> the upper loop bound (as assigned to the loop indices); instead of
> the expected 32*32 = 1024, either some number (like 4 or very large
> or negative) is returned.
> 
> While GOMP_SIMT_VOTE_ANY fixes the issue for this testcase, I
> have the feeling that at least GOMP_SIMT_LAST_LANE should be
> not copied - but I might be wrong.
> 
> Tom: Do you think GOMP_SIMT_LAST_LANE should be removed from
> that list – or any of the following added as well?
> GOMP_USE_SIMT, GOMP_SIMT_ENTER, GOMP_SIMT_ENTER_ALLOC, GOMP_SIMT_EXIT,
> GOMP_SIMT_VF, GOMP_SIMT_ORDERED_PRED, GOMP_SIMT_XCHG_BFLY,
> GOMP_SIMT_XCHG_IDX
> 
> OK for mainline?
> 
> Tobias
> 
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