Re: [Patch] + [nvptx RFH/RFC]: OpenMP: Fix SIMT for complex/float reduction with && and ||

[Tom de Vries <tdevries@suse.de>]

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On 5/6/21 12:30 PM, Jakub Jelinek wrote:
> On Thu, May 06, 2021 at 12:17:03PM +0200, Tobias Burnus wrote:
>> OpenMP: Fix SIMT for complex/float reduction with && and ||
>>
>> gcc/ChangeLog:
>>
>> 	* omp-low.c (lower_rec_input_clauses): Also handle SIMT part
>> 	for complex/float recution with && and ||.
>>
>> libgomp/ChangeLog:
>>
>> 	* testsuite/libgomp.c-c++-common/reduction-5.c: New test, testing
>> 	complex/floating-point || + && recduction with 'omp target'.
> 
> As the float/complex ||/&& reductions are IMHO just conformance issues, not
> something anyone would actually use in meaningful code - floats or complex
> aren't the most obvious or efficient holders of boolean values - I think
> punting SIMT on those isn't a workaround, but the right solution.
> 

Ack.

WIP patch below tries that approach and fixes the ICE, but this simple
example still doesn't work:
...
int
main ()
{
  float andf = 1;

  #pragma omp target parallel reduction(&&: andf)
  for (int i=0; i < 1024; ++i)
    andf = andf && 0.0;

  if ((int)andf != 0)
    __builtin_abort ();

  return 0;
}
...

Thanks,
- Tom



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diff --git a/gcc/omp-low.c b/gcc/omp-low.c
index 26ceaf74b2d..d8f2487054f 100644
--- a/gcc/omp-low.c
+++ b/gcc/omp-low.c
@@ -4389,14 +4389,28 @@ lower_rec_simd_input_clauses (tree new_var, omp_context *ctx,
 	{
 	  for (tree c = gimple_omp_for_clauses (ctx->stmt); c;
 	       c = OMP_CLAUSE_CHAIN (c))
-	    if (OMP_CLAUSE_CODE (c) == OMP_CLAUSE_REDUCTION
-		&& OMP_CLAUSE_REDUCTION_PLACEHOLDER (c))
-	      {
-		/* UDR reductions are not supported yet for SIMT, disable
-		   SIMT.  */
-		sctx->max_vf = 1;
-		break;
-	      }
+	    {
+	      if (OMP_CLAUSE_CODE (c) != OMP_CLAUSE_REDUCTION)
+		continue;
+
+	      if (OMP_CLAUSE_REDUCTION_PLACEHOLDER (c))
+		{
+		  /* UDR reductions are not supported yet for SIMT, disable
+		     SIMT.  */
+		  sctx->max_vf = 1;
+		  break;
+		}
+
+	      if (truth_value_p (OMP_CLAUSE_REDUCTION_CODE (c))
+		  && TREE_CODE (TREE_TYPE (new_var)) != BOOLEAN_TYPE)
+		{
+		  /* Doing boolean operations on non-boolean types is
+		     for conformance only, it's not worth supporting this
+		     for SIMT.  */
+		  sctx->max_vf = 1;
+		  break;
+		}
+	    }
 	}
       if (maybe_gt (sctx->max_vf, 1U))
 	{