[Bug target/100321] [OpenMP][nvptx, SIMT] (Con't) Reduction fails with optimization and 'loop'/'for simd' but not with 'for'

[vries at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100321

--- Comment #4 from Tom de Vries <vries at gcc dot gnu.org> ---
During lower_rec_input_clauses in omp-low.c, the reduction clause is handled:
...
            case OMP_CLAUSE_REDUCTION:
            case OMP_CLAUSE_IN_REDUCTION:
              /* OpenACC reductions are initialized using the                   
                 GOACC_REDUCTION internal function.  */
              if (is_gimple_omp_oacc (ctx->stmt))
                break;
              if (OMP_CLAUSE_REDUCTION_PLACEHOLDER (c))
...

AFAICT, the problem is that the the SIMT handling code is added only in the
!OMP_CLAUSE_REDUCTION_PLACEHOLDER (c) case.

For this test-case, the OMP_CLAUSE_REDUCTION_PLACEHOLDER (c) path is taken
instead.

So, something like this reflects the current state:
...
diff --git a/gcc/omp-low.c b/gcc/omp-low.c
index 7b122059c6e..a0561800977 100644
--- a/gcc/omp-low.c
+++ b/gcc/omp-low.c
@@ -6005,6 +6005,11 @@ lower_rec_input_clauses (tree clauses, gimple_seq
*ilist, gimple_seq *dlist,
                  tree placeholder = OMP_CLAUSE_REDUCTION_PLACEHOLDER (c);
                  gimple *tseq;
                  tree ptype = TREE_TYPE (placeholder);
+                 if (sctx.is_simt)
+                   {
+                     sorry ("SIMT not fully implemented");
+                     abort ();
+                   }
                  if (cond)
                    {
                      x = error_mark_node;
...