[flang-commits] [flang] [flang][OpenMP] Do not emit barrier after SECTIONS with LASTPRIVATE and NOWAIT (PR #216018)

[via flang-commits]

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@@ -3727,16 +3937,9 @@ genSectionsOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
   // Perform DataSharingProcessor's step2 out of SECTIONS
   builder.setInsertionPointAfter(sectionsOp.getOperation());
   dsp.processStep2(sectionsOp, false);
-  // Emit barrier when nowait is present and there are lastprivate copy-backs
-  // (either non-conditional or conditional).  The barrier ensures all threads
-  // have completed their work before lastprivate values are read/copied.
-  //
-  // NOTE: The LLVM OpenMP runtime currently imposes an implicit barrier
-  // inside __kmpc_reduce for tree reductions.  If the runtime were modified
-  // to release losing threads early when nowait is specified, we could use
-  // the return value from the tree reduction (case 1 = winner) to let the
-  // winner thread perform the copy-back without a separate barrier.
-  if (clauseOps.nowait && (hasNonCondLastprivate || !condLpSyms.empty()))
+  // Emit barrier when nowait is present and conditional lastprivate reduction
+  // results must be finalized before copy-back.
+  if (clauseOps.nowait && !condLpSyms.empty())
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Ritanya-B-Bharadwaj wrote:

Non-blocking nit: maybe note in the description (or here) that the barrier still shown in the `firstprivate lastprivate` test is that pre-construct one, so it's clear the removed one wasn't load-bearing.

https://github.com/llvm/llvm-project/pull/216018