[flang-commits] [flang] [mlir] [flang][OpenMP] Lower target in_reduction for host fallback (PR #199967)

[Sergio Afonso via flang-commits]

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@@ -436,18 +436,28 @@ static void bindEntryBlockArgs(lower::AbstractConverter &converter,
               .first);
   };
 
-  // Process in clause name alphabetical order to match block arguments order.
   // Do not bind host_eval variables because they cannot be used inside of the
   // corresponding region, except for very specific cases handled separately.
+  //
+  // For `omp.task` / `omp.taskloop`, `in_reduction` list items have their own
+  // entry block argument and are bound here like other private-like variables.
+  //
+  // `in_reduction` list items on `omp.target` are not given their own entry
+  // block argument (`args.inReduction` is left empty for target), so the
+  // in_reduction bind below is a no-op there. Instead they are implicitly
+  // mapped, so in-body references resolve to the `map_entries` block argument
+  // bound here; the host side uses the `in_reduction` clause metadata to
+  // redirect that mapped value to the per-task reduction-private storage during
+  // translation.
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skatrak wrote:

Nit: This information belongs in `genTargetOp` where the `ObjectEntryBlockArgs` structure is initialized, and it's already there. I'd remove it from here because there's no special handling for it.

https://github.com/llvm/llvm-project/pull/199967