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

[Sergio Afonso via flang-commits]

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@@ -8363,6 +8396,59 @@ convertOmpTarget(Operation &opInst, llvm::IRBuilderBase &builder,
   bool isOffloadEntry =
       isTargetDevice || !ompBuilder->Config.TargetTriples.empty();
 
+  // Validate and resolve in_reduction clauses on omp.target. We currently
+  // only support the non-offload host-fallback path: the per-task private
+  // pointer is obtained by calling __kmpc_task_reduction_get_th_data inside
+  // the to-be-outlined target task body. Threading that pointer through the
+  // device kernel argument list is left as follow-up work.
+  SmallVector<llvm::Value *> inRedOrigPtrs;
+  SmallVector<unsigned> inRedMapArgIdx;
+  if (!targetOp.getInReductionVars().empty()) {
+    if (isTargetDevice || isOffloadEntry)
+      return opInst.emitError(
+          "not yet implemented: in_reduction clause on omp.target with "
+          "offload / target-device compilation");
----------------
skatrak wrote:

Wouldn't this work already for both offloading and non-offloading modules? It seems that, as long as the `if (llvm::is_contained(inRedMapArgIdx, idx))` and `if (!inRedOrigPtrs.empty())` statements below also make sure that `!isTargetDevice`, then it should work. Do let me know if there are problems with this suggestion, though.
```suggestion
  if (!targetOp.getInReductionVars().empty() && !isTargetDevice) {
```

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