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

[Sergio Afonso via flang-commits]

================
@@ -2655,6 +2739,35 @@ LogicalResult TargetOp::verify() {
   if (failed(verifyPrivateVarList(*this)))
     return failure();
 
+  if (failed(verifyReductionVarList(*this, getInReductionSyms(),
+                                    getInReductionVars(),
+                                    getInReductionByref())))
+    return failure();
+
+  // An `in_reduction` operand on `omp.target` has no dedicated entry block
+  // argument; inside the region it is accessed through the block argument of a
+  // matching `map_entries` entry, and the host fallback rewrites that map
+  // argument to the reduction-private storage. Require every `in_reduction`
+  // operand to be captured by at least one `map_entries` entry whose
+  // `MapInfoOp` var_ptr is the same value, or another result of the same
+  // defining op. Flang emits e.g. `hlfir.declare`#0 for the `in_reduction`
+  // operand and `hlfir.declare`#1 for the map var_ptr, so exact value identity
+  // is not required; block arguments (no defining op) must match exactly.
----------------
skatrak wrote:

Nit: This description currently goes too in depth and re-states the checks explained in the `targetInReductionCapturedBy` function.
```suggestion
  // An `in_reduction` operand on `omp.target` has no dedicated entry block
  // argument; inside the region it is accessed through the block argument of a
  // matching `map_entries` entry, and the host fallback rewrites that map
  // argument to the reduction-private storage. Require every `in_reduction`
  // operand to be captured by at least one `map_entries` entry.
```

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