[llvm-branch-commits] [flang] [mlir] [MLIR][OpenMP] LLVM IR translation of host_eval (PR #116052)

[Sergio Afonso via llvm-branch-commits]

================
@@ -3889,6 +3889,215 @@ createDeviceArgumentAccessor(MapInfoData &mapData, llvm::Argument &arg,
   return builder.saveIP();
 }
 
+/// Follow uses of `host_eval`-defined block arguments of the given `omp.target`
+/// operation and populate output variables with their corresponding host value
+/// (i.e. operand evaluated outside of the target region), based on their uses
+/// inside of the target region.
+///
+/// Loop bounds and steps are only optionally populated, if output vectors are
+/// provided.
+static void extractHostEvalClauses(omp::TargetOp targetOp, Value &numThreads,
+                                   Value &numTeamsLower, Value &numTeamsUpper,
+                                   Value &threadLimit) {
+  auto blockArgIface = llvm::cast<omp::BlockArgOpenMPOpInterface>(*targetOp);
+  for (auto item : llvm::zip_equal(targetOp.getHostEvalVars(),
----------------
skatrak wrote:

Doing a decomposition declaration for `hostEvalVar` and `blockArg`, and then capturing these values in the `TypeSwitch` lambdas below apparently triggers a [weird corner in the C++ standard](https://stackoverflow.com/questions/46114214/lambda-implicit-capture-fails-with-variable-declared-from-structured-binding) that was disallowed at one point. So, apparently we can only do this if compiling for C++20 or later.

https://github.com/llvm/llvm-project/pull/116052