[llvm-branch-commits] [flang] [flang][OpenMP] Support lowering of metadirective (part 2) (PR #194424)

[Abid Qadeer via llvm-branch-commits]

================
@@ -4629,35 +4638,83 @@ static void genMetadirective(lower::AbstractConverter &converter,
                    queue.begin());
   };
 
-  const parser::OmpDirectiveSpecification *selected = fallback;
-  if (candidates.size() == 1) {
-    selected = candidates.front().spec;
-  } else if (!candidates.empty()) {
+  auto selectBestCandidate =
+      [](llvm::ArrayRef<unsigned> candidateIndices,
+         llvm::ArrayRef<MetadirectiveCandidate> candidates,
+         const TargetOMPContext &ompCtx) -> std::optional<unsigned> {
+    if (candidateIndices.empty())
+      return std::nullopt;
+    if (candidateIndices.size() == 1)
+      return candidateIndices.front();
+
     // The OpenMP context scorer preserves input order for tied candidates.
     // Put explicit variants first so they take precedence over implicit
     // `nothing`, as required by metadirective selection.
     llvm::SmallVector<unsigned, 4> candidateOrder;
-    candidateOrder.reserve(candidates.size());
-    for (auto [idx, candidate] : llvm::enumerate(candidates))
-      if (candidate.isExplicit)
+    candidateOrder.reserve(candidateIndices.size());
+    for (unsigned idx : candidateIndices)
+      if (candidates[idx].isExplicit)
         candidateOrder.push_back(idx);
-    for (auto [idx, candidate] : llvm::enumerate(candidates))
-      if (!candidate.isExplicit)
+    for (unsigned idx : candidateIndices)
+      if (!candidates[idx].isExplicit)
         candidateOrder.push_back(idx);
 
     llvm::SmallVector<llvm::omp::VariantMatchInfo, 4> orderedVMIs;
-    orderedVMIs.reserve(candidates.size());
+    orderedVMIs.reserve(candidateOrder.size());
     for (unsigned idx : candidateOrder)
       orderedVMIs.push_back(candidates[idx].vmi);
 
     int bestIdx = llvm::omp::getBestVariantMatchForContext(orderedVMIs, ompCtx);
     if (bestIdx >= 0) {
       assert(static_cast<size_t>(bestIdx) < candidateOrder.size() &&
              "best variant index out of range");
-      selected = candidates[candidateOrder[bestIdx]].spec;
+      return candidateOrder[bestIdx];
+    }
+    return std::nullopt;
+  };
+
+  llvm::SmallVector<unsigned, 4> remainingCandidates;
+  remainingCandidates.reserve(candidates.size());
+  for (unsigned idx = 0, end = candidates.size(); idx < end; ++idx)
+    remainingCandidates.push_back(idx);
+
+  mlir::Location loc = converter.genLocation(clauseList.source);
+  lower::StatementContext stmtCtx;
+
+  while (!remainingCandidates.empty()) {
----------------
abidh wrote:

A comment above would be helpful to briefly explain how dynamic candidates are generated in cascaded fir.if and where the fallback will be generated. 

https://github.com/llvm/llvm-project/pull/194424