[Mlir-commits] [flang] [mlir] [openmp] [MLIR][OpenMP] Add scan reduction lowering to llvm (PR #167031)

[Sergio Afonso]

================
@@ -2471,12 +2446,59 @@ genParallelOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
 
 static mlir::omp::ScanOp
 genScanOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
-          semantics::SemanticsContext &semaCtx, mlir::Location loc,
-          const ConstructQueue &queue, ConstructQueue::const_iterator item) {
+          semantics::SemanticsContext &semaCtx, lower::pft::Evaluation &eval,
+          mlir::Location loc, const ConstructQueue &queue,
+          ConstructQueue::const_iterator item) {
   mlir::omp::ScanOperands clauseOps;
   genScanClauses(converter, semaCtx, item->clauses, loc, clauseOps);
-  return mlir::omp::ScanOp::create(converter.getFirOpBuilder(),
-                                   converter.getCurrentLocation(), clauseOps);
+  mlir::omp::ScanOp scanOp = mlir::omp::ScanOp::create(
+      converter.getFirOpBuilder(), converter.getCurrentLocation(), clauseOps);
+
+  /// Scan reduction is not implemented with nested workshare loops, linear
+  /// clause, tiling
+  mlir::omp::LoopNestOp loopNestOp =
+      scanOp->getParentOfType<mlir::omp::LoopNestOp>();
+  llvm::SmallVector<mlir::omp::LoopWrapperInterface> loopWrappers;
+  loopNestOp.gatherWrappers(loopWrappers);
+  mlir::Operation *loopWrapperOp = loopWrappers.front().getOperation();
+  if (llvm::isa<mlir::omp::SimdOp>(loopWrapperOp))
+    TODO(loc, "unsupported simd");
+  if (loopWrappers.size() > 1)
+    TODO(loc, "unsupported composite");
+  mlir::omp::WsloopOp wsLoopOp = llvm::cast<mlir::omp::WsloopOp>(loopWrapperOp);
+  bool isNested =
+      (loopNestOp.getNumLoops() > 1) ||
+      (wsLoopOp && (wsLoopOp->getParentOfType<mlir::omp::WsloopOp>()));
+  if (isNested)
+    TODO(loc, "Scan directive inside nested workshare loops");
+  if (wsLoopOp && !wsLoopOp.getLinearVars().empty())
+    TODO(loc, "Scan directive with linear clause");
----------------
skatrak wrote:

Nit: These two checks might be better placed in `genWsloopClauses`. You could do something like:
```c++
  ClauseProcessor cp(converter, semaCtx, clauses);
  bool hasReduction = cp.processReduction(loc, clauseOps, reductionSyms);
  bool hasLinear = cp.processLinear(clauseOps);
  // ...
  if (hasReduction && clauseOps.reductionMod && clauseOps.reductionMod.getValue() == omp::ReductionModifier::inscan) {
    if (hasLinear)
      TODO(loc, "INSCAN and LINEAR clauses on the same loop");

    Operation *parentOp = converter.getFirOpBuilder().getInsertionBlock()->getParentOp();
    // Check if it's nested under another INSCAN reduction...
  }
```

https://github.com/llvm/llvm-project/pull/167031