[Mlir-commits] [mlir] [mlir][TilingInterface] Avoid looking at operands for getting slices to continue tile + fuse. (PR #107882)

[Quinn Dawkins]

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@@ -129,18 +132,22 @@ struct SCFTileAndFuseOptions {
   /// 2) the producer value that is to be fused
   /// 3) a boolean value set to `true` if the fusion is from
   ///    a destination operand.
-  /// It retuns two booleans
-  /// - returns `true` if the fusion should be done through the candidate slice
-  /// - returns `true` if a replacement for the fused producer needs to be
-  ///   yielded from within the tiled loop. Note that it is valid to return
-  ///   `true` only if the slice fused is disjoint across all iterations of the
-  ///   tiled loop. It is up to the caller to ensure that this is true for the
-  ///   fused producers.
-  using ControlFnTy = std::function<std::tuple<bool, bool>(
+  /// The control function returns an `std::optiona<ControlFnResult>`.
+  /// If the return value is `std::nullopt`, that implies no fusion
+  /// is to be performed along that slice.
+  struct ControlFnResult {
+    /// Set to true if the loop nest has to return a replacement value
+    /// for the fused producer.
+    bool yieldProducerReplacement = false;
+  };
+  using ControlFnTy = std::function<std::optional<ControlFnResult>(
       tensor::ExtractSliceOp candidateSliceOp, OpResult originalProducer,
       bool isDestinationOperand)>;
-  ControlFnTy fusionControlFn = [](tensor::ExtractSliceOp, OpResult, bool) {
-    return std::make_tuple(true, false);
+  /// The default control function implements greedy fusion without yielding
+  /// a replacement for any of the fused results.
+  ControlFnTy fusionControlFn = [](tensor::ExtractSliceOp, OpResult,
+                                   bool) -> std::optional<ControlFnResult> {
+    return ControlFnResult{};
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qedawkins wrote:

This does not read very clearly to me. I would normally assume an empty `ControlFnResult` would mean no fusion. Can we add another `bool doFusion = false`, even if redundant to the control function for clarity?

https://github.com/llvm/llvm-project/pull/107882