[Mlir-commits] [mlir] [mlir][scf] Extend consumer fuse to nested loop structure (PR #94190)

[Abhishek Varma]

================
@@ -1220,31 +1129,116 @@ static LogicalResult checkAssumptionForLoop(Operation *loopOp,
   return success();
 }
 
-/// A utility to fetch an untiled consumer of
-/// tensor.insert_slice/tensor.parallel_insert_slice.
-static FailureOr<OpOperand *> getUntiledConsumerFromSlice(Operation *sliceOp) {
-  if (auto insertSlice = dyn_cast<tensor::InsertSliceOp>(sliceOp)) {
-    return getUntiledConsumerFromSlice(insertSlice);
-  } else if (auto parallelInsertSlice =
-                 dyn_cast<tensor::ParallelInsertSliceOp>(sliceOp)) {
-    return getUntiledConsumerFromSlice(parallelInsertSlice);
-  } else {
+// Traverse and collect all outer loops of given sliceOp, sorted by
+// outer-to-inner. If `untilLoop` found, stop walk through in advance.
+static SmallVector<LoopLikeOpInterface> getOuterLoopsOfSliceOp(
+    OffsetSizeAndStrideOpInterface sliceOp,
+    std::optional<LoopLikeOpInterface> untilLoop = std::nullopt) {
+  SmallVector<LoopLikeOpInterface> outerLoops;
+  auto forOp = sliceOp->getParentOfType<LoopLikeOpInterface>();
+  while (forOp) {
+    outerLoops.push_back(forOp);
+    if (untilLoop.has_value() && *untilLoop == forOp)
+      break;
+    forOp = forOp->getParentOfType<LoopLikeOpInterface>();
+  }
+  return {outerLoops.rbegin(), outerLoops.rend()};
+}
+
+// Get the Result of top-level Loop which yield the target InsertSliceOp. E.g
+// ```
+// %1 = scf.for
+//  %2 = scf.for
+//   %3 = scf.for
+//      ...
+//      %4 = insert
+//      yield %4
+//   %5 = insert %3
+//   yield %5
+//  yield %2
+// ```
+// @param targetSliceOp: %4 = insert
+// @return Result Value: %1
+//         Collected insertSliceOp List during walk including targetSliceOp:
+//                %4 = insert and %5 = insert %3
+static FailureOr<std::pair<Value, SmallVector<OffsetSizeAndStrideOpInterface>>>
+getResultOfTopLevelLoopYieldInsertSliceOp(
+    OffsetSizeAndStrideOpInterface targetSliceOp, int curDepth = 0,
+    int maxDepth = 5) {
+  // control recursive time in avoid of stack overflow
+  if (curDepth > maxDepth)
+    return failure();
+
+  SmallVector<OffsetSizeAndStrideOpInterface> candidateSliceOpList;
+  candidateSliceOpList.push_back(targetSliceOp);
+  Value resultOfLoop;
+  if (auto sliceOp = dyn_cast<tensor::ParallelInsertSliceOp>(
+          targetSliceOp.getOperation())) {
+    Value destValue = sliceOp.getDest();
+    auto iterArg = cast<BlockArgument>(destValue);
+    auto forallOp = dyn_cast<scf::ForallOp>(iterArg.getOwner()->getParentOp());
+    if (!forallOp)
+      return failure();
+    resultOfLoop = forallOp.getTiedOpResult(forallOp.getTiedOpOperand(iterArg));
+  } else if (auto sliceOp = dyn_cast<tensor::InsertSliceOp>(
+                 targetSliceOp.getOperation())) {
+    Value resultValue = sliceOp.getResult();
+    for (auto &useOperand : resultValue.getUses()) {
+      if (auto yieldOp = dyn_cast<scf::YieldOp>(useOperand.getOwner())) {
+        if (llvm::detail::isPresent(resultOfLoop))
+          return failure();
+        auto forOp = dyn_cast<LoopLikeOpInterface>(yieldOp->getParentOp());
+        if (!forOp)
+          return failure();
+        resultOfLoop = forOp->getResult(useOperand.getOperandNumber());
+      }
+    }
+  }
+
+  if (!llvm::detail::isPresent(resultOfLoop))
     return failure();
+
+  while (true) {
+    bool walkThroughOuterLoop = false;
+    for (auto &useOperand : resultOfLoop.getUses()) {
+      if (auto sliceOp =
+              dyn_cast<OffsetSizeAndStrideOpInterface>(useOperand.getOwner())) {
+        auto resultAndSliceOpsPair =
+            getResultOfTopLevelLoopYieldInsertSliceOp(sliceOp, curDepth + 1);
----------------
Abhishek-Varma wrote:

Always expand `auto` here and elsewhere. It's a good practice to do so where the data type is not known explicitly from the RHS one-line context.

Eg: `dyn_cast<TYPE>(...)`, `getParentOfType<TYPE>(...)`, etc we can use `auto`, but definitely not in above cases.

https://github.com/llvm/llvm-project/pull/94190