[Mlir-commits] [mlir] [MLIR][SCF] Add an API to fuse consumer to a producer within scf loop (PR #88712)

[llvmlistbot at llvm.org]

================
@@ -1100,6 +1102,398 @@ mlir::scf::tileConsumerAndFuseProducersUsingSCF(
                                    replacements};
 }
 
+//===----------------------------------------------------------------------===//
+// tileAndFuseConsumerUsingSCF implementation.
+//===----------------------------------------------------------------------===//
+
+/// A utility function that checks whether the passed value has only one user.
+/// In case the defining operation is a tensor.insert_slice, it checks if the
+/// user is scf.yield.
+static LogicalResult checkAssumptionForFusingConsumer(Value result) {
+  Value::use_range uses = result.getUses();
+  if (!llvm::hasSingleElement(uses)) {
+    LLVM_DEBUG(llvm::dbgs() << "Too many uses of the candidate slice op\n");
+    return failure();
+  }
+  OpOperand &operandUse = (*uses.begin());
+  Operation *userOp = operandUse.getOwner();
+  if (!isa<scf::YieldOp>(userOp)) {
+    LLVM_DEBUG(llvm::dbgs()
+               << "Expected scf.yield to be the only user, but got -> "
+               << (*userOp));
+    return failure();
+  }
+  if (result.getDefiningOp()->getBlock() != userOp->getBlock()) {
+    LLVM_DEBUG(llvm::dbgs() << "Expected tensor.insert_slice and scf.yield to "
+                               "be in the same block\n");
+    return failure();
+  }
+  return success();
+}
+
+/// Fetch the first untiled consumer of a scf.for's result which is yielded by
+/// a tensor.insert_slice. This function makes the following assumptions :-
+/// 1.  tensor.insert_slice has scf.yield as its only user.
+/// 2.  scf.for's corresponding result has only one use.
+static OpOperand *
+getUntiledConsumerFromSlice(tensor::InsertSliceOp candidateSliceOp) {
+  Value sliceResult = candidateSliceOp.getResult();
+  if (failed(checkAssumptionForFusingConsumer(candidateSliceOp.getResult()))) {
+    return nullptr;
+  }
+  // Step 1. Fetch the corresponding output.
+  OpOperand &yieldOpOperand = (*sliceResult.getUses().begin());
+  unsigned resultNumber = yieldOpOperand.getOperandNumber();
+  // Step 2. Check containing op is scf.for.
+  Operation *containingOp = candidateSliceOp->getParentOp();
+  auto forOp = dyn_cast<scf::ForOp>(containingOp);
+  if (!forOp) {
+    return nullptr;
+  }
+  Value resultingValue = forOp->getResult(resultNumber);
+
+  // Step 3. Check resulting value of scf.for has exactly one use.
+  if (!llvm::hasSingleElement(resultingValue.getUses())) {
+    return nullptr;
+  }
+
+  // Step 4. Get uses.
+  OpOperand &operand = (*resultingValue.getUses().begin());
+  Operation *consumerOp = operand.getOwner();
+  // TODO: We have to init result of consumer before scf.for, use
+  //       DestinationStyleOpInterface to get result shape from init for now.
+  //       Add support for other op such as op has InferTypeOpInterface.
+  if (!isa<TilingInterface>(consumerOp) ||
+      !isa<DestinationStyleOpInterface>(consumerOp)) {
+    return nullptr;
+  }
+  if (containingOp->getBlock() != consumerOp->getBlock()) {
+    return nullptr;
+  }
+  return &operand;
+}
+
+/// Fetch the first untiled consumer of a scf.forall's result which is yielded
+/// by a tensor.parallel_insert_slice.
+static OpOperand *
+getUntiledConsumerFromSlice(tensor::ParallelInsertSliceOp candidateSliceOp) {
+  // Step 1. Fetch the corresponding output
+  Value sliceDest = candidateSliceOp.getDest();
+  auto iterArg = cast<BlockArgument>(sliceDest);
+  Operation *containingOp = iterArg.getOwner()->getParentOp();
+  // Step 2. Check that the containing op is scf.forall.
+  auto forallOp = dyn_cast<scf::ForallOp>(containingOp);
+  if (!forallOp) {
+    return nullptr;
+  }
+  Value resultingValue =
+      forallOp.getTiedOpResult(forallOp.getTiedOpOperand(iterArg));
+  // Step 3. Check resulting value of scf.forall has exactly one use.
+  Value::use_range uses = resultingValue.getUses();
+  if (!llvm::hasSingleElement(uses)) {
+    return nullptr;
+  }
+
+  // Step 4. Get uses.
+  OpOperand &operand = (*resultingValue.getUses().begin());
+  Operation *consumerOp = operand.getOwner();
+  // TODO: We have to init result of consumer before scf.forall, use
+  //       DestinationStyleOpInterface to get result shape from init for now.
+  //       Add support for other op such as op has InferTypeOpInterface.
+  if (!isa<TilingInterface>(consumerOp) ||
+      !isa<DestinationStyleOpInterface>(consumerOp)) {
+    return nullptr;
+  }
+  if (containingOp->getBlock() != consumerOp->getBlock()) {
+    return nullptr;
+  }
+  return &operand;
+}
+
+/// This utility currently checks whether the loop either :-
+/// 1. Yields exactly one result.
+/// 2. Has consumer op as its first user and other users to be in the same
+/// containing block as that of consumer op's. Currently we clone the loop op
+/// right before the consumer op in order to maintain a valid def-use chain.
+/// This utility thus helps ensuring that no invalid IR is formed due to the
+/// same.
+static LogicalResult checkAssumptionForLoop(Operation *loopOp,
+                                            Operation *consumerOp) {
+  // Check if the loop op yields one result.
+  if (loopOp->getNumResults() == 1)
+    return success();
+  // Check if the consumerOp is the first user of the loopOp and if other users
+  // are in the same containing block as that of consumer op's.
+  Block *parentBlock = consumerOp->getBlock();
----------------
MaheshRavishankar wrote:

I'd make life easier and only target single user... This works, but it has a O(N) cost if the operation order in the block has changed.

https://github.com/llvm/llvm-project/pull/88712