[mlir][MemRef] Address TODO to use early_inc to simplify elimination of uses (NFC) (llvm#155123)

Author: snarang181

mlir/lib/Dialect/MemRef/Transforms/MultiBuffer.cpp

@@ -43,50 +43,34 @@ static bool overrideBuffer(Operation *op, Value buffer) {
 /// propagate the type change and erase old subview ops.
 static void replaceUsesAndPropagateType(RewriterBase &rewriter,
                                         Operation *oldOp, Value val) {
-  SmallVector<Operation *> opsToDelete;
-  SmallVector<OpOperand *> operandsToReplace;
-
-  // Save the operand to replace / delete later (avoid iterator invalidation).
-  // TODO: can we use an early_inc iterator?
-  for (OpOperand &use : oldOp->getUses()) {
-    // Non-subview ops will be replaced by `val`.
-    auto subviewUse = dyn_cast<memref::SubViewOp>(use.getOwner());
-    if (!subviewUse) {
-      operandsToReplace.push_back(&use);
+  // Iterate with early_inc to erase current user inside the loop.
+  for (OpOperand &use : llvm::make_early_inc_range(oldOp->getUses())) {
+    Operation *user = use.getOwner();
+    if (auto subviewUse = dyn_cast<memref::SubViewOp>(user)) {
+      // `subview(old_op)` is replaced by a new `subview(val)`.
+      OpBuilder::InsertionGuard g(rewriter);
+      rewriter.setInsertionPoint(subviewUse);
+      MemRefType newType = memref::SubViewOp::inferRankReducedResultType(
+          subviewUse.getType().getShape(), cast<MemRefType>(val.getType()),
+          subviewUse.getStaticOffsets(), subviewUse.getStaticSizes(),
+          subviewUse.getStaticStrides());
+      Value newSubview = memref::SubViewOp::create(
+          rewriter, subviewUse->getLoc(), newType, val,
+          subviewUse.getMixedOffsets(), subviewUse.getMixedSizes(),
+          subviewUse.getMixedStrides());
+
+      // Ouch recursion ... is this really necessary?
+      replaceUsesAndPropagateType(rewriter, subviewUse, newSubview);
+
+      // Safe to erase.
+      rewriter.eraseOp(subviewUse);
       continue;
     }
-
-    // `subview(old_op)` is replaced by a new `subview(val)`.
-    OpBuilder::InsertionGuard g(rewriter);
-    rewriter.setInsertionPoint(subviewUse);
-    MemRefType newType = memref::SubViewOp::inferRankReducedResultType(
-        subviewUse.getType().getShape(), cast<MemRefType>(val.getType()),
-        subviewUse.getStaticOffsets(), subviewUse.getStaticSizes(),
-        subviewUse.getStaticStrides());
-    Value newSubview = memref::SubViewOp::create(
-        rewriter, subviewUse->getLoc(), newType, val,
-        subviewUse.getMixedOffsets(), subviewUse.getMixedSizes(),
-        subviewUse.getMixedStrides());
-
-    // Ouch recursion ... is this really necessary?
-    replaceUsesAndPropagateType(rewriter, subviewUse, newSubview);
-
-    opsToDelete.push_back(use.getOwner());
+    // Non-subview: replace with new value.
+    rewriter.startOpModification(user);
+    use.set(val);
+    rewriter.finalizeOpModification(user);
   }
-
-  // Perform late replacement.
-  // TODO: can we use an early_inc iterator?
-  for (OpOperand *operand : operandsToReplace) {
-    Operation *op = operand->getOwner();
-    rewriter.startOpModification(op);
-    operand->set(val);
-    rewriter.finalizeOpModification(op);
-  }
-
-  // Perform late op erasure.
-  // TODO: can we use an early_inc iterator?
-  for (Operation *op : opsToDelete)
-    rewriter.eraseOp(op);
 }
 
 // Transformation to do multi-buffering/array expansion to remove dependencies
@@ -216,8 +200,8 @@ mlir::memref::multiBuffer(RewriterBase &rewriter, memref::AllocOp allocOp,
                                             offsets, sizes, strides);
   LLVM_DEBUG(DBGS() << "--multi-buffered slice: " << subview << "\n");
 
-  // 5. Due to the recursive nature of replaceUsesAndPropagateType , we need to
-  // handle dealloc uses separately..
+  // 5. Due to the recursive nature of replaceUsesAndPropagateType , we need
+  // to handle dealloc uses separately..
   for (OpOperand &use : llvm::make_early_inc_range(allocOp->getUses())) {
     auto deallocOp = dyn_cast<memref::DeallocOp>(use.getOwner());
     if (!deallocOp)