[mlir][IR] Add notifyBlockRemoved callback to listener

mlir/include/mlir/IR/PatternMatch.h

@@ -402,6 +402,10 @@ class RewriterBase : public OpBuilder {
     Listener()
         : OpBuilder::Listener(ListenerBase::Kind::RewriterBaseListener) {}
 
+    /// Notify the listener that the specified block is about to be erased.
+    /// At this point, the block has zero uses.
+    virtual void notifyBlockRemoved(Block *block) {}
+
     /// Notify the listener that the specified operation was modified in-place.
     virtual void notifyOperationModified(Operation *op) {}
 
@@ -452,6 +456,10 @@ class RewriterBase : public OpBuilder {
     void notifyBlockCreated(Block *block) override {
       listener->notifyBlockCreated(block);
     }
+    void notifyBlockRemoved(Block *block) override {
+      if (auto *rewriteListener = dyn_cast<RewriterBase::Listener>(listener))
+        rewriteListener->notifyBlockRemoved(block);
+    }
     void notifyOperationModified(Operation *op) override {
       if (auto *rewriteListener = dyn_cast<RewriterBase::Listener>(listener))
         rewriteListener->notifyOperationModified(op);

mlir/lib/Conversion/VectorToGPU/VectorToGPU.cpp

@@ -1114,7 +1114,7 @@ static scf::ForOp replaceForOpWithNewSignature(RewriterBase &rewriter,
   scf::ForOp newLoop = rewriter.create<scf::ForOp>(
       loop.getLoc(), loop.getLowerBound(), loop.getUpperBound(), loop.getStep(),
       operands);
-  newLoop.getBody()->erase();
+  rewriter.eraseBlock(newLoop.getBody());
 
   newLoop.getRegion().getBlocks().splice(
       newLoop.getRegion().getBlocks().begin(), loop.getRegion().getBlocks());

mlir/lib/IR/PatternMatch.cpp

@@ -244,7 +244,7 @@ void RewriterBase::eraseOp(Operation *op) {
           for (BlockArgument bbArg : b->getArguments())
             bbArg.dropAllUses();
           b->dropAllUses();
-          b->erase();
+          eraseBlock(b);
         }
       }
     }
@@ -256,10 +256,17 @@ void RewriterBase::eraseOp(Operation *op) {
 }
 
 void RewriterBase::eraseBlock(Block *block) {
+  assert(block->use_empty() && "expected 'block' to have no uses");
+
   for (auto &op : llvm::make_early_inc_range(llvm::reverse(*block))) {
     assert(op.use_empty() && "expected 'op' to have no uses");
     eraseOp(&op);
   }
+
+  // Notify the listener that the block is about to be removed.
+  if (auto *rewriteListener = dyn_cast_if_present<Listener>(listener))
+    rewriteListener->notifyBlockRemoved(block);
+
   block->erase();
 }
 
@@ -311,7 +318,7 @@ void RewriterBase::inlineBlockBefore(Block *source, Block *dest,
   // Move operations from the source block to the dest block and erase the
   // source block.
   dest->getOperations().splice(before, source->getOperations());
-  source->erase();
+  eraseBlock(source);
 }
 
 void RewriterBase::inlineBlockBefore(Block *source, Operation *op,

mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp

@@ -373,6 +373,9 @@ class GreedyPatternRewriteDriver : public PatternRewriter,
   /// Notify the driver that the given block was created.
   void notifyBlockCreated(Block *block) override;
 
+  /// Notify the driver that the given block is about to be removed.
+  void notifyBlockRemoved(Block *block) override;
+
   /// For debugging only: Notify the driver of a pattern match failure.
   LogicalResult
   notifyMatchFailure(Location loc,
@@ -633,6 +636,11 @@ void GreedyPatternRewriteDriver::notifyBlockCreated(Block *block) {
     config.listener->notifyBlockCreated(block);
 }
 
+void GreedyPatternRewriteDriver::notifyBlockRemoved(Block *block) {
+  if (config.listener)
+    config.listener->notifyBlockRemoved(block);
+}
+
 void GreedyPatternRewriteDriver::notifyOperationInserted(Operation *op) {
   LLVM_DEBUG({
     logger.startLine() << "** Insert  : '" << op->getName() << "'(" << op