[mlir] GreedyPatternRewriteDriver: Do not enqueue operands of deleted ops

[springerm]

Summary

Only ops that were newly inserted or changed should be enqueued.

Patterns can match based on their operands but not based on the uses of their results.

Depends On: D144257

[springerm]

This change is needed for D144193. Otherwise, we may enqueue deleted operations when removing an op op such as:

"op"() {
 // graph region
  %a = "foo"(%b)
  %b = "foo"(%a)
}

The alternative would be to immediately erase an op after triggering notifyOperationRemoved. I.e., a walk over the op that removes nested ops one-by-one and triggers notifications. This would be less efficient than what we are doing now: a walk over an operation to send notifications, followed by a single Operation::erase (that also drops all nested ops).

[springerm]

remove dead code

[springerm]

One problem with this approach is that it increases the number of iterations needed for convergence.

mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp

 void GreedyPatternRewriteDriver::notifyOperationRemoved(Operation *op) {
   LLVM_DEBUG({
     logger.startLine() << "** Erase   : '" << op->getName() << "'(" << op
                        << ")\n";
   });
   if (config.listener)
     config.listener->notifyOperationRemoved(op);
 
-  addOperandsToWorklist(op->getOperands());
   op->walk([this](Operation *operation) {
     removeFromWorklist(operation);
     folder.notifyRemoval(operation);
   });
 
   if (config.strictMode != GreedyRewriteStrictness::AnyOp)
     strictModeFilteredOps.erase(op);
 }