[TableGen] Allocate `Operator` object on heap in `RecordOperatorMap`

Iterators for a `llvm::DenseMap` can be invalidated when an insertion occurs.
    In Pattern's `collectBoundArguments()`, we recursively handle all nested DAG
    nodes and grow the the `RecordOperatorMap`, while retaining a reference.
    This can cause the reference to be invalid and the program to behave randomly.
    Allocate each `Operator` object specifically to solve this issue.

    Also, `llvm::DenseMap` is a great way to map pointers to pointers, or map
    other small types to each other. This avoids placing the `Operator` object
    directly into the map.

--

PiperOrigin-RevId: 243281486

mlir/include/mlir/TableGen/Pattern.h

@@ -39,8 +39,14 @@ class Record;
 namespace mlir {
 namespace tblgen {
 
-// Mapping from TableGen Record to Operator wrapper object
+// Mapping from TableGen Record to Operator wrapper object.
-using RecordOperatorMap = llvm::DenseMap<const llvm::Record *, Operator>;
+//
+// We allocate each wrapper object in heap to make sure the pointer to it is
+// valid throughout the lifetime of this map. This is important because this map
+// is shared among multiple patterns to avoid creating the wrapper object for
+// the same op again and again. But this map will continuously grow.
+using RecordOperatorMap =
+    llvm::DenseMap<const llvm::Record *, std::unique_ptr<Operator>>;
 
 class Pattern;
 

mlir/lib/TableGen/Pattern.cpp

@@ -111,7 +111,11 @@ llvm::StringRef tblgen::DagNode::getOpName() const {
 
 Operator &tblgen::DagNode::getDialectOp(RecordOperatorMap *mapper) const {
   llvm::Record *opDef = cast<llvm::DefInit>(node->getOperator())->getDef();
-  return mapper->try_emplace(opDef, opDef).first->second;
+  auto it = mapper->find(opDef);
+  if (it != mapper->end())
+    return *it->second;
+  return *mapper->try_emplace(opDef, llvm::make_unique<Operator>(opDef))
+              .first->second;
 }
 
 unsigned tblgen::DagNode::getNumOps() const {