Fix some corner cases missed by D71955

* replaceAllUsesWith may be supplied with a null value.
* some compilers fail to implicitly convert single result operations to
OpaqueValue, so add an explicit OpOperand::set(Value) method.

Author: River707

mlir/include/mlir/IR/UseDefLists.h

@@ -47,8 +47,8 @@ template <typename OperandType> class IRObjectWithUseList {
   /// the IR that uses 'this' to use the other value instead.  When this returns
   /// there are zero uses of 'this'.
   void replaceAllUsesWith(typename OperandType::ValueType newValue) {
-    assert(this != OperandType::getUseList(newValue) &&
-           "cannot RAUW a value with itself");
+    assert(!newValue || this != OperandType::getUseList(newValue) &&
+                            "cannot RAUW a value with itself");
     while (!use_empty())
       use_begin()->set(newValue);
   }
@@ -126,8 +126,8 @@ class IRMultiObjectWithUseList : public IRObjectWithUseList<OperandType> {
   void replaceAllUsesWith(ValueType oldValue, ValueType newValue) {
     assert(this == OperandType::getUseList(oldValue) &&
            "value not attached to this use list");
-    assert(this != OperandType::getUseList(newValue) &&
-           "cannot RAUW a value with itself");
+    assert(!newValue || this != OperandType::getUseList(newValue) &&
+                            "cannot RAUW a value with itself");
     for (OperandType &use : llvm::make_early_inc_range(getUses(oldValue)))
       use.set(newValue);
   }
@@ -337,6 +337,9 @@ class OpOperand : public IROperand<OpOperand, detail::OpaqueValue> {
   /// Return the current value being used by this operand.
   Value get() const;
 
+  /// Set the operand to the given value.
+  void set(Value value);
+
   /// Return which operand this is in the operand list of the User.
   unsigned getOperandNumber();
 };

mlir/lib/IR/Value.cpp

@@ -111,6 +111,11 @@ Value OpOperand::get() const {
   return IROperand<OpOperand, detail::OpaqueValue>::get();
 }
 
+/// Set the operand to the given value.
+void OpOperand::set(Value value) {
+  IROperand<OpOperand, detail::OpaqueValue>::set(value);
+}
+
 /// Return which operand this is in the operand list.
 unsigned OpOperand::getOperandNumber() {
   return this - &getOwner()->getOpOperands()[0];