[mlir][ODS] Change `get...Mutable` to return `OpOperand &` for single operands (#66519)

The TableGen code generator now generates C++ code that returns a single
`OpOperand &` for `get...Mutable` of operands that are not variadic and
not optional. `OpOperand::set`/`assign` can be used to set a value (same
as `MutableOperandRange::assign`). This is safer than
`MutableOperandRange` because only single values (and no longer
`ValueRange`) can be assigned.

E.g.:
```
// Assignment of multiple values to non-variadic operand.
// Before: Compiles, but produces invalid op.
// After: Compilation error.
extractSliceOp.getSourceMutable().assign({v1, v2});
```

1 files changed, 18 insertions, 6 deletions

diff --git a/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp b/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
index 5f6a4e3..7029c0e 100644
--- a/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
+++ b/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
@@ -2071,14 +2071,26 @@ void OpEmitter::genNamedOperandSetters() {
       continue;
     std::string name = op.getGetterName(operand.name);
 
-    auto *m = opClass.addMethod(operand.isVariadicOfVariadic()
-                                    ? "::mlir::MutableOperandRangeRange"
-                                    : "::mlir::MutableOperandRange",
-                                name + "Mutable");
+    StringRef returnType;
+    if (operand.isVariadicOfVariadic()) {
+      returnType = "::mlir::MutableOperandRangeRange";
+    } else if (operand.isVariableLength()) {
+      returnType = "::mlir::MutableOperandRange";
+    } else {
+      returnType = "::mlir::OpOperand &";
+    }
+    auto *m = opClass.addMethod(returnType, name + "Mutable");
     ERROR_IF_PRUNED(m, name, op);
     auto &body = m->body();
-    body << "  auto range = getODSOperandIndexAndLength(" << i << ");\n"
-         << "  auto mutableRange = "
+    body << "  auto range = getODSOperandIndexAndLength(" << i << ");\n";
+
+    if (!operand.isVariadicOfVariadic() && !operand.isVariableLength()) {
+      // In case of a single operand, return a single OpOperand.
+      body << "  return getOperation()->getOpOperand(range.first);\n";
+      continue;
+    }
+
+    body << "  auto mutableRange = "
             "::mlir::MutableOperandRange(getOperation(), "
             "range.first, range.second";
     if (attrSizedOperands) {