[mlir] Use PyValue instead of PyOpResult in Python operand container

The PyOpOperands container was erroneously constructing objects for
individual operands as PyOpResult. Operands in fact are just values,
which may or may not be results of another operation. The code would
eventually crash if the operand was a block argument. Add a test that
exercises the behavior that previously led to crashes.

Reviewed By: stellaraccident

Differential Revision: https://reviews.llvm.org/D90917

mlir/lib/Bindings/Python/IRModules.cpp

@@ -1228,13 +1228,12 @@ public:
   }
 
   /// Returns `index`-th element in the result list.
-  PyOpResult dunderGetItem(intptr_t index) {
+  PyValue dunderGetItem(intptr_t index) {
     if (index < 0 || index >= dunderLen()) {
       throw SetPyError(PyExc_IndexError,
                        "attempt to access out of bounds region");
     }
-    PyValue value(operation, mlirOperationGetOperand(operation->get(), index));
+    return PyValue(operation, mlirOperationGetOperand(operation->get(), index));
-    return PyOpResult(value);
   }
 
   /// Defines a Python class in the bindings.

mlir/test/Bindings/Python/ir_operation.py

@@ -132,6 +132,29 @@ def testBlockArgumentList():
 run(testBlockArgumentList)
 
 
+# CHECK-LABEL: TEST: testOperationOperands
+def testOperationOperands():
+  with Context() as ctx:
+    ctx.allow_unregistered_dialects = True
+    module = Module.parse(r"""
+      func @f1(%arg0: i32) {
+        %0 = "test.producer"() : () -> i64
+        "test.consumer"(%arg0, %0) : (i32, i64) -> ()
+        return
+      }""")
+    func = module.body.operations[0]
+    entry_block = func.regions[0].blocks[0]
+    consumer = entry_block.operations[1]
+    assert len(consumer.operands) == 2
+    # CHECK: Operand 0, type i32
+    # CHECK: Operand 1, type i64
+    for i, operand in enumerate(consumer.operands):
+      print(f"Operand {i}, type {operand.type}")
+
+
+run(testOperationOperands)
+
+
 # CHECK-LABEL: TEST: testDetachedOperation
 def testDetachedOperation():
   ctx = Context()