[mlir][Python] Fix generation of accessors for Optional

[michalt]

Summary

Previously, in case there was only one Optional operand/result within
the list, we would always return None from the accessor, e.g., for a
single optional result we would generate:

return self.operation.results[0] if len(self.operation.results) > 1 else None

But what we really want is to return None only if the length of
results is smaller than the total number of element groups (i.e.,
the optional operand/result is in fact missing).

This commit also renames a few local variables in the generator to make
the distinction between isVariadic() and isVariableLength() a bit
more clear.

[michalt]

This is the first time I'm trying to do anything non-trivial with MLIR, so any feedback is very welcome (especially if I misunderstood/missed something :) Thanks!

[ftynse]

Thanks for the fix! Please let me know if you need help landing this.

mlir/test/python/dialects/python_test.py

131–132

Nit: spurious whitespace change (this file uses two newlines between functions AFAICS).

[michalt]

Fix whitespace

[michalt]

In D113855#3134009, @ftynse wrote:

Thanks for the fix! Please let me know if you need help landing this.

Thank you for a quick review! :) I don't have commit access, so it'd be great if you could land this, thanks!

[ftynse]

Something went wrong and now the diff contains only the whitespace changes. If you made them as two separate git commits, please indicate the two-commit range when updating the revision or squash them.

[michalt]

Correctly export the whatespace fix to Phab

[michalt]

In D113855#3137685, @ftynse wrote:

Something went wrong and now the diff contains only the whitespace changes. If you made them as two separate git commits, please indicate the two-commit range when updating the revision or squash them.

Yikes! I haven't used arc for a couple of years... and indeed I made a separate commit and didn't specify the range correctly when running arc diff. Sorry for that!

mlir/test/python/dialects/python_test.py

with Context() as ctx, Location.unknown():
 
     # CHECK: Unit: True
     op.unit = True
     print(f"Unit: {op.unit}")
 
     # CHECK: Unit: False
     del op.unit
     print(f"Unit: {op.unit}")
 
+
 # CHECK-LABEL: TEST: inferReturnTypes
 @run
 def inferReturnTypes():
   with Context() as ctx, Location.unknown(ctx):
     test.register_python_test_dialect(ctx)
     module = Module.create()
     with InsertionPoint(module.body):
       op = test.InferResultsOp()
       dummy = test.DummyOp()
with InsertionPoint(module.body):
       implied = test.InferResultsImpliedOp()
       # CHECK: i32
       print(implied.integer.type)
       # CHECK: f64
       print(implied.flt.type)
       # CHECK: index
       print(implied.index.type)
 
+
 # CHECK-LABEL: TEST: testOptionalOperandOp
 @run
 def testOptionalOperandOp():
   with Context() as ctx, Location.unknown():
     test.register_python_test_dialect(ctx)
 
     module = Module.create()
     with InsertionPoint(module.body):
 
       op1 = test.OptionalOperandOp(None)
       # CHECK: op1.input is None: True
       print(f"op1.input is None: {op1.input is None}")
 
       op2 = test.OptionalOperandOp(op1)
       # CHECK: op2.input is None: False
       print(f"op2.input is None: {op2.input is None}")