As reported in https://github.com/llvm/llvm-project/issues/101132, this
fixes two bugs:
1. When accessing variadic operands inside an operation, it must be
accessed as `self.operation.operands` instead of `operation.operands`
2. The implementation of the `equally_sized_accessor` function is doing
wrong arithmetics when calculating the resulting index and group sizes.
I have added a test for the `equally_sized_accessor` function, which did
not have a test previously.
3766ba44a8