missing optimization "a << (b & 63) to a << b"

[Xinliang David Li]

>> Or better way to solve the problem? Appreciated a lot!
>
> Combine / simplify-rtx should recognize this at the RTL level for
> SHIFT_COUNT_TRUNCATED targets.

IIUC, combine uses UD chains (LOG links) which is best suitable for
cases where this is only one downward uses of the def. The example
here has a single def and multiple-uses, which combine won't handle.

David

>
> Richard.
>
>> Thanks,
>> Wei.