[Bug target/70119] AArch64 should take advantage of implicit truncation of variable shift amount without defining SHIFT_COUNT_TRUNCATED

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70119

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to ktkachov from comment #3)
> Right, I see we have the same issue on aarch64 as on x86.
> So what would be the accepted solution here?
> I've been playing with a patch to simplify-rtx to move the subreg inside the
> AND and transform the AND into a QImode operation, but there were concerns
> on it pessimising other code

I think adding some special support to combine itself might be better.