[Bug rtl-optimization/109592] Failure to recognize shifts as sign/zero extension

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109592

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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           Assignee|unassigned at gcc dot gnu.org      |law at gcc dot gnu.org

--- Comment #11 from Jeffrey A. Law <law at gcc dot gnu.org> ---
So after returning to this, I think the best path forward is to drop the
simplify-rtx bits.  It's dramatically easier to handle in fwprop.

Essentially fwprop will see the nested shifts or extensions and try to simplify
it.  We can check for that case pretty easily without having to write any
recognition code.

Just posted that as a patch today.  Waiting on Richard S's feedback as he knows
that code far better than I.