[Bug rtl-optimization/93565] [9/10 regression] Combine duplicates instructions

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93565

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #11)
> (The original problem I have an idea for -- don't generate a parallel of
> two SETs with equal SET_SRC -- but that doesn't handle the new case).

For the new case, nonzero_bits should find out that the sign_extension is the
same thing as zero_extension and it would be best to just do a single and e.g.
on a paradoxical subreg of the source and a pseudo copy.