https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106888
--- Comment #9 from Vineet Gupta <vineetg at gcc dot gnu.org> ---
(In reply to Jeffrey A. Law from comment #6)
> Comment on attachment 54905 [details]
> proposed patch
>
> So that's a subset of what we've done. We initially thought that was going
> to be enough to solve this class of problems. But it's actually deeper
> than just having a zero_extension variant of this pattern.
Yeah it seems adding a new define_insn with zero_extend is not enough (nor is
the more elegant any_extend to existing "*<bitmanip_optab>disi2")
Thing is at expand time, we have gimple CTZ expand to ctz+sign_extend, so
adding zero_extend won't really help ?
(insn 6 3 7 2 (set (reg:SI 74)
(ctz:SI (subreg/s/u:SI (reg/v:DI 73 [ x ]) 0))) "pr90838-red.c":11:15
-1
(nil))
(insn 7 6 8 2 (set (reg:DI 72 [ <retval> ])
(sign_extend:DI (reg:SI 74))) "pr90838-red.c":11:15 -1
(nil))
> I'll officially submit the zero_extension pattern and the match.pd bits.
> The other pattern we wrote is fugly and I'd like to look at it one more time.
But that other pattern is needed for combine to fuse them together.
