[Bug target/122319] gcc does not know _tzcnt_u64 <= 64

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122319

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2025-10-19
           Severity|normal                      |enhancement
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
```
Trying 26 -> 29:
   26: {r127:DI=unspec[r123:DI] 98;clobber flags:CC;}
      REG_DEAD r123:DI
      REG_UNUSED flags:CC
   29: r130:SI=zero_extend(r127:DI#0)
      REG_DEAD r127:DI
Failed to match this instruction:
(set (reg:SI 130 [ _9 ])
    (zero_extend:SI (subreg:QI (unspec:DI [
                    (reg:DI 123)
                ] UNSPEC_TZCNT) 0)))
```

Most likely should recognize that as an insn that just outs a lzcnt
instruction. and then it would just work.