[Bug target/127883] x86-64: unnecessary zero-extension after byte extraction

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127883

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2026-10-14
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #2 from Drea Pinski <pinskia at gcc dot gnu.org> ---
```
Trying 7 -> 8:
    7: {r106:DI=r109:DI 0>>0x18;clobber flags:CC;}
      REG_DEAD r109:DI
      REG_UNUSED flags:CC
    8: r107:DI=zero_extend(r106:DI#0)
      REG_DEAD r106:DI
Failed to match this instruction:
(set (reg:DI 107 [ _2 ])
    (zero_extract:DI (reg:DI 109 [ xD.18372 ])
        (const_int 8 [0x8])
        (const_int 24 [0x18])))
Failed to match this instruction:
(set (reg:DI 107 [ _2 ])
    (and:DI (lshiftrt:DI (reg:DI 109 [ xD.18372 ])
            (const_int 24 [0x18]))
        (const_int 255 [0xff])))
```

This could be modeled as a subreg:SI with a shift rt.

Confirmed.