[Bug middle-end/121158] Missed optimization for condition before access to union elements of the same layout

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121158

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2025-07-18
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For aarch64 the issue could be solved in combine:
```
Failed to match this instruction:
(set (zero_extract:DI (reg:DI 115 [ D.4652+8 ])
        (const_int 32 [0x20])
        (const_int 32 [0x20]))
    (const_int 0 [0]))
Failed to match this instruction:
(set (reg:DI 115 [ D.4652+8 ])
    (ior:DI (and:DI (reg:DI 115 [ D.4652+8 ])
            (const_int 4294967295 [0xffffffff]))
        (and:DI (ashift:DI (const_int 0 [0])
                (const_int 32 [0x20]))
            (const_int -4294967296 [0xffffffff00000000]))))
```

That last insn should have been:
(set (reg:DI 115 [ D.4652+8 ])
     (and:DI (reg:DI 115 [ D.4652+8 ])
             (const_int 4294967295 [0xffffffff]))

because `0<<32 & 0xffffffff00000000` is just 0 and a | 0 is just a.