[Bug tree-optimization/128329] New: `(a == 0 ? b : 0) | a` -> `a == 0 ? b : a`

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128329

            Bug ID: 128329
           Summary: `(a == 0 ? b : 0) | a` -> `a == 0 ? b : a`
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: easyhack, missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

Created attachment 66053
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=66053&action=edit
testcase

This was found while looking into PR 127145 of trying to get a better
branchless involving the spaceship operator.

The attached testcase produces:
```
  _3 = tmp_5(D) == 0;
  tmp3_8 = _3 ? tmp1_7(D) : 0;
  _9 = tmp_5(D) | tmp3_8;
```

But this is just:
```
  _3 = tmp_5(D) == 0;
  _9 = _3 ? _3 ? tmp1_7(D) : tmp_5(D)
```

For riscv (with zicond) this does not make a difference but for targets like
aarch64 or x86, there is an extra ior.

This should be an easy 2 match patterns.