[Bug tree-optimization/118317] New: `len - (len != 0) + 1` should optimize to `len == 0 ? 1 : len`

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118317

            Bug ID: 118317
           Summary: `len - (len != 0) + 1` should optimize to `len == 0 ?
                    1 : len`
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
unsigned bar(unsigned len)
{
    unsigned t = len - (len != 0) + 1;
    return t;
}

unsigned bar1(unsigned len)
{
    return len == 0 ? 1 : len;
}
```

These 2 should produce the same code.

For unsigned, MAX_EXPR could be used.

Noticed while looking at PR 118316 on what LLVM was doing for the loop.