[Bug tree-optimization/120331] New: useless NON_LVALUE not fully elided by genmatch generated code

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120331

            Bug ID: 120331
           Summary: useless NON_LVALUE not fully elided by genmatch
                    generated code
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: internal-improvement, 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: ---

Take:
```
void g();
void f(int maxlen)
{
  maxlen = maxlen > 264 ?  264 : maxlen;
  if (maxlen > 16)
    g();
}
```

We end up with:
```
Matching expression match.pd:197, gimple-match-6.cc:22
Matching expression match.pd:181, gimple-match-7.cc:45
Matching expression match.pd:181, gimple-match-7.cc:45
Matching expression match.pd:199, gimple-match-6.cc:54
Applying pattern match.pd:1690, gimple-match-3.cc:18989
Applying pattern match.pd:4777, gimple-match-6.cc:5116
gimple_simplified to _6 = maxlen_2(D) > 16;
_1 = _6;
```

This comes from:
```
/* x & ~0 -> x  */
(simplify
 (bit_and @0 integer_all_onesp)
  (non_lvalue @0))
```
pattern.
The non_lvalue here is useless for gimple.

I noticed this while working on PR 120206 .