[Bug target/123962] New: bpf: bpf_core_lower pass not handling BIT_FIELD_REF

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123962

            Bug ID: 123962
           Summary: bpf:  bpf_core_lower pass not handling BIT_FIELD_REF
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vineetg at gcc dot gnu.org
  Target Milestone: ---

When tinkering with test in PR/123894 I ran into a reverse issue as in bitfield
extraction is actually generated and missing co-re codegen.

-O2 -gbtf # iimplies -mco-re

typedef struct  {
  int a;
  char b : 5;
} __attribute__((preserve_access_index)) my_t;

char foo(my_t *s)
{
  if (s->b)
     return 2;
  return 5;
}

This starts off as following gimple

```
char foo (struct my_t * s)
{
  char D.1949;

  _1 = BIT_FIELD_REF <*s, 8, 32>;
  _2 = _1 & 31;
  if (_2 != 0) goto <D.1947>; else goto <D.1948>;
  <D.1947>:
  D.1949 = 2;
  // predicted unlikely by early return (on trees) predictor.
  return D.1949;
  <D.1948>:
  D.1949 = 5;
  return D.1949;
}
```

But then bpy_core_lower: compute_field_expr () currently only handles
COMPONENT_REF, nit BIT_FIELD_REF and misse sout in emitting  
__builtin_core_reloc (0);