[Bug tree-optimization/126972] New: ranger could be taught about bitreverse

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126972

            Bug ID: 126972
           Summary: ranger could be taught about bitreverse
           Product: gcc
           Version: 17.0
            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
            Blocks: 85316
  Target Milestone: ---

Take:
```

int
f1 (unsigned char x)
{
  if (x != 0 && x != 1)
    return 1;
  x =  __builtin_bitreverse8 (x);
  if (((signed char)x) > 0)
       __builtin_trap();
  return x;
}

unsigned f(unsigned char a)
{
    a &=1;
    unsigned t = __builtin_bitreverseg(a);
    if (((signed char)t) > 0)
      __builtin_trap();
    return 0;
}
```

These f is handled because ccp/bit tracking handles bitreverse but ranger does
not handle the builtin so f1 is not handled. The very least bitmask/value could
be handled by the ranger.  But also it could handle the case where there is a
couple of values (not ranges) which can be reversed.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85316
[Bug 85316] [meta-bug] VRP range propagation missed cases