[Bug tree-optimization/116826] New: Optimise log (1.0 / x) into -log (x)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116826

            Bug ID: 116826
           Summary: Optimise log (1.0 / x) into -log (x)
           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: ktkachov at gcc dot gnu.org
  Target Milestone: ---

float
foo (float a)
{
  return __builtin_logf (1.0f / a);
}

We can avoid the division by folding it into -__builtin_logf (a);
under the usual -funsafe-math-optimizations group for all the various standard
logs.
More generally, log (CST / a) could be folded into log (CST) - log (a).