[Bug tree-optimization/105983] New: Failure to optimize (b != 0) && (a >= b) as well as the same pattern with binary and

gabravier at gmail dot com gcc-bugzilla@gcc.gnu.org
Tue Jun 14 21:37:26 GMT 2022


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105983

            Bug ID: 105983
           Summary: Failure to optimize (b != 0) && (a >= b) as well as
                    the same pattern with binary and
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

bool f(unsigned a, unsigned b)
{
    return (b != 0) && (a >= b);
}

This can be optimized to `return (b != 0) & (a >= b);`, which is itself
optimized to `return (b - 1) > a;`. GCC outputs code equivalent to `return (b
!= 0) & (a >= b);` (at least on x86) whereas if that code is compiled it would
output `return (b - 1) > a;`, while LLVM has no trouble directly outputting the
optimal code.


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