[Bug tree-optimization/107639] New: GCC unable to reason about range of idx/len

[jmuizelaar at mozilla dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107639

            Bug ID: 107639
           Summary: GCC unable to reason about range of idx/len
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jmuizelaar at mozilla dot com
  Target Milestone: ---

Clang 14 is able to optimize this function to just 'ret'. GCC 12.2 is not.

#include <cstddef>

void do_checks(const int* begin, const size_t len){
    size_t idx = 0;
    const auto end = begin + len;
    for (const int* it = begin; it!=end; ++it, ++idx){
        if (idx <= len){
            // Do something useful
        }
        else
        {
            throw 5;
        }
    }
}

https://godbolt.org/z/f7PjjqG9T