[Bug c++/87849] New: Missed optimization: useless for-loop must be eliminated

[zamazan4ik at tut dot by]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87849

            Bug ID: 87849
           Summary: Missed optimization: useless for-loop must be
                    eliminated
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zamazan4ik at tut dot by
  Target Milestone: ---

gcc(trunk) with -O3 -std=c++17 for this code:

#include <vector>
#include <algorithm>

int foo(std::vector<int> v) {
    int l = v[0];
    for(const auto& x : v) {
        l = std::min(l, x);
    }

    for(const auto& x : v) {
        l = std::max(l, x);
    }

    return l;
}

gcc doesn't eliminate first loop, but gcc can, because first loop has no effect
in this function.