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From: "ville.voutilainen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/112312] New: GCC fails to optimize a C++ algorithm
 with a function passed in as well as with a lambda
Date: Tue, 31 Oct 2023 11:52:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112312

            Bug ID: 112312
           Summary: GCC fails to optimize a C++ algorithm with a function
                    passed in as well as with a lambda
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ville.voutilainen at gmail dot com
  Target Milestone: ---

See=20
https://godbolt.org/z/s8dWGzb9r

When passing a (pointer to) function as a predicate argument for a C++ stdl=
ib
algorithm, various people hope that it optimizes as well as passing a lambda
that does exactly the same thing. And with clang, it does. With gcc, the
generated
code is much worse for the function case, even though the function definiti=
on
is nearby and visible.

The test code used on godbolt pasted for convenience:

#include <string>
#include <vector>
#include <algorithm>

static bool pred1(const std::string& a, const std::string& b)
{
    return false;
}

auto pred2 =3D [](const std::string& a, const std::string& b)
{
    return false;
};

bool func1(const std::vector<std::string>& vec, const std::string& needle)
{
    return std::ranges::lower_bound(vec, needle, pred1) !=3D vec.end();
}

bool func2(const std::vector<std::string>& vec, const std::string& needle)
{
    return std::ranges::lower_bound(vec, needle, pred2) !=3D vec.end();
}=