https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120945
Bug ID: 120945
Summary: Missed optimization opportunity with std::bind_front
Product: gcc
Version: 15.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: Mark_B53 at yahoo dot com
Target Milestone: ---
In the following code compiled using -O2, test2() is fully optimized to "mov
eax, 10" followed by "ret", whereas test1() invokes Foo::test in a loop. The
difference between the functions is the use of an explicit lambda (test2) vs. a
call wrapper generated by std::bind_front (test1).
#include <ranges>
#include <functional>
#include <algorithm>
struct Foo {
bool test(int idx) const { return data[idx] == 0; }
int data[10];
int count1() const {
auto fn = std::bind_front(&Foo::test, this);
return std::ranges::count_if(std::views::iota(0, 10), fn);
}
int count2() const {
auto fn = [this](int idx) { return test(idx); };
return std::ranges::count_if(std::views::iota(0, 10), fn);
}
};
__attribute__((noinline)) int test1() {
Foo foo{};
return foo.count1();
}
__attribute__((noinline)) int test2() {
Foo foo{};
return foo.count2();
}
---
clang 19.1 is able to optimize both implementations. Although this fact is
likely not relevant, I'm including it here since I am not a language lawyer on
perfect forwarding call wrappers.
