[llvm-dev] Clang++: No member name 'make_unique' in namespace 'std'

Thu Feb 11 15:18:44 PST 2021

On Thu, Feb 11, 2021 at 3:08 PM David Blaikie via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On Thu, Feb 11, 2021 at 2:53 PM users users <usertestexamples at gmail.com>
> wrote:
> >
> > Hi David,
> >
> > Thank you so much for your quick response!
> > I am very inexperienced with llvm. Please bear with me if my questions
> look stupid:
> >
> > 1. Here is the output from the command ss"clang++ -v":
> >
> >
> > $ clang++ -v
> >
> > clang version 12.0.0 (... .../llvm/llvm-project_git/clang
> 36263a7cccc0d98afc36dea55e7a004d08455811)
> >
> > Target: powerpc64le-unknown-linux-gnu
> >
> > Thread model: posix
> >
> > InstalledDir: ...
> .../llvm/llvm-project_git/build_12.0.0_36263a7_010421/bin
> >
> > Found candidate GCC installation: /usr/lib/gcc/ppc64le-redhat-linux/4.8.2
> >
> > Found candidate GCC installation: /usr/lib/gcc/ppc64le-redhat-linux/4.8.5
> >
> > Selected GCC installation: /usr/lib/gcc/ppc64le-redhat-linux/4.8.5
> >
> > Candidate multilib: .;@m64
> >
> > Selected multilib: .;@m64
> >
> >
> > Before using clang++, I removed gcc modules, because I thought clang++
> should not be dependent of any host compiler once it was built
> successfully. Or does it need to make my host compiler (such as gcc/8.2.0)
> available to it so that to compile my project?
>
> I think you may need to pass -stdlib=libc++ to use the libc++ you
> built/installed, rather than the system libstdc++ which looks a bit
> out of date (& so doesn't have std::make_unique).
>
> >
> > 2.  Here are the options I used to build llvm:
> >  -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi;openmp;parallel-libs"
> -DCMAKE_BUILD_TYPE="Release" -DLLVM_TARGETS_TO_BUILD=PowerPC
> -DLLVM_ENABLE_LIBPFM=OFF -DRUN_HAVE_GNU_POSIX_REGEX=0
> -DRUN_HAVE_THREAD_SAFETY_ATTRIBUTES=0 -Wno-dev ../llvm
> > Are these correct options to use?
>
> Mostly right except you probably want/need
> -DLLVM_ENABLE_ASSERTIONS=Off if you want a production-speed compiler.
>

This is implied by `-DCMAKE_BUILD_TYPE="Release"`:
https://github.com/llvm/llvm-project/blob/main/llvm/CMakeLists.txt#L412-L416

>
> >
> > Please advise. Thank you so much David!
> >
> > Best,
> > Shelton
> >
> >
> >
> > On Thu, Feb 11, 2021 at 4:26 PM David Blaikie <dblaikie at gmail.com>
> wrote:
> >>
> >> 1) clang++ -v will show you which standard library headers it's using,
> >> it might be using an older standard library on your system that
> >> doesn't have std::make_unique.
> >> 2) Did you build the compiler in release mode, or in debug mode? (with
> >> or without assertions enabled)
> >>
> >> On Thu, Feb 11, 2021 at 2:21 PM users users via llvm-dev
> >> <llvm-dev at lists.llvm.org> wrote:
> >> >
> >> > Dear LLVM Developers:
> >> >
> >> > 1.   Recently I built llvm/12.0 on IBM power8 using gcc/8.2.0. When
> I run clang++ with an example from
> https://en.cppreference.com/w/cpp/memory/unique_ptr/make_unique:
> >> >
> >> >  #include <iostream>
> >> >
> >> > #include <iomanip>
> >> > #include <memory>
> >> >
> >> > struct Vec3
> >> > {
> >> >     int x, y, z;
> >> >
> >> >     // following constructor is no longer needed since C++20
> >> >     Vec3(int x = 0, int y = 0, int z = 0) noexcept : x(x), y(y), z(z)
> { }
> >> >
> >> >     friend std::ostream& operator<<(std::ostream& os, const Vec3& v) {
> >> >         return os << "{ x=" << v.x << ", y=" << v.y << ", z=" << v.z
> << " }";
> >> >     }
> >> > };
> >> >
> >> > int main()
> >> > {
> >> >     // Use the default constructor.
> >> >     std::unique_ptr<Vec3> v1 = std::make_unique<Vec3>();
> >> >     // Use the constructor that matches these arguments
> >> >     std::unique_ptr<Vec3> v2 = std::make_unique<Vec3>(0,1,2);
> >> >     // Create a unique_ptr to an array of 5 elements
> >> >     std::unique_ptr<Vec3[]> v3 = std::make_unique<Vec3[]>(5);
> >> >
> >> >     std::cout << "make_unique<Vec3>():      " << *v1 << '\n'
> >> >               << "make_unique<Vec3>(0,1,2): " << *v2 << '\n'
> >> >               << "make_unique<Vec3[]>(5):   ";
> >> >     for (int i = 0; i < 5; i++) {
> >> >         std::cout << std::setw(i ? 30 : 0) << v3[i] << '\n';
> >> >     }
> >> > }
> >> >
> >> >
> >> > It failed with the following errors:
> >> >     Error: no member named 'make_unique' in namespace 'std'
> >> >        std::unique_ptr<Vec3> v1 = std::make_unique<Vec3>();
> >> >     ... ...
> >> >
> >> > Any idea and suggestion about what is going on? or have I missed
> something? The command I used to compile the code above:
> >> >      $ clang++ a.cpp
> >> >
> >> > 2.  Comparing this llvm with my current gcc/8.2.0 on a project
> (openmp code running 1 thread), it showed that llvm is almost twice as slow
> as gcc (both compile with -O3) on my IBM power8 machine. Is it suppose to
> be with such slower performance than gcc?
> >> >
> >> > Thank you very much for any advice!
> >> >
> >> > Best Regards,
> >> > Shelton
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> > _______________________________________________
> >> > LLVM Developers mailing list
> >> > llvm-dev at lists.llvm.org
> >> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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