<div dir="ltr"><div>Hi David,</div><div><br></div><div>Thank you so much for your quick response!</div><div>I am very inexperienced with llvm. Please bear with me if my questions look stupid:</div><div><br></div><div>1. Here is the output from the command ss"clang++ -v": </div><div><p class="MsoNormal"><br></p><p class="MsoNormal">$ clang++ -v<u></u><u></u></p><p class="MsoNormal">clang version 12.0.0 (... .../llvm/llvm-project_git/clang 36263a7cccc0d98afc36dea55e7a004d08455811)<u></u><u></u></p><p class="MsoNormal">Target: powerpc64le-unknown-linux-gnu<u></u><u></u></p><p class="MsoNormal">Thread model: posix<u></u><u></u></p><p class="MsoNormal">InstalledDir: ... .../llvm/llvm-project_git/build_12.0.0_36263a7_010421/bin<u></u><u></u></p><p class="MsoNormal">Found candidate GCC installation: /usr/lib/gcc/ppc64le-redhat-linux/4.8.2<u></u><u></u></p><p class="MsoNormal">Found candidate GCC installation: /usr/lib/gcc/ppc64le-redhat-linux/4.8.5<u></u><u></u></p><p class="MsoNormal">Selected GCC installation: /usr/lib/gcc/ppc64le-redhat-linux/4.8.5<u></u><u></u></p><p class="MsoNormal">Candidate multilib: .;@m64<u></u><u></u></p><p class="MsoNormal">Selected multilib: .;@m64</p></div><div><br></div><div>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? </div><div> </div><div>2. Here are the options I used to build llvm:</div><div> -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<br></div><div>Are these correct options to use?</div><div><br></div><div>Please advise. Thank you so much David!</div><div><br></div><div>Best,</div><div>Shelton</div><div><br></div><div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Feb 11, 2021 at 4:26 PM David Blaikie <<a href="mailto:dblaikie@gmail.com">dblaikie@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">1) clang++ -v will show you which standard library headers it's using,<br>
it might be using an older standard library on your system that<br>
doesn't have std::make_unique.<br>
2) Did you build the compiler in release mode, or in debug mode? (with<br>
or without assertions enabled)<br>
<br>
On Thu, Feb 11, 2021 at 2:21 PM users users via llvm-dev<br>
<<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<br>
><br>
> Dear LLVM Developers:<br>
><br>
> 1. Recently I built llvm/12.0 on IBM power8 using gcc/<a href="http://8.2.0." rel="noreferrer" target="_blank">8.2.0.</a> When I run clang++ with an example from <a href="https://en.cppreference.com/w/cpp/memory/unique_ptr/make_unique" rel="noreferrer" target="_blank">https://en.cppreference.com/w/cpp/memory/unique_ptr/make_unique</a>:<br>
><br>
> #include <iostream><br>
><br>
> #include <iomanip><br>
> #include <memory><br>
><br>
> struct Vec3<br>
> {<br>
> int x, y, z;<br>
><br>
> // following constructor is no longer needed since C++20<br>
> Vec3(int x = 0, int y = 0, int z = 0) noexcept : x(x), y(y), z(z) { }<br>
><br>
> friend std::ostream& operator<<(std::ostream& os, const Vec3& v) {<br>
> return os << "{ x=" << v.x << ", y=" << v.y << ", z=" << v.z << " }";<br>
> }<br>
> };<br>
><br>
> int main()<br>
> {<br>
> // Use the default constructor.<br>
> std::unique_ptr<Vec3> v1 = std::make_unique<Vec3>();<br>
> // Use the constructor that matches these arguments<br>
> std::unique_ptr<Vec3> v2 = std::make_unique<Vec3>(0,1,2);<br>
> // Create a unique_ptr to an array of 5 elements<br>
> std::unique_ptr<Vec3[]> v3 = std::make_unique<Vec3[]>(5);<br>
><br>
> std::cout << "make_unique<Vec3>(): " << *v1 << '\n'<br>
> << "make_unique<Vec3>(0,1,2): " << *v2 << '\n'<br>
> << "make_unique<Vec3[]>(5): ";<br>
> for (int i = 0; i < 5; i++) {<br>
> std::cout << std::setw(i ? 30 : 0) << v3[i] << '\n';<br>
> }<br>
> }<br>
><br>
><br>
> It failed with the following errors:<br>
> Error: no member named 'make_unique' in namespace 'std'<br>
> std::unique_ptr<Vec3> v1 = std::make_unique<Vec3>();<br>
> ... ...<br>
><br>
> Any idea and suggestion about what is going on? or have I missed something? The command I used to compile the code above:<br>
> $ clang++ a.cpp<br>
><br>
> 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?<br>
><br>
> Thank you very much for any advice!<br>
><br>
> Best Regards,<br>
> Shelton<br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
><br>
> _______________________________________________<br>
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</blockquote></div></div>