[gambit-list] Gambit Clang C/C++ status and compiler benchmarks?

Marc Feeley feeley at iro.umontreal.ca
Sat May 5 08:17:31 EDT 2018


GCC is still the best choice when compiling Gambit.

When configured with the usual

  ./configure --enable-single-host

the build time of a “make -j8” on my 4 core laptop is over 10x slower when using CLANG.  As for speed of the generated code, CLANG produces code that is about 3x slower than GCC.

Here are the raw results, in seconds:

                    make -j8     test4
 GCC 8.1.0           39.566      1.167
 CLANG 802.0.38     426.371      4.229

When configured with

  ./configure --enable-single-host --enable-c-opt

which uses -O2 rather than the default -O1, the results are also favourable for GCC.  However the build times are closer and, interestingly, both compilers generate slightly slower code with -O2:

                    make -j8     test4
 GCC 8.1.0          193.560      1.218
 CLANG 802.0.38     229.945      4.410

Marc



> On May 5, 2018, at 5:54 AM, Adam <adam.mlmb at gmail.com> wrote:
> 
> Hi list,
> 
> So I think I figured out the answer myself.
> 
> First, the previous benchmark that I recalled having read, is the "8) Performance of GCC and CLANG when compiling Gambit" section in Gambit's install.txt file (https://github.com/gambit/gambit/blob/edac3c75f0d93f4f56a39c2b90621511f096dd72/INSTALL.txt#L577).
> 
> The essence here is that Clang 2.6, 2.7 and 2.8 wouldn't even compile Gambit, and 2.9-3.1 would compile Gambit but be fairly slow.
> 
> A lot has happened since Clang 3.1, which is the last Clang version covered by install.txt today. The latest version today is 6.0. Ref. https://en.wikipedia.org/wiki/Clang#Status_history . Clang is now the default C/C++/Objective-C compiler choice in a handful operating systems, for AMD64 and some more architectures.
> 
> Clang's language feature set is good, ref. https://en.cppreference.com/w/cpp/compiler_support , https://clang.llvm.org/cxx_status.html .
> 
> And Clang's speed is decent, recent benchmarks tend to find that Clang and GCC have a speed difference that's in the ballpark +-30%, up or down depending on benchmark, e.g. ref. https://stackoverflow.com/questions/3187414/clang-vs-gcc-which-produces-better-binaries#15043814 .
> 
> The term "LLVM" only denotes that Clang has an internal intermediary language form, and the term LLVM has no other meaning in the direction of executable bytecode like Java JIT VM:s. I.e. Clang is only a native C/C++/Obj-C compiler. A list of the Clang/LLVM projects is on the main page at http://www.llvm.org/ .
> 
> I have not tested yet but I do expect Clang to run Gambit stably and at a totally-okay speed.
> 
> Adam
> 
> 2018-05-05 16:13 GMT+08:00 Adam <adam.mlmb at gmail.com>:
> Hi!
> 
> Does Gambit work perfectly with the Clang C/C++ compiler (compiling to assembly which is compiled to native code, nothing LLVM), if so is it for all Gambit versions, or since when?
> 
> I remember a benchmark of the time taken to, was it to compile Gambit-generated C code, or was it execution time of Gambit-C code as compiled by different GCC and Clang versions. What is the URL to that post in the mailing list archive?
> 
> Thanks!
> Adam
> 
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