Joel de Guzman wrote:
Sebastian Redl wrote:
Eric Niebler wrote:
I confess that I'm not actually benchmarking compile speed; rather, I'm benchmarking the number of template instantiations as reported by Steven's template profiler. I'm profiling TMP-heavy code like some of Proto's and xpressive's tests and cherry-picking the worst offenders. The Fusion vector_n_chooser patch knocked off 100's of template instantiations, for instance.
That's not necessarily a good benchmark, especially if you replace it by preprocessor metaprogramming which leads to more non-template code. GCC is extremely slow at instantiating templates, but this is not necessarily true for other compilers - I believe, for example, that Clang will be faster at instantiating templates than parsing raw code. (No benchmarks - but I know the code.)
Cool! I wonder how that's possible. I have it from Walter Bright (Zortech, Symantec, Digital Mars) that instantiating a template is inherently expensive, and certain features of the C++ language (ADL, partial specialization, etc.) force that to be the case. If Clang has found a way to solve these problems, that's good news indeed. I read form the Wikipedia entry that Clang's C++ support is 2-3 years from being usable, though.
Agreed 100%
OK. When compiling Fusion's vector_make.cpp test ... Before ...
$ time g++ -I ../../../.. -c vector_make.cpp
real 0m1.670s user 0m1.216s sys 0m0.325s
After ...
$ time g++ -I ../../../.. -c vector_make.cpp
real 0m1.208s user 0m0.684s sys 0m0.309s
From the user time, my recent changes make this test compile twice as fast for gcc-3.4 (cygwin). For MSVC, the wins are less dramatic. Your point is taken, though ... instantiation count is merely a rule of thumb and the real measure is clock time. It is, in my experience and with compilers actually in use today, a very good rule of thumb, though. -- Eric Niebler BoostPro Computing http://www.boostpro.com