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Subject: [boost] [boostcon12]Trouble with tuples very compiler dependent
From: Larry Evans (cppljevans_at_[hidden])
Date: 2012-11-19 11:19:13

This thread is a continuation of that started here:

It's been renamed because the new name is more topical.

The tree_builder benchmarks mentioned here:

were refactored into:


and various other .hpp files. The benchmark was run as shown in the
attached filt.compilation. The output after line:


shows with compiler=gcc4_8, the bcon12_horizontal implementation is
slower than the bcon12_vertical. This agrees, at least qualitatively,
with the page 12 bar chart from Eric's boostcon12 pdf file:


downloadable from here:

and in the mon directory.

The variadic bar in the pag12 bar chart corresponds to the:


tuple implementation in the sandbox slim/test directory.

The unrolled bar in the pag12 bar chart corresponds to the:


In contrast to the gcc4_8 compiler, with the clangxx compiler, the
relative qualitative performance, is just the opposite. IOW, the
bcon12_horizontal implementation is faster than the bcon12_vertical
implementation. In fact, the rate of change of the performance
difference accelerates as tree depth goes from 2 to 4. The rate of
change is so stark that it suggests, at least to me, there may be some
bug in clang. Of course that conclusion is based on almost no
knowledge, on my part, of the clang implementation.

The can be modified to filter out other parts
of the benchmark run output, which is here:

In conclusion, whether it's best to use vertical or horizontal
tuple implementation depends on the compiler.


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