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GCC-4.5.0 comparison with previous releases and LLVM-2.7 on SPEC2000 for x86/x86_64


 GCC-4.5.0 and LLVM-2.7 were released recently.  To understand
where we stand after releasing GCC-4.5.0 I benchmarked it on SPEC2000
for x86/x86-64 and posted the comparison of it with the
previous GCC releases and LLVM-2.7.

 Even benchmarking SPEC2000 takes a lot of time on the fastest
machine I have. So I don't plan to use SPEC2006 for this in near
future.

 You can find the comparison on
http://vmakarov.fedorapeople.org/spec/ (please just click links at the
bottom of the left frame starting with link "GCC release comparison").

 If you need exact numbers, please use the tables (the links to them
are also given) which were used to generate the corresponding bar
graphs.


In general GCC-4.5.0 became faster (upto 10%) in -O2 mode. This is first considerable compilation speed improvement since GCC-4.2. GCC-4.5.0 generates a better (1-2% in average upto 4% for x86-64 SPECFP2000 in -O2 mode) code too in comparison with the previous release. That is not including LTO and Graphite which can gives even more (especially LTO) in many cases.

 GCC-4.5.0 has new big optimizations LTO and Graphite (more
accurately graphite was introduced in the previous release).
Therefore I ran additional benchmarks to test them.

 LTO is a promising technology especially for integer benchmarks for
which it results in smaller and faster code.  But it might result in
degradations too on SPECFP2000 mainly because of big degradations on a
few benchmarks like wupwise or facerec.  Another annoying thing about
LTO, it considerably slows down the compiler.

 Currently Graphite gives small improvements on x86 (one exception is
2% for peak x86 SPECFP2000) and mostly degradation on x86_64 (with
maximum one more than 10% for SPECFP2000 because of big degradations
on mgrid and swim).  So further work is needed on the project because
it seems not mature yet.

 As for LLVM, LLVM became slower (e.g. in comparison with llvm-2.5 on
15%-50% for x86-64).  So the gap between compilation speed of GCC and
LLVM decreased and sometimes achieves 4% on x86_64 and 8% on x86 (both
for SPECInt2000 in -O2 mode).  May be I am wrong but I don't think
CLANG will improve this situation significantly (in -O2 and -O3 mode)
because optimizations still take most of time of any serious
optimizing compiler.

 LLVM did a progress in code performance especially for floating
point benchmarks.  But the gap between LLVM-2.7 and GCC-4.5 in peak
performance (not including GCC LTO and Graphite) still 6-7% on
SPECInt200 and 13-17% on SPECFP2000.

In general, IMHO GCC-4.5.0 is a good and promising release.


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