Performance degradation on g++ 4.6

[Oleg Smolsky]

Hi there, I have compiled and run a set of C++ benchmarks on a 
CentOS4/64 box using the following compilers:
     a) g++4.1 that is available for this distro (GCC version 4.1.2 
20071124 (Red Hat 4.1.2-42)
     b) g++4.6 that I built (stock version 4.6.1)

The machine has two Intel quad core processors in x86_64 mode 
(/proc/cpuinfo attached)

Benchmarks were taken from this page:
     http://stlab.adobe.com/performance/

Results:
     - some of these tests showed 20..30% performance degradation
       (eg the second section in the simple_types_constant_folding test: 
30s -> 44s)
     - a few were quicker
     - full reports are attached

I would assume that performance of the generated code is closely 
monitored by the dev community and obvious blunders should not sneak 
in... However, my findings are reproducible with these synthetic 
benchmarks as well as production code at work. The latter shows 
approximately 25% degradation on CPU bound tests.

Is there a trick to building the compiler or using a specific 
-mtune/-march flag for my CPU? I built the compiler with all the default 
options (it just has a distinct installation path):
     ../gcc-%{version}/configure --prefix=/work/tools/gcc46 
--enable-languages=c,c++ --with-system-zlib 
--with-mpfr=/work/tools/mpfr24 --with-gmp=/work/tools/gmp 
--with-mpc=/work/tools/mpc 
LD_LIBRARY_PATH=/work/tools/mpfr/lib24:/work/tools/gmp/lib:/work/tools/mpc/lib

Are there any published benchmarks? I'd appreciate any advice or pointers.

Thanks in advance,
Oleg.
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