Some thoughts about steerring commitee work

[Vladimir N. Makarov]

Eric Botcazou wrote:

>>Please, just look at those charts
>>
>>https://vmakarov.108.redhat.com/nonav/spec/comparison.html
>>
>>The compilation speed decrease without a performance improving (at least
>>for the default case) is really scary.
>>    
>>
>
>Right, I also found those charts a bit depressing, given the time and energy 
>that have been put in the compiler since GCC 3.2.3.  For example, it seems 
>that the Tree-SSA infrastructure has brought very little benefit in terms of 
>performance in the generic case, in exchange for a massive dump of new code.
>  
>
Yes, the compilation speed and SPECINT scores looks a bit depressive.  
But gcc has now more optimizations and there is more possibility to 
generate a better code for a program. Also the code size became smaller 
too.  More people use C++ than C now.  There is really improvement for 
C++ code (SPECINT contains only 1 C++ benchmark of 12 ones).

Fortunately gcc 4.3 will have also faster compilation speed than 4.2 
even with the df infrastructure (which may be, and I hope, helps to 
improve the code finally).  That is because some work was done to speed 
up tree-SSA infrastructure (and Paolo Bonizini's frwprop) to improve the 
compilation speed.

I think LTO will speed up the generated code too although with, I think, 
some signficant compilation slowdown.  And it might be not usefull for 
big programs (e.g. i remember my experience when I forced ICC to compile 
a program for half hour when with less agressive optimizations it would 
compile for a few minutes).