Hello, On 01 Jul 2014, at 06:54, vijay nag <vijunag@xxxxxxxxx> wrote: > Hello GCC, > > Gcc upgrade from 3.3.2(i586 target) to 4.7.2(i686) is yielding a > performance gain of around 20% in our code base. > > It would be interesting to know where/how exactly the code has been > optimized by the latest compiler. What is the best way to know where > exactly the newer compiler has performed better than the older one ? > In general, when a compiler is upgraded how do we make a comparative > study between the old and the new one ? This is difficult to answer without knowing the details of your code base. It could be that one particular optimization that is done by the 4.7 compiler causes the 20% improvement. It could also be different optimizations playing together to your benefit. You can compare the assembler output of the compilers by using e.g. the -save-temps option, although that might be impractical for large code bases. Alternatively you can go through the release notes of each version from 3.3.2 on (e.g. https://gcc.gnu.org/gcc-4.7/changes.html) and extract the optimizations that have been added in each version and which options are available to control them (https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#Optimize-Options). Then, disable those optimizations and observe the effects on your code base. Cheers, Oleg
