To see how the GCC 4.7 release is shaping up, for your viewing pleasure today are benchmarks of GCC 4.2 through a recent GCC 4.7 development snapshot. GCC 4.7 will be released next March/April with many significant changes, so here's some numbers to find out if you can expect to see any broad performance improvements. Making things more interesting, the benchmarks are being done from an AMD FX-8150 to allow you to see how the performance of this latest-generation AMD processor architecture is affected going back by GNU Compiler Collection releases long before this open-source compiler had any optimizations in place.
GCC 4.2.4, 4.3.6, 4.4.6, 4.5.3, 4.6.1, and 4.7.0-20111022 were the GCC releases tested. Each version was built on Ubuntu 11.10 64-bit by its default GCC 4.6.1 compiler. Each GCC release had been built with the "--enable-checking=release" argument. When each of these compiler releases had built the open-source C/C++ benchmarks, the CFLAGS/CXXFLAGS were set to "-march=native -mtune=native -O3" as the default optimizations.
rest here