When it comes to GCC 4.6 and hardware, on the embedded front this open-source compiler now supports the ARM Cortex-M4, basic support for the Cortex-A15, and various other ARM improvements and optimizations. There's also (finally) Intel Core 2 optimizations for GCC that can be tapped using core2 with the mtune and march options. At the same time there's also optimizations for first-generation Intel Core i3, Core i5, and Core i7 CPUs using the corei7 tuning option.
Making this release even better are optimizations already for Intel's recently released second-generation Core "Sandy Bridge" CPUs that feature support for the AVX (Advanced Vector eXtensions) instruction set. Those optimizations can be tapped in GCC 4.6 using the corei7-avx value. There's also greater AVX support in GCC 4.6.0 in general via AVX floating-point math support. We recently looked at and benchmarked AVX support in GCC using the new Intel Sandy Bridge CPUs. AMD's Bulldozer CPUs later this year will also possess support for AVX. On the AMD side, GCC 4.6 has support for AMD Bobcat CPUs via btver1 and there's also now support for AMD BMI (Bit Manipulation) functions and code generation.
Aside from hardware improvements in this major GCC update, GCC 4.6 now has support for Google's Android Bionic C library. This means GCC can build native libraries and applications for Google's Android platform, but currently this is only working for the ARM-based version of Android.
Not only is Android getting some love in GCC 4.6, but Google's Go is now supported in GCC. The Go programming language is disabled by default, but support can be enabled for building it with GCC 4.6.
Code/language changes in GCC 4.6 include improved support for the experimental C++0x standard, experimental support for some features of the upcoming C1X revision to the C language, initial support for ADA 2012, inter-procedural optimization improvements, link-time optimization improvements, and a new general optimization level (-Ofast).
The full list of changes for GCC 4.6.0 can be found on this GNU.org page. You can find GCC 4.6 right now on GCC mirrors such as at FU Berlin.
GCC 4.6.0 is not the default compiler for the upcoming Ubuntu 11.04 release, but it will be in Red Hat's Fedora 15. I've been running some GCC 4.6 benchmarks versus GCC 4.5.2 along with LLVM 2.9 SVN and the LLVM Clang compiler and LLVM's DragonEgg optimizer for GCC. Those benchmarks should be on Phoronix this coming Monday. LLVM 2.9 is scheduled for release in early April.