There are ten P1 regressions (the highest priority) remaining in the current GCC 4.6 trunk, which is a decrease of 21 regressions since the last status report, but still those regressions need to be cleared up before a release candidate can be tagged. There's also 101 regressions of P2 status outstanding (only a drop of eight since the last report) and then 21 regressions of P3 status (a decrease of seven). Today's status report can be read on the GCC mailing list.
When version 4.6 of the GNU Compiler Collection is ready, it will bring a new general optimization level (via -0fast), link-time optimization improvements, inter-procedural optimization improvements, improved code compilation performance / time, experimental support for some features of the C1X revision of the ISO C standard, improved support for the C++0x ISO standard, and support for Google's Go programming language. The GCC Go support is not currently enabled by default, but must be set via the --enable-languages configure argument.
Other enhancements to GCC 4.6 also include support for the ARM Cortex-M4 processor, support for the new Intel Sandy Bridge Core i3/i5/i7 processors with the AVX extensions via the -march=corei7-avx and -mtune=corei7-avx options. There's also other optimizations for the Intel Core 2 and Intel Core i3/i5/i7 series of previous generations. The Advanced Vector Extensions (AVX) have proven to be a very valuable x86 instruction set extension under Windows that is backed by both AMD and Intel, so it will be interesting to benchmark and see how the corei7-avx option carries over into GCC 4.6 under Linux. AMD's upcoming Bulldozer CPUs will bring support for AVX on that side of the table. On an unrelated note, GCC 4.6 also has a tuning option for AMD Bobcat (Family 14) processors.
As yet another item to look at with GCC 4.6 is its support for the Bionic C library to build native libraries and applications for Google's Android platform using the -mandroid and -mbionic options, but this support is currently only enabled for the ARM-based Android.
GCC 4.6.0 should be quite an exciting release when it's out there in the coming months.