The GNU Compiler Collection 5 won't be released until sometime around early-to-mid 2015. In the months since the GCC 4.9 release there's been continued work on Link-Time Optimizations, Intel contributing its MIC runtime offloading library, and continued work towards C++14 support. Much more work is expected in the months ahead and we're still waiting to see GCC's OpenACC 2.0 support with a NVIDIA GPU back-end, support for upcoming Intel and AMD CPUs, more ARM/ARM64 optimizations, and much more.
Anyhow, the tentative GCC 5 release notes were updated this week to reflect some more of the developer-facing changes coming to this next release. You can find the tentative, in-development release notes for GCC 5.0 via the GNU.org documentation. Besides GCC's G++ now supporting C++14 variable templates, GCC for Fortran 2003 supporting the intrinsic IEEE modules, experimental support for Fortran 2008's co-arrays, and new parallel features in Fortran, there's a number of new command-line switches.
In GCC 5 the UndefinedBehaviorSanitizer is getting new sanitization options for floating-point division by zeros, a check to ensure floating-point type to integer conversions don't overflow, instrumentation of array bounds and out-of-bound access detection, and alignment checking for objects. These new sanitization options are exposed via various -fsanitize= values.
GCC 5's C family support also has a number of new command-line options for exposing additional compiler warnings: -Wswitch-bool, -Wlogical-not-parentheses, -Wsizeof-array-argument, and -Wbool-compare. For the C support is also new -Wc90-c99-compat, -Wc99-c11-compat, and -Wno-incompatible-pointer-types options.
Stay tuned for more GCC 5.0 coverage in the months ahead along with fresh compiler benchmarks on Phoronix.