Silvermont is Intel's forthcoming CPU core to be debuted before year's end for mobile/tablet use and found within the Valley View SoC / Bay Trail. Silvermont was documented in more detail earlier this month at Computex.
Anyhow, the news is that with GCC 4.9, one can target Intel Silvermont optimized binaries now by using -march=slm. The low-power Silvermont CPUs don't present any new CPU instruction set extensions or even the new Haswell instructions like AVX2/BMI/BMI2/FMA, but the "slm" CPU type just enables MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, and SSE4.2. Over the original Atom CPU type for GCC, the Silvermont CPU type exposes SSE 4.1 and SSE 4.2.
Look for GCC 4.9 to be likely released in H1'2014. The different CPU types currently offered by the GNU Compiler Collection can be found via their updated online documentation.