> Read Dark Shikari's blog posts about x264 if you want to see how much good use of SSE matters for video encoding.

Like http://x264dev.multimedia.cx/archives/486? "Now that I’ve written a thousand or two lines of assembly code..." etc. Programmers who know and care about these processor-level micro-optimizations use assembly code, for which by definition you do not need a compiler.

Then again if you really care about graphics performance, you're using a GPU in which case there is no compiler since the driver is just an opaque binary blob.