title: Acceptability of regular usage of r10 and r11
body: <p>I have been recently doing a lot of x64 assembly programming (on Linux)
  for integration with my C/C++ programs.</p>
  
  <p>Since I am mostly concerned about efficiency I like to use as few different regs/memory addresses as possible as well as trying not to create any stack frames or preserve registers (every cycle counts).</p>
  
  <p>According to the cdecl r10 and r11 registers are not preserved and I wish to use them as temporary variables in my functions preferably without preserving.
  Does it cause any incomparability issues / bugs with any compiler (haven't experienced any so far but it is a concern)?</p>