Use of register 17 on x86

[Richard Kenner]

    > Also, why isn't x86 using CC0 anymore?  That would seem to be the most
    > efficient, both in terms of generated code and compilation speed.

    It's is impossible to represent a comparison followed by multiple
    cmove instructions.

True.

    Given the improvements in code generation with the new backend, I
    think that gives lie to CC0 being more efficient in terms of generated
    code.

Maybe, but the downside is that you have the explicit clobber of the register
in many arithmetic insns, making it harder to optimize them because you
can't just insert one without knowing if reg 17 is dead there.