A plan for eliminating cc0

[Paul Koning]

>>>>> "tm" == tm gccmail <tm_gccmail@kloo.net> writes:

 tm> On 25 Mar 2005, Ian Lance Taylor wrote:
 >> Safe but very costly.  It assumes that every processor has a cheap
 >> way to save and restore the condition codes in user mode, which is
 >> not necessarily the case.  And it assumes that the save and
 >> restore can be removed when not required, which is not obvious to
 >> me.

 tm> Not necessarily.

 tm> You need the ability to regenerate the condition code. There's at
 tm> least two ways of doing this:

 tm> 1. Saving/restoring the condition code

 tm> 2. Rematerializing the condition code. This would usually be a
 tm> simple load which is faster than the save/load combo of #1.

"is faster" -- on some processors, yes.  Not on all.  For example, an
MFPS/MTPS pair to a register on a PDP-11 (when available) is likely to
be faster than a load that references memory.

   paul