On Sat, Jul 22, 2006 at 09:52:44AM -0700, Ian Lance Taylor wrote: > This may be right, but I'm not sure that it is. If it is OK to > unconditionally execute rdhwr, then it should be OK to put it in a > delay slot. Unless that will break something when rdhwr is emulated. > Or will the emulation code run slower when rdhwr is in a delay slot? > That is, slower than it would if rdhwr were emulated without being in > a delay slot?
Yes. Much, much slower. There's a fast path support for rdhwr (I'm not sure if it is committed yet but it's definitely floating around) which only handles the non-branch-delay case. It will still work in a delay slot, but it's a much heavier-weight operation. So, until and unless there is a revision of the MIPS architecture on which this instruction is not guaranteed to trap, I think we should not put it in a delay slot. -- Daniel Jacobowitz CodeSourcery
