On 25 Mar 2005, Ian Lance Taylor wrote: > Paul Schlie <[EMAIL PROTECTED]> writes: > > > > 2) Reload requires the ability to insert arbitrary instructions > > > between any pair of instructions. The instructions inserted by > > > reload will load registers from memory, store registers to memory, > > > and possibly, depending on the port, move values between different > > > classes of registers and add constants to base registers. If > > > reload can't do that without affecting the dependencies between > > > instructions, then it will break. And I don't think reload will be > > > able to do that between your two instructions above, on a typical > > > cc0 machine in which every move affects the condition codes. > > > > - Understood, however along a similar line of though; it would seem "safe" > > to simply "save/restore" the global condition-state around all potentially > > destructive memory operations. > > 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.
Not necessarily. You need the ability to regenerate the condition code. There's at least two ways of doing this: 1. Saving/restoring the condition code 2. Rematerializing the condition code. This would usually be a simple load which is faster than the save/load combo of #1. Toshi
