On Tue, Nov 17, 2015 at 02:31:29PM -0700, Jeff Law wrote: > >- There is a plausible work-around with extended asm, which (mostly) has > >clear semantics regarding clobbers. > Converting an old-style asm to extended asm can be painful. ANd in the > case of legacy code the conversion process itself is a potential source > of bugs.
> >- While the change probably won't introduce bad code, if it does it will > >be in ways that are going to be difficult to track down, in an area > >where few have the expertise to debug. > >- Existing code that currently does things 'right' (ie push/pop any > >modified registers) will suddenly be doing things 'wrong,' or at least > >wastefully. Basic asm does not do this, and hasn't for a very long time. So there simply cannot be existing users that rely on this behaviour. fwprop1 removes the save/restore already, in most cases. > The fact that it wasn't documented that way eons ago is simply a > documentation bug -- likely due to the fact that back when the > documentation for traditional asms was written, there were virtually no > optimizations of memory referencing instructions -- essentially folks > didn't ponder (much less document) how these asms would interact with > memory. _Does_ basic asm as currently implemented have a memory clobber? If not, it seems we can just remove basic asm completely and everything would still work the same! Segher
