Re: [Valgrind-developers] flags suck

[Jeremy F. <je...@go...>]

On Mon, 2002-11-25 at 15:57, Julian Seward wrote:

> > Which should be
> >
> > 	add	%edx, %eax
> > 	adc	%ecx, %ebx
> >
> > of course.
> 
> Doesn't the mythical lazy-eflags-save/restore pass clean up this particular
> case?

Should do.  Doesn't look that hard to implement either.  I was vaguely
thinking of hanging a mechanism off VG_(new_emit), by adding "uses" and
"sets" flagset arguments to it, and have it manage flag saves and
restores.  new_emit seemed like a nice place to hang it, since its
already being called in all the right places.

> Good icc handling is known to be difficult in dynamic translators.  I think
> we can say we're running up against the limits of our local analysis.  Most
> systems which do better (WABI, Daisy, surely others) translate groups of
> bbs at a time and track/optimise icc liveness across the whole group.
> Also, that would allow register allocation across the whole group.  If I
> had another spare year and reimplemented the JIT from scratch I'd think about
> something like this.  However, reality being what it is ...

Well, I think a longer term, but not completely impractical, approach is
the extended basic block idea.  It gives us translation of multiple BBs
(including register allocation) more or less within our existing
infrastructure.

        J