Re: PR rtl-optimization/15248 -- semi-latent reload bug

[Bernd Schmidt <bernds_cb1 at t-online dot de>]

Jeffrey A Law wrote:
> On Thu, 2005-05-05 at 19:22 +0200, Bernd Schmidt wrote:
>
> > Jeffrey A Law wrote:
> >
> > > On Thu, 2005-04-21 at 20:52 +0200, Bernd Schmidt wrote:
> > >
> > >
> > > > Yes, that is exactly the thing that I'm not getting here.  If the pseudo 
> > > > is equivalent to readonly memory, why is it ever written to? 
> > >
> > > Because in the initial insn stream the pseudo had to be initialized.
> > > It's the replacement of the pseudo with its equivalent memory location
> > > in the initializing insn that causes the fault.
> > >
> > > Normally the initialization insns are removed.  However, that's not the
> > > case if the RHS of the equivalencing insn is not the equivalent
> > > memory location (in this case the RHS of the equivalencing insn is
> > > another pseudo which we know happens to hold the proper value).
> >
> > Ok.  Still, we should be able to delete the initializing insn in this 
> > case if it has no other side effects, correct?
>
> Assuming you can find them all and safely eliminate the store side
> affect.  Again, consider that the store might be buried inside a
> PARALLEL.  That's a non-trivial problem.

Could be done by forcing an output reload that doesn't get stored 
anywhere.  We have machinery to do this for regs with REG_UNUSED notes etc.


Bernd