[RFC] Fix PR rtl-optimization/33732

[Paolo Bonzini]

> rask, i am sorry if i sounded like i went off the deep end.  but eric
> seemed to have been talking about doing something very simple that
> evolved just being more conservative when converting the reg dead notes,
> and that seemed like the right level of fix for this problem.  I do not
> know what happened with that direction. 

He posted a patch that should avoid creating the bad REG_DEAD notes.

> I do not know how aggressive that vlad is planning to be with his new
> ra.  He has told me that he plans not to use reload for the spilling.  I
> think that when we get a stack that looks like that, we will certainly
> be able to draw a sharp line between the register allocator and what is
> left of reload and start reload with a clean set of dataflow information. 

I am quite negative, unfortunately, that this will allow us to simplify 
the way dataflow is handled around the boundary of reload.  The way to 
go would be the instruction selection pass (aka alternative selection, 
or pre-reload) that we even have a branch for...

> Major surgery can fix
> this, but there were a lot of other major surgery projects in the
> dataflow port and we did not want this to be one of them.  Likewise, now
> is not the time for major surgery.

I think it's more bugfixes than major surgery, *if you accept to add an 
additional full df scan*.  But unfortunately, I do think that an 
additional df scan is a no-no after all the pain we went through to 
eliminate them (that's what prompted the final "rush" on RTL-sharing 
verification, among other things).

Paolo