[LLVMdev] undefs in phis

[David Greene]

On Monday 02 February 2009 23:55, Evan Cheng wrote:

> >> Think about what will happen the 2nd iteration.  %v1177 will have
> >> the value of
> >> %v1645 which is wrong.  This is because %v1176 in bb74 will be
> >> replaced with
> >> %v1177.  That's incorrect.
> >
> > Ok, right. The trick to fixing is to make sure the valno of the def of
> > v1177 hasPHIKill to true and make sure the coalescer checks it.

What does hasPHIKill mean, what are the consequences of using it and how do I 
know when I can set it?  I assume this would have been set by someone.  Or is 
that part of the bug?

> Actually liveintervals can construct a v1177 live range starting from  
> the beginning mbb with a val# of unknown def.

What's "the beginning mbb?"  The start of the bb containing the phi (bb74 in 
this case)?  Again, how would I instruct liveintervals to do this?  The 
IMPLICIT_DEF is already gone by that point.

                                                   -Dave