Re: [tree-ssa] How to increase PHI capacity?

[law at redhat dot com]

In message <1060010146.9010.35.camel@steven.lr-s.tudelft.nl>, Steven Bosscher w
rites:
 >Hi,
 >
 >I'm trying to kill jumps to jumps.  We seem to create lots of them and
 >it should be not too difficult to get rid of them at the tree level.  
 >
 >I was playing with some ideas and I bumped into this problem with PHI
 >node capacity.  Consider these three basic blocks: bb ends with a jump
 >to old_dest which is nothing else but another jump to new_dest:
Note that the infrastructure you need to do this would go a long way to
solving a couple problems with us missing redundancies.  So I'm quite
interested in your work.

 >arg 1(220) has to be duplicated for the edge from 22 to 222.  But the
 >PHI_CAPACITY of the PHIs is only 3; there's no room for a fourth
 >argument...  Gives me an abort in add_phi_arg(), of course.
 >
 >There doesn't seem to be an easy way to increase the capacity of a PHI,
 >at least I can't find it.  Is this just missing, or have my thoughts
 >completely misguided me here?
I don't believe there is an interface to increase a PHI argument's
capacity -- those are pre-computed during PHI insertion.  We allow them
to shrink, but not expand.

It's rather icky, but you could "expand" the PHI node by creating a new
PHI of the desired size and copying all the existing data from the old
one into the new one.  Then you could call add_phi_arg on the new phi
nodes to add your arguments.

Alternately you could make the PHI arguments a virtual array.  Those can
shrink/grow as needed.  Note that I don't think we necessarily have the
ability to have a varray type in our tree structure, so you might need to
add that.

jeff