Re: Question re: SSA Aggressive Dead Code Elimination

[law at redhat dot com]

  In message <Pine.LNX.4.33.0106271412090.1968-100000@www.cgsoftware.com>you wr
ite:
  > > We follow the source regs in PHI nodes and mark their definition sites as
  > > important.  But that's insufficient in this case as the definition sites
  > > are both in block 0 due to the copy propagation.
  > 
  > Ahh, here's the kicker. You need to mark the control transfer instructions
  > from the source blocks in our phi nodes as important too. Or so the
  > comments in all three compilers say.
Agreed.

  > The example pass code i pasted claims to be doing it using the
  > reverse dominance frontier to figure out  which nodes it's really control
  > dependent on, and marking any of the control transfer instructions in
  > those nodes as important.
  > Since we already have the edge pointers, i don't think we need the RDF to
  > do this, we should just be able to mark the edges based on the alternative
  > in the phi node.
Yup.   It's pretty trivial to fix now that we're sure what the right fix is :-)


Thanks again,
jeff