[MLton] PRE for MLton

[Stephen Weeks]

Neal Glew pointed me to a CC04 paper on PRE that seems like it might
be usefully applied to MLton, which lacks a PRE pass in its SSA
optimizer.  The paper is

  Value-Based Partial Redundancy Elimination

and is available at

  http://www.cs.purdue.edu/homes/hosking/papers.html
  ftp://ftp.cs.purdue.edu/pub/hosking/papers/a-ssapre.pdf

It looks like this paper might solve the problems that Tom Murphy
encountered when he tried to apply SSAPRE to MLton.

  http://www-2.cs.cmu.edu/~tom7/ssapre/