advanced value range propagation for tree-ssa

[zhouyi zhou <zhouzhouyi at gmail dot com>]

High, 
   Currently gcc can optimize following program by threading a block:
int
fn(int s, int w) {
  int i;

  i = 2;

  if (s)
   i = 1;

  if (s)
   printf("%d\n", i);

  return 0;
}

  While it cannot handle programs of following kind:
int
fn(int s, int w) {
  int i;

  i = 2;

  if (s)
   i = 1;

  if (w)
   goto out1;

  if (s)
   printf("%d\n", i);

out1:
  return 0;
}

The advanced value range propagation:
http://wiki.freebsd.org/ZhouyiZHOU?action=AttachFile&do=get&target=avrp.patch

nicely handles the above case

      2 (if s)
    /   \
   8     3
    \     |
     \__ 4----
        / 
      5(if s)  
    /  \
   6   10

The advanced value range propagation 
1) identify the candidate basic block pairs by 
recurively matching the dom son and dom parent (in our case block 5 and block 2 are
selected)
2) identiy the threadable edge pairs:
here edge pair 8-4 and 5-6, 3-4 and 5-10 are selected
3) thread the edges (duplicate the basic blocks between)
      2
    /  \
   8    3
   |     \
   4'-    4''-
   |      |
   5'     5''
  /       |
 6        10

The patch is being compiled and bootstraped on i686-linux m-32.
and passed most of regression test by make -k check (the not passed tests
 are caused the wrong configuration of my machine like libgmp and libmpfr)

The patch is rudimentary and very dirty written currently, I will clean it in the future

Your review and reply are greatly appreciated.
Zhouyi
and libmpfr