Perform range analysis after GVN.

Perform range analysis after GVN.

This eliminate redundant HChange instructions and allows range information of
converted values propagated across control-flow splits.

It fixes the performance regression on code like:

if (x > 1) {
  y = x - 1;
}

where we should eliminate the overflow check on the sub inside the if-statement.
Committed: http://code.google.com/p/v8/source/detail?r=8997

[Kevin Millikin (Chromium), 2011-08-23 10:57:37]

LGTM.