The patch switches to a hybrid EVRP pass which utilizes both the Ranger 
and the classic EVRP pass.

it introduces a new undocumented option:

-fevrp-mode=   which can be one of the following options

evrp-only    : This is classic EVRP mode, identical to whats in trunk now.
rvrp-only     : This runs EVRP using *only* the ranger for ranges.
*evrp-first *   : This is a hybrid mode, which uses EVRP to satisfy 
simplifications first, and if that fails, then tries with the ranger
rvrp-first     : Another hybrid mode, this time it tries to simplify 
with the ranger first, then with EVRP.
rvrp-trace    : same as rvrp-only, except a lot of tracing information 
is also dumped to the listing file
rvrp-debug   : This is similar to rvrp-trace, except it also include a 
lot of debug information fo the on-entry caches.
trace            :This runs in EVRP-first mode, but turns on tracing in 
the ranger

The default option currently enabled is *evrp_first*
This gives us similar functionality to what trunk current has, except 
its enhanced by trying to use the ranger to find additional cases.

We see numerous places where the ranger provides enhanced result, the 
primary cases are
   a) When switches are involved.. we provide very precise ranges to 
each switch case, including default,  and we see cases where we can 
eliminate branches due to that
   b) We track ranges on edges quite accurately, and are not limited to 
single entry blocks. In particular we are seeing a number of places 
where ranges are being propagated into PHIs that were not before:

ie, from PR 81192:

   if (j_8(D) != 2147483647)
     goto <bb 4>; [50.00%]
   else
     goto <bb 5>; [50.00%]
<bb 4> :
   iftmp.2_11 = j_8(D) + 1;
<bb 5> :
   # iftmp.2_12 = PHI <j_8(D)(3), iftmp.2_11(4)>

hybrid mode now recognizes a constant can be propagated into the 3->5 
edge and
produces
   # iftmp.2_12 = PHI <2147483647(3), iftmp.2_11(4)>

As a result, we're finding a lot of jump threading opportunities are 
being exposed earlier.


The patch provides 3 EVRP passes, and uses the option to choose which of 
the 3 are invoked. You can see from the patch how interchangeable we 
have managed to make the range engines.

The goal here is to continue exercising both engines regularly, which 
making it easy to detect when one engine is better.  when a dump_file is 
requested for the pass, any time there is a variance in results between 
the 2 engines will be highlighted by lines such as

    EVRP:hybrid: RVRP found singleton 3
    EVRP:hybrid: EVRP found singleton -1B
    EVRP:hybrid: Second query simplifed stmt

We'll be using these to work on identifying differences/issues  as we 
move towards replacing EVRP/VRP fully.

Andrew