[COMMITTED 0/3] Add a FAST VRP pass.

[COMMITTED 0/3] Add a FAST VRP pass.

[Andrew MacLeod]

the following set of 3 patches provide the infrastructure for a fast vrp 
pass.

The pass is currently not invoked anywhere, but I wanted to get the 
infrastructure bits in place now... just in case we want to use it 
somewhere.

It clearly bootstraps with no regressions since it isn't being invoked 
:-)   I have however bootstrapped it with calls to the new fast-vrp pass 
immediately following the EVRP, and as an EVRP replacement .  This is to 
primarily ensure it isn't doing anything harmful.  That is a test of 
sorts :-).

I also ran it instead of EVRP, and it bootstraps, but does trigger a few 
regressions, all related to relation processing, which it doesn't do.

Patch one provides a new API for GORI which simply provides a list of 
all the ranges that it can generate on an outgoing edge. It utilizes the 
sparse ssa-cache, and simply sets the outgoing range as determines by 
the edge.  Its very efficient, only walking up the chain once and not 
generating any other utillity structures.  This provides fats an easy 
access to any info an edge may provide.  There is a second API for 
querying a specific name instead of asking for all the ranges.   It 
should be pretty solid as is simply invokes ranges-ops and other 
components the same way the larger GORI engine does, it just puts them 
together in a different way

Patch 2 is the new DOM ranger.  It assumes it will be called in DOM 
order, and evaluates the statements, and tracks any ranges on outgoing 
edges.  Queries for ranges walk the dom tree looking for a range until 
it finds one on an edge or hits the definition block.   There are 
additional efficiencies that can be employed, and I'll eventually get 
back to them.

Patch 3 is the FAST VRP pass and folder.  Its pretty straightforward, 
invokes the new DOM ranger, and enables  you to add  MAKE_PASS 
(pass_fast_vrp)  in passes. def.

Timewise, it is currently about twice as fast as EVRP.  It does basic 
range evaluation and fold PHIs, etc. It does *not* do relation 
processing or any of the fancier things we do (like statement side 
effects).   A little additional  work can reduce the memory footprint 
further too.  I have done no experiments as yet as to the cot of adding 
relations, but it would be pretty straightforward as it is just reusing 
all the same components the main ranger does

Andrew