Interest in integer auto-upcasting pass for normalization and optimization?

[Albert Cohen]

Sebastian Pop and I have been discussing the option of designing a new 
pass, based on vrp, to normalize integer types towards a canonical 
supertype typically a machine word, equivalent to signed long, or to 
truncate to a smaller-size word when it makes sense. This would be a 
very simple pass (on top of not-so-simple vrp), but arguably a quite 
regression-prone one as well (due to aliases/escape and common C 
standard violations).

The pass could be parameterized with three different objectives, 
depending on where it is scheduled in the pass manager.

(1) canonicalize to the supertype aggressively, to facilitate the 
application of further passes like autovect which require very precise 
understanding of the type conversions;
(2) compress the types to increase vectorization factor and reduce 
register pressure (assuming the target supports sub-word register 
allocation with register aliases);
(3) optimize the types to minimize the dynamic number of casts that 
result in actual ASM instructions.

Graphite and the vectorizer would clearly benefit from such a pass, at 
least if it implemented objective (1).

I wonder if some of this is already implemented somewhere, or if someone 
played with it in the past, or is interesting in contributing.

Nothing is planned yet on our side, and temporary fixes exist in the 
short term (as far as Graphite and the vectorizer are concerned), but it 
would potentially be of great help.

Feedback welcome,
Albert