[LLVMdev] llvm ir vs dag

[reed kotler]

It seems to me that a lot of the transformations done on DAG could more 
easily and cleanly be done in the IR.

It could require some ability to extend IR for targets but this could be 
useful anyway.
With inline assembly, one can already place assembly in the IR.

Some things that could be done in IR:

1) call and return lowering and related functions
2) atomic
3) soft float
4) ... many others

This could eliminate a lot of messy coding takes place in target 
lowering and DAG to DAG.

The average person doing porting should not, IMO, be exposed to many of 
the details of chains, glue and other complexities and idiosyncrasies of 
the Selection DAG.

The main idea is to eliminate or shrink considerably XXXTargetLowering  
and XXXISelDagToDag.

There could also be some Machine IR added to the current IR that is not 
target specific.

My 2c.

Reed