[LLVMdev] Type Legalizer Question.

[sanjiv gupta]

On Thu, 2008-10-02 at 08:53 -0700, Chris Lattner wrote:
> On Oct 2, 2008, at 8:38 AM, Eli Friedman wrote:
> 
> > On Thu, Oct 2, 2008 at 7:34 AM, Evan Cheng <evan.cheng at apple.com>  
> > wrote:
> >>
> >> On Oct 2, 2008, at 2:01 AM, sanjiv gupta wrote:
> >>
> >>>
> >>>>
> >>>> So you have a i16 register class which makes the type legal. You  
> >>>> can
> >>>> make loads and stores legal (can you?). But you will have to custom
> >>>> lower all other i16 operations. This will work, but it requires a  
> >>>> lot
> >>>> of target specific code.
> >>>
> >>> True. If we add the i16 reg class we will need to write a lot of
> >>> target specific code.
> >>> To avoid that our idea was not to tell the legalizer about the i16
> >>> regclass and let it expand everything but ignore the pointers.
> >>
> >> You can try just marking all i16 operations, other than load and
> >> store, as "expand". Would that work?
> >
> > Won't work; LLVM expects at least some basic operations, like add, to
> > be legal in legal register types.
> 
> That sounds like a bug, not a feature.
> -Chris

The -enable-legalize-types infrastructure is entirely based upon
getVTAction (), so it will be completely ignored once we have i16
regclass,
ditto with ExpandOp of LegalizeDAG. 
And LegalizeDAG::LegalizeOp() allows very few things to be auto expanded.

-Sanjiv
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