[PATCH] [GC] Turn {undef,null} transforms into strategy

[Philip Reames]

Sanjoy's response covered much of what I would otherwise say.  One small 
addition:  If we do add a hook to the GCStrategy class to control these 
optimizations, the location of the optimization should not change.  The 
intent of my "Move ownership of GCStrategy objects to LLVMContext" 
change (up for review now) is to allow InstCombine and other passes to 
get at properties of the GCStrategy in play.

Philip

On 01/04/2015 03:53 PM, Ramkumar Ramachandra wrote:
> I'm just following what I think I understood from your comment: "There might be some weird collector this property does not hold for." -- so, I thought there should be a way to define a custom lowering pass for "relocate undef" or "relocate null" instead of turning them into "undef" and "null" everytime. Did I misunderstand? What are those TODO comments about?
>
> GCStrategy code is invoked on a gc "..." annotation, irrespective of whether it uses the gcroot mechanism, no?
>
>
> http://reviews.llvm.org/D6837
>
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