[llvm-commits] [llvm] r166865 - /llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp

[Nadav Rotem]

Hi Duncan, 


On Oct 28, 2012, at 7:39 AM, Duncan Sands <baldrick at free.fr> wrote:

> does this mean you are querying target lowering info to get these cost
> estimates?  That doesn't make any sense to me.

Yes.  We ask TLI if the operation is legal (or custom or promote) or if it is 'expand'. This works in many cases. 
The idea is to provide a basic cost information for all targets.  The cost information that we get is inaccurate, but it gives us a ballpark figure. 
The next step is to define backend-specific cost model that will give more accurate information. 

>  Can't the whole cost
> estimate thing be its own independent world?

I don't understand this. 

>  In fact it would be nice
> to have cost information for all targets regardless of whether codegen
> support for that target is even built (but maybe that's going too far).


I agree.  This is what I want to get with the default implementation. 
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