[LLVMdev] TargetLowering vs. TargetTransform

[Nadav Rotem]

Hi Renato, 

I think that we need to improve ::isTruncateFree, ::isZextFree, etc to include all of the free conversions. Vector and Scalar.

Non-free conversions are marked with setOperationAction so the generic parts of TTI should be able to give a reasonable cost estimation.

The cost tables should contain cases that are not handled by TTI.  So, if we have a clever DAGCombine optimization (that TLI can't detect because it is not in the operations table) then we need to add it to the cost table. 

Thanks,
Nadav

On Jan 25, 2013, at 8:21 AM, Renato Golin <renato.golin at linaro.org> wrote:

> Hi all,
> 
> I'm looking for a place where to put the costs of vector (and scalar) cast operations for ARM, but I noticed the TargetTransform methods call the TargetLowering ones when unsure.
> 
> Now, I'm not sure...
> 
> Many casts on ARM are free, and I could build a list of cases where it is true, but should I put this on the lowering or the transform? My main motivation is to get the costs right for the vectorization pass, but I think this should be generally available to any pass that needs it.
> 
> What are the uses of each and, is there a general rule of thumb for using them?
> 
> cheers,
> --renato