llvm dev - Jan 2013 - [LLVMdev] RFC: Can we make TargetTransformInfo an analysis group?

I know, I said a bad word -- analysis group.

But it works pretty much the way I think we want here. We *always* want a
TargetTransformInfo, and we have reasonable (conservative) stubs in place.
We would just like the option of providing one from the target that has
very clever implementations.

I would propose that we make TargetTransformInfo be an analysis group, and
provide NoTargetTransformInfo as the shim implementation, and each target
provide the more detailed one. This will allow consumers to use normal
getAnalysis methods, etc.

As part of this, I'm planning to move all of TargetTransformInfo to
lib/Analysis.

I'd like to do this soon, so speak up if this sounds like a bad idea. =]
-Chandler
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130104/770988ee/attachment.html>

On Jan 4, 2013, at 8:15 PM, Chandler Carruth <chandlerc at google.com>
wrote:
> I know, I said a bad word -- analysis group.
> 
> But it works pretty much the way I think we want here. We *always* want a
TargetTransformInfo, and we have reasonable (conservative) stubs in place. We
would just like the option of providing one from the target that has very clever
implementations.
> 
I just want to make sure that targets could implement a subset of the
implementation and fallback to the default implementation when needed.

For example the function below uses the default implementation for most cases
and only handles abnormal instructions:

X86VectorTargetTransformInfo::getArithmeticInstrCost  in
https://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?view=markup

> I would propose that we make TargetTransformInfo be an analysis group, and
provide NoTargetTransformInfo as the shim implementation, and each target
provide the more detailed one. This will allow consumers to use normal
getAnalysis methods, etc.
> 
> As part of this, I'm planning to move all of TargetTransformInfo to
lib/Analysis.
> 
> I'd like to do this soon, so speak up if this sounds like a bad idea.
=]
> -Chandler
It sounds like a good idea. I like it.