[LLVMdev] TLI vs. TTI

[Matt Arsenault]

On Jul 18, 2014, at 12:14 PM, Hal Finkel <hfinkel at anl.gov> wrote:

> ----- Original Message -----
>> From: "Matt Arsenault" <arsenm2 at gmail.com>
>> To: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>
>> Sent: Friday, July 18, 2014 1:15:14 PM
>> Subject: [LLVMdev] TLI vs. TTI
>> 
>> Hi,
>> 
>> I noticed many functions in the TargetTransformInfo interface are
>> duplicates of those already in TargetLowering (e.g. isTruncateFree).
>> Is the expectation really that targets will reimplement the same
>> functions twice? AArch64’s TTI uses some TLI calls in some of its
>> implementations, but why doesn’t the base TargetTransformInfo call
>> the TargetLowering versions by default?
> 
> Are the implementations different? The default TTI implementation does use the relevant TLI function:
> 
> bool BasicTTI::isTruncateFree(Type *Ty1, Type *Ty2) const {
>  return getTLI()->isTruncateFree(Ty1, Ty2);
> }
> 
> -Hal


Oh, I’ve been looking in TargetTransformInfo.cpp at what I thought were the default implementations, but these are apparently for “NoTTI”. The ones in BasicTTI make much more sense