[llvm-dev] RFC: Exposing TargetTransformInfo factories from TargetMachine

[Sanjoy Das via llvm-dev]

On Mon, Dec 18, 2017 at 6:26 PM, Eric Christopher <echristo at gmail.com> wrote:
> Instead, is there any reason why TTI for a given Subtarget shouldn't live on
> the Subtarget? Just construct it the same way we do TargetLowering, etc?

Then stuff that depends on Analysis today will have to depend on
CodeGen, which is probably not ideal.

I think I'll go with Matthias' idea -- remove the function pointer
indirection altogether, and instead just have a virtual
getTargetTransformInfo(Function&) in TargetMachine.

I was also wondering if it makes sense to make the llvm::Function
argument optional -- that'll help make XLA's use case slightly cleaner
since we don't (yet) have per-function target attributes.

-- Sanjoy

>
> -eric
>
>
> On Fri, Dec 15, 2017 at 10:13 AM Sanjoy Das via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>>
>> On Fri, Dec 15, 2017 at 5:30 AM, Hal Finkel <hfinkel at anl.gov> wrote:
>> > Are there reasons why we might not want to do this? Other options we
>> > should
>> > consider?
>>
>> It does make the TargetMachine -> TargetIRAnalysis path less abstract,
>> but given that all targets have the same pattern of instantiating a
>> TargetIRAnalysis with a Function->TargetTransformInfo hook, the
>> abstraction does not seem particularly useful.
>>
>> I might do even a simpler form of the patch though -- instead of
>> returning a function pointer from TargetMachine, just add a virtual
>> function to TargetMachine that creates the TargetTransformInfo
>> directly from a Function.
>>
>> -- Sanjoy
>>
>> >
>> >  -Hal
>> >
>> >>
>> >> [0]:  XLA is a machine learning focussed linear algebra compiler
>> >> https://www.tensorflow.org/performance/xla/ that uses LLVM for its CPU
>> >> and GPU backends.
>> >>
>> >> -- Sanjoy
>> >> _______________________________________________
>> >> LLVM Developers mailing list
>> >> llvm-dev at lists.llvm.org
>> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>> >
>> >
>> > --
>> > Hal Finkel
>> > Lead, Compiler Technology and Programming Languages
>> > Leadership Computing Facility
>> > Argonne National Laboratory
>> >
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