[PATCH] D146198: [RISCV] Make ResourceCycles relevant to LMUL

[Michael Maitland via Phabricator via llvm-commits]

michaelmaitland added a comment.

In D146198#4205441 <https://reviews.llvm.org/D146198#4205441>, @pcwang-thead wrote:

> In D146198#4202168 <https://reviews.llvm.org/D146198#4202168>, @michaelmaitland wrote:
>
>>> If there are some microarchitectures that can't be modeled, just add a new subroutine to upstream if approved.
>>
>> Does this mean that subtarget routines must be added to the RISCVScheduleV file since the following function needs to know about the custom subroutine to do its isa checks:
>>
>>   // Helper class for generating a list of resource cycles of different LMULs.
>>   class ResourceCycles<list<ResourceCycle> resourceCycles, string mx> {
>>
>> I am concerned that the `RISCVScheduleV` file will take on bloat due to holding subtarget related routines if this is the case.
>
> Yes. So I posted this patch here just to discuss how we should handle this.
> For example, solutions may be:
>
> 1. Add routines to `RISCVScheduleV.td` just as what I have done.
> 2. Extend `TableGen` to support pass functions:
>
>   // Supposes that we have a Function class to present a function object that its parameters are function parameters.
>   class TargetSubroutine<int base, string mx> : Function;
>   
>   // Then. Supposes that we have a new bang operator to apply this function to input parameters and the result is `ret`.
>   class ResourceCycles<list<TargetSubroutine> subroutines, int base, string mx> {
>     list<int> value = !foreach(subroutine, subroutines,
>                                !apply(subroutine, base, mx)
>                               );
>   }
>   
>   // In SchedXXX.td, we can define our own routines.
>   class Multiplier<int base, string mx>:TargetSubroutine {
>    // We return an int value calculated from mx.
>    int ret = !mul(base, multiplier<mx>.value);
>   }
>
> 3. Some templates are flexible to specify cycles according to LMULs (I haven't figured out one...).

What stops us from doing something like this:
https://github.com/llvm/llvm-project/blob/0c0468e6df2bcabd207858891c2387357857b0bc/llvm/lib/Target/SystemZ/SystemZScheduleZ13.td#L95https://github.com/llvm/llvm-project/blob/0c0468e6df2bcabd207858891c2387357857b0bc/llvm/lib/Target/SystemZ/SystemZScheduleZ13.td#L95
or
https://github.com/llvm/llvm-project/blob/0c0468e6df2bcabd207858891c2387357857b0bc/llvm/lib/Target/AMDGPU/SISchedule.td#L160
?

`Num` or `2` could be replaced with something like `MyTargetGetCycles<mx>.c` without needing to extend the tablegen language. For example:

  class MyTargetGetCycles<string mx> {
    int c = !cond(
      !eq(mx, "M1") : 1,
      !eq(mx, "M2") : 1,
      !eq(mx, "M4") : 1,
      !eq(mx, "M8") : 1,
      !eq(mx, "MF2") : 1,
      !eq(mx, "MF4") : 1,
      !eq(mx, "MF8") : 1,
      !eq(mx, "UpperBound") : 1
    );
  }
  
  foreach mx = SchedMxList in {
    defvar Cycles = MyTargetGetCycles<mx>.c;
    let Latency = Cycles, ResourceCycles = [Cycles] in {
      defm "" : LMULWriteResMX<"WriteVLDE",   [MyTargetSomeResource], mx>;
      defm "" : LMULWriteResMX<"WriteVSTE",   [MyTargetSomeResource], mx>;
    }
  }


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