[AMDGPU] Don't implement GCNHazardRecognizer::PreEmitNoops(SUnit *)

Authored by foad on May 6 2020, 3:16 AM.


[AMDGPU] Don't implement GCNHazardRecognizer::PreEmitNoops(SUnit *)

When called from the post-RA scheduler, hazards have already been
handled by getHazardType returning NoopHazard, so PreEmitNoops always
returns zero. Remove it. NFC.

Historical note: PreEmitNoops was added to the hazard recognizer
interface as an optional feature to support dispatch group formation on
the POWER target:
So it seems right that we shouldn't need to implement it.

We do still implement the other overload PreEmitNoops(MachineInstr *)
because that is used by the PostRAHazardRecognizer pass.

Differential Revision: https://reviews.llvm.org/D79476