[PATCH] D90591: [ARM] Introduce t2DoLoopStartTP

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: samparker, samtebbs, SjoerdMeijer, efriedma, simon_tatham.
Herald added subscribers: danielkiss, nikic, hiraditya, kristof.beyls.
Herald added a project: LLVM.
dmgreen requested review of this revision.

This introduces a new pseudo instruction, almost identical to a t2DoLoopStart but taking 2 parameters - the original loop iteration count needed for a low overhead loop, plus the VCTP element count needed for a DLSTP instruction setting up a tail predicated loop. The idea is that the instruction holds both values and the backend ARMLowOverheadLoops pass can pick between the two, depending on whether it creates a tail predicated loop or falls back to a low overhead loop.

To do that there needs to be something that converts a t2DoLoopStart to a t2DoLoopStartTP, for which this patch repurposes the MVEVPTOptimisationsPass as a "tail predication and vpt optimisation" pass. The extra operand for the t2DoLoopStartTP is chosen based on the operands of VCTP's in the loop, and the instruction is moved as late in the block as possible to attempt to increase the likelihood of making tail predicated loops.


https://reviews.llvm.org/D90591

Files:
  llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
  llvm/lib/Target/ARM/ARMBaseInstrInfo.h
  llvm/lib/Target/ARM/ARMInstrThumb2.td
  llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
  llvm/lib/Target/ARM/MVEVPTOptimisationsPass.cpp
  llvm/test/CodeGen/ARM/O3-pipeline.ll
  llvm/test/CodeGen/Thumb2/LowOverheadLoops/exitcount.ll
  llvm/test/CodeGen/Thumb2/LowOverheadLoops/fast-fp-loops.ll
  llvm/test/CodeGen/Thumb2/LowOverheadLoops/mov-operand.ll
  llvm/test/CodeGen/Thumb2/LowOverheadLoops/mve-tail-data-types.ll
  llvm/test/CodeGen/Thumb2/LowOverheadLoops/reductions.ll
  llvm/test/CodeGen/Thumb2/mve-fma-loops.ll
  llvm/test/CodeGen/Thumb2/mve-gather-scatter-tailpred.ll
  llvm/test/CodeGen/Thumb2/mve-postinc-dct.ll
  llvm/test/CodeGen/Thumb2/mve-postinc-lsr.ll
  llvm/test/CodeGen/Thumb2/mve-vldshuffle.ll

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