[PATCH] D77201: [CodeGen][SelectionDAG] Flip Booleans More Often

[Pierre van Houtryve via Phabricator via llvm-commits]

Pierre-vh created this revision.
Pierre-vh added a reviewer: dmgreen.
Herald added subscribers: llvm-commits, danielkiss, hiraditya, kristof.beyls.
Herald added a project: LLVM.
Pierre-vh added a parent revision: D76847: [Target][ARM] Replace re-uses of old VPR values with VPNOTs.

This change should increase the chance that something like `not(setcc)` becomes `setcc` with an opposite cond.

Note that I'm unsure about this patch, so I'll need some feedback. 
It looks fine to me, and it improves codegen in the ARM backend without affecting other backends, but I'm not sure this change is correct. 
Is this a good place for this fix, or should this fix be done in the ARM backend instead?

Example result:

  // Before the patch
  vpnot                    // VPR = !VPR
  vpsel q0, q1, q2  // q0 = VPR ? q1 : q2
  // After the patch
  vpsel q0, q2, q1 // q0 = VPR ? q2 : q1 


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D77201

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/Thumb2/mve-pred-or.ll
  llvm/test/CodeGen/Thumb2/mve-vcmpf.ll
  llvm/test/CodeGen/Thumb2/mve-vcmpfr.ll
  llvm/test/CodeGen/Thumb2/mve-vcmpfz.ll

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