[PATCH] D55652: [RegAllocGreedy] IMPLICIT_DEF values shouldn't prefer registers

[John Brawn via Phabricator via llvm-commits]

john.brawn created this revision.
john.brawn added reviewers: dfukalov, rampitec, niravd, qcolombet.
Herald added subscribers: nhaehnle, jvesely, MatzeB.

It costs nothing to spill an IMPLICIT_DEF value (the only spill code that's generated is a KILL of the value), so when creating split constraints if the live-out value is IMPLICIT_DEF the exit constraint should be DontCare instead of PrefReg.


Repository:
  rL LLVM

https://reviews.llvm.org/D55652

Files:
  lib/CodeGen/RegAllocGreedy.cpp
  test/CodeGen/AMDGPU/subreg-split-live-in-error.mir
  test/CodeGen/Thumb/ragreedy-implicit-def.ll
  test/CodeGen/X86/pr38795.ll

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