[PATCH] AArch64: Enable subregister liveness tracking.

[Matthias Braun]

Hi t.p.northover, qcolombet,

Splitting this into an own commit to get some visibility.

After doing some extensive benchmarking wiht llvm test-suite, I see no correctness or compiletime changes. I see some very slight benchmark runtime improvements (which may or may not be noise). The only noticeable regression is in a benchmark were literally 6 lines of assembly changed for the better, so that must be cache issues.

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D8474

Files:
  lib/Target/AArch64/AArch64Subtarget.h

Index: lib/Target/AArch64/AArch64Subtarget.h
===================================================================
--- lib/Target/AArch64/AArch64Subtarget.h
+++ lib/Target/AArch64/AArch64Subtarget.h
@@ -91,6 +91,7 @@
   bool enablePostMachineScheduler() const override {
     return isCortexA53() || isCortexA57();
   }
+  bool enableSubRegLiveness() const override { return true; }
 
   bool hasZeroCycleRegMove() const { return HasZeroCycleRegMove; }

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