CodeGen: Refactor renameDisconnectedComponents() as a pass

Refactor LiveIntervals::renameDisconnectedComponents() to be a pass.
Also change the name to "RenameIndependentSubregs":

- renameDisconnectedComponents() worked on a MachineFunction at a time
  so it is a natural candidate for a machine function pass.

- The algorithm is testable with a .mir test now.

- This also fixes a problem where the lazy renaming as part of the
  MachineScheduler introduced IMPLICIT_DEF instructions after the number
  of a nodes in a region were counted leading to a mismatch.

Differential Revision: http://reviews.llvm.org/D20507

llvm-svn: 271345

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TargetPassConfig.cpp b/llvm/lib/CodeGen/TargetPassConfig.cpp
index 4aebf76d779..a62ebadcb7f 100644
--- a/llvm/lib/CodeGen/TargetPassConfig.cpp
+++ b/llvm/lib/CodeGen/TargetPassConfig.cpp
@@ -775,6 +775,11 @@ void TargetPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
   addPass(&TwoAddressInstructionPassID, false);
   addPass(&RegisterCoalescerID);
 
+  // The machine scheduler may accidentally create disconnected components
+  // when moving subregister definitions around, avoid this by splitting them to
+  // separate vregs before. Splitting can also improve reg. allocation quality.
+  addPass(&RenameIndependentSubregsID);
+
   // PreRA instruction scheduling.
   addPass(&MachineSchedulerID);