EXTRACT_SUBREG coalescing support. The coalescer now treats EXTRACT_SUBREG like

(almost) a register copy. However, it always coalesced to the register of the
RHS (the super-register). All uses of the result of a EXTRACT_SUBREG are sub-
register uses which adds subtle complications to load folding, spiller rewrite,
etc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42899 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineInstr.h

@@ -418,6 +418,10 @@ public:
   /// none is found.
   int findFirstPredOperandIdx() const;
   
+  /// isRegReDefinedByTwoAddr - Returns true if the Reg re-definition is due
+  /// to two addr elimination.
+  bool isRegReDefinedByTwoAddr(unsigned Reg) const;
+
   /// copyKillDeadInfo - Copies kill / dead operand properties from MI.
   ///
   void copyKillDeadInfo(const MachineInstr *MI);