Subzero: Cleanly implement register allocation after phi lowering.

src/IceRegAlloc.h

 //===- subzero/src/IceRegAlloc.h - Linear-scan reg. allocation --*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 21 matching lines @@
   void init(RegAllocKind Kind);
   void scan(const llvm::SmallBitVector &RegMask, bool Randomized);
   void dump(Cfg *Func) const;
 
 private:
   typedef std::vector<Variable *> OrderedRanges;
   typedef std::vector<Variable *> UnorderedRanges;
 
   void initForGlobal();
   void initForInfOnly();
+  /// Free up a register for infinite-weight Cur by spilling and reloading some
+  /// register that isn't used during Cur's live range.
+  void addSpillFill(Variable *Cur, llvm::SmallBitVector RegMask);
   /// Move an item from the From set to the To set.  From[Index] is
   /// pushed onto the end of To[], then the item is efficiently removed
   /// from From[] by effectively swapping it with the last item in
   /// From[] and then popping it from the back.  As such, the caller is
   /// best off iterating over From[] in reverse order to avoid the need
   /// for special handling of the iterator.
   void moveItem(UnorderedRanges &From, SizeT Index, UnorderedRanges &To) {
     To.push_back(From[Index]);
     From[Index] = From.back();
     From.pop_back();
   }
 
   Cfg *const Func;
   OrderedRanges Unhandled;
   /// UnhandledPrecolored is a subset of Unhandled, specially collected
   /// for faster processing.
   OrderedRanges UnhandledPrecolored;
   UnorderedRanges Active, Inactive, Handled;
   std::vector<InstNumberT> Kills;
+  RegAllocKind Kind = RAK_Unknown;
   bool FindPreference = false;
   bool FindOverlap = false;
-  // TODO(stichnot): We're not really using FindOverlap yet, but we
-  // may want a flavor of register allocation where FindPreference is
-  // useful but we didn't want to initialize VMetadata with VMK_All
-  // and therefore we can't safely allow overlap.
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEREGALLOC_H