Subzero: Use the linear-scan register allocator for Om1 as well.

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.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the LinearScan data structure used during
 // linear-scan register allocation, which holds the various work
 // queues for the linear-scan algorithm.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEREGALLOC_H
 #define SUBZERO_SRC_ICEREGALLOC_H
 
 #include "IceDefs.h"
 #include "IceTypes.h"
 
 namespace Ice {
 
 class LinearScan {
   LinearScan(const LinearScan &) = delete;
   LinearScan &operator=(const LinearScan &) = delete;
 
 public:
-  LinearScan(Cfg *Func) : Func(Func) {}
-  void initForGlobalAlloc();
+  LinearScan(Cfg *Func)
+      : Func(Func), FindPreference(false), FindOverlap(false) {}
+  void init(RegAllocKind Kind);
   void scan(const llvm::SmallBitVector &RegMask);
   void dump(Cfg *Func) const;
 
 private:
+  void initForGlobal();
+  void initForInfOnly();
+
   Cfg *const Func;
   typedef std::vector<Variable *> OrderedRanges;
   typedef std::list<Variable *> UnorderedRanges;
   OrderedRanges Unhandled;
   // UnhandledPrecolored is a subset of Unhandled, specially collected
   // for faster processing.
   OrderedRanges UnhandledPrecolored;
   UnorderedRanges Active, Inactive, Handled;
   std::vector<InstNumberT> Kills;
+  bool FindPreference;
+  bool FindOverlap;
+  // 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