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diff --git a/lib/CodeGen/LiveRegMatrix.h b/lib/CodeGen/LiveRegMatrix.h
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+//===-- LiveRegMatrix.h - Track register interference ---------*- C++ -*---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The LiveRegMatrix analysis pass keeps track of virtual register interference
+// along two dimensions: Slot indexes and register units. The matrix is used by
+// register allocators to ensure that no interfering virtual registers get
+// assigned to overlapping physical registers.
+//
+// Register units are defined in MCRegisterInfo.h, they represent the smallest
+// unit of interference when dealing with overlapping physical registers. The
+// LiveRegMatrix is represented as a LiveIntervalUnion per register unit. When
+// a virtual register is assigned to a physicval register, the live range for
+// the virtual register is inserted into the LiveIntervalUnion for each regunit
+// in the physreg.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_LIVEREGMATRIX_H
+#define LLVM_CODEGEN_LIVEREGMATRIX_H
+
+#include "LiveIntervalUnion.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/OwningPtr.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+
+namespace llvm {
+
+class LiveInterval;
+class LiveIntervalAnalysis;
+class MachineRegisterInfo;
+class TargetRegisterInfo;
+class VirtRegMap;
+
+class LiveRegMatrix : public MachineFunctionPass {
+  const TargetRegisterInfo *TRI;
+  MachineRegisterInfo *MRI;
+  LiveIntervals *LIS;
+  VirtRegMap *VRM;
+
+  // UserTag changes whenever virtual registers have been modified.
+  unsigned UserTag;
+
+  // The matrix is represented as a LiveIntervalUnion per register unit.
+  LiveIntervalUnion::Allocator LIUAlloc;
+  LiveIntervalUnion::Array Matrix;
+
+  // Cached queries per register unit.
+  OwningArrayPtr<LiveIntervalUnion::Query> Queries;
+
+  // Cached register mask interference info.
+  unsigned RegMaskTag;
+  unsigned RegMaskVirtReg;
+  BitVector RegMaskUsable;
+
+  // MachineFunctionPass boilerplate.
+  virtual void getAnalysisUsage(AnalysisUsage&) const;
+  virtual bool runOnMachineFunction(MachineFunction&);
+  virtual void releaseMemory();
+public:
+  static char ID;
+  LiveRegMatrix();
+
+  //===--------------------------------------------------------------------===//
+  // High-level interface.
+  //===--------------------------------------------------------------------===//
+  //
+  // Check for interference before assigning virtual registers to physical
+  // registers.
+  //
+
+  /// Invalidate cached interference queries after modifying virtual register
+  /// live ranges. Interference checks may return stale information unless
+  /// caches are invalidated.
+  void invalidateVirtRegs() { ++UserTag; }
+
+  enum InterferenceKind {
+    /// No interference, go ahead and assign.
+    IK_Free = 0,
+
+    /// Virtual register interference. There are interfering virtual registers
+    /// assigned to PhysReg or its aliases. This interference could be resolved
+    /// by unassigning those other virtual registers.
+    IK_VirtReg,
+
+    /// Register unit interference. A fixed live range is in the way, typically
+    /// argument registers for a call. This can't be resolved by unassigning
+    /// other virtual registers.
+    IK_RegUnit,
+
+    /// RegMask interference. The live range is crossing an instruction with a
+    /// regmask operand that doesn't preserve PhysReg. This typically means
+    /// VirtReg is live across a call, and PhysReg isn't call-preserved.
+    IK_RegMask
+  };
+
+  /// Check for interference before assigning VirtReg to PhysReg.
+  /// If this function returns IK_Free, it is legal to assign(VirtReg, PhysReg).
+  /// When there is more than one kind of interference, the InterferenceKind
+  /// with the highest enum value is returned.
+  InterferenceKind checkInterference(LiveInterval &VirtReg, unsigned PhysReg);
+
+  /// Assign VirtReg to PhysReg.
+  /// This will mark VirtReg's live range as occupied in the LiveRegMatrix and
+  /// update VirtRegMap. The live range is expected to be available in PhysReg.
+  void assign(LiveInterval &VirtReg, unsigned PhysReg);
+
+  /// Unassign VirtReg from its PhysReg.
+  /// Assuming that VirtReg was previously assigned to a PhysReg, this undoes
+  /// the assignment and updates VirtRegMap accordingly.
+  void unassign(LiveInterval &VirtReg);
+
+  //===--------------------------------------------------------------------===//
+  // Low-level interface.
+  //===--------------------------------------------------------------------===//
+  //
+  // Provide access to the underlying LiveIntervalUnions.
+  //
+
+  /// Check for regmask interference only.
+  /// Return true if VirtReg crosses a regmask operand that clobbers PhysReg.
+  bool checkRegMaskInterference(LiveInterval &VirtReg, unsigned PhysReg);
+
+  /// Check for regunit interference only.
+  /// Return true if VirtReg overlaps a fixed assignment of one of PhysRegs's
+  /// register units.
+  bool checkRegUnitInterference(LiveInterval &VirtReg, unsigned PhysReg);
+
+  /// Query a line of the assigned virtual register matrix directly.
+  /// Use MCRegUnitIterator to enumerate all regunits in the desired PhysReg.
+  /// This returns a reference to an internal Query data structure that is only
+  /// valid until the next query() call.
+  LiveIntervalUnion::Query &query(LiveInterval &VirtReg, unsigned RegUnit);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_CODEGEN_LIVEREGMATRIX_H