Initial check in of register scavenger. Its only current functionality is tracking live registers per MBB.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34511 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/RegisterScavenging.h

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+//===-- RegisterScavenging.h - Machine register scavenging ------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the Evan Cheng and is distributed under the
+// University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the machine register scavenger class. It can provide
+// information such as unused register at any point in a machine basic block.
+// It also provides a mechanism to make registers availbale by evicting them
+// to spill slots.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_REGISTER_SCAVENGING_H
+#define LLVM_CODEGEN_REGISTER_SCAVENGING_H
+
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/ADT/BitVector.h"
+
+namespace llvm {
+
+class TargetRegisterClass;
+
+class RegScavenger {
+  MachineBasicBlock *MBB;
+  MachineBasicBlock::iterator MBBI;
+  unsigned NumPhysRegs;
+
+  /// RegStates - The current state of all the physical registers immediately
+  /// before MBBI. One bit per physical register. If bit is set that means it's
+  /// available, unset means the register is currently being used.
+  BitVector RegStates;
+
+public:
+  RegScavenger(MachineBasicBlock *mbb);
+
+  /// forward / backward - Move the internal MBB iterator and update register
+  /// states.
+  void forward();
+  void backward();
+
+  /// isReserved - Returns true if a register is reserved. It is never "unused".
+  bool isReserved(unsigned Reg) const { return ReservedRegs[Reg]; }
+
+  /// isUsed / isUsed - Test if a register is currently being used.
+  ///
+  bool isUsed(unsigned Reg) const   { return !RegStates[Reg]; }
+  bool isUnused(unsigned Reg) const { return RegStates[Reg]; }
+
+  /// setUsed / setUnused - Mark the state of one or a number of registers.
+  ///
+  void setUsed(unsigned Reg)     { RegStates.reset(Reg); }
+  void setUsed(BitVector Regs)   { RegStates &= ~Regs; }
+  void setUnused(unsigned Reg)   { RegStates.set(Reg); }
+  void setUnused(BitVector Regs) { RegStates |= Regs; }
+
+  /// FindUnusedReg - Find a unused register of the specified register class.
+  /// Exclude callee saved registers if directed. It return 0 is none is found.
+  unsigned FindUnusedReg(const TargetRegisterClass *RegClass,
+                         bool ExCalleeSaved = false) const;
+
+private:
+  /// CalleeSavedrRegs - A bitvector of callee saved registers for the target.
+  BitVector CalleeSavedRegs;
+
+  /// ReservedRegs - A bitvector of reserved registers.
+  BitVector ReservedRegs;
+};
+ 
+} // End llvm namespace
+
+#endif