Initial check in of register scavenger. Its only current functionality is tracking...

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

diff --git a/include/llvm/CodeGen/RegisterScavenging.h b/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

diff --git a/lib/CodeGen/RegisterScavenging.cpp b/lib/CodeGen/RegisterScavenging.cpp
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+//===-- RegisterScavenging.cpp - Machine register scavenging --------------===//
+//
+//                     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 implements the machine register scavenger. 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.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "reg-scavenging"
+#include "llvm/CodeGen/RegisterScavenging.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/Target/MRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+using namespace llvm;
+
+RegScavenger::RegScavenger(MachineBasicBlock *mbb)
+  : MBB(mbb), MBBI(mbb->begin()) {
+  const MachineFunction &MF = *MBB->getParent();
+  const TargetMachine &TM = MF.getTarget();
+  const MRegisterInfo *RegInfo = TM.getRegisterInfo();
+
+  NumPhysRegs = RegInfo->getNumRegs();
+  RegStates.resize(NumPhysRegs, true);
+
+  // Create reserved registers bitvector.
+  ReservedRegs = RegInfo->getReservedRegs(MF);
+  RegStates ^= ReservedRegs;
+
+  // Create callee-saved registers bitvector.
+  CalleeSavedRegs.resize(NumPhysRegs);
+  const unsigned *CSRegs = RegInfo->getCalleeSavedRegs();
+  if (CSRegs != NULL)
+    for (unsigned i = 0; CSRegs[i]; ++i)
+      CalleeSavedRegs.set(CSRegs[i]);
+}
+
+void RegScavenger::forward() {
+  MachineInstr *MI = MBBI;
+  // Process uses first.
+  BitVector ChangedRegs(NumPhysRegs);
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg() || !MO.isUse())
+      continue;
+    unsigned Reg = MO.getReg();
+    if (Reg == 0)
+      continue;
+    assert(isUsed(Reg));
+    if (MO.isKill() && !isReserved(Reg))
+      ChangedRegs.set(Reg);
+  }
+  // Change states of all registers after all the uses are processed to guard
+  // against multiple uses.
+  setUnused(ChangedRegs);
+
+  // Process defs.
+  const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg() || !MO.isDef())
+      continue;
+    // Skip two-address destination operand.
+    if (TID->findTiedToSrcOperand(i) != -1)
+      continue;
+    unsigned Reg = MO.getReg();
+    assert(isUnused(Reg) || isReserved(Reg));
+    if (!MO.isDead())
+      setUsed(Reg);
+  }
+
+  ++MBBI;
+}
+
+void RegScavenger::backward() {
+  MachineInstr *MI = --MBBI;
+  // Process defs first.
+  const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg() || !MO.isDef())
+      continue;
+    // Skip two-address destination operand.
+    if (TID->findTiedToSrcOperand(i) != -1)
+      continue;
+    unsigned Reg = MO.getReg();
+    assert(isUsed(Reg));
+    if (!isReserved(Reg))
+      setUnused(Reg);
+  }
+
+  // Process uses.
+  BitVector ChangedRegs(NumPhysRegs);
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isReg() || !MO.isUse())
+      continue;
+    unsigned Reg = MO.getReg();
+    if (Reg == 0)
+      continue;
+    assert(isUnused(Reg) || isReserved(Reg));
+    ChangedRegs.set(Reg);
+  }
+  setUsed(ChangedRegs);
+}
+
+/// CreateRegClassMask - Set the bits that represent the registers in the
+/// TargetRegisterClass.
+static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) {
+  for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); I != E;
+       ++I)
+    Mask.set(*I);
+}
+
+unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass,
+                                     bool ExCalleeSaved) const {
+  // Mask off the registers which are not in the TargetRegisterClass.
+  BitVector RegStatesCopy(NumPhysRegs, false);
+  CreateRegClassMask(RegClass, RegStatesCopy);
+  RegStatesCopy &= RegStates;
+
+  // If looking for a non-callee-saved register, mask off all the callee-saved
+  // registers.
+  if (ExCalleeSaved)
+    RegStatesCopy &= ~CalleeSavedRegs;
+
+  // Returns the first unused (bit is set) register, or 0 is none is found.
+  int Reg = RegStatesCopy.find_first();
+  return (Reg == -1) ? 0 : Reg;
+}