1 //===-- RegisterScavenging.cpp - Machine register scavenging --------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the Evan Cheng and is distributed under the
6 // University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the machine register scavenger. It can provide
11 // information such as unused register at any point in a machine basic block.
12 // It also provides a mechanism to make registers availbale by evicting them
15 //===----------------------------------------------------------------------===//
17 #define DEBUG_TYPE "reg-scavenging"
18 #include "llvm/CodeGen/RegisterScavenging.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineBasicBlock.h"
21 #include "llvm/CodeGen/MachineInstr.h"
22 #include "llvm/Target/MRegisterInfo.h"
23 #include "llvm/Target/TargetInstrInfo.h"
24 #include "llvm/Target/TargetMachine.h"
25 #include "llvm/ADT/STLExtras.h"
28 void RegScavenger::init() {
29 const MachineFunction &MF = *MBB->getParent();
30 const TargetMachine &TM = MF.getTarget();
31 const MRegisterInfo *RegInfo = TM.getRegisterInfo();
34 NumPhysRegs = RegInfo->getNumRegs();
35 RegStates.resize(NumPhysRegs, true);
37 // Create reserved registers bitvector.
38 ReservedRegs = RegInfo->getReservedRegs(MF);
39 RegStates ^= ReservedRegs;
41 // Create callee-saved registers bitvector.
42 CalleeSavedRegs.resize(NumPhysRegs);
43 const unsigned *CSRegs = RegInfo->getCalleeSavedRegs();
45 for (unsigned i = 0; CSRegs[i]; ++i)
46 CalleeSavedRegs.set(CSRegs[i]);
48 // Live-in registers are in use.
49 if (!MBB->livein_empty())
50 for (MachineBasicBlock::const_livein_iterator I = MBB->livein_begin(),
51 E = MBB->livein_end(); I != E; ++I)
57 void RegScavenger::forward() {
58 assert(MBBI != MBB->end() && "Already at the end of the basic block!");
65 MachineInstr *MI = MBBI;
66 // Process uses first.
67 BitVector ChangedRegs(NumPhysRegs);
68 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
69 const MachineOperand &MO = MI->getOperand(i);
70 if (!MO.isReg() || !MO.isUse())
72 unsigned Reg = MO.getReg();
76 if (MO.isKill() && !isReserved(Reg))
79 // Change states of all registers after all the uses are processed to guard
80 // against multiple uses.
81 setUnused(ChangedRegs);
84 const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
85 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
86 const MachineOperand &MO = MI->getOperand(i);
87 if (!MO.isReg() || !MO.isDef())
89 unsigned Reg = MO.getReg();
90 // Skip two-address destination operand.
91 if (TID->findTiedToSrcOperand(i) != -1) {
95 assert(isUnused(Reg) || isReserved(Reg));
101 void RegScavenger::backward() {
102 assert(MBBI != MBB->begin() && "Already at start of basic block!");
103 // Move ptr backward.
106 MachineInstr *MI = MBBI;
107 // Process defs first.
108 const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
109 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
110 const MachineOperand &MO = MI->getOperand(i);
111 if (!MO.isReg() || !MO.isDef())
113 // Skip two-address destination operand.
114 if (TID->findTiedToSrcOperand(i) != -1)
116 unsigned Reg = MO.getReg();
118 if (!isReserved(Reg))
123 BitVector ChangedRegs(NumPhysRegs);
124 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
125 const MachineOperand &MO = MI->getOperand(i);
126 if (!MO.isReg() || !MO.isUse())
128 unsigned Reg = MO.getReg();
131 assert(isUnused(Reg) || isReserved(Reg));
132 ChangedRegs.set(Reg);
134 setUsed(ChangedRegs);
137 /// CreateRegClassMask - Set the bits that represent the registers in the
138 /// TargetRegisterClass.
139 static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) {
140 for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); I != E;
145 unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass,
146 bool ExCalleeSaved) const {
147 // Mask off the registers which are not in the TargetRegisterClass.
148 BitVector RegStatesCopy(NumPhysRegs, false);
149 CreateRegClassMask(RegClass, RegStatesCopy);
150 RegStatesCopy &= RegStates;
152 // If looking for a non-callee-saved register, mask off all the callee-saved
155 RegStatesCopy &= ~CalleeSavedRegs;
157 // Returns the first unused (bit is set) register, or 0 is none is found.
158 int Reg = RegStatesCopy.find_first();
159 return (Reg == -1) ? 0 : Reg;
162 void RegScavenger::clear() {