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(MachineBasicBlock *mbb) {
29 const MachineFunction &MF = *mbb->getParent();
30 const TargetMachine &TM = MF.getTarget();
31 const MRegisterInfo *RegInfo = TM.getRegisterInfo();
33 assert((NumPhysRegs == 0 || NumPhysRegs == RegInfo->getNumRegs()) &&
37 NumPhysRegs = RegInfo->getNumRegs();
38 ReservedRegs = RegInfo->getReservedRegs(MF);
39 RegStates.resize(NumPhysRegs);
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]);
51 // All registers started out unused.
54 // Create reserved registers bitvector.
55 RegStates ^= ReservedRegs;
57 // Live-in registers are in use.
58 if (!MBB->livein_empty())
59 for (MachineBasicBlock::const_livein_iterator I = MBB->livein_begin(),
60 E = MBB->livein_end(); I != E; ++I)
64 void RegScavenger::forward() {
70 assert(MBBI != MBB->end() && "Already at the end of the basic block!");
74 MachineInstr *MI = MBBI;
75 // Process uses first.
76 BitVector ChangedRegs(NumPhysRegs);
77 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
78 const MachineOperand &MO = MI->getOperand(i);
79 if (!MO.isReg() || !MO.isUse())
81 unsigned Reg = MO.getReg();
85 if (MO.isKill() && !isReserved(Reg))
88 // Change states of all registers after all the uses are processed to guard
89 // against multiple uses.
90 setUnused(ChangedRegs);
93 const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
94 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
95 const MachineOperand &MO = MI->getOperand(i);
96 if (!MO.isReg() || !MO.isDef())
98 unsigned Reg = MO.getReg();
99 // Skip two-address destination operand.
100 if (TID->findTiedToSrcOperand(i) != -1) {
104 assert(isUnused(Reg) || isReserved(Reg));
110 void RegScavenger::backward() {
111 assert(Tracking && "Not tracking states!");
112 assert(MBBI != MBB->begin() && "Already at start of basic block!");
113 // Move ptr backward.
116 MachineInstr *MI = MBBI;
117 // Process defs first.
118 const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
119 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
120 const MachineOperand &MO = MI->getOperand(i);
121 if (!MO.isReg() || !MO.isDef())
123 // Skip two-address destination operand.
124 if (TID->findTiedToSrcOperand(i) != -1)
126 unsigned Reg = MO.getReg();
128 if (!isReserved(Reg))
133 BitVector ChangedRegs(NumPhysRegs);
134 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
135 const MachineOperand &MO = MI->getOperand(i);
136 if (!MO.isReg() || !MO.isUse())
138 unsigned Reg = MO.getReg();
141 assert(isUnused(Reg) || isReserved(Reg));
142 ChangedRegs.set(Reg);
144 setUsed(ChangedRegs);
147 /// CreateRegClassMask - Set the bits that represent the registers in the
148 /// TargetRegisterClass.
149 static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) {
150 for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); I != E;
155 unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass,
156 bool ExCalleeSaved) const {
157 // Mask off the registers which are not in the TargetRegisterClass.
158 BitVector RegStatesCopy(NumPhysRegs, false);
159 CreateRegClassMask(RegClass, RegStatesCopy);
160 RegStatesCopy &= RegStates;
162 // If looking for a non-callee-saved register, mask off all the callee-saved
165 RegStatesCopy &= ~CalleeSavedRegs;
167 // Returns the first unused (bit is set) register, or 0 is none is found.
168 int Reg = RegStatesCopy.find_first();
169 return (Reg == -1) ? 0 : Reg;
172 void RegScavenger::clear() {