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"
27 RegScavenger::RegScavenger(MachineBasicBlock *mbb)
28 : MBB(mbb), MBBI(mbb->begin()) {
29 const MachineFunction &MF = *MBB->getParent();
30 const TargetMachine &TM = MF.getTarget();
31 const MRegisterInfo *RegInfo = TM.getRegisterInfo();
33 NumPhysRegs = RegInfo->getNumRegs();
34 RegStates.resize(NumPhysRegs, true);
36 // Create reserved registers bitvector.
37 ReservedRegs = RegInfo->getReservedRegs(MF);
38 RegStates ^= ReservedRegs;
40 // Create callee-saved registers bitvector.
41 CalleeSavedRegs.resize(NumPhysRegs);
42 const unsigned *CSRegs = RegInfo->getCalleeSavedRegs();
44 for (unsigned i = 0; CSRegs[i]; ++i)
45 CalleeSavedRegs.set(CSRegs[i]);
48 void RegScavenger::forward() {
49 MachineInstr *MI = MBBI;
50 // Process uses first.
51 BitVector ChangedRegs(NumPhysRegs);
52 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
53 const MachineOperand &MO = MI->getOperand(i);
54 if (!MO.isReg() || !MO.isUse())
56 unsigned Reg = MO.getReg();
60 if (MO.isKill() && !isReserved(Reg))
63 // Change states of all registers after all the uses are processed to guard
64 // against multiple uses.
65 setUnused(ChangedRegs);
68 const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
69 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
70 const MachineOperand &MO = MI->getOperand(i);
71 if (!MO.isReg() || !MO.isDef())
73 // Skip two-address destination operand.
74 if (TID->findTiedToSrcOperand(i) != -1)
76 unsigned Reg = MO.getReg();
77 assert(isUnused(Reg) || isReserved(Reg));
85 void RegScavenger::backward() {
86 MachineInstr *MI = --MBBI;
87 // Process defs first.
88 const TargetInstrDescriptor *TID = MI->getInstrDescriptor();
89 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
90 const MachineOperand &MO = MI->getOperand(i);
91 if (!MO.isReg() || !MO.isDef())
93 // Skip two-address destination operand.
94 if (TID->findTiedToSrcOperand(i) != -1)
96 unsigned Reg = MO.getReg();
103 BitVector ChangedRegs(NumPhysRegs);
104 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
105 const MachineOperand &MO = MI->getOperand(i);
106 if (!MO.isReg() || !MO.isUse())
108 unsigned Reg = MO.getReg();
111 assert(isUnused(Reg) || isReserved(Reg));
112 ChangedRegs.set(Reg);
114 setUsed(ChangedRegs);
117 /// CreateRegClassMask - Set the bits that represent the registers in the
118 /// TargetRegisterClass.
119 static void CreateRegClassMask(const TargetRegisterClass *RC, BitVector &Mask) {
120 for (TargetRegisterClass::iterator I = RC->begin(), E = RC->end(); I != E;
125 unsigned RegScavenger::FindUnusedReg(const TargetRegisterClass *RegClass,
126 bool ExCalleeSaved) const {
127 // Mask off the registers which are not in the TargetRegisterClass.
128 BitVector RegStatesCopy(NumPhysRegs, false);
129 CreateRegClassMask(RegClass, RegStatesCopy);
130 RegStatesCopy &= RegStates;
132 // If looking for a non-callee-saved register, mask off all the callee-saved
135 RegStatesCopy &= ~CalleeSavedRegs;
137 // Returns the first unused (bit is set) register, or 0 is none is found.
138 int Reg = RegStatesCopy.find_first();
139 return (Reg == -1) ? 0 : Reg;