1 //===-- RegAllocSimple.cpp - A simple generic register allocator --- ------===//
3 // This file implements a simple register allocator. *Very* simple.
5 //===----------------------------------------------------------------------===//
7 #include "llvm/Function.h"
8 #include "llvm/iTerminators.h"
10 #include "llvm/Constants.h"
11 #include "llvm/Pass.h"
12 #include "llvm/CodeGen/MachineInstr.h"
13 #include "llvm/CodeGen/MachineFunction.h"
14 #include "llvm/CodeGen/MachineInstrBuilder.h"
15 #include "llvm/Target/MRegisterInfo.h"
16 #include "llvm/Target/MachineRegInfo.h"
17 #include "llvm/Target/TargetMachine.h"
18 #include "llvm/Support/InstVisitor.h"
19 #include "Support/Statistic.h"
23 struct RegAllocSimple : public FunctionPass {
25 MachineBasicBlock *CurrMBB;
28 const MRegisterInfo *RegInfo;
29 unsigned NumBytesAllocated, ByteAlignment;
31 // Maps SSA Regs => offsets on the stack where these values are stored
32 std::map<unsigned, unsigned> RegMap; // FIXME: change name to OffsetMap
34 // Maps SSA Regs => physical regs
35 std::map<unsigned, unsigned> SSA2PhysRegMap;
37 // Maps RegClass => which index we can take a register from. Since this is a
38 // simple register allocator, when we need a register of a certain class, we
39 // just take the next available one.
40 std::map<unsigned, unsigned> RegsUsed;
41 std::map<const TargetRegisterClass*, unsigned> RegClassIdx;
43 RegAllocSimple(TargetMachine &tm) : TM(tm), CurrMBB(0), maxOffset(0),
44 RegInfo(tm.getRegisterInfo()),
45 NumBytesAllocated(0), ByteAlignment(4)
47 RegsUsed[RegInfo->getFramePointer()] = 1;
48 RegsUsed[RegInfo->getStackPointer()] = 1;
51 bool isAvailableReg(unsigned Reg) {
52 // assert(Reg < MRegisterInfo::FirstVirtualReg && "...");
53 return RegsUsed.find(Reg) == RegsUsed.end();
57 unsigned allocateStackSpaceFor(unsigned VirtReg,
58 const TargetRegisterClass *regClass);
60 /// Given size (in bytes), returns a register that is currently unused
61 /// Side effect: marks that register as being used until manually cleared
62 unsigned getFreeReg(unsigned virtualReg);
64 /// Returns all `borrowed' registers back to the free pool
69 /// Moves value from memory into that register
70 MachineBasicBlock::iterator
71 moveUseToReg (MachineBasicBlock::iterator I, unsigned VirtReg,
74 /// Saves reg value on the stack (maps virtual register to stack value)
75 MachineBasicBlock::iterator
76 saveRegToStack (MachineBasicBlock::iterator I, unsigned VirtReg,
79 /// runOnFunction - Top level implementation of instruction selection for
80 /// the entire function.
82 bool runOnMachineFunction(MachineFunction &Fn);
84 bool runOnFunction(Function &Fn) {
85 return runOnMachineFunction(MachineFunction::get(&Fn));
91 unsigned RegAllocSimple::allocateStackSpaceFor(unsigned VirtReg,
92 const TargetRegisterClass *regClass)
94 if (RegMap.find(VirtReg) == RegMap.end()) {
95 unsigned size = regClass->getDataSize();
96 unsigned over = NumBytesAllocated - (NumBytesAllocated % ByteAlignment);
97 if (size >= ByteAlignment - over) {
98 // need to pad by (ByteAlignment - over)
99 NumBytesAllocated += ByteAlignment - over;
101 RegMap[VirtReg] = NumBytesAllocated;
102 NumBytesAllocated += size;
104 return RegMap[VirtReg];
107 unsigned RegAllocSimple::getFreeReg(unsigned virtualReg) {
108 const TargetRegisterClass* regClass = MF->getRegClass(virtualReg);
111 if (RegClassIdx.find(regClass) != RegClassIdx.end()) {
112 unsigned regIdx = RegClassIdx[regClass]++;
113 assert(regIdx < regClass->getNumRegs() && "Not enough registers!");
114 physReg = regClass->getRegister(regIdx);
116 physReg = regClass->getRegister(0);
117 // assert(physReg < regClass->getNumRegs() && "No registers in class!");
118 RegClassIdx[regClass] = 1;
121 if (isAvailableReg(physReg))
124 return getFreeReg(virtualReg);
128 MachineBasicBlock::iterator
129 RegAllocSimple::moveUseToReg (MachineBasicBlock::iterator I,
130 unsigned VirtReg, unsigned &PhysReg)
132 const TargetRegisterClass* regClass = MF->getRegClass(VirtReg);
135 unsigned stackOffset = allocateStackSpaceFor(VirtReg, regClass);
136 PhysReg = getFreeReg(VirtReg);
138 // FIXME: increment the frame pointer
140 // Add move instruction(s)
141 return RegInfo->loadRegOffset2Reg(CurrMBB, I, PhysReg,
142 RegInfo->getFramePointer(),
143 stackOffset, regClass->getDataSize());
146 MachineBasicBlock::iterator
147 RegAllocSimple::saveRegToStack (MachineBasicBlock::iterator I,
148 unsigned VirtReg, unsigned PhysReg)
150 const TargetRegisterClass* regClass = MF->getRegClass(VirtReg);
153 unsigned offset = allocateStackSpaceFor(VirtReg, regClass);
155 // Add move instruction(s)
156 return RegInfo->storeReg2RegOffset(CurrMBB, I, PhysReg,
157 RegInfo->getFramePointer(),
158 offset, regClass->getDataSize());
161 bool RegAllocSimple::runOnMachineFunction(MachineFunction &Fn) {
163 unsigned virtualReg, physReg;
164 DEBUG(std::cerr << "Machine Function " << "\n");
166 // FIXME: add prolog. we should preserve callee-save registers...
168 for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
173 //loop over each basic block
174 for (MachineBasicBlock::iterator I = MBB->begin(); I != MBB->end(); ++I)
176 MachineInstr *MI = *I;
178 DEBUG(std::cerr << "instr: ";
179 MI->print(std::cerr, TM));
181 // Loop over each instruction:
182 // uses, move from memory into registers
183 for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
184 MachineOperand &op = MI->getOperand(i);
186 if (op.getType() == MachineOperand::MO_SignExtendedImmed ||
187 op.getType() == MachineOperand::MO_UnextendedImmed)
189 DEBUG(std::cerr << "const\n");
190 } else if (op.isVirtualRegister()) {
191 virtualReg = (unsigned) op.getAllocatedRegNum();
192 // save register to stack if it's a def
193 DEBUG(std::cerr << "op: " << op << "\n");
194 DEBUG(std::cerr << "\t inst[" << i << "]: ";
195 MI->print(std::cerr, TM));
197 physReg = getFreeReg(virtualReg);
198 MachineBasicBlock::iterator J = I;
199 I = saveRegToStack(++J, virtualReg, physReg);
201 I = moveUseToReg(I, virtualReg, physReg);
203 MI->SetMachineOperandReg(i, physReg);
204 DEBUG(std::cerr << "virt: " << virtualReg <<
205 ", phys: " << op.getAllocatedRegNum() << "\n");
214 // FIXME: add epilog. we should preserve callee-save registers...
216 return false; // We never modify the LLVM itself.
219 Pass *createSimpleX86RegisterAllocator(TargetMachine &TM) {
220 return new RegAllocSimple(TM);