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 // FIXME: change name to VirtReg2OffsetMap
33 std::map<unsigned, unsigned> RegMap;
35 // Maps SSA Regs => physical regs
36 std::map<unsigned, unsigned> SSA2PhysRegMap;
38 // Maps physical register to their register classes
39 std::map<unsigned, const TargetRegisterClass*> PhysReg2RegClassMap;
41 // Maps RegClass => which index we can take a register from. Since this is a
42 // simple register allocator, when we need a register of a certain class, we
43 // just take the next available one.
44 std::map<unsigned, unsigned> RegsUsed;
45 std::map<const TargetRegisterClass*, unsigned> RegClassIdx;
47 RegAllocSimple(TargetMachine &tm) : TM(tm), CurrMBB(0), maxOffset(0),
48 RegInfo(tm.getRegisterInfo()),
49 NumBytesAllocated(0), ByteAlignment(4)
51 // build reverse mapping for physReg -> register class
52 RegInfo->buildReg2RegClassMap(PhysReg2RegClassMap);
54 RegsUsed[RegInfo->getFramePointer()] = 1;
55 RegsUsed[RegInfo->getStackPointer()] = 1;
58 bool isAvailableReg(unsigned Reg) {
59 // assert(Reg < MRegisterInfo::FirstVirtualReg && "...");
60 return RegsUsed.find(Reg) == RegsUsed.end();
64 unsigned allocateStackSpaceFor(unsigned VirtReg,
65 const TargetRegisterClass *regClass);
67 /// Given size (in bytes), returns a register that is currently unused
68 /// Side effect: marks that register as being used until manually cleared
69 unsigned getFreeReg(unsigned virtualReg);
71 /// Returns all `borrowed' registers back to the free pool
76 /// Moves value from memory into that register
77 MachineBasicBlock::iterator
78 moveUseToReg (MachineBasicBlock::iterator I, unsigned VirtReg,
81 /// Saves reg value on the stack (maps virtual register to stack value)
82 MachineBasicBlock::iterator
83 saveVirtRegToStack (MachineBasicBlock::iterator I, unsigned VirtReg,
86 MachineBasicBlock::iterator
87 savePhysRegToStack (MachineBasicBlock::iterator I, unsigned PhysReg);
89 /// runOnFunction - Top level implementation of instruction selection for
90 /// the entire function.
92 bool runOnMachineFunction(MachineFunction &Fn);
94 bool runOnFunction(Function &Fn) {
95 return runOnMachineFunction(MachineFunction::get(&Fn));
101 unsigned RegAllocSimple::allocateStackSpaceFor(unsigned VirtReg,
102 const TargetRegisterClass *regClass)
104 if (RegMap.find(VirtReg) == RegMap.end()) {
105 unsigned size = regClass->getDataSize();
106 unsigned over = NumBytesAllocated - (NumBytesAllocated % ByteAlignment);
107 if (size >= ByteAlignment - over) {
108 // need to pad by (ByteAlignment - over)
109 NumBytesAllocated += ByteAlignment - over;
111 RegMap[VirtReg] = NumBytesAllocated;
112 NumBytesAllocated += size;
114 return RegMap[VirtReg];
117 unsigned RegAllocSimple::getFreeReg(unsigned virtualReg) {
118 const TargetRegisterClass* regClass = MF->getRegClass(virtualReg);
121 if (RegClassIdx.find(regClass) != RegClassIdx.end()) {
122 unsigned regIdx = RegClassIdx[regClass]++;
123 assert(regIdx < regClass->getNumRegs() && "Not enough registers!");
124 physReg = regClass->getRegister(regIdx);
126 physReg = regClass->getRegister(0);
127 // assert(physReg < regClass->getNumRegs() && "No registers in class!");
128 RegClassIdx[regClass] = 1;
131 if (isAvailableReg(physReg))
134 return getFreeReg(virtualReg);
138 MachineBasicBlock::iterator
139 RegAllocSimple::moveUseToReg (MachineBasicBlock::iterator I,
140 unsigned VirtReg, unsigned &PhysReg)
142 const TargetRegisterClass* regClass = MF->getRegClass(VirtReg);
145 unsigned stackOffset = allocateStackSpaceFor(VirtReg, regClass);
146 PhysReg = getFreeReg(VirtReg);
148 // FIXME: increment the frame pointer
150 // Add move instruction(s)
151 return RegInfo->loadRegOffset2Reg(CurrMBB, I, PhysReg,
152 RegInfo->getFramePointer(),
153 stackOffset, regClass->getDataSize());
156 MachineBasicBlock::iterator
157 RegAllocSimple::saveVirtRegToStack (MachineBasicBlock::iterator I,
158 unsigned VirtReg, unsigned PhysReg)
160 const TargetRegisterClass* regClass = MF->getRegClass(VirtReg);
163 unsigned offset = allocateStackSpaceFor(VirtReg, regClass);
165 // Add move instruction(s)
166 return RegInfo->storeReg2RegOffset(CurrMBB, I, PhysReg,
167 RegInfo->getFramePointer(),
168 offset, regClass->getDataSize());
171 MachineBasicBlock::iterator
172 RegAllocSimple::savePhysRegToStack (MachineBasicBlock::iterator I,
175 const TargetRegisterClass* regClass = MF->getRegClass(PhysReg);
178 unsigned offset = allocateStackSpaceFor(PhysReg, regClass);
180 // Add move instruction(s)
181 return RegInfo->storeReg2RegOffset(CurrMBB, I, PhysReg,
182 RegInfo->getFramePointer(),
183 offset, regClass->getDataSize());
186 bool RegAllocSimple::runOnMachineFunction(MachineFunction &Fn) {
188 unsigned virtualReg, physReg;
189 DEBUG(std::cerr << "Machine Function " << "\n");
193 // FIXME: add prolog. we should preserve callee-save registers...
194 MachineFunction::iterator Fi = Fn.begin();
195 MachineBasicBlock &MBB = *Fi;
196 MachineBasicBlock::iterator MBBi = MBB.begin()
197 const unsigned* calleeSaveRegs = tm.getCalleeSaveRegs();
198 while (*calleeSaveRegs) {
199 //MBBi = saveRegToStack(MBBi, *calleeSaveRegs,
204 for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
209 //loop over each basic block
210 for (MachineBasicBlock::iterator I = MBB->begin(); I != MBB->end(); ++I)
212 MachineInstr *MI = *I;
214 DEBUG(std::cerr << "instr: ";
215 MI->print(std::cerr, TM));
217 // FIXME: add a preliminary pass that will invalidate any registers that
218 // are used by the instruction (including implicit uses)
221 // Loop over each instruction:
222 // uses, move from memory into registers
223 for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
224 MachineOperand &op = MI->getOperand(i);
226 if (op.getType() == MachineOperand::MO_SignExtendedImmed ||
227 op.getType() == MachineOperand::MO_UnextendedImmed)
229 DEBUG(std::cerr << "const\n");
230 } else if (op.isVirtualRegister()) {
231 virtualReg = (unsigned) op.getAllocatedRegNum();
232 // save register to stack if it's a def
233 DEBUG(std::cerr << "op: " << op << "\n");
234 DEBUG(std::cerr << "\t inst[" << i << "]: ";
235 MI->print(std::cerr, TM));
237 physReg = getFreeReg(virtualReg);
238 MachineBasicBlock::iterator J = I;
239 J = saveVirtRegToStack(++J, virtualReg, physReg);
242 I = moveUseToReg(I, virtualReg, physReg);
244 MI->SetMachineOperandReg(i, physReg);
245 DEBUG(std::cerr << "virt: " << virtualReg <<
246 ", phys: " << op.getAllocatedRegNum() << "\n");
255 // FIXME: add epilog. we should preserve callee-save registers...
257 return false; // We never modify the LLVM itself.
260 Pass *createSimpleX86RegisterAllocator(TargetMachine &TM) {
261 return new RegAllocSimple(TM);