PrologEpilogInserter.cpp revision 5037a1591070247af4f83316ec479829846cc734
1//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass is responsible for finalizing the functions frame layout, saving 11// callee saved registers, and for emitting prolog & epilog code for the 12// function. 13// 14// This pass must be run after register allocation. After this pass is 15// executed, it is illegal to construct MO_FrameIndex operands. 16// 17//===----------------------------------------------------------------------===// 18 19#include "llvm/CodeGen/Passes.h" 20#include "llvm/CodeGen/MachineFunctionPass.h" 21#include "llvm/CodeGen/MachineInstr.h" 22#include "llvm/CodeGen/MachineFrameInfo.h" 23#include "llvm/Target/TargetMachine.h" 24#include "llvm/Target/MRegisterInfo.h" 25#include "llvm/Target/TargetFrameInfo.h" 26#include "llvm/Target/TargetInstrInfo.h" 27using namespace llvm; 28 29namespace { 30 struct PEI : public MachineFunctionPass { 31 const char *getPassName() const { 32 return "Prolog/Epilog Insertion & Frame Finalization"; 33 } 34 35 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract 36 /// frame indexes with appropriate references. 37 /// 38 bool runOnMachineFunction(MachineFunction &Fn) { 39 // Scan the function for modified caller saved registers and insert spill 40 // code for any caller saved registers that are modified. Also calculate 41 // the MaxCallFrameSize and HasCalls variables for the function's frame 42 // information and eliminates call frame pseudo instructions. 43 calculateCallerSavedRegisters(Fn); 44 45 // Add the code to save and restore the caller saved registers 46 saveCallerSavedRegisters(Fn); 47 48 // Allow the target machine to make final modifications to the function 49 // before the frame layout is finalized. 50 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn); 51 52 // Calculate actual frame offsets for all of the abstract stack objects... 53 calculateFrameObjectOffsets(Fn); 54 55 // Add prolog and epilog code to the function. This function is required 56 // to align the stack frame as necessary for any stack variables or 57 // called functions. Because of this, calculateCallerSavedRegisters 58 // must be called before this function in order to set the HasCalls 59 // and MaxCallFrameSize variables. 60 insertPrologEpilogCode(Fn); 61 62 // Replace all MO_FrameIndex operands with physical register references 63 // and actual offsets. 64 // 65 replaceFrameIndices(Fn); 66 67 RegsToSave.clear(); 68 StackSlots.clear(); 69 return true; 70 } 71 72 private: 73 std::vector<unsigned> RegsToSave; 74 std::vector<int> StackSlots; 75 76 void calculateCallerSavedRegisters(MachineFunction &Fn); 77 void saveCallerSavedRegisters(MachineFunction &Fn); 78 void calculateFrameObjectOffsets(MachineFunction &Fn); 79 void replaceFrameIndices(MachineFunction &Fn); 80 void insertPrologEpilogCode(MachineFunction &Fn); 81 }; 82} 83 84 85/// createPrologEpilogCodeInserter - This function returns a pass that inserts 86/// prolog and epilog code, and eliminates abstract frame references. 87/// 88FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); } 89 90 91/// calculateCallerSavedRegisters - Scan the function for modified caller saved 92/// registers. Also calculate the MaxCallFrameSize and HasCalls variables for 93/// the function's frame information and eliminates call frame pseudo 94/// instructions. 95/// 96void PEI::calculateCallerSavedRegisters(MachineFunction &Fn) { 97 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 98 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo(); 99 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 100 101 // Get the callee saved register list... 102 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs(); 103 104 // Get the function call frame set-up and tear-down instruction opcode 105 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode(); 106 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode(); 107 108 // Early exit for targets which have no callee saved registers and no call 109 // frame setup/destroy pseudo instructions. 110 if ((CSRegs == 0 || CSRegs[0] == 0) && 111 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1) 112 return; 113 114 // This bitset contains an entry for each physical register for the target... 115 std::vector<bool> ModifiedRegs(RegInfo->getNumRegs()); 116 unsigned MaxCallFrameSize = 0; 117 bool HasCalls = false; 118 119 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 120 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) 121 if (I->getOpcode() == FrameSetupOpcode || 122 I->getOpcode() == FrameDestroyOpcode) { 123 assert(I->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo" 124 " instructions should have a single immediate argument!"); 125 unsigned Size = I->getOperand(0).getImmedValue(); 126 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size; 127 HasCalls = true; 128 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I++); 129 } else { 130 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 131 MachineOperand &MO = I->getOperand(i); 132 if (MO.isRegister() && MO.isDef()) { 133 assert(MRegisterInfo::isPhysicalRegister(MO.getReg()) && 134 "Register allocation must be performed!"); 135 ModifiedRegs[MO.getReg()] = true; // Register is modified 136 } 137 138 // Mark any implicitly defined registers as being modified. 139 for (const unsigned *ImpDefs = TII.getImplicitDefs(I->getOpcode()); 140 *ImpDefs; ++ImpDefs) 141 ModifiedRegs[*ImpDefs] = true; 142 } 143 ++I; 144 } 145 146 MachineFrameInfo *FFI = Fn.getFrameInfo(); 147 FFI->setHasCalls(HasCalls); 148 FFI->setMaxCallFrameSize(MaxCallFrameSize); 149 150 // Now figure out which *callee saved* registers are modified by the current 151 // function, thus needing to be saved and restored in the prolog/epilog. 152 // 153 for (unsigned i = 0; CSRegs[i]; ++i) { 154 unsigned Reg = CSRegs[i]; 155 if (ModifiedRegs[Reg]) { 156 RegsToSave.push_back(Reg); // If modified register... 157 } else { 158 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg); 159 *AliasSet; ++AliasSet) { // Check alias registers too... 160 if (ModifiedRegs[*AliasSet]) { 161 RegsToSave.push_back(Reg); 162 break; 163 } 164 } 165 } 166 } 167 168 if (RegsToSave.empty()) 169 return; // Early exit if no caller saved registers are modified! 170 171 unsigned NumFixedSpillSlots; 172 const std::pair<unsigned,int> *FixedSpillSlots = 173 TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots); 174 175 // Now that we know which registers need to be saved and restored, allocate 176 // stack slots for them. 177 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 178 unsigned Reg = RegsToSave[i]; 179 180 // Check to see if this physreg must be spilled to a particular stack slot 181 // on this target. 182 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots; 183 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots && 184 FixedSlot->first != Reg) 185 ++FixedSlot; 186 187 int FrameIdx; 188 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) { 189 // Nope, just spill it anywhere convenient. 190 FrameIdx = FFI->CreateStackObject(RegInfo->getSpillSize(Reg)/8, 191 RegInfo->getSpillAlignment(Reg)/8); 192 } else { 193 // Spill it to the stack where we must. 194 FrameIdx = FFI->CreateFixedObject(RegInfo->getSpillSize(Reg)/8, 195 FixedSlot->second); 196 } 197 StackSlots.push_back(FrameIdx); 198 } 199} 200 201/// saveCallerSavedRegisters - Insert spill code for any caller saved registers 202/// that are modified in the function. 203/// 204void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { 205 // Early exit if no caller saved registers are modified! 206 if (RegsToSave.empty()) 207 return; 208 209 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 210 211 // Now that we have a stack slot for each register to be saved, insert spill 212 // code into the entry block... 213 MachineBasicBlock *MBB = Fn.begin(); 214 MachineBasicBlock::iterator I = MBB->begin(); 215 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 216 // Insert the spill to the stack frame. 217 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i]); 218 } 219 220 // Add code to restore the callee-save registers in each exiting block. 221 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 222 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) { 223 // If last instruction is a return instruction, add an epilogue 224 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) { 225 MBB = FI; 226 I = MBB->end(); --I; 227 228 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 229 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i], StackSlots[i]); 230 assert(I != MBB->begin() && 231 "loadRegFromStackSlot didn't insert any code!"); 232 --I; // Insert in reverse order 233 } 234 } 235 } 236} 237 238 239/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 240/// abstract stack objects... 241/// 242void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 243 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo(); 244 245 bool StackGrowsDown = 246 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 247 248 // Loop over all of the stack objects, assigning sequential addresses... 249 MachineFrameInfo *FFI = Fn.getFrameInfo(); 250 251 unsigned StackAlignment = TFI.getStackAlignment(); 252 253 // Start at the beginning of the local area. 254 // The Offset is the distance from the stack top in the direction 255 // of stack growth -- so it's always positive. 256 int Offset = TFI.getOffsetOfLocalArea(); 257 if (StackGrowsDown) 258 Offset = -Offset; 259 assert(Offset >= 0 260 && "Local area offset should be in direction of stack growth"); 261 262 // If there are fixed sized objects that are preallocated in the local area, 263 // non-fixed objects can't be allocated right at the start of local area. 264 // We currently don't support filling in holes in between fixed sized objects, 265 // so we adjust 'Offset' to point to the end of last fixed sized 266 // preallocated object. 267 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) { 268 int FixedOff; 269 if (StackGrowsDown) { 270 // The maximum distance from the stack pointer is at lower address of 271 // the object -- which is given by offset. For down growing stack 272 // the offset is negative, so we negate the offset to get the distance. 273 FixedOff = -FFI->getObjectOffset(i); 274 } else { 275 // The maximum distance from the start pointer is at the upper 276 // address of the object. 277 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i); 278 } 279 if (FixedOff > Offset) Offset = FixedOff; 280 } 281 282 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 283 // If stack grows down, we need to add size of find the lowest 284 // address of the object. 285 if (StackGrowsDown) 286 Offset += FFI->getObjectSize(i); 287 288 unsigned Align = FFI->getObjectAlignment(i); 289 assert(Align <= StackAlignment && "Cannot align stack object to higher " 290 "alignment boundary than the stack itself!"); 291 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... 292 293 if (StackGrowsDown) { 294 FFI->setObjectOffset(i, -Offset); // Set the computed offset 295 } else { 296 FFI->setObjectOffset(i, Offset); 297 Offset += FFI->getObjectSize(i); 298 } 299 } 300 301 // Align the final stack pointer offset, but only if there are calls in the 302 // function. This ensures that any calls to subroutines have their stack 303 // frames suitable aligned. 304 if (FFI->hasCalls()) 305 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 306 307 // Set the final value of the stack pointer... 308 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea()); 309} 310 311 312/// insertPrologEpilogCode - Scan the function for modified caller saved 313/// registers, insert spill code for these caller saved registers, then add 314/// prolog and epilog code to the function. 315/// 316void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 317 // Add prologue to the function... 318 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 319 320 // Add epilogue to restore the callee-save registers in each exiting block 321 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 322 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 323 // If last instruction is a return instruction, add an epilogue 324 if (!I->empty() && TII.isReturn(I->back().getOpcode())) 325 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 326 } 327} 328 329 330/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 331/// register references and actual offsets. 332/// 333void PEI::replaceFrameIndices(MachineFunction &Fn) { 334 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 335 336 const TargetMachine &TM = Fn.getTarget(); 337 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 338 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 339 340 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 341 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 342 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 343 if (I->getOperand(i).isFrameIndex()) { 344 // If this instruction has a FrameIndex operand, we need to use that 345 // target machine register info object to eliminate it. 346 MRI.eliminateFrameIndex(I); 347 break; 348 } 349} 350