PrologEpilogInserter.cpp revision 3563015b0df358cfc4ec310eb0df195015ea54a5
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 unsigned MaxCallFrameSize = 0; 115 bool HasCalls = false; 116 117 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 118 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) 119 if (I->getOpcode() == FrameSetupOpcode || 120 I->getOpcode() == FrameDestroyOpcode) { 121 assert(I->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo" 122 " instructions should have a single immediate argument!"); 123 unsigned Size = I->getOperand(0).getImmedValue(); 124 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size; 125 HasCalls = true; 126 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I++); 127 } else { 128 ++I; 129 } 130 131 MachineFrameInfo *FFI = Fn.getFrameInfo(); 132 FFI->setHasCalls(HasCalls); 133 FFI->setMaxCallFrameSize(MaxCallFrameSize); 134 135 // Now figure out which *callee saved* registers are modified by the current 136 // function, thus needing to be saved and restored in the prolog/epilog. 137 // 138 const bool *PhysRegsUsed = Fn.getUsedPhysregs(); 139 for (unsigned i = 0; CSRegs[i]; ++i) { 140 unsigned Reg = CSRegs[i]; 141 if (PhysRegsUsed[Reg]) { 142 RegsToSave.push_back(Reg); // If the reg is modified, save it! 143 } else { 144 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg); 145 *AliasSet; ++AliasSet) { // Check alias registers too. 146 if (PhysRegsUsed[*AliasSet]) { 147 RegsToSave.push_back(Reg); 148 break; 149 } 150 } 151 } 152 } 153 154 if (RegsToSave.empty()) 155 return; // Early exit if no caller saved registers are modified! 156 157 unsigned NumFixedSpillSlots; 158 const std::pair<unsigned,int> *FixedSpillSlots = 159 TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots); 160 161 // Now that we know which registers need to be saved and restored, allocate 162 // stack slots for them. 163 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 164 unsigned Reg = RegsToSave[i]; 165 166 // Check to see if this physreg must be spilled to a particular stack slot 167 // on this target. 168 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots; 169 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots && 170 FixedSlot->first != Reg) 171 ++FixedSlot; 172 173 int FrameIdx; 174 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) { 175 // Nope, just spill it anywhere convenient. 176 FrameIdx = FFI->CreateStackObject(RegInfo->getSpillSize(Reg)/8, 177 RegInfo->getSpillAlignment(Reg)/8); 178 } else { 179 // Spill it to the stack where we must. 180 FrameIdx = FFI->CreateFixedObject(RegInfo->getSpillSize(Reg)/8, 181 FixedSlot->second); 182 } 183 StackSlots.push_back(FrameIdx); 184 } 185} 186 187/// saveCallerSavedRegisters - Insert spill code for any caller saved registers 188/// that are modified in the function. 189/// 190void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { 191 // Early exit if no caller saved registers are modified! 192 if (RegsToSave.empty()) 193 return; 194 195 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 196 197 // Now that we have a stack slot for each register to be saved, insert spill 198 // code into the entry block. 199 MachineBasicBlock *MBB = Fn.begin(); 200 MachineBasicBlock::iterator I = MBB->begin(); 201 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 202 // Insert the spill to the stack frame. 203 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i]); 204 } 205 206 // Add code to restore the callee-save registers in each exiting block. 207 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 208 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) 209 // If last instruction is a return instruction, add an epilogue. 210 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) { 211 MBB = FI; 212 I = MBB->end(); --I; 213 214 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 215 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i], StackSlots[i]); 216 assert(I != MBB->begin() && 217 "loadRegFromStackSlot didn't insert any code!"); 218 --I; // Insert in reverse order 219 } 220 } 221} 222 223 224/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 225/// abstract stack objects. 226/// 227void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 228 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo(); 229 230 bool StackGrowsDown = 231 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 232 233 // Loop over all of the stack objects, assigning sequential addresses... 234 MachineFrameInfo *FFI = Fn.getFrameInfo(); 235 236 unsigned StackAlignment = TFI.getStackAlignment(); 237 238 // Start at the beginning of the local area. 239 // The Offset is the distance from the stack top in the direction 240 // of stack growth -- so it's always positive. 241 int Offset = TFI.getOffsetOfLocalArea(); 242 if (StackGrowsDown) 243 Offset = -Offset; 244 assert(Offset >= 0 245 && "Local area offset should be in direction of stack growth"); 246 247 // If there are fixed sized objects that are preallocated in the local area, 248 // non-fixed objects can't be allocated right at the start of local area. 249 // We currently don't support filling in holes in between fixed sized objects, 250 // so we adjust 'Offset' to point to the end of last fixed sized 251 // preallocated object. 252 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) { 253 int FixedOff; 254 if (StackGrowsDown) { 255 // The maximum distance from the stack pointer is at lower address of 256 // the object -- which is given by offset. For down growing stack 257 // the offset is negative, so we negate the offset to get the distance. 258 FixedOff = -FFI->getObjectOffset(i); 259 } else { 260 // The maximum distance from the start pointer is at the upper 261 // address of the object. 262 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i); 263 } 264 if (FixedOff > Offset) Offset = FixedOff; 265 } 266 267 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 268 // If stack grows down, we need to add size of find the lowest 269 // address of the object. 270 if (StackGrowsDown) 271 Offset += FFI->getObjectSize(i); 272 273 unsigned Align = FFI->getObjectAlignment(i); 274 assert(Align <= StackAlignment && "Cannot align stack object to higher " 275 "alignment boundary than the stack itself!"); 276 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... 277 278 if (StackGrowsDown) { 279 FFI->setObjectOffset(i, -Offset); // Set the computed offset 280 } else { 281 FFI->setObjectOffset(i, Offset); 282 Offset += FFI->getObjectSize(i); 283 } 284 } 285 286 // Align the final stack pointer offset, but only if there are calls in the 287 // function. This ensures that any calls to subroutines have their stack 288 // frames suitable aligned. 289 if (FFI->hasCalls()) 290 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 291 292 // Set the final value of the stack pointer... 293 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea()); 294} 295 296 297/// insertPrologEpilogCode - Scan the function for modified caller saved 298/// registers, insert spill code for these caller saved registers, then add 299/// prolog and epilog code to the function. 300/// 301void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 302 // Add prologue to the function... 303 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 304 305 // Add epilogue to restore the callee-save registers in each exiting block 306 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); 307 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 308 // If last instruction is a return instruction, add an epilogue 309 if (!I->empty() && TII.isReturn(I->back().getOpcode())) 310 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 311 } 312} 313 314 315/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 316/// register references and actual offsets. 317/// 318void PEI::replaceFrameIndices(MachineFunction &Fn) { 319 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 320 321 const TargetMachine &TM = Fn.getTarget(); 322 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 323 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 324 325 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 326 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 327 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 328 if (I->getOperand(i).isFrameIndex()) { 329 // If this instruction has a FrameIndex operand, we need to use that 330 // target machine register info object to eliminate it. 331 MRI.eliminateFrameIndex(I); 332 break; 333 } 334} 335