PrologEpilogInserter.cpp revision 4d7af65903cbc858464362e70a6adf499982ec8a
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" 27 28namespace llvm { 29 30namespace { 31 struct PEI : public MachineFunctionPass { 32 const char *getPassName() const { 33 return "Prolog/Epilog Insertion & Frame Finalization"; 34 } 35 36 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract 37 /// frame indexes with appropriate references. 38 /// 39 bool runOnMachineFunction(MachineFunction &Fn) { 40 // Scan the function for modified caller saved registers and insert spill 41 // code for any caller saved registers that are modified. Also calculate 42 // the MaxCallFrameSize and HasCalls variables for the function's frame 43 // information and eliminates call frame pseudo instructions. 44 saveCallerSavedRegisters(Fn); 45 46 // Allow the target machine to make final modifications to the function 47 // before the frame layout is finalized. 48 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn); 49 50 // Calculate actual frame offsets for all of the abstract stack objects... 51 calculateFrameObjectOffsets(Fn); 52 53 // Add prolog and epilog code to the function. 54 insertPrologEpilogCode(Fn); 55 56 // Replace all MO_FrameIndex operands with physical register references 57 // and actual offsets. 58 // 59 replaceFrameIndices(Fn); 60 return true; 61 } 62 63 private: 64 void saveCallerSavedRegisters(MachineFunction &Fn); 65 void calculateFrameObjectOffsets(MachineFunction &Fn); 66 void replaceFrameIndices(MachineFunction &Fn); 67 void insertPrologEpilogCode(MachineFunction &Fn); 68 }; 69} 70 71 72/// createPrologEpilogCodeInserter - This function returns a pass that inserts 73/// prolog and epilog code, and eliminates abstract frame references. 74/// 75FunctionPass *createPrologEpilogCodeInserter() { return new PEI(); } 76 77 78/// saveCallerSavedRegisters - Scan the function for modified caller saved 79/// registers and insert spill code for any caller saved registers that are 80/// modified. Also calculate the MaxCallFrameSize and HasCalls variables for 81/// the function's frame information and eliminates call frame pseudo 82/// instructions. 83/// 84void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { 85 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); 86 const TargetFrameInfo &FrameInfo = Fn.getTarget().getFrameInfo(); 87 88 // Get the callee saved register list... 89 const unsigned *CSRegs = RegInfo->getCalleeSaveRegs(); 90 91 // Get the function call frame set-up and tear-down instruction opcode 92 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode(); 93 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode(); 94 95 // Early exit for targets which have no callee saved registers and no call 96 // frame setup/destroy pseudo instructions. 97 if ((CSRegs == 0 || CSRegs[0] == 0) && 98 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1) 99 return; 100 101 // This bitset contains an entry for each physical register for the target... 102 std::vector<bool> ModifiedRegs(MRegisterInfo::FirstVirtualRegister); 103 unsigned MaxCallFrameSize = 0; 104 bool HasCalls = false; 105 106 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 107 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) 108 if ((*I)->getOpcode() == FrameSetupOpcode || 109 (*I)->getOpcode() == FrameDestroyOpcode) { 110 assert((*I)->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo" 111 " instructions should have a single immediate argument!"); 112 unsigned Size = (*I)->getOperand(0).getImmedValue(); 113 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size; 114 HasCalls = true; 115 RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I); 116 } else { 117 for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) { 118 MachineOperand &MO = (*I)->getOperand(i); 119 assert(!MO.isVirtualRegister() && 120 "Register allocation must be performed!"); 121 if (MO.isPhysicalRegister() && MO.isDef()) 122 ModifiedRegs[MO.getReg()] = true; // Register is modified 123 } 124 ++I; 125 } 126 127 MachineFrameInfo *FFI = Fn.getFrameInfo(); 128 FFI->setHasCalls(HasCalls); 129 FFI->setMaxCallFrameSize(MaxCallFrameSize); 130 131 // Now figure out which *callee saved* registers are modified by the current 132 // function, thus needing to be saved and restored in the prolog/epilog. 133 // 134 std::vector<unsigned> RegsToSave; 135 for (unsigned i = 0; CSRegs[i]; ++i) { 136 unsigned Reg = CSRegs[i]; 137 if (ModifiedRegs[Reg]) { 138 RegsToSave.push_back(Reg); // If modified register... 139 } else { 140 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg); 141 *AliasSet; ++AliasSet) { // Check alias registers too... 142 if (ModifiedRegs[*AliasSet]) { 143 RegsToSave.push_back(Reg); 144 break; 145 } 146 } 147 } 148 } 149 150 if (RegsToSave.empty()) 151 return; // Early exit if no caller saved registers are modified! 152 153 // Now that we know which registers need to be saved and restored, allocate 154 // stack slots for them. 155 std::vector<int> StackSlots; 156 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 157 int FrameIdx = FFI->CreateStackObject(RegInfo->getRegClass(RegsToSave[i])); 158 StackSlots.push_back(FrameIdx); 159 } 160 161 // Now that we have a stack slot for each register to be saved, insert spill 162 // code into the entry block... 163 MachineBasicBlock *MBB = Fn.begin(); 164 MachineBasicBlock::iterator I = MBB->begin(); 165 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 166 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); 167 168 // Insert the spill to the stack frame... 169 RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i], RC); 170 } 171 172 // Add code to restore the callee-save registers in each exiting block. 173 const TargetInstrInfo &TII = Fn.getTarget().getInstrInfo(); 174 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) { 175 // If last instruction is a return instruction, add an epilogue 176 if (!FI->empty() && TII.isReturn(FI->back()->getOpcode())) { 177 MBB = FI; I = MBB->end()-1; 178 179 for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { 180 const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); 181 RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i],StackSlots[i], RC); 182 --I; // Insert in reverse order 183 } 184 } 185 } 186} 187 188 189/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the 190/// abstract stack objects... 191/// 192void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { 193 const TargetFrameInfo &TFI = Fn.getTarget().getFrameInfo(); 194 195 bool StackGrowsDown = 196 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; 197 assert(StackGrowsDown && "Only tested on stack down growing targets!"); 198 199 // Loop over all of the stack objects, assigning sequential addresses... 200 MachineFrameInfo *FFI = Fn.getFrameInfo(); 201 202 unsigned StackAlignment = TFI.getStackAlignment(); 203 204 // Start at the beginning of the local area... 205 int Offset = TFI.getOffsetOfLocalArea(); 206 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { 207 Offset += FFI->getObjectSize(i); // Allocate Size bytes... 208 209 unsigned Align = FFI->getObjectAlignment(i); 210 assert(Align <= StackAlignment && "Cannot align stack object to higher " 211 "alignment boundary than the stack itself!"); 212 Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... 213 214 FFI->setObjectOffset(i, -Offset); // Set the computed offset 215 } 216 217 // Align the final stack pointer offset... 218 Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; 219 220 // Set the final value of the stack pointer... 221 FFI->setStackSize(Offset-TFI.getOffsetOfLocalArea()); 222} 223 224 225/// insertPrologEpilogCode - Scan the function for modified caller saved 226/// registers, insert spill code for these caller saved registers, then add 227/// prolog and epilog code to the function. 228/// 229void PEI::insertPrologEpilogCode(MachineFunction &Fn) { 230 // Add prologue to the function... 231 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); 232 233 // Add epilogue to restore the callee-save registers in each exiting block 234 const TargetInstrInfo &TII = Fn.getTarget().getInstrInfo(); 235 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { 236 // If last instruction is a return instruction, add an epilogue 237 if (!I->empty() && TII.isReturn(I->back()->getOpcode())) 238 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); 239 } 240} 241 242 243/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical 244/// register references and actual offsets. 245/// 246void PEI::replaceFrameIndices(MachineFunction &Fn) { 247 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? 248 249 const TargetMachine &TM = Fn.getTarget(); 250 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); 251 const MRegisterInfo &MRI = *TM.getRegisterInfo(); 252 253 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) 254 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) 255 for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) 256 if ((*I)->getOperand(i).isFrameIndex()) { 257 // If this instruction has a FrameIndex operand, we need to use that 258 // target machine register info object to eliminate it. 259 MRI.eliminateFrameIndex(Fn, I); 260 break; 261 } 262} 263 264} // End llvm namespace 265