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Diffstat (limited to 'lib/CodeGen/PrologEpilogInserter.cpp')
| -rw-r--r-- | lib/CodeGen/PrologEpilogInserter.cpp | 247 |
1 files changed, 247 insertions, 0 deletions
diff --git a/lib/CodeGen/PrologEpilogInserter.cpp b/lib/CodeGen/PrologEpilogInserter.cpp new file mode 100644 index 0000000000..adf6308eef --- /dev/null +++ b/lib/CodeGen/PrologEpilogInserter.cpp @@ -0,0 +1,247 @@ +//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===// +// +// This pass is responsible for finalizing the functions frame layout, saving +// callee saved registers, and for emitting prolog & epilog code for the +// function. +// +// This pass must be run after register allocation. After this pass is +// executed, it is illegal to construct MO_FrameIndex operands. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Pass.h" +#include "llvm/CodeGen/MachineFunction.h" +#include "llvm/CodeGen/MachineInstr.h" +#include "llvm/CodeGen/FunctionFrameInfo.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Target/MRegisterInfo.h" +#include "llvm/Target/MachineFrameInfo.h" +#include "llvm/Target/MachineInstrInfo.h" + +namespace { + struct PEI : public FunctionPass { + bool runOnFunction(Function &Fn) { + return runOnMachineFunction(MachineFunction::get(&Fn)); + } + + /// runOnMachineFunction - Insert prolog/epilog code and replace abstract + /// frame indexes with appropriate references. + /// + bool runOnMachineFunction(MachineFunction &Fn) { + // Scan the function for modified caller saved registers and insert spill + // code for any caller saved registers that are modified. Also calculate + // the MaxCallFrameSize and HasCalls variables for the function's frame + // information and eliminates call frame pseudo instructions. + saveCallerSavedRegisters(Fn); + + // Allow the target machine to make final modifications to the function + // before the frame layout is finalized. + Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn); + + // Calculate actual frame offsets for all of the abstract stack objects... + calculateFrameObjectOffsets(Fn); + + // Replace all MO_FrameIndex operands with physical register references + // and actual offsets. + // + replaceFrameIndices(Fn); + + // Add prolog and epilog code to the function. + insertPrologEpilogCode(Fn); + return true; + } + + private: + void saveCallerSavedRegisters(MachineFunction &Fn); + void calculateFrameObjectOffsets(MachineFunction &Fn); + void replaceFrameIndices(MachineFunction &Fn); + void insertPrologEpilogCode(MachineFunction &Fn); + }; +} + +/// createPrologEpilogCodeInserter - This function returns a pass that inserts +/// prolog and epilog code, and eliminates abstract frame references. +/// +Pass *createPrologEpilogCodeInserter() { return new PEI(); } + + +/// saveCallerSavedRegisters - Scan the function for modified caller saved +/// registers and insert spill code for any caller saved registers that are +/// modified. Also calculate the MaxCallFrameSize and HasCalls variables for +/// the function's frame information and eliminates call frame pseudo +/// instructions. +/// +void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { + const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); + const TargetFrameInfo &FrameInfo = Fn.getTarget().getFrameInfo(); + + // Get the callee saved register list... + const unsigned *CSRegs = RegInfo->getCalleeSaveRegs(); + + // Get the function call frame set-up and tear-down instruction opcode + int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode(); + int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode(); + + // Early exit for targets which have no callee saved registers and no call + // frame setup/destroy pseudo instructions. + if ((CSRegs == 0 || CSRegs[0] == 0) && + FrameSetupOpcode == -1 && FrameDestroyOpcode == -1) + return; + + // This bitset contains an entry for each physical register for the target... + std::vector<bool> ModifiedRegs(MRegisterInfo::FirstVirtualRegister); + unsigned MaxCallFrameSize = 0; + bool HasCalls = false; + + for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) + for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) + if ((*I)->getOpcode() == FrameSetupOpcode || + (*I)->getOpcode() == FrameDestroyOpcode) { + assert((*I)->getNumOperands() == 1 && "Call Frame Setup/Destroy Pseudo" + " instructions should have a single immediate argument!"); + unsigned Size = (*I)->getOperand(0).getImmedValue(); + if (Size > MaxCallFrameSize) MaxCallFrameSize = Size; + HasCalls = true; + RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I); + } else { + for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) { + MachineOperand &MO = (*I)->getOperand(i); + assert(!MO.isVirtualRegister() && + "Register allocation must be performed!"); + if (MO.isPhysicalRegister() && MO.opIsDef()) + ModifiedRegs[MO.getReg()] = true; // Register is modified + } + ++I; + } + + FunctionFrameInfo *FFI = Fn.getFrameInfo(); + FFI->setHasCalls(HasCalls); + FFI->setMaxCallFrameSize(MaxCallFrameSize); + + // Now figure out which *callee saved* registers are modified by the current + // function, thus needing to be saved and restored in the prolog/epilog. + // + std::vector<unsigned> RegsToSave; + for (unsigned i = 0; CSRegs[i]; ++i) { + unsigned Reg = CSRegs[i]; + if (ModifiedRegs[Reg]) { + RegsToSave.push_back(Reg); // If modified register... + } else if (const unsigned *AliasSet = RegInfo->getAliasSet(Reg)) + for (unsigned j = 0; AliasSet[j]; ++j) // Check alias registers too... + if (ModifiedRegs[AliasSet[j]]) { + RegsToSave.push_back(Reg); + break; + } + } + + if (RegsToSave.empty()) + return; // Early exit if no caller saved registers are modified! + + // Now that we know which registers need to be saved and restored, allocate + // stack slots for them. + std::vector<int> StackSlots; + for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { + const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); + int FrameIdx = FFI->CreateStackObject(RC->getSize(), RC->getAlignment()); + StackSlots.push_back(FrameIdx); + } + + // Now that we have a stack slot for each register to be saved, insert spill + // code into the entry block... + MachineBasicBlock *MBB = Fn.begin(); + MachineBasicBlock::iterator I = MBB->begin(); + for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { + const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); + + // Insert the spill to the stack frame... + RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i], StackSlots[i], RC); + } + + // Add code to restore the callee-save registers in each exiting block. + const MachineInstrInfo &MII = Fn.getTarget().getInstrInfo(); + for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI) { + // If last instruction is a return instruction, add an epilogue + if (MII.isReturn(FI->back()->getOpcode())) { + MBB = FI; I = MBB->end()-1; + + for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { + const TargetRegisterClass *RC = RegInfo->getRegClass(RegsToSave[i]); + RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i],StackSlots[i], RC); + --I; // Insert in reverse order + } + } + } +} + + +/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the +/// abstract stack objects... +/// +void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) { + const TargetFrameInfo &TFI = Fn.getTarget().getFrameInfo(); + + bool StackGrowsDown = + TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown; + assert(StackGrowsDown && "Only tested on stack down growing targets!"); + + // Loop over all of the stack objects, assigning sequential addresses... + FunctionFrameInfo *FFI = Fn.getFrameInfo(); + + // Start at the beginning of the local area... + int Offset = -TFI.getOffsetOfLocalArea(); + for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { + Offset += FFI->getObjectSize(i); // Allocate Size bytes... + + unsigned Align = FFI->getObjectAlignment(i); + Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... + + FFI->setObjectOffset(i, -Offset); // Set the computed offset + } + + // Align the final stack pointer offset... + unsigned StackAlign = TFI.getStackAlignment(); + Offset = (Offset+StackAlign-1)/StackAlign*StackAlign; + + // Set the final value of the stack pointer... + FFI->setStackSize(Offset); +} + + +/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical +/// register references and actual offsets. +/// +void PEI::replaceFrameIndices(MachineFunction &Fn) { + if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do? + + const TargetMachine &TM = Fn.getTarget(); + assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!"); + const MRegisterInfo &MRI = *TM.getRegisterInfo(); + + for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) + for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) + for (unsigned i = 0, e = (*I)->getNumOperands(); i != e; ++i) + if ((*I)->getOperand(i).isFrameIndex()) { + // If this instruction has a FrameIndex operand, we need to use that + // target machine register info object to eliminate it. + MRI.eliminateFrameIndex(Fn, I); + break; + } +} + + +/// insertPrologEpilogCode - Scan the function for modified caller saved +/// registers, insert spill code for these caller saved registers, then add +/// prolog and epilog code to the function. +/// +void PEI::insertPrologEpilogCode(MachineFunction &Fn) { + // Add prologue to the function... + Fn.getTarget().getRegisterInfo()->emitPrologue(Fn); + + // Add epilogue to restore the callee-save registers in each exiting block + const MachineInstrInfo &MII = Fn.getTarget().getInstrInfo(); + for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) { + // If last instruction is a return instruction, add an epilogue + if (MII.isReturn(I->back()->getOpcode())) + Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); + } +} |