diff options
Diffstat (limited to 'lib/CodeGen/PrologEpilogInserter.cpp')
| -rw-r--r-- | lib/CodeGen/PrologEpilogInserter.cpp | 358 |
1 files changed, 358 insertions, 0 deletions
diff --git a/lib/CodeGen/PrologEpilogInserter.cpp b/lib/CodeGen/PrologEpilogInserter.cpp new file mode 100644 index 0000000000..e38c740e8d --- /dev/null +++ b/lib/CodeGen/PrologEpilogInserter.cpp @@ -0,0 +1,358 @@ +//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===// +// +// The LLVM Compiler Infrastructure +// +// This file was developed by the LLVM research group and is distributed under +// the University of Illinois Open Source License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// 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/CodeGen/Passes.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineInstr.h" +#include "llvm/CodeGen/MachineFrameInfo.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Target/MRegisterInfo.h" +#include "llvm/Target/TargetFrameInfo.h" +#include "llvm/Target/TargetInstrInfo.h" +using namespace llvm; + +namespace { + struct PEI : public MachineFunctionPass { + const char *getPassName() const { + return "Prolog/Epilog Insertion & Frame Finalization"; + } + + /// 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. + calculateCallerSavedRegisters(Fn); + + // Add the code to save and restore the caller saved registers + 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); + + // Add prolog and epilog code to the function. This function is required + // to align the stack frame as necessary for any stack variables or + // called functions. Because of this, calculateCallerSavedRegisters + // must be called before this function in order to set the HasCalls + // and MaxCallFrameSize variables. + insertPrologEpilogCode(Fn); + + // Replace all MO_FrameIndex operands with physical register references + // and actual offsets. + // + replaceFrameIndices(Fn); + + RegsToSave.clear(); + StackSlots.clear(); + return true; + } + + private: + std::vector<std::pair<unsigned, const TargetRegisterClass*> > RegsToSave; + std::vector<int> StackSlots; + + void calculateCallerSavedRegisters(MachineFunction &Fn); + 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. +/// +FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); } + + +/// calculateCallerSavedRegisters - Scan the function for modified caller saved +/// registers. Also calculate the MaxCallFrameSize and HasCalls variables for +/// the function's frame information and eliminates call frame pseudo +/// instructions. +/// +void PEI::calculateCallerSavedRegisters(MachineFunction &Fn) { + const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); + const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo(); + const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo(); + + // 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; + + 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 { + ++I; + } + + MachineFrameInfo *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. + // + const bool *PhysRegsUsed = Fn.getUsedPhysregs(); + const TargetRegisterClass* const *CSRegClasses = + RegInfo->getCalleeSaveRegClasses(); + for (unsigned i = 0; CSRegs[i]; ++i) { + unsigned Reg = CSRegs[i]; + if (PhysRegsUsed[Reg]) { + // If the reg is modified, save it! + RegsToSave.push_back(std::make_pair(Reg, CSRegClasses[i])); + } else { + for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg); + *AliasSet; ++AliasSet) { // Check alias registers too. + if (PhysRegsUsed[*AliasSet]) { + RegsToSave.push_back(std::make_pair(Reg, CSRegClasses[i])); + break; + } + } + } + } + + if (RegsToSave.empty()) + return; // Early exit if no caller saved registers are modified! + + unsigned NumFixedSpillSlots; + const std::pair<unsigned,int> *FixedSpillSlots = + TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots); + + // Now that we know which registers need to be saved and restored, allocate + // stack slots for them. + for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { + unsigned Reg = RegsToSave[i].first; + const TargetRegisterClass *RC = RegsToSave[i].second; + + // Check to see if this physreg must be spilled to a particular stack slot + // on this target. + const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots; + while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots && + FixedSlot->first != Reg) + ++FixedSlot; + + int FrameIdx; + if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) { + // Nope, just spill it anywhere convenient. + FrameIdx = FFI->CreateStackObject(RC->getSize(), RC->getAlignment()); + } else { + // Spill it to the stack where we must. + FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second); + } + StackSlots.push_back(FrameIdx); + } +} + +/// saveCallerSavedRegisters - Insert spill code for any caller saved registers +/// that are modified in the function. +/// +void PEI::saveCallerSavedRegisters(MachineFunction &Fn) { + // Early exit if no caller saved registers are modified! + if (RegsToSave.empty()) + return; + + const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo(); + + // 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) { + // Insert the spill to the stack frame. + RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i].first, StackSlots[i], + RegsToSave[i].second); + } + + // Add code to restore the callee-save registers in each exiting block. + const TargetInstrInfo &TII = *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 (!FI->empty() && TII.isReturn(FI->back().getOpcode())) { + MBB = FI; + I = MBB->end(); --I; + + // Skip over all terminator instructions, which are part of the return + // sequence. + MachineBasicBlock::iterator I2 = I; + while (I2 != MBB->begin() && TII.isTerminatorInstr((--I2)->getOpcode())) + I = I2; + + bool AtStart = I == MBB->begin(); + MachineBasicBlock::iterator BeforeI = I; + if (!AtStart) + --BeforeI; + + // Restore all registers immediately before the return and any terminators + // that preceed it. + for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) { + RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i].first, + StackSlots[i], RegsToSave[i].second); + assert(I != MBB->begin() && + "loadRegFromStackSlot didn't insert any code!"); + // Insert in reverse order. loadRegFromStackSlot can insert multiple + // instructions. + if (AtStart) + I = MBB->begin(); + else { + I = BeforeI; + ++I; + } + } + } +} + + +/// 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; + + // Loop over all of the stack objects, assigning sequential addresses... + MachineFrameInfo *FFI = Fn.getFrameInfo(); + + unsigned StackAlignment = TFI.getStackAlignment(); + + // Start at the beginning of the local area. + // The Offset is the distance from the stack top in the direction + // of stack growth -- so it's always positive. + int Offset = TFI.getOffsetOfLocalArea(); + if (StackGrowsDown) + Offset = -Offset; + assert(Offset >= 0 + && "Local area offset should be in direction of stack growth"); + + // If there are fixed sized objects that are preallocated in the local area, + // non-fixed objects can't be allocated right at the start of local area. + // We currently don't support filling in holes in between fixed sized objects, + // so we adjust 'Offset' to point to the end of last fixed sized + // preallocated object. + for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) { + int FixedOff; + if (StackGrowsDown) { + // The maximum distance from the stack pointer is at lower address of + // the object -- which is given by offset. For down growing stack + // the offset is negative, so we negate the offset to get the distance. + FixedOff = -FFI->getObjectOffset(i); + } else { + // The maximum distance from the start pointer is at the upper + // address of the object. + FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i); + } + if (FixedOff > Offset) Offset = FixedOff; + } + + for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) { + // If stack grows down, we need to add size of find the lowest + // address of the object. + if (StackGrowsDown) + Offset += FFI->getObjectSize(i); + + unsigned Align = FFI->getObjectAlignment(i); + assert(Align <= StackAlignment && "Cannot align stack object to higher " + "alignment boundary than the stack itself!"); + Offset = (Offset+Align-1)/Align*Align; // Adjust to Alignment boundary... + + if (StackGrowsDown) { + FFI->setObjectOffset(i, -Offset); // Set the computed offset + } else { + FFI->setObjectOffset(i, Offset); + Offset += FFI->getObjectSize(i); + } + } + + // Align the final stack pointer offset, but only if there are calls in the + // function. This ensures that any calls to subroutines have their stack + // frames suitable aligned. + if (FFI->hasCalls()) + Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment; + + // Set the final value of the stack pointer... + FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea()); +} + + +/// 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 TargetInstrInfo &TII = *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 (!I->empty() && TII.isReturn(I->back().getOpcode())) + Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I); + } +} + + +/// 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(I); + break; + } +} |