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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24227 91177308-0d34-0410-b5e6-96231b3b80d8
366 lines
14 KiB
C++
366 lines
14 KiB
C++
//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass is responsible for finalizing the functions frame layout, saving
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// callee saved registers, and for emitting prolog & epilog code for the
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// function.
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//
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// This pass must be run after register allocation. After this pass is
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// executed, it is illegal to construct MO_FrameIndex operands.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineFrameInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/MRegisterInfo.h"
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#include "llvm/Target/TargetFrameInfo.h"
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#include "llvm/Target/TargetInstrInfo.h"
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using namespace llvm;
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namespace {
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struct PEI : public MachineFunctionPass {
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const char *getPassName() const {
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return "Prolog/Epilog Insertion & Frame Finalization";
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}
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/// runOnMachineFunction - Insert prolog/epilog code and replace abstract
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/// frame indexes with appropriate references.
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///
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bool runOnMachineFunction(MachineFunction &Fn) {
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// Scan the function for modified caller saved registers and insert spill
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// code for any caller saved registers that are modified. Also calculate
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// the MaxCallFrameSize and HasCalls variables for the function's frame
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// information and eliminates call frame pseudo instructions.
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calculateCallerSavedRegisters(Fn);
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// Add the code to save and restore the caller saved registers
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saveCallerSavedRegisters(Fn);
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// Allow the target machine to make final modifications to the function
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// before the frame layout is finalized.
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Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn);
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// Calculate actual frame offsets for all of the abstract stack objects...
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calculateFrameObjectOffsets(Fn);
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// Add prolog and epilog code to the function. This function is required
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// to align the stack frame as necessary for any stack variables or
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// called functions. Because of this, calculateCallerSavedRegisters
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// must be called before this function in order to set the HasCalls
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// and MaxCallFrameSize variables.
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insertPrologEpilogCode(Fn);
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// Replace all MO_FrameIndex operands with physical register references
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// and actual offsets.
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//
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replaceFrameIndices(Fn);
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RegsToSave.clear();
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StackSlots.clear();
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return true;
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}
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private:
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std::vector<std::pair<unsigned, const TargetRegisterClass*> > RegsToSave;
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std::vector<int> StackSlots;
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void calculateCallerSavedRegisters(MachineFunction &Fn);
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void saveCallerSavedRegisters(MachineFunction &Fn);
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void calculateFrameObjectOffsets(MachineFunction &Fn);
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void replaceFrameIndices(MachineFunction &Fn);
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void insertPrologEpilogCode(MachineFunction &Fn);
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};
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}
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/// createPrologEpilogCodeInserter - This function returns a pass that inserts
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/// prolog and epilog code, and eliminates abstract frame references.
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///
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FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
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/// calculateCallerSavedRegisters - Scan the function for modified caller saved
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/// registers. Also calculate the MaxCallFrameSize and HasCalls variables for
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/// the function's frame information and eliminates call frame pseudo
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/// instructions.
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///
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void PEI::calculateCallerSavedRegisters(MachineFunction &Fn) {
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const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
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const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo();
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const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
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// Get the callee saved register list...
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const unsigned *CSRegs = RegInfo->getCalleeSaveRegs();
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// Get the function call frame set-up and tear-down instruction opcode
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int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
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int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
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// Early exit for targets which have no callee saved registers and no call
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// frame setup/destroy pseudo instructions.
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if ((CSRegs == 0 || CSRegs[0] == 0) &&
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FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
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return;
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unsigned MaxCallFrameSize = 0;
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bool HasCalls = false;
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for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
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for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); )
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if (I->getOpcode() == FrameSetupOpcode ||
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I->getOpcode() == FrameDestroyOpcode) {
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assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo"
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" instructions should have a single immediate argument!");
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unsigned Size = I->getOperand(0).getImmedValue();
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if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
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HasCalls = true;
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RegInfo->eliminateCallFramePseudoInstr(Fn, *BB, I++);
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} else {
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++I;
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}
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MachineFrameInfo *FFI = Fn.getFrameInfo();
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FFI->setHasCalls(HasCalls);
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FFI->setMaxCallFrameSize(MaxCallFrameSize);
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// Now figure out which *callee saved* registers are modified by the current
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// function, thus needing to be saved and restored in the prolog/epilog.
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//
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const bool *PhysRegsUsed = Fn.getUsedPhysregs();
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const TargetRegisterClass* const *CSRegClasses =
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RegInfo->getCalleeSaveRegClasses();
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for (unsigned i = 0; CSRegs[i]; ++i) {
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unsigned Reg = CSRegs[i];
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if (PhysRegsUsed[Reg]) {
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// If the reg is modified, save it!
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RegsToSave.push_back(std::make_pair(Reg, CSRegClasses[i]));
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} else {
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for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
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*AliasSet; ++AliasSet) { // Check alias registers too.
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if (PhysRegsUsed[*AliasSet]) {
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RegsToSave.push_back(std::make_pair(Reg, CSRegClasses[i]));
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break;
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}
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}
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}
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}
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if (RegsToSave.empty())
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return; // Early exit if no caller saved registers are modified!
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unsigned NumFixedSpillSlots;
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const std::pair<unsigned,int> *FixedSpillSlots =
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TFI->getCalleeSaveSpillSlots(NumFixedSpillSlots);
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// Now that we know which registers need to be saved and restored, allocate
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// stack slots for them.
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for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
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unsigned Reg = RegsToSave[i].first;
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const TargetRegisterClass *RC = RegsToSave[i].second;
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// Check to see if this physreg must be spilled to a particular stack slot
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// on this target.
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const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots;
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while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots &&
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FixedSlot->first != Reg)
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++FixedSlot;
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int FrameIdx;
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if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) {
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// Nope, just spill it anywhere convenient.
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FrameIdx = FFI->CreateStackObject(RC->getSize(), RC->getAlignment());
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} else {
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// Spill it to the stack where we must.
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FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second);
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}
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StackSlots.push_back(FrameIdx);
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}
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}
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/// saveCallerSavedRegisters - Insert spill code for any caller saved registers
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/// that are modified in the function.
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///
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void PEI::saveCallerSavedRegisters(MachineFunction &Fn) {
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// Early exit if no caller saved registers are modified!
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if (RegsToSave.empty())
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return;
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const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
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// Now that we have a stack slot for each register to be saved, insert spill
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// code into the entry block.
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MachineBasicBlock *MBB = Fn.begin();
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MachineBasicBlock::iterator I = MBB->begin();
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for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
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// Insert the spill to the stack frame.
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RegInfo->storeRegToStackSlot(*MBB, I, RegsToSave[i].first, StackSlots[i],
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RegsToSave[i].second);
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}
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// Add code to restore the callee-save registers in each exiting block.
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const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
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for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI)
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// If last instruction is a return instruction, add an epilogue.
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if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) {
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MBB = FI;
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I = MBB->end(); --I;
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// Skip over all terminator instructions, which are part of the return
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// sequence.
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MachineBasicBlock::iterator I2 = I;
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while (I2 != MBB->begin() && TII.isTerminatorInstr((--I2)->getOpcode()))
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I = I2;
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bool AtStart = I == MBB->begin();
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MachineBasicBlock::iterator BeforeI = I;
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if (!AtStart)
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--BeforeI;
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// Restore all registers immediately before the return and any terminators
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// that preceed it.
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for (unsigned i = 0, e = RegsToSave.size(); i != e; ++i) {
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RegInfo->loadRegFromStackSlot(*MBB, I, RegsToSave[i].first,
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StackSlots[i], RegsToSave[i].second);
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assert(I != MBB->begin() &&
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"loadRegFromStackSlot didn't insert any code!");
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// Insert in reverse order. loadRegFromStackSlot can insert multiple
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// instructions.
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if (AtStart)
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I = MBB->begin();
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else {
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I = BeforeI;
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++I;
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}
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}
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}
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}
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/// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
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/// abstract stack objects.
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///
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void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
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const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo();
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bool StackGrowsDown =
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TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
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// Loop over all of the stack objects, assigning sequential addresses...
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MachineFrameInfo *FFI = Fn.getFrameInfo();
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unsigned StackAlignment = TFI.getStackAlignment();
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unsigned MaxAlign = 0;
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// Start at the beginning of the local area.
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// The Offset is the distance from the stack top in the direction
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// of stack growth -- so it's always positive.
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int Offset = TFI.getOffsetOfLocalArea();
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if (StackGrowsDown)
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Offset = -Offset;
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assert(Offset >= 0
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&& "Local area offset should be in direction of stack growth");
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// If there are fixed sized objects that are preallocated in the local area,
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// non-fixed objects can't be allocated right at the start of local area.
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// We currently don't support filling in holes in between fixed sized objects,
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// so we adjust 'Offset' to point to the end of last fixed sized
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// preallocated object.
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for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) {
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int FixedOff;
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if (StackGrowsDown) {
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// The maximum distance from the stack pointer is at lower address of
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// the object -- which is given by offset. For down growing stack
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// the offset is negative, so we negate the offset to get the distance.
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FixedOff = -FFI->getObjectOffset(i);
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} else {
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// The maximum distance from the start pointer is at the upper
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// address of the object.
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FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i);
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}
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if (FixedOff > Offset) Offset = FixedOff;
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}
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for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
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// If stack grows down, we need to add size of find the lowest
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// address of the object.
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if (StackGrowsDown)
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Offset += FFI->getObjectSize(i);
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unsigned Align = FFI->getObjectAlignment(i);
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// If the alignment of this object is greater than that of the stack, then
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// increase the stack alignment to match.
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MaxAlign = std::max(MaxAlign, Align);
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// Adjust to alignment boundary
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Offset = (Offset+Align-1)/Align*Align;
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if (StackGrowsDown) {
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FFI->setObjectOffset(i, -Offset); // Set the computed offset
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} else {
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FFI->setObjectOffset(i, Offset);
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Offset += FFI->getObjectSize(i);
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}
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}
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// Align the final stack pointer offset, but only if there are calls in the
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// function. This ensures that any calls to subroutines have their stack
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// frames suitable aligned.
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if (FFI->hasCalls())
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Offset = (Offset+StackAlignment-1)/StackAlignment*StackAlignment;
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// Set the final value of the stack pointer...
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FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea());
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// Remember the required stack alignment in case targets need it to perform
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// dynamic stack alignment.
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FFI->setMaxAlignment(MaxAlign);
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}
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/// insertPrologEpilogCode - Scan the function for modified caller saved
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/// registers, insert spill code for these caller saved registers, then add
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/// prolog and epilog code to the function.
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///
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void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
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// Add prologue to the function...
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Fn.getTarget().getRegisterInfo()->emitPrologue(Fn);
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// Add epilogue to restore the callee-save registers in each exiting block
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const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
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for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
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// If last instruction is a return instruction, add an epilogue
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if (!I->empty() && TII.isReturn(I->back().getOpcode()))
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Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I);
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}
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}
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/// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
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/// register references and actual offsets.
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///
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void PEI::replaceFrameIndices(MachineFunction &Fn) {
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if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
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const TargetMachine &TM = Fn.getTarget();
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assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
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const MRegisterInfo &MRI = *TM.getRegisterInfo();
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for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
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for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
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if (I->getOperand(i).isFrameIndex()) {
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// If this instruction has a FrameIndex operand, we need to use that
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// target machine register info object to eliminate it.
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MRI.eliminateFrameIndex(I);
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break;
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}
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}
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