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//===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===//
//
// The LLVM Compiler Infrastructure
//
// This file 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/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetFrameInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Support/Compiler.h"
#include "llvm/ADT/STLExtras.h"
#include <climits>
using namespace llvm;
namespace {
struct VISIBILITY_HIDDEN PEI : public MachineFunctionPass {
static char ID;
PEI() : MachineFunctionPass(&ID) {}
const char *getPassName() const {
return "Prolog/Epilog Insertion & Frame Finalization";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - Insert prolog/epilog code and replace abstract
/// frame indexes with appropriate references.
///
bool runOnMachineFunction(MachineFunction &Fn) {
const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : NULL;
// Get MachineModuleInfo so that we can track the construction of the
// frame.
if (MachineModuleInfo *MMI = getAnalysisIfAvailable<MachineModuleInfo>())
Fn.getFrameInfo()->setMachineModuleInfo(MMI);
// Allow the target machine to make some adjustments to the function
// e.g. UsedPhysRegs before calculateCalleeSavedRegisters.
TRI->processFunctionBeforeCalleeSavedScan(Fn, RS);
// Scan the function for modified callee saved registers and insert spill
// code for any callee saved registers that are modified. Also calculate
// the MaxCallFrameSize and HasCalls variables for the function's frame
// information and eliminates call frame pseudo instructions.
calculateCalleeSavedRegisters(Fn);
// Add the code to save and restore the callee saved registers
saveCalleeSavedRegisters(Fn);
// Allow the target machine to make final modifications to the function
// before the frame layout is finalized.
TRI->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, calculateCalleeSavedRegisters
// 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);
delete RS;
return true;
}
private:
RegScavenger *RS;
// MinCSFrameIndex, MaxCSFrameIndex - Keeps the range of callee saved
// stack frame indexes.
unsigned MinCSFrameIndex, MaxCSFrameIndex;
void calculateCalleeSavedRegisters(MachineFunction &Fn);
void saveCalleeSavedRegisters(MachineFunction &Fn);
void calculateFrameObjectOffsets(MachineFunction &Fn);
void replaceFrameIndices(MachineFunction &Fn);
void insertPrologEpilogCode(MachineFunction &Fn);
};
char PEI::ID = 0;
}
/// createPrologEpilogCodeInserter - This function returns a pass that inserts
/// prolog and epilog code, and eliminates abstract frame references.
///
FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
/// calculateCalleeSavedRegisters - Scan the function for modified callee saved
/// registers. Also calculate the MaxCallFrameSize and HasCalls variables for
/// the function's frame information and eliminates call frame pseudo
/// instructions.
///
void PEI::calculateCalleeSavedRegisters(MachineFunction &Fn) {
const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo();
// Get the callee saved register list...
const unsigned *CSRegs = RegInfo->getCalleeSavedRegs(&Fn);
// Get the function call frame set-up and tear-down instruction opcode
int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
// These are used to keep track the callee-save area. Initialize them.
MinCSFrameIndex = INT_MAX;
MaxCSFrameIndex = 0;
// 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;
std::vector<MachineBasicBlock::iterator> FrameSDOps;
for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
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).getImm();
if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
HasCalls = true;
FrameSDOps.push_back(I);
}
MachineFrameInfo *FFI = Fn.getFrameInfo();
FFI->setHasCalls(HasCalls);
FFI->setMaxCallFrameSize(MaxCallFrameSize);
for (unsigned i = 0, e = FrameSDOps.size(); i != e; ++i) {
MachineBasicBlock::iterator I = FrameSDOps[i];
// If call frames are not being included as part of the stack frame,
// and there is no dynamic allocation (therefore referencing frame slots
// off sp), leave the pseudo ops alone. We'll eliminate them later.
if (RegInfo->hasReservedCallFrame(Fn) || RegInfo->hasFP(Fn))
RegInfo->eliminateCallFramePseudoInstr(Fn, *I->getParent(), I);
}
// 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 TargetRegisterClass* const *CSRegClasses =
RegInfo->getCalleeSavedRegClasses(&Fn);
std::vector<CalleeSavedInfo> CSI;
for (unsigned i = 0; CSRegs[i]; ++i) {
unsigned Reg = CSRegs[i];
if (Fn.getRegInfo().isPhysRegUsed(Reg)) {
// If the reg is modified, save it!
CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i]));
} else {
for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
*AliasSet; ++AliasSet) { // Check alias registers too.
if (Fn.getRegInfo().isPhysRegUsed(*AliasSet)) {
CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i]));
break;
}
}
}
}
if (CSI.empty())
return; // Early exit if no callee saved registers are modified!
unsigned NumFixedSpillSlots;
const std::pair<unsigned,int> *FixedSpillSlots =
TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots);
// Now that we know which registers need to be saved and restored, allocate
// stack slots for them.
for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
unsigned Reg = CSI[i].getReg();
const TargetRegisterClass *RC = CSI[i].getRegClass();
// 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.
unsigned Align = RC->getAlignment();
unsigned StackAlign = TFI->getStackAlignment();
// We may not be able to sastify the desired alignment specification of
// the TargetRegisterClass if the stack alignment is smaller. Use the min.
Align = std::min(Align, StackAlign);
FrameIdx = FFI->CreateStackObject(RC->getSize(), Align);
if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
} else {
// Spill it to the stack where we must.
FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second);
}
CSI[i].setFrameIdx(FrameIdx);
}
FFI->setCalleeSavedInfo(CSI);
}
/// saveCalleeSavedRegisters - Insert spill code for any callee saved registers
/// that are modified in the function.
///
void PEI::saveCalleeSavedRegisters(MachineFunction &Fn) {
// Get callee saved register information.
MachineFrameInfo *FFI = Fn.getFrameInfo();
const std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo();
// Early exit if no callee saved registers are modified!
if (CSI.empty())
return;
const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
// 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();
if (!TII.spillCalleeSavedRegisters(*MBB, I, CSI)) {
for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
// Add the callee-saved register as live-in. It's killed at the spill.
MBB->addLiveIn(CSI[i].getReg());
// Insert the spill to the stack frame.
TII.storeRegToStackSlot(*MBB, I, CSI[i].getReg(), true,
CSI[i].getFrameIdx(), CSI[i].getRegClass());
}
}
// Add code to restore the callee-save registers in each exiting block.
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() && FI->back().getDesc().isReturn()) {
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() && (--I2)->getDesc().isTerminator())
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.
if (!TII.restoreCalleeSavedRegisters(*MBB, I, CSI)) {
for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
TII.loadRegFromStackSlot(*MBB, I, CSI[i].getReg(),
CSI[i].getFrameIdx(),
CSI[i].getRegClass());
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;
}
}
}
}
}
/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
static inline void
AdjustStackOffset(MachineFrameInfo *FFI, int FrameIdx,
bool StackGrowsDown, int64_t &Offset,
unsigned &MaxAlign) {
// If stack grows down, we need to add size of find the lowest address of the
// object.
if (StackGrowsDown)
Offset += FFI->getObjectSize(FrameIdx);
unsigned Align = FFI->getObjectAlignment(FrameIdx);
// If the alignment of this object is greater than that of the stack, then
// increase the stack alignment to match.
MaxAlign = std::max(MaxAlign, Align);
// Adjust to alignment boundary.
Offset = (Offset + Align - 1) / Align * Align;
if (StackGrowsDown) {
FFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
} else {
FFI->setObjectOffset(FrameIdx, Offset);
Offset += FFI->getObjectSize(FrameIdx);
}
}
/// 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 MaxAlign = FFI->getMaxAlignment();
// 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 nonnegative.
int64_t 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) {
int64_t 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;
}
// First assign frame offsets to stack objects that are used to spill
// callee saved registers.
if (StackGrowsDown) {
for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
// If stack grows down, we need to add size of find the lowest
// address of the object.
Offset += FFI->getObjectSize(i);
unsigned Align = FFI->getObjectAlignment(i);
// If the alignment of this object is greater than that of the stack, then
// increase the stack alignment to match.
MaxAlign = std::max(MaxAlign, Align);
// Adjust to alignment boundary
Offset = (Offset+Align-1)/Align*Align;
FFI->setObjectOffset(i, -Offset); // Set the computed offset
}
} else {
int MaxCSFI = MaxCSFrameIndex, MinCSFI = MinCSFrameIndex;
for (int i = MaxCSFI; i >= MinCSFI ; --i) {
unsigned Align = FFI->getObjectAlignment(i);
// If the alignment of this object is greater than that of the stack, then
// increase the stack alignment to match.
MaxAlign = std::max(MaxAlign, Align);
// Adjust to alignment boundary
Offset = (Offset+Align-1)/Align*Align;
FFI->setObjectOffset(i, Offset);
Offset += FFI->getObjectSize(i);
}
}
// Make sure the special register scavenging spill slot is closest to the
// frame pointer if a frame pointer is required.
const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
if (RS && RegInfo->hasFP(Fn)) {
int SFI = RS->getScavengingFrameIndex();
if (SFI >= 0)
AdjustStackOffset(FFI, SFI, StackGrowsDown, Offset, MaxAlign);
}
// Make sure that the stack protector comes before the local variables on the
// stack.
if (FFI->getStackProtectorIndex() >= 0)
AdjustStackOffset(FFI, FFI->getStackProtectorIndex(), StackGrowsDown,
Offset, MaxAlign);
// Then assign frame offsets to stack objects that are not used to spill
// callee saved registers.
for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
continue;
if (RS && (int)i == RS->getScavengingFrameIndex())
continue;
if (FFI->isDeadObjectIndex(i))
continue;
if (FFI->getStackProtectorIndex() == (int)i)
continue;
AdjustStackOffset(FFI, i, StackGrowsDown, Offset, MaxAlign);
}
// Make sure the special register scavenging spill slot is closest to the
// stack pointer.
if (RS && !RegInfo->hasFP(Fn)) {
int SFI = RS->getScavengingFrameIndex();
if (SFI >= 0)
AdjustStackOffset(FFI, SFI, StackGrowsDown, Offset, MaxAlign);
}
// Round up the size to a multiple of the alignment, but only if there are
// calls or alloca's in the function. This ensures that any calls to
// subroutines have their stack frames suitable aligned.
// Also do this if we need runtime alignment of the stack. In this case
// offsets will be relative to SP not FP; round up the stack size so this
// works.
if (!RegInfo->targetHandlesStackFrameRounding() &&
(FFI->hasCalls() || FFI->hasVarSizedObjects() ||
(RegInfo->needsStackRealignment(Fn) &&
FFI->getObjectIndexEnd() != 0))) {
// If we have reserved argument space for call sites in the function
// immediately on entry to the current function, count it as part of the
// overall stack size.
if (RegInfo->hasReservedCallFrame(Fn))
Offset += FFI->getMaxCallFrameSize();
unsigned AlignMask = std::max(TFI.getStackAlignment(),MaxAlign) - 1;
Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
}
// Update frame info to pretend that this is part of the stack...
FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea());
// Remember the required stack alignment in case targets need it to perform
// dynamic stack alignment.
FFI->setMaxAlignment(MaxAlign);
}
/// insertPrologEpilogCode - Scan the function for modified callee saved
/// registers, insert spill code for these callee saved registers, then add
/// prolog and epilog code to the function.
///
void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
// Add prologue to the function...
TRI->emitPrologue(Fn);
// Add epilogue to restore the callee-save registers in each exiting block
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() && I->back().getDesc().isReturn())
TRI->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 TargetRegisterInfo &TRI = *TM.getRegisterInfo();
const TargetFrameInfo *TFI = TM.getFrameInfo();
bool StackGrowsDown =
TFI->getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
int FrameSetupOpcode = TRI.getCallFrameSetupOpcode();
int FrameDestroyOpcode = TRI.getCallFrameDestroyOpcode();
for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
int SPAdj = 0; // SP offset due to call frame setup / destroy.
if (RS) RS->enterBasicBlock(BB);
for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
MachineInstr *MI = I;
if (I->getOpcode() == TargetInstrInfo::DECLARE) {
// Ignore it.
++I;
continue;
}
if (I->getOpcode() == FrameSetupOpcode ||
I->getOpcode() == FrameDestroyOpcode) {
// Remember how much SP has been adjusted to create the call
// frame.
int Size = I->getOperand(0).getImm();
if ((!StackGrowsDown && I->getOpcode() == FrameSetupOpcode) ||
(StackGrowsDown && I->getOpcode() == FrameDestroyOpcode))
Size = -Size;
SPAdj += Size;
MachineBasicBlock::iterator PrevI = prior(I);
TRI.eliminateCallFramePseudoInstr(Fn, *BB, I);
// Visit the instructions created by eliminateCallFramePseudoInstr().
I = next(PrevI);
continue;
}
bool DoIncr = true;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
if (MI->getOperand(i).isFI()) {
// Some instructions (e.g. inline asm instructions) can have
// multiple frame indices and/or cause eliminateFrameIndex
// to insert more than one instruction. We need the register
// scavenger to go through all of these instructions so that
// it can update its register information. We keep the
// iterator at the point before insertion so that we can
// revisit them in full.
bool AtBeginning = (I == BB->begin());
if (!AtBeginning) --I;
// If this instruction has a FrameIndex operand, we need to
// use that target machine register info object to eliminate
// it.
TRI.eliminateFrameIndex(MI, SPAdj, RS);
// Reset the iterator if we were at the beginning of the BB.
if (AtBeginning) {
I = BB->begin();
DoIncr = false;
}
MI = 0;
break;
}
if (DoIncr) ++I;
// Update register states.
if (RS && MI) RS->forward(MI);
}
assert(SPAdj == 0 && "Unbalanced call frame setup / destroy pairs?");
}
}
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