1 //===-- PrologEpilogInserter.cpp - Insert Prolog/Epilog code in function --===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass is responsible for finalizing the functions frame layout, saving
11 // callee saved registers, and for emitting prolog & epilog code for the
14 // This pass must be run after register allocation. After this pass is
15 // executed, it is illegal to construct MO_FrameIndex operands.
17 //===----------------------------------------------------------------------===//
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/CodeGen/MachineModuleInfo.h"
24 #include "llvm/CodeGen/MachineRegisterInfo.h"
25 #include "llvm/CodeGen/RegisterScavenging.h"
26 #include "llvm/Target/TargetMachine.h"
27 #include "llvm/Target/TargetRegisterInfo.h"
28 #include "llvm/Target/TargetFrameInfo.h"
29 #include "llvm/Target/TargetInstrInfo.h"
30 #include "llvm/Support/Compiler.h"
31 #include "llvm/ADT/STLExtras.h"
36 struct VISIBILITY_HIDDEN PEI : public MachineFunctionPass {
38 PEI() : MachineFunctionPass(&ID) {}
40 const char *getPassName() const {
41 return "Prolog/Epilog Insertion & Frame Finalization";
44 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
45 AU.addPreservedID(MachineLoopInfoID);
46 AU.addPreservedID(MachineDominatorsID);
47 MachineFunctionPass::getAnalysisUsage(AU);
50 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
51 /// frame indexes with appropriate references.
53 bool runOnMachineFunction(MachineFunction &Fn) {
54 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
55 RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : NULL;
57 // Get MachineModuleInfo so that we can track the construction of the
59 if (MachineModuleInfo *MMI = getAnalysisIfAvailable<MachineModuleInfo>())
60 Fn.getFrameInfo()->setMachineModuleInfo(MMI);
62 // Allow the target machine to make some adjustments to the function
63 // e.g. UsedPhysRegs before calculateCalleeSavedRegisters.
64 TRI->processFunctionBeforeCalleeSavedScan(Fn, RS);
66 // Scan the function for modified callee saved registers and insert spill
67 // code for any callee saved registers that are modified. Also calculate
68 // the MaxCallFrameSize and HasCalls variables for the function's frame
69 // information and eliminates call frame pseudo instructions.
70 calculateCalleeSavedRegisters(Fn);
72 // Add the code to save and restore the callee saved registers
73 saveCalleeSavedRegisters(Fn);
75 // Allow the target machine to make final modifications to the function
76 // before the frame layout is finalized.
77 TRI->processFunctionBeforeFrameFinalized(Fn);
79 // Calculate actual frame offsets for all of the abstract stack objects...
80 calculateFrameObjectOffsets(Fn);
82 // Add prolog and epilog code to the function. This function is required
83 // to align the stack frame as necessary for any stack variables or
84 // called functions. Because of this, calculateCalleeSavedRegisters
85 // must be called before this function in order to set the HasCalls
86 // and MaxCallFrameSize variables.
87 insertPrologEpilogCode(Fn);
89 // Replace all MO_FrameIndex operands with physical register references
90 // and actual offsets.
92 replaceFrameIndices(Fn);
101 // MinCSFrameIndex, MaxCSFrameIndex - Keeps the range of callee saved
102 // stack frame indexes.
103 unsigned MinCSFrameIndex, MaxCSFrameIndex;
105 void calculateCalleeSavedRegisters(MachineFunction &Fn);
106 void saveCalleeSavedRegisters(MachineFunction &Fn);
107 void calculateFrameObjectOffsets(MachineFunction &Fn);
108 void replaceFrameIndices(MachineFunction &Fn);
109 void insertPrologEpilogCode(MachineFunction &Fn);
115 /// createPrologEpilogCodeInserter - This function returns a pass that inserts
116 /// prolog and epilog code, and eliminates abstract frame references.
118 FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
121 /// calculateCalleeSavedRegisters - Scan the function for modified callee saved
122 /// registers. Also calculate the MaxCallFrameSize and HasCalls variables for
123 /// the function's frame information and eliminates call frame pseudo
126 void PEI::calculateCalleeSavedRegisters(MachineFunction &Fn) {
127 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
128 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo();
130 // Get the callee saved register list...
131 const unsigned *CSRegs = RegInfo->getCalleeSavedRegs(&Fn);
133 // Get the function call frame set-up and tear-down instruction opcode
134 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
135 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
137 // These are used to keep track the callee-save area. Initialize them.
138 MinCSFrameIndex = INT_MAX;
141 // Early exit for targets which have no callee saved registers and no call
142 // frame setup/destroy pseudo instructions.
143 if ((CSRegs == 0 || CSRegs[0] == 0) &&
144 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
147 unsigned MaxCallFrameSize = 0;
148 bool HasCalls = false;
150 std::vector<MachineBasicBlock::iterator> FrameSDOps;
151 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
152 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
153 if (I->getOpcode() == FrameSetupOpcode ||
154 I->getOpcode() == FrameDestroyOpcode) {
155 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo"
156 " instructions should have a single immediate argument!");
157 unsigned Size = I->getOperand(0).getImm();
158 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
160 FrameSDOps.push_back(I);
163 MachineFrameInfo *FFI = Fn.getFrameInfo();
164 FFI->setHasCalls(HasCalls);
165 FFI->setMaxCallFrameSize(MaxCallFrameSize);
167 for (unsigned i = 0, e = FrameSDOps.size(); i != e; ++i) {
168 MachineBasicBlock::iterator I = FrameSDOps[i];
169 // If call frames are not being included as part of the stack frame,
170 // and there is no dynamic allocation (therefore referencing frame slots
171 // off sp), leave the pseudo ops alone. We'll eliminate them later.
172 if (RegInfo->hasReservedCallFrame(Fn) || RegInfo->hasFP(Fn))
173 RegInfo->eliminateCallFramePseudoInstr(Fn, *I->getParent(), I);
176 // Now figure out which *callee saved* registers are modified by the current
177 // function, thus needing to be saved and restored in the prolog/epilog.
179 const TargetRegisterClass* const *CSRegClasses =
180 RegInfo->getCalleeSavedRegClasses(&Fn);
181 std::vector<CalleeSavedInfo> CSI;
182 for (unsigned i = 0; CSRegs[i]; ++i) {
183 unsigned Reg = CSRegs[i];
184 if (Fn.getRegInfo().isPhysRegUsed(Reg)) {
185 // If the reg is modified, save it!
186 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i]));
188 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
189 *AliasSet; ++AliasSet) { // Check alias registers too.
190 if (Fn.getRegInfo().isPhysRegUsed(*AliasSet)) {
191 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i]));
199 return; // Early exit if no callee saved registers are modified!
201 unsigned NumFixedSpillSlots;
202 const std::pair<unsigned,int> *FixedSpillSlots =
203 TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots);
205 // Now that we know which registers need to be saved and restored, allocate
206 // stack slots for them.
207 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
208 unsigned Reg = CSI[i].getReg();
209 const TargetRegisterClass *RC = CSI[i].getRegClass();
211 // Check to see if this physreg must be spilled to a particular stack slot
213 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots;
214 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots &&
215 FixedSlot->first != Reg)
219 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) {
220 // Nope, just spill it anywhere convenient.
221 unsigned Align = RC->getAlignment();
222 unsigned StackAlign = TFI->getStackAlignment();
223 // We may not be able to sastify the desired alignment specification of
224 // the TargetRegisterClass if the stack alignment is smaller. Use the min.
225 Align = std::min(Align, StackAlign);
226 FrameIdx = FFI->CreateStackObject(RC->getSize(), Align);
227 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
228 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
230 // Spill it to the stack where we must.
231 FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second);
233 CSI[i].setFrameIdx(FrameIdx);
236 FFI->setCalleeSavedInfo(CSI);
239 /// saveCalleeSavedRegisters - Insert spill code for any callee saved registers
240 /// that are modified in the function.
242 void PEI::saveCalleeSavedRegisters(MachineFunction &Fn) {
243 // Get callee saved register information.
244 MachineFrameInfo *FFI = Fn.getFrameInfo();
245 const std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo();
247 // Early exit if no callee saved registers are modified!
251 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
253 // Now that we have a stack slot for each register to be saved, insert spill
254 // code into the entry block.
255 MachineBasicBlock *MBB = Fn.begin();
256 MachineBasicBlock::iterator I = MBB->begin();
258 if (!TII.spillCalleeSavedRegisters(*MBB, I, CSI)) {
259 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
260 // Add the callee-saved register as live-in. It's killed at the spill.
261 MBB->addLiveIn(CSI[i].getReg());
263 // Insert the spill to the stack frame.
264 TII.storeRegToStackSlot(*MBB, I, CSI[i].getReg(), true,
265 CSI[i].getFrameIdx(), CSI[i].getRegClass());
269 // Add code to restore the callee-save registers in each exiting block.
270 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI)
271 // If last instruction is a return instruction, add an epilogue.
272 if (!FI->empty() && FI->back().getDesc().isReturn()) {
276 // Skip over all terminator instructions, which are part of the return
278 MachineBasicBlock::iterator I2 = I;
279 while (I2 != MBB->begin() && (--I2)->getDesc().isTerminator())
282 bool AtStart = I == MBB->begin();
283 MachineBasicBlock::iterator BeforeI = I;
287 // Restore all registers immediately before the return and any terminators
289 if (!TII.restoreCalleeSavedRegisters(*MBB, I, CSI)) {
290 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
291 TII.loadRegFromStackSlot(*MBB, I, CSI[i].getReg(),
292 CSI[i].getFrameIdx(),
293 CSI[i].getRegClass());
294 assert(I != MBB->begin() &&
295 "loadRegFromStackSlot didn't insert any code!");
296 // Insert in reverse order. loadRegFromStackSlot can insert multiple
309 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
311 AdjustStackOffset(MachineFrameInfo *FFI, int FrameIdx,
312 bool StackGrowsDown, int64_t &Offset,
313 unsigned &MaxAlign) {
314 // If stack grows down, we need to add size of find the lowest address of the
317 Offset += FFI->getObjectSize(FrameIdx);
319 unsigned Align = FFI->getObjectAlignment(FrameIdx);
321 // If the alignment of this object is greater than that of the stack, then
322 // increase the stack alignment to match.
323 MaxAlign = std::max(MaxAlign, Align);
325 // Adjust to alignment boundary.
326 Offset = (Offset + Align - 1) / Align * Align;
328 if (StackGrowsDown) {
329 FFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
331 FFI->setObjectOffset(FrameIdx, Offset);
332 Offset += FFI->getObjectSize(FrameIdx);
336 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
337 /// abstract stack objects.
339 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
340 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo();
342 bool StackGrowsDown =
343 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
345 // Loop over all of the stack objects, assigning sequential addresses...
346 MachineFrameInfo *FFI = Fn.getFrameInfo();
348 unsigned MaxAlign = FFI->getMaxAlignment();
350 // Start at the beginning of the local area.
351 // The Offset is the distance from the stack top in the direction
352 // of stack growth -- so it's always nonnegative.
353 int64_t Offset = TFI.getOffsetOfLocalArea();
357 && "Local area offset should be in direction of stack growth");
359 // If there are fixed sized objects that are preallocated in the local area,
360 // non-fixed objects can't be allocated right at the start of local area.
361 // We currently don't support filling in holes in between fixed sized objects,
362 // so we adjust 'Offset' to point to the end of last fixed sized
363 // preallocated object.
364 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) {
366 if (StackGrowsDown) {
367 // The maximum distance from the stack pointer is at lower address of
368 // the object -- which is given by offset. For down growing stack
369 // the offset is negative, so we negate the offset to get the distance.
370 FixedOff = -FFI->getObjectOffset(i);
372 // The maximum distance from the start pointer is at the upper
373 // address of the object.
374 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i);
376 if (FixedOff > Offset) Offset = FixedOff;
379 // First assign frame offsets to stack objects that are used to spill
380 // callee saved registers.
381 if (StackGrowsDown) {
382 for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
383 // If stack grows down, we need to add size of find the lowest
384 // address of the object.
385 Offset += FFI->getObjectSize(i);
387 unsigned Align = FFI->getObjectAlignment(i);
388 // If the alignment of this object is greater than that of the stack, then
389 // increase the stack alignment to match.
390 MaxAlign = std::max(MaxAlign, Align);
391 // Adjust to alignment boundary
392 Offset = (Offset+Align-1)/Align*Align;
394 FFI->setObjectOffset(i, -Offset); // Set the computed offset
397 int MaxCSFI = MaxCSFrameIndex, MinCSFI = MinCSFrameIndex;
398 for (int i = MaxCSFI; i >= MinCSFI ; --i) {
399 unsigned Align = FFI->getObjectAlignment(i);
400 // If the alignment of this object is greater than that of the stack, then
401 // increase the stack alignment to match.
402 MaxAlign = std::max(MaxAlign, Align);
403 // Adjust to alignment boundary
404 Offset = (Offset+Align-1)/Align*Align;
406 FFI->setObjectOffset(i, Offset);
407 Offset += FFI->getObjectSize(i);
411 // Make sure the special register scavenging spill slot is closest to the
412 // frame pointer if a frame pointer is required.
413 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
414 if (RS && RegInfo->hasFP(Fn)) {
415 int SFI = RS->getScavengingFrameIndex();
417 AdjustStackOffset(FFI, SFI, StackGrowsDown, Offset, MaxAlign);
420 // Make sure that the stack protector comes before the local variables on the
422 if (FFI->getStackProtectorIndex() >= 0)
423 AdjustStackOffset(FFI, FFI->getStackProtectorIndex(), StackGrowsDown,
426 // Then assign frame offsets to stack objects that are not used to spill
427 // callee saved registers.
428 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
429 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
431 if (RS && (int)i == RS->getScavengingFrameIndex())
433 if (FFI->isDeadObjectIndex(i))
435 if (FFI->getStackProtectorIndex() == (int)i)
438 AdjustStackOffset(FFI, i, StackGrowsDown, Offset, MaxAlign);
441 // Make sure the special register scavenging spill slot is closest to the
443 if (RS && !RegInfo->hasFP(Fn)) {
444 int SFI = RS->getScavengingFrameIndex();
446 AdjustStackOffset(FFI, SFI, StackGrowsDown, Offset, MaxAlign);
449 // Round up the size to a multiple of the alignment, but only if there are
450 // calls or alloca's in the function. This ensures that any calls to
451 // subroutines have their stack frames suitable aligned.
452 // Also do this if we need runtime alignment of the stack. In this case
453 // offsets will be relative to SP not FP; round up the stack size so this
455 if (!RegInfo->targetHandlesStackFrameRounding() &&
456 (FFI->hasCalls() || FFI->hasVarSizedObjects() ||
457 (RegInfo->needsStackRealignment(Fn) &&
458 FFI->getObjectIndexEnd() != 0))) {
459 // If we have reserved argument space for call sites in the function
460 // immediately on entry to the current function, count it as part of the
461 // overall stack size.
462 if (RegInfo->hasReservedCallFrame(Fn))
463 Offset += FFI->getMaxCallFrameSize();
465 unsigned AlignMask = std::max(TFI.getStackAlignment(),MaxAlign) - 1;
466 Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
469 // Update frame info to pretend that this is part of the stack...
470 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea());
472 // Remember the required stack alignment in case targets need it to perform
473 // dynamic stack alignment.
474 FFI->setMaxAlignment(MaxAlign);
478 /// insertPrologEpilogCode - Scan the function for modified callee saved
479 /// registers, insert spill code for these callee saved registers, then add
480 /// prolog and epilog code to the function.
482 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
483 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
485 // Add prologue to the function...
486 TRI->emitPrologue(Fn);
488 // Add epilogue to restore the callee-save registers in each exiting block
489 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
490 // If last instruction is a return instruction, add an epilogue
491 if (!I->empty() && I->back().getDesc().isReturn())
492 TRI->emitEpilogue(Fn, *I);
497 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
498 /// register references and actual offsets.
500 void PEI::replaceFrameIndices(MachineFunction &Fn) {
501 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
503 const TargetMachine &TM = Fn.getTarget();
504 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
505 const TargetRegisterInfo &TRI = *TM.getRegisterInfo();
506 const TargetFrameInfo *TFI = TM.getFrameInfo();
507 bool StackGrowsDown =
508 TFI->getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
509 int FrameSetupOpcode = TRI.getCallFrameSetupOpcode();
510 int FrameDestroyOpcode = TRI.getCallFrameDestroyOpcode();
512 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
513 int SPAdj = 0; // SP offset due to call frame setup / destroy.
514 if (RS) RS->enterBasicBlock(BB);
515 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
516 MachineInstr *MI = I;
518 if (I->getOpcode() == TargetInstrInfo::DECLARE) {
524 if (I->getOpcode() == FrameSetupOpcode ||
525 I->getOpcode() == FrameDestroyOpcode) {
526 // Remember how much SP has been adjusted to create the call
528 int Size = I->getOperand(0).getImm();
530 if ((!StackGrowsDown && I->getOpcode() == FrameSetupOpcode) ||
531 (StackGrowsDown && I->getOpcode() == FrameDestroyOpcode))
536 MachineBasicBlock::iterator PrevI = prior(I);
537 TRI.eliminateCallFramePseudoInstr(Fn, *BB, I);
539 // Visit the instructions created by eliminateCallFramePseudoInstr().
546 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
547 if (MI->getOperand(i).isFI()) {
548 // Some instructions (e.g. inline asm instructions) can have
549 // multiple frame indices and/or cause eliminateFrameIndex
550 // to insert more than one instruction. We need the register
551 // scavenger to go through all of these instructions so that
552 // it can update its register information. We keep the
553 // iterator at the point before insertion so that we can
554 // revisit them in full.
555 bool AtBeginning = (I == BB->begin());
556 if (!AtBeginning) --I;
558 // If this instruction has a FrameIndex operand, we need to
559 // use that target machine register info object to eliminate
561 TRI.eliminateFrameIndex(MI, SPAdj, RS);
563 // Reset the iterator if we were at the beginning of the BB.
575 // Update register states.
576 if (RS && MI) RS->forward(MI);
579 assert(SPAdj == 0 && "Unbalanced call frame setup / destroy pairs?");