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/MRegisterInfo.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((intptr_t)&ID) {}
40 const char *getPassName() const {
41 return "Prolog/Epilog Insertion & Frame Finalization";
44 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
45 /// frame indexes with appropriate references.
47 bool runOnMachineFunction(MachineFunction &Fn) {
48 const MRegisterInfo *MRI = Fn.getTarget().getRegisterInfo();
49 RS = MRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : NULL;
51 // Get MachineModuleInfo so that we can track the construction of the
53 if (MachineModuleInfo *MMI = getAnalysisToUpdate<MachineModuleInfo>())
54 Fn.getFrameInfo()->setMachineModuleInfo(MMI);
56 // Allow the target machine to make some adjustments to the function
57 // e.g. UsedPhysRegs before calculateCalleeSavedRegisters.
58 MRI->processFunctionBeforeCalleeSavedScan(Fn, RS);
60 // Scan the function for modified callee saved registers and insert spill
61 // code for any callee saved registers that are modified. Also calculate
62 // the MaxCallFrameSize and HasCalls variables for the function's frame
63 // information and eliminates call frame pseudo instructions.
64 calculateCalleeSavedRegisters(Fn);
66 // Add the code to save and restore the callee saved registers
67 saveCalleeSavedRegisters(Fn);
69 // Allow the target machine to make final modifications to the function
70 // before the frame layout is finalized.
71 Fn.getTarget().getRegisterInfo()->processFunctionBeforeFrameFinalized(Fn);
73 // Calculate actual frame offsets for all of the abstract stack objects...
74 calculateFrameObjectOffsets(Fn);
76 // Add prolog and epilog code to the function. This function is required
77 // to align the stack frame as necessary for any stack variables or
78 // called functions. Because of this, calculateCalleeSavedRegisters
79 // must be called before this function in order to set the HasCalls
80 // and MaxCallFrameSize variables.
81 insertPrologEpilogCode(Fn);
83 // Replace all MO_FrameIndex operands with physical register references
84 // and actual offsets.
86 replaceFrameIndices(Fn);
95 // MinCSFrameIndex, MaxCSFrameIndex - Keeps the range of callee saved
96 // stack frame indexes.
97 unsigned MinCSFrameIndex, MaxCSFrameIndex;
99 void calculateCalleeSavedRegisters(MachineFunction &Fn);
100 void saveCalleeSavedRegisters(MachineFunction &Fn);
101 void calculateFrameObjectOffsets(MachineFunction &Fn);
102 void replaceFrameIndices(MachineFunction &Fn);
103 void insertPrologEpilogCode(MachineFunction &Fn);
109 /// createPrologEpilogCodeInserter - This function returns a pass that inserts
110 /// prolog and epilog code, and eliminates abstract frame references.
112 FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
115 /// calculateCalleeSavedRegisters - Scan the function for modified callee saved
116 /// registers. Also calculate the MaxCallFrameSize and HasCalls variables for
117 /// the function's frame information and eliminates call frame pseudo
120 void PEI::calculateCalleeSavedRegisters(MachineFunction &Fn) {
121 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
122 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo();
124 // Get the callee saved register list...
125 const unsigned *CSRegs = RegInfo->getCalleeSavedRegs(&Fn);
127 // Get the function call frame set-up and tear-down instruction opcode
128 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
129 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
131 // These are used to keep track the callee-save area. Initialize them.
132 MinCSFrameIndex = INT_MAX;
135 // Early exit for targets which have no callee saved registers and no call
136 // frame setup/destroy pseudo instructions.
137 if ((CSRegs == 0 || CSRegs[0] == 0) &&
138 FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
141 unsigned MaxCallFrameSize = 0;
142 bool HasCalls = false;
144 std::vector<MachineBasicBlock::iterator> FrameSDOps;
145 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
146 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
147 if (I->getOpcode() == FrameSetupOpcode ||
148 I->getOpcode() == FrameDestroyOpcode) {
149 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo"
150 " instructions should have a single immediate argument!");
151 unsigned Size = I->getOperand(0).getImm();
152 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
154 FrameSDOps.push_back(I);
157 MachineFrameInfo *FFI = Fn.getFrameInfo();
158 FFI->setHasCalls(HasCalls);
159 FFI->setMaxCallFrameSize(MaxCallFrameSize);
161 for (unsigned i = 0, e = FrameSDOps.size(); i != e; ++i) {
162 MachineBasicBlock::iterator I = FrameSDOps[i];
163 // If call frames are not being included as part of the stack frame,
164 // and there is no dynamic allocation (therefore referencing frame slots
165 // off sp), leave the pseudo ops alone. We'll eliminate them later.
166 if (RegInfo->hasReservedCallFrame(Fn) || RegInfo->hasFP(Fn))
167 RegInfo->eliminateCallFramePseudoInstr(Fn, *I->getParent(), I);
170 // Now figure out which *callee saved* registers are modified by the current
171 // function, thus needing to be saved and restored in the prolog/epilog.
173 const TargetRegisterClass* const *CSRegClasses =
174 RegInfo->getCalleeSavedRegClasses(&Fn);
175 std::vector<CalleeSavedInfo> CSI;
176 for (unsigned i = 0; CSRegs[i]; ++i) {
177 unsigned Reg = CSRegs[i];
178 if (Fn.getRegInfo().isPhysRegUsed(Reg)) {
179 // If the reg is modified, save it!
180 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i]));
182 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
183 *AliasSet; ++AliasSet) { // Check alias registers too.
184 if (Fn.getRegInfo().isPhysRegUsed(*AliasSet)) {
185 CSI.push_back(CalleeSavedInfo(Reg, CSRegClasses[i]));
193 return; // Early exit if no callee saved registers are modified!
195 unsigned NumFixedSpillSlots;
196 const std::pair<unsigned,int> *FixedSpillSlots =
197 TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots);
199 // Now that we know which registers need to be saved and restored, allocate
200 // stack slots for them.
201 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
202 unsigned Reg = CSI[i].getReg();
203 const TargetRegisterClass *RC = CSI[i].getRegClass();
205 // Check to see if this physreg must be spilled to a particular stack slot
207 const std::pair<unsigned,int> *FixedSlot = FixedSpillSlots;
208 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots &&
209 FixedSlot->first != Reg)
213 if (FixedSlot == FixedSpillSlots+NumFixedSpillSlots) {
214 // Nope, just spill it anywhere convenient.
215 unsigned Align = RC->getAlignment();
216 unsigned StackAlign = TFI->getStackAlignment();
217 // We may not be able to sastify the desired alignment specification of
218 // the TargetRegisterClass if the stack alignment is smaller. Use the min.
219 Align = std::min(Align, StackAlign);
220 FrameIdx = FFI->CreateStackObject(RC->getSize(), Align);
221 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
222 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
224 // Spill it to the stack where we must.
225 FrameIdx = FFI->CreateFixedObject(RC->getSize(), FixedSlot->second);
227 CSI[i].setFrameIdx(FrameIdx);
230 FFI->setCalleeSavedInfo(CSI);
233 /// saveCalleeSavedRegisters - Insert spill code for any callee saved registers
234 /// that are modified in the function.
236 void PEI::saveCalleeSavedRegisters(MachineFunction &Fn) {
237 // Get callee saved register information.
238 MachineFrameInfo *FFI = Fn.getFrameInfo();
239 const std::vector<CalleeSavedInfo> &CSI = FFI->getCalleeSavedInfo();
241 // Early exit if no callee saved registers are modified!
245 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
247 // Now that we have a stack slot for each register to be saved, insert spill
248 // code into the entry block.
249 MachineBasicBlock *MBB = Fn.begin();
250 MachineBasicBlock::iterator I = MBB->begin();
251 if (!TII.spillCalleeSavedRegisters(*MBB, I, CSI)) {
252 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
253 // Add the callee-saved register as live-in. It's killed at the spill.
254 MBB->addLiveIn(CSI[i].getReg());
256 // Insert the spill to the stack frame.
257 TII.storeRegToStackSlot(*MBB, I, CSI[i].getReg(), true,
258 CSI[i].getFrameIdx(), CSI[i].getRegClass());
262 // Add code to restore the callee-save registers in each exiting block.
263 for (MachineFunction::iterator FI = Fn.begin(), E = Fn.end(); FI != E; ++FI)
264 // If last instruction is a return instruction, add an epilogue.
265 if (!FI->empty() && TII.isReturn(FI->back().getOpcode())) {
269 // Skip over all terminator instructions, which are part of the return
271 MachineBasicBlock::iterator I2 = I;
272 while (I2 != MBB->begin() && TII.isTerminatorInstr((--I2)->getOpcode()))
275 bool AtStart = I == MBB->begin();
276 MachineBasicBlock::iterator BeforeI = I;
280 // Restore all registers immediately before the return and any terminators
282 if (!TII.restoreCalleeSavedRegisters(*MBB, I, CSI)) {
283 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
284 TII.loadRegFromStackSlot(*MBB, I, CSI[i].getReg(),
285 CSI[i].getFrameIdx(),
286 CSI[i].getRegClass());
287 assert(I != MBB->begin() &&
288 "loadRegFromStackSlot didn't insert any code!");
289 // Insert in reverse order. loadRegFromStackSlot can insert multiple
303 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
304 /// abstract stack objects.
306 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
307 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo();
309 bool StackGrowsDown =
310 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
312 // Loop over all of the stack objects, assigning sequential addresses...
313 MachineFrameInfo *FFI = Fn.getFrameInfo();
315 unsigned MaxAlign = 0;
317 // Start at the beginning of the local area.
318 // The Offset is the distance from the stack top in the direction
319 // of stack growth -- so it's always positive.
320 int64_t Offset = TFI.getOffsetOfLocalArea();
324 && "Local area offset should be in direction of stack growth");
326 // If there are fixed sized objects that are preallocated in the local area,
327 // non-fixed objects can't be allocated right at the start of local area.
328 // We currently don't support filling in holes in between fixed sized objects,
329 // so we adjust 'Offset' to point to the end of last fixed sized
330 // preallocated object.
331 for (int i = FFI->getObjectIndexBegin(); i != 0; ++i) {
333 if (StackGrowsDown) {
334 // The maximum distance from the stack pointer is at lower address of
335 // the object -- which is given by offset. For down growing stack
336 // the offset is negative, so we negate the offset to get the distance.
337 FixedOff = -FFI->getObjectOffset(i);
339 // The maximum distance from the start pointer is at the upper
340 // address of the object.
341 FixedOff = FFI->getObjectOffset(i) + FFI->getObjectSize(i);
343 if (FixedOff > Offset) Offset = FixedOff;
346 // First assign frame offsets to stack objects that are used to spill
347 // callee saved registers.
348 if (StackGrowsDown) {
349 for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
350 // If stack grows down, we need to add size of find the lowest
351 // address of the object.
352 Offset += FFI->getObjectSize(i);
354 unsigned Align = FFI->getObjectAlignment(i);
355 // If the alignment of this object is greater than that of the stack, then
356 // increase the stack alignment to match.
357 MaxAlign = std::max(MaxAlign, Align);
358 // Adjust to alignment boundary
359 Offset = (Offset+Align-1)/Align*Align;
361 FFI->setObjectOffset(i, -Offset); // Set the computed offset
364 for (unsigned i = MaxCSFrameIndex; i >= MinCSFrameIndex; --i) {
365 unsigned Align = FFI->getObjectAlignment(i);
366 // If the alignment of this object is greater than that of the stack, then
367 // increase the stack alignment to match.
368 MaxAlign = std::max(MaxAlign, Align);
369 // Adjust to alignment boundary
370 Offset = (Offset+Align-1)/Align*Align;
372 FFI->setObjectOffset(i, Offset);
373 Offset += FFI->getObjectSize(i);
377 // Make sure the special register scavenging spill slot is closest to the
378 // frame pointer if a frame pointer is required.
379 const MRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
380 if (RS && RegInfo->hasFP(Fn)) {
381 int SFI = RS->getScavengingFrameIndex();
383 // If stack grows down, we need to add size of the lowest
384 // address of the object.
386 Offset += FFI->getObjectSize(SFI);
388 unsigned Align = FFI->getObjectAlignment(SFI);
389 // Adjust to alignment boundary
390 Offset = (Offset+Align-1)/Align*Align;
392 if (StackGrowsDown) {
393 FFI->setObjectOffset(SFI, -Offset); // Set the computed offset
395 FFI->setObjectOffset(SFI, Offset);
396 Offset += FFI->getObjectSize(SFI);
401 // Then assign frame offsets to stack objects that are not used to spill
402 // callee saved registers.
403 for (unsigned i = 0, e = FFI->getObjectIndexEnd(); i != e; ++i) {
404 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
406 if (RS && (int)i == RS->getScavengingFrameIndex())
409 // If stack grows down, we need to add size of find the lowest
410 // address of the object.
412 Offset += FFI->getObjectSize(i);
414 unsigned Align = FFI->getObjectAlignment(i);
415 // If the alignment of this object is greater than that of the stack, then
416 // increase the stack alignment to match.
417 MaxAlign = std::max(MaxAlign, Align);
418 // Adjust to alignment boundary
419 Offset = (Offset+Align-1)/Align*Align;
421 if (StackGrowsDown) {
422 FFI->setObjectOffset(i, -Offset); // Set the computed offset
424 FFI->setObjectOffset(i, Offset);
425 Offset += FFI->getObjectSize(i);
429 // Make sure the special register scavenging spill slot is closest to the
431 if (RS && !RegInfo->hasFP(Fn)) {
432 int SFI = RS->getScavengingFrameIndex();
434 // If stack grows down, we need to add size of find the lowest
435 // address of the object.
437 Offset += FFI->getObjectSize(SFI);
439 unsigned Align = FFI->getObjectAlignment(SFI);
440 // Adjust to alignment boundary
441 Offset = (Offset+Align-1)/Align*Align;
443 if (StackGrowsDown) {
444 FFI->setObjectOffset(SFI, -Offset); // Set the computed offset
446 FFI->setObjectOffset(SFI, Offset);
447 Offset += FFI->getObjectSize(SFI);
452 // Round up the size to a multiple of the alignment, but only if there are
453 // calls or alloca's in the function. This ensures that any calls to
454 // subroutines have their stack frames suitable aligned.
455 if (!RegInfo->targetHandlesStackFrameRounding() &&
456 (FFI->hasCalls() || FFI->hasVarSizedObjects())) {
457 // If we have reserved argument space for call sites in the function
458 // immediately on entry to the current function, count it as part of the
459 // overall stack size.
460 if (RegInfo->hasReservedCallFrame(Fn))
461 Offset += FFI->getMaxCallFrameSize();
463 unsigned AlignMask = TFI.getStackAlignment() - 1;
464 Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
467 // Update frame info to pretend that this is part of the stack...
468 FFI->setStackSize(Offset+TFI.getOffsetOfLocalArea());
470 // Remember the required stack alignment in case targets need it to perform
471 // dynamic stack alignment.
472 assert(FFI->getMaxAlignment() == MaxAlign &&
473 "Stack alignment calculation broken!");
477 /// insertPrologEpilogCode - Scan the function for modified callee saved
478 /// registers, insert spill code for these callee saved registers, then add
479 /// prolog and epilog code to the function.
481 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
482 // Add prologue to the function...
483 Fn.getTarget().getRegisterInfo()->emitPrologue(Fn);
485 // Add epilogue to restore the callee-save registers in each exiting block
486 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
487 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
488 // If last instruction is a return instruction, add an epilogue
489 if (!I->empty() && TII.isReturn(I->back().getOpcode()))
490 Fn.getTarget().getRegisterInfo()->emitEpilogue(Fn, *I);
495 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
496 /// register references and actual offsets.
498 void PEI::replaceFrameIndices(MachineFunction &Fn) {
499 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
501 const TargetMachine &TM = Fn.getTarget();
502 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
503 const MRegisterInfo &MRI = *TM.getRegisterInfo();
504 const TargetFrameInfo *TFI = TM.getFrameInfo();
505 bool StackGrowsDown =
506 TFI->getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
507 int FrameSetupOpcode = MRI.getCallFrameSetupOpcode();
508 int FrameDestroyOpcode = MRI.getCallFrameDestroyOpcode();
510 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
511 int SPAdj = 0; // SP offset due to call frame setup / destroy.
512 if (RS) RS->enterBasicBlock(BB);
513 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
514 MachineInstr *MI = I;
516 // Remember how much SP has been adjustment to create the call frame.
517 if (I->getOpcode() == FrameSetupOpcode ||
518 I->getOpcode() == FrameDestroyOpcode) {
519 int Size = I->getOperand(0).getImm();
520 if ((!StackGrowsDown && I->getOpcode() == FrameSetupOpcode) ||
521 (StackGrowsDown && I->getOpcode() == FrameDestroyOpcode))
524 MachineBasicBlock::iterator PrevI = prior(I);
525 MRI.eliminateCallFramePseudoInstr(Fn, *BB, I);
526 // Visit the instructions created by eliminateCallFramePseudoInstr().
531 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
532 if (MI->getOperand(i).isFrameIndex()) {
533 // If this instruction has a FrameIndex operand, we need to use that
534 // target machine register info object to eliminate it.
535 MRI.eliminateFrameIndex(MI, SPAdj, RS);
537 // Revisit the instruction in full. Some instructions (e.g. inline
538 // asm instructions) can have multiple frame indices.
544 // Update register states.
545 if (RS && MI) RS->forward(MI);
547 assert(SPAdj == 0 && "Unbalanced call frame setup / destroy pairs?");