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/ADT/STLExtras.h"
20 #include "llvm/ADT/SetVector.h"
21 #include "llvm/ADT/SmallSet.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/CodeGen/MachineDominators.h"
24 #include "llvm/CodeGen/MachineFrameInfo.h"
25 #include "llvm/CodeGen/MachineInstr.h"
26 #include "llvm/CodeGen/MachineLoopInfo.h"
27 #include "llvm/CodeGen/MachineModuleInfo.h"
28 #include "llvm/CodeGen/MachineRegisterInfo.h"
29 #include "llvm/CodeGen/Passes.h"
30 #include "llvm/CodeGen/RegisterScavenging.h"
31 #include "llvm/CodeGen/StackProtector.h"
32 #include "llvm/CodeGen/WinEHFuncInfo.h"
33 #include "llvm/IR/DiagnosticInfo.h"
34 #include "llvm/IR/InlineAsm.h"
35 #include "llvm/IR/LLVMContext.h"
36 #include "llvm/Support/CommandLine.h"
37 #include "llvm/Support/Debug.h"
38 #include "llvm/Support/raw_ostream.h"
39 #include "llvm/Target/TargetFrameLowering.h"
40 #include "llvm/Target/TargetInstrInfo.h"
41 #include "llvm/Target/TargetMachine.h"
42 #include "llvm/Target/TargetRegisterInfo.h"
43 #include "llvm/Target/TargetSubtargetInfo.h"
48 #define DEBUG_TYPE "pei"
50 typedef SmallVector<MachineBasicBlock *, 4> MBBVector;
51 static void doSpillCalleeSavedRegs(MachineFunction &MF, RegScavenger *RS,
52 unsigned &MinCSFrameIndex,
53 unsigned &MaxCXFrameIndex,
54 const MBBVector &SaveBlocks,
55 const MBBVector &RestoreBlocks);
57 static void doScavengeFrameVirtualRegs(MachineFunction &MF, RegScavenger *RS);
60 class PEI : public MachineFunctionPass {
63 explicit PEI(const TargetMachine *TM = nullptr) : MachineFunctionPass(ID) {
64 initializePEIPass(*PassRegistry::getPassRegistry());
66 if (TM && (!TM->usesPhysRegsForPEI())) {
67 SpillCalleeSavedRegisters = [](MachineFunction &, RegScavenger *,
68 unsigned &, unsigned &, const MBBVector &,
69 const MBBVector &) {};
70 ScavengeFrameVirtualRegs = [](MachineFunction &, RegScavenger *) {};
72 SpillCalleeSavedRegisters = doSpillCalleeSavedRegs;
73 ScavengeFrameVirtualRegs = doScavengeFrameVirtualRegs;
74 UsesCalleeSaves = true;
78 void getAnalysisUsage(AnalysisUsage &AU) const override;
80 MachineFunctionProperties getRequiredProperties() const override {
81 MachineFunctionProperties MFP;
83 MFP.set(MachineFunctionProperties::Property::NoVRegs);
87 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
88 /// frame indexes with appropriate references.
90 bool runOnMachineFunction(MachineFunction &Fn) override;
93 std::function<void(MachineFunction &MF, RegScavenger *RS,
94 unsigned &MinCSFrameIndex, unsigned &MaxCSFrameIndex,
95 const MBBVector &SaveBlocks,
96 const MBBVector &RestoreBlocks)>
97 SpillCalleeSavedRegisters;
98 std::function<void(MachineFunction &MF, RegScavenger *RS)>
99 ScavengeFrameVirtualRegs;
101 bool UsesCalleeSaves = false;
105 // MinCSFrameIndex, MaxCSFrameIndex - Keeps the range of callee saved
106 // stack frame indexes.
107 unsigned MinCSFrameIndex = std::numeric_limits<unsigned>::max();
108 unsigned MaxCSFrameIndex = 0;
110 // Save and Restore blocks of the current function. Typically there is a
111 // single save block, unless Windows EH funclets are involved.
112 MBBVector SaveBlocks;
113 MBBVector RestoreBlocks;
115 // Flag to control whether to use the register scavenger to resolve
116 // frame index materialization registers. Set according to
117 // TRI->requiresFrameIndexScavenging() for the current function.
118 bool FrameIndexVirtualScavenging;
120 // Flag to control whether the scavenger should be passed even though
121 // FrameIndexVirtualScavenging is used.
122 bool FrameIndexEliminationScavenging;
124 void calculateCallFrameInfo(MachineFunction &Fn);
125 void calculateSaveRestoreBlocks(MachineFunction &Fn);
127 void calculateFrameObjectOffsets(MachineFunction &Fn);
128 void replaceFrameIndices(MachineFunction &Fn);
129 void replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
131 void insertPrologEpilogCode(MachineFunction &Fn);
136 char &llvm::PrologEpilogCodeInserterID = PEI::ID;
138 static cl::opt<unsigned>
139 WarnStackSize("warn-stack-size", cl::Hidden, cl::init((unsigned)-1),
140 cl::desc("Warn for stack size bigger than the given"
143 INITIALIZE_TM_PASS_BEGIN(PEI, "prologepilog", "Prologue/Epilogue Insertion",
145 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
146 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
147 INITIALIZE_PASS_DEPENDENCY(StackProtector)
148 INITIALIZE_TM_PASS_END(PEI, "prologepilog",
149 "Prologue/Epilogue Insertion & Frame Finalization",
152 MachineFunctionPass *
153 llvm::createPrologEpilogInserterPass(const TargetMachine *TM) {
157 STATISTIC(NumScavengedRegs, "Number of frame index regs scavenged");
158 STATISTIC(NumBytesStackSpace,
159 "Number of bytes used for stack in all functions");
161 void PEI::getAnalysisUsage(AnalysisUsage &AU) const {
162 AU.setPreservesCFG();
163 AU.addPreserved<MachineLoopInfo>();
164 AU.addPreserved<MachineDominatorTree>();
165 AU.addRequired<StackProtector>();
166 MachineFunctionPass::getAnalysisUsage(AU);
170 /// StackObjSet - A set of stack object indexes
171 typedef SmallSetVector<int, 8> StackObjSet;
173 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
174 /// frame indexes with appropriate references.
176 bool PEI::runOnMachineFunction(MachineFunction &Fn) {
177 const Function* F = Fn.getFunction();
178 const TargetRegisterInfo *TRI = Fn.getSubtarget().getRegisterInfo();
179 const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
181 RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : nullptr;
182 FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(Fn);
183 FrameIndexEliminationScavenging = (RS && !FrameIndexVirtualScavenging) ||
184 TRI->requiresFrameIndexReplacementScavenging(Fn);
186 // Calculate the MaxCallFrameSize and AdjustsStack variables for the
187 // function's frame information. Also eliminates call frame pseudo
189 calculateCallFrameInfo(Fn);
191 // Determine placement of CSR spill/restore code and prolog/epilog code:
192 // place all spills in the entry block, all restores in return blocks.
193 calculateSaveRestoreBlocks(Fn);
195 // Handle CSR spilling and restoring, for targets that need it.
196 SpillCalleeSavedRegisters(Fn, RS, MinCSFrameIndex, MaxCSFrameIndex,
197 SaveBlocks, RestoreBlocks);
199 // Allow the target machine to make final modifications to the function
200 // before the frame layout is finalized.
201 TFI->processFunctionBeforeFrameFinalized(Fn, RS);
203 // Calculate actual frame offsets for all abstract stack objects...
204 calculateFrameObjectOffsets(Fn);
206 // Add prolog and epilog code to the function. This function is required
207 // to align the stack frame as necessary for any stack variables or
208 // called functions. Because of this, calculateCalleeSavedRegisters()
209 // must be called before this function in order to set the AdjustsStack
210 // and MaxCallFrameSize variables.
211 if (!F->hasFnAttribute(Attribute::Naked))
212 insertPrologEpilogCode(Fn);
214 // Replace all MO_FrameIndex operands with physical register references
215 // and actual offsets.
217 replaceFrameIndices(Fn);
219 // If register scavenging is needed, as we've enabled doing it as a
220 // post-pass, scavenge the virtual registers that frame index elimination
222 if (TRI->requiresRegisterScavenging(Fn) && FrameIndexVirtualScavenging) {
223 ScavengeFrameVirtualRegs(Fn, RS);
225 // Clear any vregs created by virtual scavenging.
226 Fn.getRegInfo().clearVirtRegs();
229 // Warn on stack size when we exceeds the given limit.
230 MachineFrameInfo &MFI = Fn.getFrameInfo();
231 uint64_t StackSize = MFI.getStackSize();
232 if (WarnStackSize.getNumOccurrences() > 0 && WarnStackSize < StackSize) {
233 DiagnosticInfoStackSize DiagStackSize(*F, StackSize);
234 F->getContext().diagnose(DiagStackSize);
239 RestoreBlocks.clear();
240 MFI.setSavePoint(nullptr);
241 MFI.setRestorePoint(nullptr);
245 /// Calculate the MaxCallFrameSize and AdjustsStack
246 /// variables for the function's frame information and eliminate call frame
247 /// pseudo instructions.
248 void PEI::calculateCallFrameInfo(MachineFunction &Fn) {
249 const TargetInstrInfo &TII = *Fn.getSubtarget().getInstrInfo();
250 const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
251 MachineFrameInfo &MFI = Fn.getFrameInfo();
253 unsigned MaxCallFrameSize = 0;
254 bool AdjustsStack = MFI.adjustsStack();
256 // Get the function call frame set-up and tear-down instruction opcode
257 unsigned FrameSetupOpcode = TII.getCallFrameSetupOpcode();
258 unsigned FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
260 // Early exit for targets which have no call frame setup/destroy pseudo
262 if (FrameSetupOpcode == ~0u && FrameDestroyOpcode == ~0u)
265 std::vector<MachineBasicBlock::iterator> FrameSDOps;
266 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
267 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
268 if (I->getOpcode() == FrameSetupOpcode ||
269 I->getOpcode() == FrameDestroyOpcode) {
270 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo"
271 " instructions should have a single immediate argument!");
272 unsigned Size = I->getOperand(0).getImm();
273 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
275 FrameSDOps.push_back(I);
276 } else if (I->isInlineAsm()) {
277 // Some inline asm's need a stack frame, as indicated by operand 1.
278 unsigned ExtraInfo = I->getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
279 if (ExtraInfo & InlineAsm::Extra_IsAlignStack)
283 MFI.setAdjustsStack(AdjustsStack);
284 MFI.setMaxCallFrameSize(MaxCallFrameSize);
286 for (std::vector<MachineBasicBlock::iterator>::iterator
287 i = FrameSDOps.begin(), e = FrameSDOps.end(); i != e; ++i) {
288 MachineBasicBlock::iterator I = *i;
290 // If call frames are not being included as part of the stack frame, and
291 // the target doesn't indicate otherwise, remove the call frame pseudos
292 // here. The sub/add sp instruction pairs are still inserted, but we don't
293 // need to track the SP adjustment for frame index elimination.
294 if (TFI->canSimplifyCallFramePseudos(Fn))
295 TFI->eliminateCallFramePseudoInstr(Fn, *I->getParent(), I);
299 /// Compute the sets of entry and return blocks for saving and restoring
300 /// callee-saved registers, and placing prolog and epilog code.
301 void PEI::calculateSaveRestoreBlocks(MachineFunction &Fn) {
302 const MachineFrameInfo &MFI = Fn.getFrameInfo();
304 // Even when we do not change any CSR, we still want to insert the
305 // prologue and epilogue of the function.
306 // So set the save points for those.
308 // Use the points found by shrink-wrapping, if any.
309 if (MFI.getSavePoint()) {
310 SaveBlocks.push_back(MFI.getSavePoint());
311 assert(MFI.getRestorePoint() && "Both restore and save must be set");
312 MachineBasicBlock *RestoreBlock = MFI.getRestorePoint();
313 // If RestoreBlock does not have any successor and is not a return block
314 // then the end point is unreachable and we do not need to insert any
316 if (!RestoreBlock->succ_empty() || RestoreBlock->isReturnBlock())
317 RestoreBlocks.push_back(RestoreBlock);
321 // Save refs to entry and return blocks.
322 SaveBlocks.push_back(&Fn.front());
323 for (MachineBasicBlock &MBB : Fn) {
324 if (MBB.isEHFuncletEntry())
325 SaveBlocks.push_back(&MBB);
326 if (MBB.isReturnBlock())
327 RestoreBlocks.push_back(&MBB);
331 static void assignCalleeSavedSpillSlots(MachineFunction &F,
332 const BitVector &SavedRegs,
333 unsigned &MinCSFrameIndex,
334 unsigned &MaxCSFrameIndex) {
335 if (SavedRegs.empty())
338 const TargetRegisterInfo *RegInfo = F.getSubtarget().getRegisterInfo();
339 const MCPhysReg *CSRegs = RegInfo->getCalleeSavedRegs(&F);
341 std::vector<CalleeSavedInfo> CSI;
342 for (unsigned i = 0; CSRegs[i]; ++i) {
343 unsigned Reg = CSRegs[i];
344 if (SavedRegs.test(Reg))
345 CSI.push_back(CalleeSavedInfo(Reg));
348 const TargetFrameLowering *TFI = F.getSubtarget().getFrameLowering();
349 MachineFrameInfo &MFI = F.getFrameInfo();
350 if (!TFI->assignCalleeSavedSpillSlots(F, RegInfo, CSI)) {
351 // If target doesn't implement this, use generic code.
354 return; // Early exit if no callee saved registers are modified!
356 unsigned NumFixedSpillSlots;
357 const TargetFrameLowering::SpillSlot *FixedSpillSlots =
358 TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots);
360 // Now that we know which registers need to be saved and restored, allocate
361 // stack slots for them.
362 for (auto &CS : CSI) {
363 unsigned Reg = CS.getReg();
364 const TargetRegisterClass *RC = RegInfo->getMinimalPhysRegClass(Reg);
367 if (RegInfo->hasReservedSpillSlot(F, Reg, FrameIdx)) {
368 CS.setFrameIdx(FrameIdx);
372 // Check to see if this physreg must be spilled to a particular stack slot
374 const TargetFrameLowering::SpillSlot *FixedSlot = FixedSpillSlots;
375 while (FixedSlot != FixedSpillSlots + NumFixedSpillSlots &&
376 FixedSlot->Reg != Reg)
379 if (FixedSlot == FixedSpillSlots + NumFixedSpillSlots) {
380 // Nope, just spill it anywhere convenient.
381 unsigned Align = RC->getAlignment();
382 unsigned StackAlign = TFI->getStackAlignment();
384 // We may not be able to satisfy the desired alignment specification of
385 // the TargetRegisterClass if the stack alignment is smaller. Use the
387 Align = std::min(Align, StackAlign);
388 FrameIdx = MFI.CreateStackObject(RC->getSize(), Align, true);
389 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
390 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
392 // Spill it to the stack where we must.
394 MFI.CreateFixedSpillStackObject(RC->getSize(), FixedSlot->Offset);
397 CS.setFrameIdx(FrameIdx);
401 MFI.setCalleeSavedInfo(CSI);
404 /// Helper function to update the liveness information for the callee-saved
406 static void updateLiveness(MachineFunction &MF) {
407 MachineFrameInfo &MFI = MF.getFrameInfo();
408 // Visited will contain all the basic blocks that are in the region
409 // where the callee saved registers are alive:
410 // - Anything that is not Save or Restore -> LiveThrough.
412 // - Restore -> LiveOut.
413 // The live-out is not attached to the block, so no need to keep
414 // Restore in this set.
415 SmallPtrSet<MachineBasicBlock *, 8> Visited;
416 SmallVector<MachineBasicBlock *, 8> WorkList;
417 MachineBasicBlock *Entry = &MF.front();
418 MachineBasicBlock *Save = MFI.getSavePoint();
424 WorkList.push_back(Entry);
425 Visited.insert(Entry);
427 Visited.insert(Save);
429 MachineBasicBlock *Restore = MFI.getRestorePoint();
431 // By construction Restore cannot be visited, otherwise it
432 // means there exists a path to Restore that does not go
434 WorkList.push_back(Restore);
436 while (!WorkList.empty()) {
437 const MachineBasicBlock *CurBB = WorkList.pop_back_val();
438 // By construction, the region that is after the save point is
439 // dominated by the Save and post-dominated by the Restore.
440 if (CurBB == Save && Save != Restore)
442 // Enqueue all the successors not already visited.
443 // Those are by construction either before Save or after Restore.
444 for (MachineBasicBlock *SuccBB : CurBB->successors())
445 if (Visited.insert(SuccBB).second)
446 WorkList.push_back(SuccBB);
449 const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
451 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
452 for (MachineBasicBlock *MBB : Visited) {
453 MCPhysReg Reg = CSI[i].getReg();
454 // Add the callee-saved register as live-in.
455 // It's killed at the spill.
456 if (!MBB->isLiveIn(Reg))
462 /// insertCSRSpillsAndRestores - Insert spill and restore code for
463 /// callee saved registers used in the function.
465 static void insertCSRSpillsAndRestores(MachineFunction &Fn,
466 const MBBVector &SaveBlocks,
467 const MBBVector &RestoreBlocks) {
468 // Get callee saved register information.
469 MachineFrameInfo &MFI = Fn.getFrameInfo();
470 const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
472 MFI.setCalleeSavedInfoValid(true);
474 // Early exit if no callee saved registers are modified!
478 const TargetInstrInfo &TII = *Fn.getSubtarget().getInstrInfo();
479 const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
480 const TargetRegisterInfo *TRI = Fn.getSubtarget().getRegisterInfo();
481 MachineBasicBlock::iterator I;
483 // Spill using target interface.
484 for (MachineBasicBlock *SaveBlock : SaveBlocks) {
485 I = SaveBlock->begin();
486 if (!TFI->spillCalleeSavedRegisters(*SaveBlock, I, CSI, TRI)) {
487 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
488 // Insert the spill to the stack frame.
489 unsigned Reg = CSI[i].getReg();
490 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
491 TII.storeRegToStackSlot(*SaveBlock, I, Reg, true, CSI[i].getFrameIdx(),
495 // Update the live-in information of all the blocks up to the save point.
499 // Restore using target interface.
500 for (MachineBasicBlock *MBB : RestoreBlocks) {
503 // Skip over all terminator instructions, which are part of the return
505 MachineBasicBlock::iterator I2 = I;
506 while (I2 != MBB->begin() && (--I2)->isTerminator())
509 bool AtStart = I == MBB->begin();
510 MachineBasicBlock::iterator BeforeI = I;
514 // Restore all registers immediately before the return and any
515 // terminators that precede it.
516 if (!TFI->restoreCalleeSavedRegisters(*MBB, I, CSI, TRI)) {
517 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
518 unsigned Reg = CSI[i].getReg();
519 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
520 TII.loadRegFromStackSlot(*MBB, I, Reg, CSI[i].getFrameIdx(), RC, TRI);
521 assert(I != MBB->begin() &&
522 "loadRegFromStackSlot didn't insert any code!");
523 // Insert in reverse order. loadRegFromStackSlot can insert
524 // multiple instructions.
536 static void doSpillCalleeSavedRegs(MachineFunction &Fn, RegScavenger *RS,
537 unsigned &MinCSFrameIndex,
538 unsigned &MaxCSFrameIndex,
539 const MBBVector &SaveBlocks,
540 const MBBVector &RestoreBlocks) {
541 const Function *F = Fn.getFunction();
542 const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
543 MinCSFrameIndex = std::numeric_limits<unsigned>::max();
546 // Determine which of the registers in the callee save list should be saved.
548 TFI->determineCalleeSaves(Fn, SavedRegs, RS);
550 // Assign stack slots for any callee-saved registers that must be spilled.
551 assignCalleeSavedSpillSlots(Fn, SavedRegs, MinCSFrameIndex, MaxCSFrameIndex);
553 // Add the code to save and restore the callee saved registers.
554 if (!F->hasFnAttribute(Attribute::Naked))
555 insertCSRSpillsAndRestores(Fn, SaveBlocks, RestoreBlocks);
558 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
560 AdjustStackOffset(MachineFrameInfo &MFI, int FrameIdx,
561 bool StackGrowsDown, int64_t &Offset,
562 unsigned &MaxAlign, unsigned Skew) {
563 // If the stack grows down, add the object size to find the lowest address.
565 Offset += MFI.getObjectSize(FrameIdx);
567 unsigned Align = MFI.getObjectAlignment(FrameIdx);
569 // If the alignment of this object is greater than that of the stack, then
570 // increase the stack alignment to match.
571 MaxAlign = std::max(MaxAlign, Align);
573 // Adjust to alignment boundary.
574 Offset = alignTo(Offset, Align, Skew);
576 if (StackGrowsDown) {
577 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
578 MFI.setObjectOffset(FrameIdx, -Offset); // Set the computed offset
580 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset << "]\n");
581 MFI.setObjectOffset(FrameIdx, Offset);
582 Offset += MFI.getObjectSize(FrameIdx);
586 /// Compute which bytes of fixed and callee-save stack area are unused and keep
587 /// track of them in StackBytesFree.
590 computeFreeStackSlots(MachineFrameInfo &MFI, bool StackGrowsDown,
591 unsigned MinCSFrameIndex, unsigned MaxCSFrameIndex,
592 int64_t FixedCSEnd, BitVector &StackBytesFree) {
593 // Avoid undefined int64_t -> int conversion below in extreme case.
594 if (FixedCSEnd > std::numeric_limits<int>::max())
597 StackBytesFree.resize(FixedCSEnd, true);
599 SmallVector<int, 16> AllocatedFrameSlots;
600 // Add fixed objects.
601 for (int i = MFI.getObjectIndexBegin(); i != 0; ++i)
602 AllocatedFrameSlots.push_back(i);
603 // Add callee-save objects.
604 for (int i = MinCSFrameIndex; i <= (int)MaxCSFrameIndex; ++i)
605 AllocatedFrameSlots.push_back(i);
607 for (int i : AllocatedFrameSlots) {
608 // These are converted from int64_t, but they should always fit in int
609 // because of the FixedCSEnd check above.
610 int ObjOffset = MFI.getObjectOffset(i);
611 int ObjSize = MFI.getObjectSize(i);
612 int ObjStart, ObjEnd;
613 if (StackGrowsDown) {
614 // ObjOffset is negative when StackGrowsDown is true.
615 ObjStart = -ObjOffset - ObjSize;
618 ObjStart = ObjOffset;
619 ObjEnd = ObjOffset + ObjSize;
621 // Ignore fixed holes that are in the previous stack frame.
623 StackBytesFree.reset(ObjStart, ObjEnd);
627 /// Assign frame object to an unused portion of the stack in the fixed stack
628 /// object range. Return true if the allocation was successful.
630 static inline bool scavengeStackSlot(MachineFrameInfo &MFI, int FrameIdx,
631 bool StackGrowsDown, unsigned MaxAlign,
632 BitVector &StackBytesFree) {
633 if (MFI.isVariableSizedObjectIndex(FrameIdx))
636 if (StackBytesFree.none()) {
637 // clear it to speed up later scavengeStackSlot calls to
638 // StackBytesFree.none()
639 StackBytesFree.clear();
643 unsigned ObjAlign = MFI.getObjectAlignment(FrameIdx);
644 if (ObjAlign > MaxAlign)
647 int64_t ObjSize = MFI.getObjectSize(FrameIdx);
649 for (FreeStart = StackBytesFree.find_first(); FreeStart != -1;
650 FreeStart = StackBytesFree.find_next(FreeStart)) {
652 // Check that free space has suitable alignment.
653 unsigned ObjStart = StackGrowsDown ? FreeStart + ObjSize : FreeStart;
654 if (alignTo(ObjStart, ObjAlign) != ObjStart)
657 if (FreeStart + ObjSize > StackBytesFree.size())
660 bool AllBytesFree = true;
661 for (unsigned Byte = 0; Byte < ObjSize; ++Byte)
662 if (!StackBytesFree.test(FreeStart + Byte)) {
663 AllBytesFree = false;
673 if (StackGrowsDown) {
674 int ObjStart = -(FreeStart + ObjSize);
675 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") scavenged at SP[" << ObjStart
677 MFI.setObjectOffset(FrameIdx, ObjStart);
679 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") scavenged at SP[" << FreeStart
681 MFI.setObjectOffset(FrameIdx, FreeStart);
684 StackBytesFree.reset(FreeStart, FreeStart + ObjSize);
688 /// AssignProtectedObjSet - Helper function to assign large stack objects (i.e.,
689 /// those required to be close to the Stack Protector) to stack offsets.
691 AssignProtectedObjSet(const StackObjSet &UnassignedObjs,
692 SmallSet<int, 16> &ProtectedObjs,
693 MachineFrameInfo &MFI, bool StackGrowsDown,
694 int64_t &Offset, unsigned &MaxAlign, unsigned Skew) {
696 for (StackObjSet::const_iterator I = UnassignedObjs.begin(),
697 E = UnassignedObjs.end(); I != E; ++I) {
699 AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign, Skew);
700 ProtectedObjs.insert(i);
704 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
705 /// abstract stack objects.
707 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
708 const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
709 StackProtector *SP = &getAnalysis<StackProtector>();
711 bool StackGrowsDown =
712 TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
714 // Loop over all of the stack objects, assigning sequential addresses...
715 MachineFrameInfo &MFI = Fn.getFrameInfo();
717 // Start at the beginning of the local area.
718 // The Offset is the distance from the stack top in the direction
719 // of stack growth -- so it's always nonnegative.
720 int LocalAreaOffset = TFI.getOffsetOfLocalArea();
722 LocalAreaOffset = -LocalAreaOffset;
723 assert(LocalAreaOffset >= 0
724 && "Local area offset should be in direction of stack growth");
725 int64_t Offset = LocalAreaOffset;
727 // Skew to be applied to alignment.
728 unsigned Skew = TFI.getStackAlignmentSkew(Fn);
730 // If there are fixed sized objects that are preallocated in the local area,
731 // non-fixed objects can't be allocated right at the start of local area.
732 // Adjust 'Offset' to point to the end of last fixed sized preallocated
734 for (int i = MFI.getObjectIndexBegin(); i != 0; ++i) {
736 if (StackGrowsDown) {
737 // The maximum distance from the stack pointer is at lower address of
738 // the object -- which is given by offset. For down growing stack
739 // the offset is negative, so we negate the offset to get the distance.
740 FixedOff = -MFI.getObjectOffset(i);
742 // The maximum distance from the start pointer is at the upper
743 // address of the object.
744 FixedOff = MFI.getObjectOffset(i) + MFI.getObjectSize(i);
746 if (FixedOff > Offset) Offset = FixedOff;
749 // First assign frame offsets to stack objects that are used to spill
750 // callee saved registers.
751 if (StackGrowsDown) {
752 for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
753 // If the stack grows down, we need to add the size to find the lowest
754 // address of the object.
755 Offset += MFI.getObjectSize(i);
757 unsigned Align = MFI.getObjectAlignment(i);
758 // Adjust to alignment boundary
759 Offset = alignTo(Offset, Align, Skew);
761 DEBUG(dbgs() << "alloc FI(" << i << ") at SP[" << -Offset << "]\n");
762 MFI.setObjectOffset(i, -Offset); // Set the computed offset
764 } else if (MaxCSFrameIndex >= MinCSFrameIndex) {
765 // Be careful about underflow in comparisons agains MinCSFrameIndex.
766 for (unsigned i = MaxCSFrameIndex; i != MinCSFrameIndex - 1; --i) {
767 unsigned Align = MFI.getObjectAlignment(i);
768 // Adjust to alignment boundary
769 Offset = alignTo(Offset, Align, Skew);
771 DEBUG(dbgs() << "alloc FI(" << i << ") at SP[" << Offset << "]\n");
772 MFI.setObjectOffset(i, Offset);
773 Offset += MFI.getObjectSize(i);
777 // FixedCSEnd is the stack offset to the end of the fixed and callee-save
779 int64_t FixedCSEnd = Offset;
780 unsigned MaxAlign = MFI.getMaxAlignment();
782 // Make sure the special register scavenging spill slot is closest to the
783 // incoming stack pointer if a frame pointer is required and is closer
784 // to the incoming rather than the final stack pointer.
785 const TargetRegisterInfo *RegInfo = Fn.getSubtarget().getRegisterInfo();
786 bool EarlyScavengingSlots = (TFI.hasFP(Fn) &&
787 TFI.isFPCloseToIncomingSP() &&
788 RegInfo->useFPForScavengingIndex(Fn) &&
789 !RegInfo->needsStackRealignment(Fn));
790 if (RS && EarlyScavengingSlots) {
791 SmallVector<int, 2> SFIs;
792 RS->getScavengingFrameIndices(SFIs);
793 for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
794 IE = SFIs.end(); I != IE; ++I)
795 AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign, Skew);
798 // FIXME: Once this is working, then enable flag will change to a target
799 // check for whether the frame is large enough to want to use virtual
800 // frame index registers. Functions which don't want/need this optimization
801 // will continue to use the existing code path.
802 if (MFI.getUseLocalStackAllocationBlock()) {
803 unsigned Align = MFI.getLocalFrameMaxAlign();
805 // Adjust to alignment boundary.
806 Offset = alignTo(Offset, Align, Skew);
808 DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
810 // Resolve offsets for objects in the local block.
811 for (unsigned i = 0, e = MFI.getLocalFrameObjectCount(); i != e; ++i) {
812 std::pair<int, int64_t> Entry = MFI.getLocalFrameObjectMap(i);
813 int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
814 DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" <<
816 MFI.setObjectOffset(Entry.first, FIOffset);
818 // Allocate the local block
819 Offset += MFI.getLocalFrameSize();
821 MaxAlign = std::max(Align, MaxAlign);
824 // Retrieve the Exception Handler registration node.
825 int EHRegNodeFrameIndex = INT_MAX;
826 if (const WinEHFuncInfo *FuncInfo = Fn.getWinEHFuncInfo())
827 EHRegNodeFrameIndex = FuncInfo->EHRegNodeFrameIndex;
829 // Make sure that the stack protector comes before the local variables on the
831 SmallSet<int, 16> ProtectedObjs;
832 if (MFI.getStackProtectorIndex() >= 0) {
833 StackObjSet LargeArrayObjs;
834 StackObjSet SmallArrayObjs;
835 StackObjSet AddrOfObjs;
837 AdjustStackOffset(MFI, MFI.getStackProtectorIndex(), StackGrowsDown,
838 Offset, MaxAlign, Skew);
840 // Assign large stack objects first.
841 for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
842 if (MFI.isObjectPreAllocated(i) &&
843 MFI.getUseLocalStackAllocationBlock())
845 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
847 if (RS && RS->isScavengingFrameIndex((int)i))
849 if (MFI.isDeadObjectIndex(i))
851 if (MFI.getStackProtectorIndex() == (int)i ||
852 EHRegNodeFrameIndex == (int)i)
855 switch (SP->getSSPLayout(MFI.getObjectAllocation(i))) {
856 case StackProtector::SSPLK_None:
858 case StackProtector::SSPLK_SmallArray:
859 SmallArrayObjs.insert(i);
861 case StackProtector::SSPLK_AddrOf:
862 AddrOfObjs.insert(i);
864 case StackProtector::SSPLK_LargeArray:
865 LargeArrayObjs.insert(i);
868 llvm_unreachable("Unexpected SSPLayoutKind.");
871 AssignProtectedObjSet(LargeArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
872 Offset, MaxAlign, Skew);
873 AssignProtectedObjSet(SmallArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
874 Offset, MaxAlign, Skew);
875 AssignProtectedObjSet(AddrOfObjs, ProtectedObjs, MFI, StackGrowsDown,
876 Offset, MaxAlign, Skew);
879 SmallVector<int, 8> ObjectsToAllocate;
881 // Then prepare to assign frame offsets to stack objects that are not used to
882 // spill callee saved registers.
883 for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
884 if (MFI.isObjectPreAllocated(i) && MFI.getUseLocalStackAllocationBlock())
886 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
888 if (RS && RS->isScavengingFrameIndex((int)i))
890 if (MFI.isDeadObjectIndex(i))
892 if (MFI.getStackProtectorIndex() == (int)i ||
893 EHRegNodeFrameIndex == (int)i)
895 if (ProtectedObjs.count(i))
898 // Add the objects that we need to allocate to our working set.
899 ObjectsToAllocate.push_back(i);
902 // Allocate the EH registration node first if one is present.
903 if (EHRegNodeFrameIndex != INT_MAX)
904 AdjustStackOffset(MFI, EHRegNodeFrameIndex, StackGrowsDown, Offset,
907 // Give the targets a chance to order the objects the way they like it.
908 if (Fn.getTarget().getOptLevel() != CodeGenOpt::None &&
909 Fn.getTarget().Options.StackSymbolOrdering)
910 TFI.orderFrameObjects(Fn, ObjectsToAllocate);
912 // Keep track of which bytes in the fixed and callee-save range are used so we
913 // can use the holes when allocating later stack objects. Only do this if
914 // stack protector isn't being used and the target requests it and we're
916 BitVector StackBytesFree;
917 if (!ObjectsToAllocate.empty() &&
918 Fn.getTarget().getOptLevel() != CodeGenOpt::None &&
919 MFI.getStackProtectorIndex() < 0 && TFI.enableStackSlotScavenging(Fn))
920 computeFreeStackSlots(MFI, StackGrowsDown, MinCSFrameIndex, MaxCSFrameIndex,
921 FixedCSEnd, StackBytesFree);
923 // Now walk the objects and actually assign base offsets to them.
924 for (auto &Object : ObjectsToAllocate)
925 if (!scavengeStackSlot(MFI, Object, StackGrowsDown, MaxAlign,
927 AdjustStackOffset(MFI, Object, StackGrowsDown, Offset, MaxAlign, Skew);
929 // Make sure the special register scavenging spill slot is closest to the
931 if (RS && !EarlyScavengingSlots) {
932 SmallVector<int, 2> SFIs;
933 RS->getScavengingFrameIndices(SFIs);
934 for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
935 IE = SFIs.end(); I != IE; ++I)
936 AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign, Skew);
939 if (!TFI.targetHandlesStackFrameRounding()) {
940 // If we have reserved argument space for call sites in the function
941 // immediately on entry to the current function, count it as part of the
942 // overall stack size.
943 if (MFI.adjustsStack() && TFI.hasReservedCallFrame(Fn))
944 Offset += MFI.getMaxCallFrameSize();
946 // Round up the size to a multiple of the alignment. If the function has
947 // any calls or alloca's, align to the target's StackAlignment value to
948 // ensure that the callee's frame or the alloca data is suitably aligned;
949 // otherwise, for leaf functions, align to the TransientStackAlignment
952 if (MFI.adjustsStack() || MFI.hasVarSizedObjects() ||
953 (RegInfo->needsStackRealignment(Fn) && MFI.getObjectIndexEnd() != 0))
954 StackAlign = TFI.getStackAlignment();
956 StackAlign = TFI.getTransientStackAlignment();
958 // If the frame pointer is eliminated, all frame offsets will be relative to
959 // SP not FP. Align to MaxAlign so this works.
960 StackAlign = std::max(StackAlign, MaxAlign);
961 Offset = alignTo(Offset, StackAlign, Skew);
964 // Update frame info to pretend that this is part of the stack...
965 int64_t StackSize = Offset - LocalAreaOffset;
966 MFI.setStackSize(StackSize);
967 NumBytesStackSpace += StackSize;
970 /// insertPrologEpilogCode - Scan the function for modified callee saved
971 /// registers, insert spill code for these callee saved registers, then add
972 /// prolog and epilog code to the function.
974 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
975 const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
977 // Add prologue to the function...
978 for (MachineBasicBlock *SaveBlock : SaveBlocks)
979 TFI.emitPrologue(Fn, *SaveBlock);
981 // Add epilogue to restore the callee-save registers in each exiting block.
982 for (MachineBasicBlock *RestoreBlock : RestoreBlocks)
983 TFI.emitEpilogue(Fn, *RestoreBlock);
985 for (MachineBasicBlock *SaveBlock : SaveBlocks)
986 TFI.inlineStackProbe(Fn, *SaveBlock);
988 // Emit additional code that is required to support segmented stacks, if
989 // we've been asked for it. This, when linked with a runtime with support
990 // for segmented stacks (libgcc is one), will result in allocating stack
991 // space in small chunks instead of one large contiguous block.
992 if (Fn.shouldSplitStack()) {
993 for (MachineBasicBlock *SaveBlock : SaveBlocks)
994 TFI.adjustForSegmentedStacks(Fn, *SaveBlock);
997 // Emit additional code that is required to explicitly handle the stack in
998 // HiPE native code (if needed) when loaded in the Erlang/OTP runtime. The
999 // approach is rather similar to that of Segmented Stacks, but it uses a
1000 // different conditional check and another BIF for allocating more stack
1002 if (Fn.getFunction()->getCallingConv() == CallingConv::HiPE)
1003 for (MachineBasicBlock *SaveBlock : SaveBlocks)
1004 TFI.adjustForHiPEPrologue(Fn, *SaveBlock);
1007 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
1008 /// register references and actual offsets.
1010 void PEI::replaceFrameIndices(MachineFunction &Fn) {
1011 const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
1012 if (!TFI.needsFrameIndexResolution(Fn)) return;
1014 // Store SPAdj at exit of a basic block.
1015 SmallVector<int, 8> SPState;
1016 SPState.resize(Fn.getNumBlockIDs());
1017 df_iterator_default_set<MachineBasicBlock*> Reachable;
1019 // Iterate over the reachable blocks in DFS order.
1020 for (auto DFI = df_ext_begin(&Fn, Reachable), DFE = df_ext_end(&Fn, Reachable);
1021 DFI != DFE; ++DFI) {
1023 // Check the exit state of the DFS stack predecessor.
1024 if (DFI.getPathLength() >= 2) {
1025 MachineBasicBlock *StackPred = DFI.getPath(DFI.getPathLength() - 2);
1026 assert(Reachable.count(StackPred) &&
1027 "DFS stack predecessor is already visited.\n");
1028 SPAdj = SPState[StackPred->getNumber()];
1030 MachineBasicBlock *BB = *DFI;
1031 replaceFrameIndices(BB, Fn, SPAdj);
1032 SPState[BB->getNumber()] = SPAdj;
1035 // Handle the unreachable blocks.
1036 for (auto &BB : Fn) {
1037 if (Reachable.count(&BB))
1038 // Already handled in DFS traversal.
1041 replaceFrameIndices(&BB, Fn, SPAdj);
1045 void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
1047 assert(Fn.getSubtarget().getRegisterInfo() &&
1048 "getRegisterInfo() must be implemented!");
1049 const TargetInstrInfo &TII = *Fn.getSubtarget().getInstrInfo();
1050 const TargetRegisterInfo &TRI = *Fn.getSubtarget().getRegisterInfo();
1051 const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
1052 unsigned FrameSetupOpcode = TII.getCallFrameSetupOpcode();
1053 unsigned FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
1055 if (RS && FrameIndexEliminationScavenging)
1056 RS->enterBasicBlock(*BB);
1058 bool InsideCallSequence = false;
1060 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
1062 if (I->getOpcode() == FrameSetupOpcode ||
1063 I->getOpcode() == FrameDestroyOpcode) {
1064 InsideCallSequence = (I->getOpcode() == FrameSetupOpcode);
1065 SPAdj += TII.getSPAdjust(*I);
1067 I = TFI->eliminateCallFramePseudoInstr(Fn, *BB, I);
1071 MachineInstr &MI = *I;
1073 bool DidFinishLoop = true;
1074 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
1075 if (!MI.getOperand(i).isFI())
1078 // Frame indices in debug values are encoded in a target independent
1079 // way with simply the frame index and offset rather than any
1080 // target-specific addressing mode.
1081 if (MI.isDebugValue()) {
1082 assert(i == 0 && "Frame indices can only appear as the first "
1083 "operand of a DBG_VALUE machine instruction");
1085 MachineOperand &Offset = MI.getOperand(1);
1088 TFI->getFrameIndexReference(Fn, MI.getOperand(0).getIndex(), Reg));
1089 MI.getOperand(0).ChangeToRegister(Reg, false /*isDef*/);
1093 // TODO: This code should be commoned with the code for
1094 // PATCHPOINT. There's no good reason for the difference in
1095 // implementation other than historical accident. The only
1096 // remaining difference is the unconditional use of the stack
1097 // pointer as the base register.
1098 if (MI.getOpcode() == TargetOpcode::STATEPOINT) {
1099 assert((!MI.isDebugValue() || i == 0) &&
1100 "Frame indicies can only appear as the first operand of a "
1101 "DBG_VALUE machine instruction");
1103 MachineOperand &Offset = MI.getOperand(i + 1);
1104 int refOffset = TFI->getFrameIndexReferencePreferSP(
1105 Fn, MI.getOperand(i).getIndex(), Reg, /*IgnoreSPUpdates*/ false);
1106 Offset.setImm(Offset.getImm() + refOffset);
1107 MI.getOperand(i).ChangeToRegister(Reg, false /*isDef*/);
1111 // Some instructions (e.g. inline asm instructions) can have
1112 // multiple frame indices and/or cause eliminateFrameIndex
1113 // to insert more than one instruction. We need the register
1114 // scavenger to go through all of these instructions so that
1115 // it can update its register information. We keep the
1116 // iterator at the point before insertion so that we can
1117 // revisit them in full.
1118 bool AtBeginning = (I == BB->begin());
1119 if (!AtBeginning) --I;
1121 // If this instruction has a FrameIndex operand, we need to
1122 // use that target machine register info object to eliminate
1124 TRI.eliminateFrameIndex(MI, SPAdj, i,
1125 FrameIndexEliminationScavenging ? RS : nullptr);
1127 // Reset the iterator if we were at the beginning of the BB.
1133 DidFinishLoop = false;
1137 // If we are looking at a call sequence, we need to keep track of
1138 // the SP adjustment made by each instruction in the sequence.
1139 // This includes both the frame setup/destroy pseudos (handled above),
1140 // as well as other instructions that have side effects w.r.t the SP.
1141 // Note that this must come after eliminateFrameIndex, because
1142 // if I itself referred to a frame index, we shouldn't count its own
1144 if (DidFinishLoop && InsideCallSequence)
1145 SPAdj += TII.getSPAdjust(MI);
1147 if (DoIncr && I != BB->end()) ++I;
1149 // Update register states.
1150 if (RS && FrameIndexEliminationScavenging && DidFinishLoop)
1155 /// doScavengeFrameVirtualRegs - Replace all frame index virtual registers
1156 /// with physical registers. Use the register scavenger to find an
1157 /// appropriate register to use.
1159 /// FIXME: Iterating over the instruction stream is unnecessary. We can simply
1160 /// iterate over the vreg use list, which at this point only contains machine
1161 /// operands for which eliminateFrameIndex need a new scratch reg.
1163 doScavengeFrameVirtualRegs(MachineFunction &MF, RegScavenger *RS) {
1164 // Run through the instructions and find any virtual registers.
1165 MachineRegisterInfo &MRI = MF.getRegInfo();
1166 for (MachineBasicBlock &MBB : MF) {
1167 RS->enterBasicBlock(MBB);
1171 // The instruction stream may change in the loop, so check MBB.end()
1173 for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ) {
1174 // We might end up here again with a NULL iterator if we scavenged a
1175 // register for which we inserted spill code for definition by what was
1176 // originally the first instruction in MBB.
1177 if (I == MachineBasicBlock::iterator(nullptr))
1180 const MachineInstr &MI = *I;
1181 MachineBasicBlock::iterator J = std::next(I);
1182 MachineBasicBlock::iterator P =
1183 I == MBB.begin() ? MachineBasicBlock::iterator(nullptr)
1186 // RS should process this instruction before we might scavenge at this
1187 // location. This is because we might be replacing a virtual register
1188 // defined by this instruction, and if so, registers killed by this
1189 // instruction are available, and defined registers are not.
1192 for (const MachineOperand &MO : MI.operands()) {
1195 unsigned Reg = MO.getReg();
1196 if (!TargetRegisterInfo::isVirtualRegister(Reg))
1199 // When we first encounter a new virtual register, it
1200 // must be a definition.
1201 assert(MO.isDef() && "frame index virtual missing def!");
1202 // Scavenge a new scratch register
1203 const TargetRegisterClass *RC = MRI.getRegClass(Reg);
1204 unsigned ScratchReg = RS->scavengeRegister(RC, J, SPAdj);
1208 // Replace this reference to the virtual register with the
1209 // scratch register.
1210 assert(ScratchReg && "Missing scratch register!");
1211 MRI.replaceRegWith(Reg, ScratchReg);
1213 // Because this instruction was processed by the RS before this
1214 // register was allocated, make sure that the RS now records the
1215 // register as being used.
1216 RS->setRegUsed(ScratchReg);
1219 // If the scavenger needed to use one of its spill slots, the
1220 // spill code will have been inserted in between I and J. This is a
1221 // problem because we need the spill code before I: Move I to just
1223 if (I != std::prev(J)) {
1224 MBB.splice(J, &MBB, I);
1226 // Before we move I, we need to prepare the RS to visit I again.
1227 // Specifically, RS will assert if it sees uses of registers that
1228 // it believes are undefined. Because we have already processed
1229 // register kills in I, when it visits I again, it will believe that
1230 // those registers are undefined. To avoid this situation, unprocess
1231 // the instruction I.
1232 assert(RS->getCurrentPosition() == I &&
1233 "The register scavenger has an unexpected position");