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 (TII.isFrameInstr(*I)) {
269 unsigned Size = TII.getFrameSize(*I);
270 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
272 FrameSDOps.push_back(I);
273 } else if (I->isInlineAsm()) {
274 // Some inline asm's need a stack frame, as indicated by operand 1.
275 unsigned ExtraInfo = I->getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
276 if (ExtraInfo & InlineAsm::Extra_IsAlignStack)
280 MFI.setAdjustsStack(AdjustsStack);
281 MFI.setMaxCallFrameSize(MaxCallFrameSize);
283 for (std::vector<MachineBasicBlock::iterator>::iterator
284 i = FrameSDOps.begin(), e = FrameSDOps.end(); i != e; ++i) {
285 MachineBasicBlock::iterator I = *i;
287 // If call frames are not being included as part of the stack frame, and
288 // the target doesn't indicate otherwise, remove the call frame pseudos
289 // here. The sub/add sp instruction pairs are still inserted, but we don't
290 // need to track the SP adjustment for frame index elimination.
291 if (TFI->canSimplifyCallFramePseudos(Fn))
292 TFI->eliminateCallFramePseudoInstr(Fn, *I->getParent(), I);
296 /// Compute the sets of entry and return blocks for saving and restoring
297 /// callee-saved registers, and placing prolog and epilog code.
298 void PEI::calculateSaveRestoreBlocks(MachineFunction &Fn) {
299 const MachineFrameInfo &MFI = Fn.getFrameInfo();
301 // Even when we do not change any CSR, we still want to insert the
302 // prologue and epilogue of the function.
303 // So set the save points for those.
305 // Use the points found by shrink-wrapping, if any.
306 if (MFI.getSavePoint()) {
307 SaveBlocks.push_back(MFI.getSavePoint());
308 assert(MFI.getRestorePoint() && "Both restore and save must be set");
309 MachineBasicBlock *RestoreBlock = MFI.getRestorePoint();
310 // If RestoreBlock does not have any successor and is not a return block
311 // then the end point is unreachable and we do not need to insert any
313 if (!RestoreBlock->succ_empty() || RestoreBlock->isReturnBlock())
314 RestoreBlocks.push_back(RestoreBlock);
318 // Save refs to entry and return blocks.
319 SaveBlocks.push_back(&Fn.front());
320 for (MachineBasicBlock &MBB : Fn) {
321 if (MBB.isEHFuncletEntry())
322 SaveBlocks.push_back(&MBB);
323 if (MBB.isReturnBlock())
324 RestoreBlocks.push_back(&MBB);
328 static void assignCalleeSavedSpillSlots(MachineFunction &F,
329 const BitVector &SavedRegs,
330 unsigned &MinCSFrameIndex,
331 unsigned &MaxCSFrameIndex) {
332 if (SavedRegs.empty())
335 const TargetRegisterInfo *RegInfo = F.getSubtarget().getRegisterInfo();
336 const MCPhysReg *CSRegs = F.getRegInfo().getCalleeSavedRegs();
338 std::vector<CalleeSavedInfo> CSI;
339 for (unsigned i = 0; CSRegs[i]; ++i) {
340 unsigned Reg = CSRegs[i];
341 if (SavedRegs.test(Reg))
342 CSI.push_back(CalleeSavedInfo(Reg));
345 const TargetFrameLowering *TFI = F.getSubtarget().getFrameLowering();
346 MachineFrameInfo &MFI = F.getFrameInfo();
347 if (!TFI->assignCalleeSavedSpillSlots(F, RegInfo, CSI)) {
348 // If target doesn't implement this, use generic code.
351 return; // Early exit if no callee saved registers are modified!
353 unsigned NumFixedSpillSlots;
354 const TargetFrameLowering::SpillSlot *FixedSpillSlots =
355 TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots);
357 // Now that we know which registers need to be saved and restored, allocate
358 // stack slots for them.
359 for (auto &CS : CSI) {
360 unsigned Reg = CS.getReg();
361 const TargetRegisterClass *RC = RegInfo->getMinimalPhysRegClass(Reg);
364 if (RegInfo->hasReservedSpillSlot(F, Reg, FrameIdx)) {
365 CS.setFrameIdx(FrameIdx);
369 // Check to see if this physreg must be spilled to a particular stack slot
371 const TargetFrameLowering::SpillSlot *FixedSlot = FixedSpillSlots;
372 while (FixedSlot != FixedSpillSlots + NumFixedSpillSlots &&
373 FixedSlot->Reg != Reg)
376 unsigned Size = RegInfo->getSpillSize(*RC);
377 if (FixedSlot == FixedSpillSlots + NumFixedSpillSlots) {
378 // Nope, just spill it anywhere convenient.
379 unsigned Align = RegInfo->getSpillAlignment(*RC);
380 unsigned StackAlign = TFI->getStackAlignment();
382 // We may not be able to satisfy the desired alignment specification of
383 // the TargetRegisterClass if the stack alignment is smaller. Use the
385 Align = std::min(Align, StackAlign);
386 FrameIdx = MFI.CreateStackObject(Size, Align, true);
387 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
388 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
390 // Spill it to the stack where we must.
391 FrameIdx = MFI.CreateFixedSpillStackObject(Size, FixedSlot->Offset);
394 CS.setFrameIdx(FrameIdx);
398 MFI.setCalleeSavedInfo(CSI);
401 /// Helper function to update the liveness information for the callee-saved
403 static void updateLiveness(MachineFunction &MF) {
404 MachineFrameInfo &MFI = MF.getFrameInfo();
405 // Visited will contain all the basic blocks that are in the region
406 // where the callee saved registers are alive:
407 // - Anything that is not Save or Restore -> LiveThrough.
409 // - Restore -> LiveOut.
410 // The live-out is not attached to the block, so no need to keep
411 // Restore in this set.
412 SmallPtrSet<MachineBasicBlock *, 8> Visited;
413 SmallVector<MachineBasicBlock *, 8> WorkList;
414 MachineBasicBlock *Entry = &MF.front();
415 MachineBasicBlock *Save = MFI.getSavePoint();
421 WorkList.push_back(Entry);
422 Visited.insert(Entry);
424 Visited.insert(Save);
426 MachineBasicBlock *Restore = MFI.getRestorePoint();
428 // By construction Restore cannot be visited, otherwise it
429 // means there exists a path to Restore that does not go
431 WorkList.push_back(Restore);
433 while (!WorkList.empty()) {
434 const MachineBasicBlock *CurBB = WorkList.pop_back_val();
435 // By construction, the region that is after the save point is
436 // dominated by the Save and post-dominated by the Restore.
437 if (CurBB == Save && Save != Restore)
439 // Enqueue all the successors not already visited.
440 // Those are by construction either before Save or after Restore.
441 for (MachineBasicBlock *SuccBB : CurBB->successors())
442 if (Visited.insert(SuccBB).second)
443 WorkList.push_back(SuccBB);
446 const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
448 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
449 for (MachineBasicBlock *MBB : Visited) {
450 MCPhysReg Reg = CSI[i].getReg();
451 // Add the callee-saved register as live-in.
452 // It's killed at the spill.
453 if (!MBB->isLiveIn(Reg))
459 /// insertCSRSpillsAndRestores - Insert spill and restore code for
460 /// callee saved registers used in the function.
462 static void insertCSRSpillsAndRestores(MachineFunction &Fn,
463 const MBBVector &SaveBlocks,
464 const MBBVector &RestoreBlocks) {
465 // Get callee saved register information.
466 MachineFrameInfo &MFI = Fn.getFrameInfo();
467 const std::vector<CalleeSavedInfo> &CSI = MFI.getCalleeSavedInfo();
469 MFI.setCalleeSavedInfoValid(true);
471 // Early exit if no callee saved registers are modified!
475 const TargetInstrInfo &TII = *Fn.getSubtarget().getInstrInfo();
476 const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
477 const TargetRegisterInfo *TRI = Fn.getSubtarget().getRegisterInfo();
478 MachineBasicBlock::iterator I;
480 // Spill using target interface.
481 for (MachineBasicBlock *SaveBlock : SaveBlocks) {
482 I = SaveBlock->begin();
483 if (!TFI->spillCalleeSavedRegisters(*SaveBlock, I, CSI, TRI)) {
484 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
485 // Insert the spill to the stack frame.
486 unsigned Reg = CSI[i].getReg();
487 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
488 TII.storeRegToStackSlot(*SaveBlock, I, Reg, true, CSI[i].getFrameIdx(),
492 // Update the live-in information of all the blocks up to the save point.
496 // Restore using target interface.
497 for (MachineBasicBlock *MBB : RestoreBlocks) {
500 // Skip over all terminator instructions, which are part of the return
502 MachineBasicBlock::iterator I2 = I;
503 while (I2 != MBB->begin() && (--I2)->isTerminator())
506 bool AtStart = I == MBB->begin();
507 MachineBasicBlock::iterator BeforeI = I;
511 // Restore all registers immediately before the return and any
512 // terminators that precede it.
513 if (!TFI->restoreCalleeSavedRegisters(*MBB, I, CSI, TRI)) {
514 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
515 unsigned Reg = CSI[i].getReg();
516 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
517 TII.loadRegFromStackSlot(*MBB, I, Reg, CSI[i].getFrameIdx(), RC, TRI);
518 assert(I != MBB->begin() &&
519 "loadRegFromStackSlot didn't insert any code!");
520 // Insert in reverse order. loadRegFromStackSlot can insert
521 // multiple instructions.
533 static void doSpillCalleeSavedRegs(MachineFunction &Fn, RegScavenger *RS,
534 unsigned &MinCSFrameIndex,
535 unsigned &MaxCSFrameIndex,
536 const MBBVector &SaveBlocks,
537 const MBBVector &RestoreBlocks) {
538 const Function *F = Fn.getFunction();
539 const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
540 MinCSFrameIndex = std::numeric_limits<unsigned>::max();
543 // Determine which of the registers in the callee save list should be saved.
545 TFI->determineCalleeSaves(Fn, SavedRegs, RS);
547 // Assign stack slots for any callee-saved registers that must be spilled.
548 assignCalleeSavedSpillSlots(Fn, SavedRegs, MinCSFrameIndex, MaxCSFrameIndex);
550 // Add the code to save and restore the callee saved registers.
551 if (!F->hasFnAttribute(Attribute::Naked))
552 insertCSRSpillsAndRestores(Fn, SaveBlocks, RestoreBlocks);
555 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
557 AdjustStackOffset(MachineFrameInfo &MFI, int FrameIdx,
558 bool StackGrowsDown, int64_t &Offset,
559 unsigned &MaxAlign, unsigned Skew) {
560 // If the stack grows down, add the object size to find the lowest address.
562 Offset += MFI.getObjectSize(FrameIdx);
564 unsigned Align = MFI.getObjectAlignment(FrameIdx);
566 // If the alignment of this object is greater than that of the stack, then
567 // increase the stack alignment to match.
568 MaxAlign = std::max(MaxAlign, Align);
570 // Adjust to alignment boundary.
571 Offset = alignTo(Offset, Align, Skew);
573 if (StackGrowsDown) {
574 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
575 MFI.setObjectOffset(FrameIdx, -Offset); // Set the computed offset
577 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset << "]\n");
578 MFI.setObjectOffset(FrameIdx, Offset);
579 Offset += MFI.getObjectSize(FrameIdx);
583 /// Compute which bytes of fixed and callee-save stack area are unused and keep
584 /// track of them in StackBytesFree.
587 computeFreeStackSlots(MachineFrameInfo &MFI, bool StackGrowsDown,
588 unsigned MinCSFrameIndex, unsigned MaxCSFrameIndex,
589 int64_t FixedCSEnd, BitVector &StackBytesFree) {
590 // Avoid undefined int64_t -> int conversion below in extreme case.
591 if (FixedCSEnd > std::numeric_limits<int>::max())
594 StackBytesFree.resize(FixedCSEnd, true);
596 SmallVector<int, 16> AllocatedFrameSlots;
597 // Add fixed objects.
598 for (int i = MFI.getObjectIndexBegin(); i != 0; ++i)
599 AllocatedFrameSlots.push_back(i);
600 // Add callee-save objects.
601 for (int i = MinCSFrameIndex; i <= (int)MaxCSFrameIndex; ++i)
602 AllocatedFrameSlots.push_back(i);
604 for (int i : AllocatedFrameSlots) {
605 // These are converted from int64_t, but they should always fit in int
606 // because of the FixedCSEnd check above.
607 int ObjOffset = MFI.getObjectOffset(i);
608 int ObjSize = MFI.getObjectSize(i);
609 int ObjStart, ObjEnd;
610 if (StackGrowsDown) {
611 // ObjOffset is negative when StackGrowsDown is true.
612 ObjStart = -ObjOffset - ObjSize;
615 ObjStart = ObjOffset;
616 ObjEnd = ObjOffset + ObjSize;
618 // Ignore fixed holes that are in the previous stack frame.
620 StackBytesFree.reset(ObjStart, ObjEnd);
624 /// Assign frame object to an unused portion of the stack in the fixed stack
625 /// object range. Return true if the allocation was successful.
627 static inline bool scavengeStackSlot(MachineFrameInfo &MFI, int FrameIdx,
628 bool StackGrowsDown, unsigned MaxAlign,
629 BitVector &StackBytesFree) {
630 if (MFI.isVariableSizedObjectIndex(FrameIdx))
633 if (StackBytesFree.none()) {
634 // clear it to speed up later scavengeStackSlot calls to
635 // StackBytesFree.none()
636 StackBytesFree.clear();
640 unsigned ObjAlign = MFI.getObjectAlignment(FrameIdx);
641 if (ObjAlign > MaxAlign)
644 int64_t ObjSize = MFI.getObjectSize(FrameIdx);
646 for (FreeStart = StackBytesFree.find_first(); FreeStart != -1;
647 FreeStart = StackBytesFree.find_next(FreeStart)) {
649 // Check that free space has suitable alignment.
650 unsigned ObjStart = StackGrowsDown ? FreeStart + ObjSize : FreeStart;
651 if (alignTo(ObjStart, ObjAlign) != ObjStart)
654 if (FreeStart + ObjSize > StackBytesFree.size())
657 bool AllBytesFree = true;
658 for (unsigned Byte = 0; Byte < ObjSize; ++Byte)
659 if (!StackBytesFree.test(FreeStart + Byte)) {
660 AllBytesFree = false;
670 if (StackGrowsDown) {
671 int ObjStart = -(FreeStart + ObjSize);
672 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") scavenged at SP[" << ObjStart
674 MFI.setObjectOffset(FrameIdx, ObjStart);
676 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") scavenged at SP[" << FreeStart
678 MFI.setObjectOffset(FrameIdx, FreeStart);
681 StackBytesFree.reset(FreeStart, FreeStart + ObjSize);
685 /// AssignProtectedObjSet - Helper function to assign large stack objects (i.e.,
686 /// those required to be close to the Stack Protector) to stack offsets.
688 AssignProtectedObjSet(const StackObjSet &UnassignedObjs,
689 SmallSet<int, 16> &ProtectedObjs,
690 MachineFrameInfo &MFI, bool StackGrowsDown,
691 int64_t &Offset, unsigned &MaxAlign, unsigned Skew) {
693 for (StackObjSet::const_iterator I = UnassignedObjs.begin(),
694 E = UnassignedObjs.end(); I != E; ++I) {
696 AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign, Skew);
697 ProtectedObjs.insert(i);
701 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
702 /// abstract stack objects.
704 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
705 const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
706 StackProtector *SP = &getAnalysis<StackProtector>();
708 bool StackGrowsDown =
709 TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
711 // Loop over all of the stack objects, assigning sequential addresses...
712 MachineFrameInfo &MFI = Fn.getFrameInfo();
714 // Start at the beginning of the local area.
715 // The Offset is the distance from the stack top in the direction
716 // of stack growth -- so it's always nonnegative.
717 int LocalAreaOffset = TFI.getOffsetOfLocalArea();
719 LocalAreaOffset = -LocalAreaOffset;
720 assert(LocalAreaOffset >= 0
721 && "Local area offset should be in direction of stack growth");
722 int64_t Offset = LocalAreaOffset;
724 // Skew to be applied to alignment.
725 unsigned Skew = TFI.getStackAlignmentSkew(Fn);
727 // If there are fixed sized objects that are preallocated in the local area,
728 // non-fixed objects can't be allocated right at the start of local area.
729 // Adjust 'Offset' to point to the end of last fixed sized preallocated
731 for (int i = MFI.getObjectIndexBegin(); i != 0; ++i) {
733 if (StackGrowsDown) {
734 // The maximum distance from the stack pointer is at lower address of
735 // the object -- which is given by offset. For down growing stack
736 // the offset is negative, so we negate the offset to get the distance.
737 FixedOff = -MFI.getObjectOffset(i);
739 // The maximum distance from the start pointer is at the upper
740 // address of the object.
741 FixedOff = MFI.getObjectOffset(i) + MFI.getObjectSize(i);
743 if (FixedOff > Offset) Offset = FixedOff;
746 // First assign frame offsets to stack objects that are used to spill
747 // callee saved registers.
748 if (StackGrowsDown) {
749 for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
750 // If the stack grows down, we need to add the size to find the lowest
751 // address of the object.
752 Offset += MFI.getObjectSize(i);
754 unsigned Align = MFI.getObjectAlignment(i);
755 // Adjust to alignment boundary
756 Offset = alignTo(Offset, Align, Skew);
758 DEBUG(dbgs() << "alloc FI(" << i << ") at SP[" << -Offset << "]\n");
759 MFI.setObjectOffset(i, -Offset); // Set the computed offset
761 } else if (MaxCSFrameIndex >= MinCSFrameIndex) {
762 // Be careful about underflow in comparisons agains MinCSFrameIndex.
763 for (unsigned i = MaxCSFrameIndex; i != MinCSFrameIndex - 1; --i) {
764 unsigned Align = MFI.getObjectAlignment(i);
765 // Adjust to alignment boundary
766 Offset = alignTo(Offset, Align, Skew);
768 DEBUG(dbgs() << "alloc FI(" << i << ") at SP[" << Offset << "]\n");
769 MFI.setObjectOffset(i, Offset);
770 Offset += MFI.getObjectSize(i);
774 // FixedCSEnd is the stack offset to the end of the fixed and callee-save
776 int64_t FixedCSEnd = Offset;
777 unsigned MaxAlign = MFI.getMaxAlignment();
779 // Make sure the special register scavenging spill slot is closest to the
780 // incoming stack pointer if a frame pointer is required and is closer
781 // to the incoming rather than the final stack pointer.
782 const TargetRegisterInfo *RegInfo = Fn.getSubtarget().getRegisterInfo();
783 bool EarlyScavengingSlots = (TFI.hasFP(Fn) &&
784 TFI.isFPCloseToIncomingSP() &&
785 RegInfo->useFPForScavengingIndex(Fn) &&
786 !RegInfo->needsStackRealignment(Fn));
787 if (RS && EarlyScavengingSlots) {
788 SmallVector<int, 2> SFIs;
789 RS->getScavengingFrameIndices(SFIs);
790 for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
791 IE = SFIs.end(); I != IE; ++I)
792 AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign, Skew);
795 // FIXME: Once this is working, then enable flag will change to a target
796 // check for whether the frame is large enough to want to use virtual
797 // frame index registers. Functions which don't want/need this optimization
798 // will continue to use the existing code path.
799 if (MFI.getUseLocalStackAllocationBlock()) {
800 unsigned Align = MFI.getLocalFrameMaxAlign();
802 // Adjust to alignment boundary.
803 Offset = alignTo(Offset, Align, Skew);
805 DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
807 // Resolve offsets for objects in the local block.
808 for (unsigned i = 0, e = MFI.getLocalFrameObjectCount(); i != e; ++i) {
809 std::pair<int, int64_t> Entry = MFI.getLocalFrameObjectMap(i);
810 int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
811 DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" <<
813 MFI.setObjectOffset(Entry.first, FIOffset);
815 // Allocate the local block
816 Offset += MFI.getLocalFrameSize();
818 MaxAlign = std::max(Align, MaxAlign);
821 // Retrieve the Exception Handler registration node.
822 int EHRegNodeFrameIndex = INT_MAX;
823 if (const WinEHFuncInfo *FuncInfo = Fn.getWinEHFuncInfo())
824 EHRegNodeFrameIndex = FuncInfo->EHRegNodeFrameIndex;
826 // Make sure that the stack protector comes before the local variables on the
828 SmallSet<int, 16> ProtectedObjs;
829 if (MFI.getStackProtectorIndex() >= 0) {
830 StackObjSet LargeArrayObjs;
831 StackObjSet SmallArrayObjs;
832 StackObjSet AddrOfObjs;
834 AdjustStackOffset(MFI, MFI.getStackProtectorIndex(), StackGrowsDown,
835 Offset, MaxAlign, Skew);
837 // Assign large stack objects first.
838 for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
839 if (MFI.isObjectPreAllocated(i) &&
840 MFI.getUseLocalStackAllocationBlock())
842 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
844 if (RS && RS->isScavengingFrameIndex((int)i))
846 if (MFI.isDeadObjectIndex(i))
848 if (MFI.getStackProtectorIndex() == (int)i ||
849 EHRegNodeFrameIndex == (int)i)
852 switch (SP->getSSPLayout(MFI.getObjectAllocation(i))) {
853 case StackProtector::SSPLK_None:
855 case StackProtector::SSPLK_SmallArray:
856 SmallArrayObjs.insert(i);
858 case StackProtector::SSPLK_AddrOf:
859 AddrOfObjs.insert(i);
861 case StackProtector::SSPLK_LargeArray:
862 LargeArrayObjs.insert(i);
865 llvm_unreachable("Unexpected SSPLayoutKind.");
868 AssignProtectedObjSet(LargeArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
869 Offset, MaxAlign, Skew);
870 AssignProtectedObjSet(SmallArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
871 Offset, MaxAlign, Skew);
872 AssignProtectedObjSet(AddrOfObjs, ProtectedObjs, MFI, StackGrowsDown,
873 Offset, MaxAlign, Skew);
876 SmallVector<int, 8> ObjectsToAllocate;
878 // Then prepare to assign frame offsets to stack objects that are not used to
879 // spill callee saved registers.
880 for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
881 if (MFI.isObjectPreAllocated(i) && MFI.getUseLocalStackAllocationBlock())
883 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
885 if (RS && RS->isScavengingFrameIndex((int)i))
887 if (MFI.isDeadObjectIndex(i))
889 if (MFI.getStackProtectorIndex() == (int)i ||
890 EHRegNodeFrameIndex == (int)i)
892 if (ProtectedObjs.count(i))
895 // Add the objects that we need to allocate to our working set.
896 ObjectsToAllocate.push_back(i);
899 // Allocate the EH registration node first if one is present.
900 if (EHRegNodeFrameIndex != INT_MAX)
901 AdjustStackOffset(MFI, EHRegNodeFrameIndex, StackGrowsDown, Offset,
904 // Give the targets a chance to order the objects the way they like it.
905 if (Fn.getTarget().getOptLevel() != CodeGenOpt::None &&
906 Fn.getTarget().Options.StackSymbolOrdering)
907 TFI.orderFrameObjects(Fn, ObjectsToAllocate);
909 // Keep track of which bytes in the fixed and callee-save range are used so we
910 // can use the holes when allocating later stack objects. Only do this if
911 // stack protector isn't being used and the target requests it and we're
913 BitVector StackBytesFree;
914 if (!ObjectsToAllocate.empty() &&
915 Fn.getTarget().getOptLevel() != CodeGenOpt::None &&
916 MFI.getStackProtectorIndex() < 0 && TFI.enableStackSlotScavenging(Fn))
917 computeFreeStackSlots(MFI, StackGrowsDown, MinCSFrameIndex, MaxCSFrameIndex,
918 FixedCSEnd, StackBytesFree);
920 // Now walk the objects and actually assign base offsets to them.
921 for (auto &Object : ObjectsToAllocate)
922 if (!scavengeStackSlot(MFI, Object, StackGrowsDown, MaxAlign,
924 AdjustStackOffset(MFI, Object, StackGrowsDown, Offset, MaxAlign, Skew);
926 // Make sure the special register scavenging spill slot is closest to the
928 if (RS && !EarlyScavengingSlots) {
929 SmallVector<int, 2> SFIs;
930 RS->getScavengingFrameIndices(SFIs);
931 for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
932 IE = SFIs.end(); I != IE; ++I)
933 AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign, Skew);
936 if (!TFI.targetHandlesStackFrameRounding()) {
937 // If we have reserved argument space for call sites in the function
938 // immediately on entry to the current function, count it as part of the
939 // overall stack size.
940 if (MFI.adjustsStack() && TFI.hasReservedCallFrame(Fn))
941 Offset += MFI.getMaxCallFrameSize();
943 // Round up the size to a multiple of the alignment. If the function has
944 // any calls or alloca's, align to the target's StackAlignment value to
945 // ensure that the callee's frame or the alloca data is suitably aligned;
946 // otherwise, for leaf functions, align to the TransientStackAlignment
949 if (MFI.adjustsStack() || MFI.hasVarSizedObjects() ||
950 (RegInfo->needsStackRealignment(Fn) && MFI.getObjectIndexEnd() != 0))
951 StackAlign = TFI.getStackAlignment();
953 StackAlign = TFI.getTransientStackAlignment();
955 // If the frame pointer is eliminated, all frame offsets will be relative to
956 // SP not FP. Align to MaxAlign so this works.
957 StackAlign = std::max(StackAlign, MaxAlign);
958 Offset = alignTo(Offset, StackAlign, Skew);
961 // Update frame info to pretend that this is part of the stack...
962 int64_t StackSize = Offset - LocalAreaOffset;
963 MFI.setStackSize(StackSize);
964 NumBytesStackSpace += StackSize;
967 /// insertPrologEpilogCode - Scan the function for modified callee saved
968 /// registers, insert spill code for these callee saved registers, then add
969 /// prolog and epilog code to the function.
971 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
972 const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
974 // Add prologue to the function...
975 for (MachineBasicBlock *SaveBlock : SaveBlocks)
976 TFI.emitPrologue(Fn, *SaveBlock);
978 // Add epilogue to restore the callee-save registers in each exiting block.
979 for (MachineBasicBlock *RestoreBlock : RestoreBlocks)
980 TFI.emitEpilogue(Fn, *RestoreBlock);
982 for (MachineBasicBlock *SaveBlock : SaveBlocks)
983 TFI.inlineStackProbe(Fn, *SaveBlock);
985 // Emit additional code that is required to support segmented stacks, if
986 // we've been asked for it. This, when linked with a runtime with support
987 // for segmented stacks (libgcc is one), will result in allocating stack
988 // space in small chunks instead of one large contiguous block.
989 if (Fn.shouldSplitStack()) {
990 for (MachineBasicBlock *SaveBlock : SaveBlocks)
991 TFI.adjustForSegmentedStacks(Fn, *SaveBlock);
994 // Emit additional code that is required to explicitly handle the stack in
995 // HiPE native code (if needed) when loaded in the Erlang/OTP runtime. The
996 // approach is rather similar to that of Segmented Stacks, but it uses a
997 // different conditional check and another BIF for allocating more stack
999 if (Fn.getFunction()->getCallingConv() == CallingConv::HiPE)
1000 for (MachineBasicBlock *SaveBlock : SaveBlocks)
1001 TFI.adjustForHiPEPrologue(Fn, *SaveBlock);
1004 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
1005 /// register references and actual offsets.
1007 void PEI::replaceFrameIndices(MachineFunction &Fn) {
1008 const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
1009 if (!TFI.needsFrameIndexResolution(Fn)) return;
1011 // Store SPAdj at exit of a basic block.
1012 SmallVector<int, 8> SPState;
1013 SPState.resize(Fn.getNumBlockIDs());
1014 df_iterator_default_set<MachineBasicBlock*> Reachable;
1016 // Iterate over the reachable blocks in DFS order.
1017 for (auto DFI = df_ext_begin(&Fn, Reachable), DFE = df_ext_end(&Fn, Reachable);
1018 DFI != DFE; ++DFI) {
1020 // Check the exit state of the DFS stack predecessor.
1021 if (DFI.getPathLength() >= 2) {
1022 MachineBasicBlock *StackPred = DFI.getPath(DFI.getPathLength() - 2);
1023 assert(Reachable.count(StackPred) &&
1024 "DFS stack predecessor is already visited.\n");
1025 SPAdj = SPState[StackPred->getNumber()];
1027 MachineBasicBlock *BB = *DFI;
1028 replaceFrameIndices(BB, Fn, SPAdj);
1029 SPState[BB->getNumber()] = SPAdj;
1032 // Handle the unreachable blocks.
1033 for (auto &BB : Fn) {
1034 if (Reachable.count(&BB))
1035 // Already handled in DFS traversal.
1038 replaceFrameIndices(&BB, Fn, SPAdj);
1042 void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
1044 assert(Fn.getSubtarget().getRegisterInfo() &&
1045 "getRegisterInfo() must be implemented!");
1046 const TargetInstrInfo &TII = *Fn.getSubtarget().getInstrInfo();
1047 const TargetRegisterInfo &TRI = *Fn.getSubtarget().getRegisterInfo();
1048 const TargetFrameLowering *TFI = Fn.getSubtarget().getFrameLowering();
1050 if (RS && FrameIndexEliminationScavenging)
1051 RS->enterBasicBlock(*BB);
1053 bool InsideCallSequence = false;
1055 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
1057 if (TII.isFrameInstr(*I)) {
1058 InsideCallSequence = TII.isFrameSetup(*I);
1059 SPAdj += TII.getSPAdjust(*I);
1060 I = TFI->eliminateCallFramePseudoInstr(Fn, *BB, I);
1064 MachineInstr &MI = *I;
1066 bool DidFinishLoop = true;
1067 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
1068 if (!MI.getOperand(i).isFI())
1071 // Frame indices in debug values are encoded in a target independent
1072 // way with simply the frame index and offset rather than any
1073 // target-specific addressing mode.
1074 if (MI.isDebugValue()) {
1075 assert(i == 0 && "Frame indices can only appear as the first "
1076 "operand of a DBG_VALUE machine instruction");
1078 MachineOperand &Offset = MI.getOperand(1);
1081 TFI->getFrameIndexReference(Fn, MI.getOperand(0).getIndex(), Reg));
1082 MI.getOperand(0).ChangeToRegister(Reg, false /*isDef*/);
1086 // TODO: This code should be commoned with the code for
1087 // PATCHPOINT. There's no good reason for the difference in
1088 // implementation other than historical accident. The only
1089 // remaining difference is the unconditional use of the stack
1090 // pointer as the base register.
1091 if (MI.getOpcode() == TargetOpcode::STATEPOINT) {
1092 assert((!MI.isDebugValue() || i == 0) &&
1093 "Frame indicies can only appear as the first operand of a "
1094 "DBG_VALUE machine instruction");
1096 MachineOperand &Offset = MI.getOperand(i + 1);
1097 int refOffset = TFI->getFrameIndexReferencePreferSP(
1098 Fn, MI.getOperand(i).getIndex(), Reg, /*IgnoreSPUpdates*/ false);
1099 Offset.setImm(Offset.getImm() + refOffset);
1100 MI.getOperand(i).ChangeToRegister(Reg, false /*isDef*/);
1104 // Some instructions (e.g. inline asm instructions) can have
1105 // multiple frame indices and/or cause eliminateFrameIndex
1106 // to insert more than one instruction. We need the register
1107 // scavenger to go through all of these instructions so that
1108 // it can update its register information. We keep the
1109 // iterator at the point before insertion so that we can
1110 // revisit them in full.
1111 bool AtBeginning = (I == BB->begin());
1112 if (!AtBeginning) --I;
1114 // If this instruction has a FrameIndex operand, we need to
1115 // use that target machine register info object to eliminate
1117 TRI.eliminateFrameIndex(MI, SPAdj, i,
1118 FrameIndexEliminationScavenging ? RS : nullptr);
1120 // Reset the iterator if we were at the beginning of the BB.
1126 DidFinishLoop = false;
1130 // If we are looking at a call sequence, we need to keep track of
1131 // the SP adjustment made by each instruction in the sequence.
1132 // This includes both the frame setup/destroy pseudos (handled above),
1133 // as well as other instructions that have side effects w.r.t the SP.
1134 // Note that this must come after eliminateFrameIndex, because
1135 // if I itself referred to a frame index, we shouldn't count its own
1137 if (DidFinishLoop && InsideCallSequence)
1138 SPAdj += TII.getSPAdjust(MI);
1140 if (DoIncr && I != BB->end()) ++I;
1142 // Update register states.
1143 if (RS && FrameIndexEliminationScavenging && DidFinishLoop)
1148 /// doScavengeFrameVirtualRegs - Replace all frame index virtual registers
1149 /// with physical registers. Use the register scavenger to find an
1150 /// appropriate register to use.
1152 /// FIXME: Iterating over the instruction stream is unnecessary. We can simply
1153 /// iterate over the vreg use list, which at this point only contains machine
1154 /// operands for which eliminateFrameIndex need a new scratch reg.
1156 doScavengeFrameVirtualRegs(MachineFunction &MF, RegScavenger *RS) {
1157 // Run through the instructions and find any virtual registers.
1158 MachineRegisterInfo &MRI = MF.getRegInfo();
1159 for (MachineBasicBlock &MBB : MF) {
1160 RS->enterBasicBlock(MBB);
1164 // The instruction stream may change in the loop, so check MBB.end()
1166 for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ) {
1167 // We might end up here again with a NULL iterator if we scavenged a
1168 // register for which we inserted spill code for definition by what was
1169 // originally the first instruction in MBB.
1170 if (I == MachineBasicBlock::iterator(nullptr))
1173 const MachineInstr &MI = *I;
1174 MachineBasicBlock::iterator J = std::next(I);
1175 MachineBasicBlock::iterator P =
1176 I == MBB.begin() ? MachineBasicBlock::iterator(nullptr)
1179 // RS should process this instruction before we might scavenge at this
1180 // location. This is because we might be replacing a virtual register
1181 // defined by this instruction, and if so, registers killed by this
1182 // instruction are available, and defined registers are not.
1185 for (const MachineOperand &MO : MI.operands()) {
1188 unsigned Reg = MO.getReg();
1189 if (!TargetRegisterInfo::isVirtualRegister(Reg))
1192 // When we first encounter a new virtual register, it
1193 // must be a definition.
1194 assert(MO.isDef() && "frame index virtual missing def!");
1195 // Scavenge a new scratch register
1196 const TargetRegisterClass *RC = MRI.getRegClass(Reg);
1197 unsigned ScratchReg = RS->scavengeRegister(RC, J, SPAdj);
1201 // Replace this reference to the virtual register with the
1202 // scratch register.
1203 assert(ScratchReg && "Missing scratch register!");
1204 MRI.replaceRegWith(Reg, ScratchReg);
1206 // Because this instruction was processed by the RS before this
1207 // register was allocated, make sure that the RS now records the
1208 // register as being used.
1209 RS->setRegUsed(ScratchReg);
1212 // If the scavenger needed to use one of its spill slots, the
1213 // spill code will have been inserted in between I and J. This is a
1214 // problem because we need the spill code before I: Move I to just
1216 if (I != std::prev(J)) {
1217 MBB.splice(J, &MBB, I);
1219 // Before we move I, we need to prepare the RS to visit I again.
1220 // Specifically, RS will assert if it sees uses of registers that
1221 // it believes are undefined. Because we have already processed
1222 // register kills in I, when it visits I again, it will believe that
1223 // those registers are undefined. To avoid this situation, unprocess
1224 // the instruction I.
1225 assert(RS->getCurrentPosition() == I &&
1226 "The register scavenger has an unexpected position");
1234 MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs);