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 "PrologEpilogInserter.h"
20 #include "llvm/ADT/IndexedMap.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/ADT/SetVector.h"
23 #include "llvm/ADT/SmallSet.h"
24 #include "llvm/ADT/Statistic.h"
25 #include "llvm/CodeGen/MachineDominators.h"
26 #include "llvm/CodeGen/MachineFrameInfo.h"
27 #include "llvm/CodeGen/MachineInstr.h"
28 #include "llvm/CodeGen/MachineLoopInfo.h"
29 #include "llvm/CodeGen/MachineModuleInfo.h"
30 #include "llvm/CodeGen/MachineRegisterInfo.h"
31 #include "llvm/CodeGen/RegisterScavenging.h"
32 #include "llvm/CodeGen/StackProtector.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/Compiler.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/raw_ostream.h"
40 #include "llvm/Target/TargetFrameLowering.h"
41 #include "llvm/Target/TargetInstrInfo.h"
42 #include "llvm/Target/TargetMachine.h"
43 #include "llvm/Target/TargetRegisterInfo.h"
48 #define DEBUG_TYPE "pei"
51 char &llvm::PrologEpilogCodeInserterID = PEI::ID;
53 static cl::opt<unsigned>
54 WarnStackSize("warn-stack-size", cl::Hidden, cl::init((unsigned)-1),
55 cl::desc("Warn for stack size bigger than the given"
58 INITIALIZE_PASS_BEGIN(PEI, "prologepilog",
59 "Prologue/Epilogue Insertion", false, false)
60 INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
61 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
62 INITIALIZE_PASS_DEPENDENCY(StackProtector)
63 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
64 INITIALIZE_PASS_END(PEI, "prologepilog",
65 "Prologue/Epilogue Insertion & Frame Finalization",
68 STATISTIC(NumScavengedRegs, "Number of frame index regs scavenged");
69 STATISTIC(NumBytesStackSpace,
70 "Number of bytes used for stack in all functions");
72 void PEI::getAnalysisUsage(AnalysisUsage &AU) const {
74 AU.addPreserved<MachineLoopInfo>();
75 AU.addPreserved<MachineDominatorTree>();
76 AU.addRequired<StackProtector>();
77 AU.addRequired<TargetPassConfig>();
78 MachineFunctionPass::getAnalysisUsage(AU);
81 bool PEI::isReturnBlock(MachineBasicBlock* MBB) {
82 return (MBB && !MBB->empty() && MBB->back().isReturn());
85 /// Compute the set of return blocks
86 void PEI::calculateSets(MachineFunction &Fn) {
87 // Sets used to compute spill, restore placement sets.
88 const std::vector<CalleeSavedInfo> &CSI =
89 Fn.getFrameInfo()->getCalleeSavedInfo();
91 // If no CSRs used, we are done.
95 // Save refs to entry and return blocks.
96 EntryBlock = Fn.begin();
97 for (MachineFunction::iterator MBB = Fn.begin(), E = Fn.end();
99 if (isReturnBlock(MBB))
100 ReturnBlocks.push_back(MBB);
105 /// StackObjSet - A set of stack object indexes
106 typedef SmallSetVector<int, 8> StackObjSet;
108 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
109 /// frame indexes with appropriate references.
111 bool PEI::runOnMachineFunction(MachineFunction &Fn) {
112 const Function* F = Fn.getFunction();
113 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
114 const TargetFrameLowering *TFI = Fn.getTarget().getFrameLowering();
116 assert(!Fn.getRegInfo().getNumVirtRegs() && "Regalloc must assign all vregs");
118 RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : nullptr;
119 FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(Fn);
121 // Calculate the MaxCallFrameSize and AdjustsStack variables for the
122 // function's frame information. Also eliminates call frame pseudo
124 calculateCallsInformation(Fn);
126 // Allow the target machine to make some adjustments to the function
127 // e.g. UsedPhysRegs before calculateCalleeSavedRegisters.
128 TFI->processFunctionBeforeCalleeSavedScan(Fn, RS);
130 // Scan the function for modified callee saved registers and insert spill code
131 // for any callee saved registers that are modified.
132 calculateCalleeSavedRegisters(Fn);
134 // Determine placement of CSR spill/restore code:
135 // place all spills in the entry block, all restores in return blocks.
138 // Add the code to save and restore the callee saved registers
139 if (!F->hasFnAttribute(Attribute::Naked))
140 insertCSRSpillsAndRestores(Fn);
142 // Allow the target machine to make final modifications to the function
143 // before the frame layout is finalized.
144 TFI->processFunctionBeforeFrameFinalized(Fn, RS);
146 // Calculate actual frame offsets for all abstract stack objects...
147 calculateFrameObjectOffsets(Fn);
149 // Add prolog and epilog code to the function. This function is required
150 // to align the stack frame as necessary for any stack variables or
151 // called functions. Because of this, calculateCalleeSavedRegisters()
152 // must be called before this function in order to set the AdjustsStack
153 // and MaxCallFrameSize variables.
154 if (!F->hasFnAttribute(Attribute::Naked))
155 insertPrologEpilogCode(Fn);
157 // Replace all MO_FrameIndex operands with physical register references
158 // and actual offsets.
160 replaceFrameIndices(Fn);
162 // If register scavenging is needed, as we've enabled doing it as a
163 // post-pass, scavenge the virtual registers that frame index elimination
165 if (TRI->requiresRegisterScavenging(Fn) && FrameIndexVirtualScavenging)
166 scavengeFrameVirtualRegs(Fn);
168 // Clear any vregs created by virtual scavenging.
169 Fn.getRegInfo().clearVirtRegs();
171 // Warn on stack size when we exceeds the given limit.
172 MachineFrameInfo *MFI = Fn.getFrameInfo();
173 uint64_t StackSize = MFI->getStackSize();
174 if (WarnStackSize.getNumOccurrences() > 0 && WarnStackSize < StackSize) {
175 DiagnosticInfoStackSize DiagStackSize(*F, StackSize);
176 F->getContext().diagnose(DiagStackSize);
180 ReturnBlocks.clear();
184 /// calculateCallsInformation - Calculate the MaxCallFrameSize and AdjustsStack
185 /// variables for the function's frame information and eliminate call frame
186 /// pseudo instructions.
187 void PEI::calculateCallsInformation(MachineFunction &Fn) {
188 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
189 const TargetFrameLowering *TFI = Fn.getTarget().getFrameLowering();
190 MachineFrameInfo *MFI = Fn.getFrameInfo();
192 unsigned MaxCallFrameSize = 0;
193 bool AdjustsStack = MFI->adjustsStack();
195 // Get the function call frame set-up and tear-down instruction opcode
196 int FrameSetupOpcode = TII.getCallFrameSetupOpcode();
197 int FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
199 // Early exit for targets which have no call frame setup/destroy pseudo
201 if (FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
204 std::vector<MachineBasicBlock::iterator> FrameSDOps;
205 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
206 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
207 if (I->getOpcode() == FrameSetupOpcode ||
208 I->getOpcode() == FrameDestroyOpcode) {
209 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo"
210 " instructions should have a single immediate argument!");
211 unsigned Size = I->getOperand(0).getImm();
212 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
214 FrameSDOps.push_back(I);
215 } else if (I->isInlineAsm()) {
216 // Some inline asm's need a stack frame, as indicated by operand 1.
217 unsigned ExtraInfo = I->getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
218 if (ExtraInfo & InlineAsm::Extra_IsAlignStack)
222 MFI->setAdjustsStack(AdjustsStack);
223 MFI->setMaxCallFrameSize(MaxCallFrameSize);
225 for (std::vector<MachineBasicBlock::iterator>::iterator
226 i = FrameSDOps.begin(), e = FrameSDOps.end(); i != e; ++i) {
227 MachineBasicBlock::iterator I = *i;
229 // If call frames are not being included as part of the stack frame, and
230 // the target doesn't indicate otherwise, remove the call frame pseudos
231 // here. The sub/add sp instruction pairs are still inserted, but we don't
232 // need to track the SP adjustment for frame index elimination.
233 if (TFI->canSimplifyCallFramePseudos(Fn))
234 TFI->eliminateCallFramePseudoInstr(Fn, *I->getParent(), I);
239 /// calculateCalleeSavedRegisters - Scan the function for modified callee saved
241 void PEI::calculateCalleeSavedRegisters(MachineFunction &F) {
242 const TargetRegisterInfo *RegInfo = F.getTarget().getRegisterInfo();
243 const TargetFrameLowering *TFI = F.getTarget().getFrameLowering();
244 MachineFrameInfo *MFI = F.getFrameInfo();
246 // Get the callee saved register list...
247 const MCPhysReg *CSRegs = RegInfo->getCalleeSavedRegs(&F);
249 // These are used to keep track the callee-save area. Initialize them.
250 MinCSFrameIndex = INT_MAX;
253 // Early exit for targets which have no callee saved registers.
254 if (!CSRegs || CSRegs[0] == 0)
257 // In Naked functions we aren't going to save any registers.
258 if (F.getFunction()->hasFnAttribute(Attribute::Naked))
261 std::vector<CalleeSavedInfo> CSI;
262 for (unsigned i = 0; CSRegs[i]; ++i) {
263 unsigned Reg = CSRegs[i];
264 // Functions which call __builtin_unwind_init get all their registers saved.
265 if (F.getRegInfo().isPhysRegUsed(Reg) || F.getMMI().callsUnwindInit()) {
266 // If the reg is modified, save it!
267 CSI.push_back(CalleeSavedInfo(Reg));
271 if (!TFI->assignCalleeSavedSpillSlots(F, RegInfo, CSI)) {
272 // If target doesn't implement this, use generic code.
275 return; // Early exit if no callee saved registers are modified!
277 unsigned NumFixedSpillSlots;
278 const TargetFrameLowering::SpillSlot *FixedSpillSlots =
279 TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots);
281 // Now that we know which registers need to be saved and restored, allocate
282 // stack slots for them.
283 for (std::vector<CalleeSavedInfo>::iterator I = CSI.begin(), E = CSI.end();
285 unsigned Reg = I->getReg();
286 const TargetRegisterClass *RC = RegInfo->getMinimalPhysRegClass(Reg);
289 if (RegInfo->hasReservedSpillSlot(F, Reg, FrameIdx)) {
290 I->setFrameIdx(FrameIdx);
294 // Check to see if this physreg must be spilled to a particular stack slot
296 const TargetFrameLowering::SpillSlot *FixedSlot = FixedSpillSlots;
297 while (FixedSlot != FixedSpillSlots + NumFixedSpillSlots &&
298 FixedSlot->Reg != Reg)
301 if (FixedSlot == FixedSpillSlots + NumFixedSpillSlots) {
302 // Nope, just spill it anywhere convenient.
303 unsigned Align = RC->getAlignment();
304 unsigned StackAlign = TFI->getStackAlignment();
306 // We may not be able to satisfy the desired alignment specification of
307 // the TargetRegisterClass if the stack alignment is smaller. Use the
309 Align = std::min(Align, StackAlign);
310 FrameIdx = MFI->CreateStackObject(RC->getSize(), Align, true);
311 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
312 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
314 // Spill it to the stack where we must.
316 MFI->CreateFixedSpillStackObject(RC->getSize(), FixedSlot->Offset);
319 I->setFrameIdx(FrameIdx);
323 MFI->setCalleeSavedInfo(CSI);
326 /// insertCSRSpillsAndRestores - Insert spill and restore code for
327 /// callee saved registers used in the function.
329 void PEI::insertCSRSpillsAndRestores(MachineFunction &Fn) {
330 // Get callee saved register information.
331 MachineFrameInfo *MFI = Fn.getFrameInfo();
332 const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
334 MFI->setCalleeSavedInfoValid(true);
336 // Early exit if no callee saved registers are modified!
340 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
341 const TargetFrameLowering *TFI = Fn.getTarget().getFrameLowering();
342 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
343 MachineBasicBlock::iterator I;
345 // Spill using target interface.
346 I = EntryBlock->begin();
347 if (!TFI->spillCalleeSavedRegisters(*EntryBlock, I, CSI, TRI)) {
348 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
349 // Add the callee-saved register as live-in.
350 // It's killed at the spill.
351 EntryBlock->addLiveIn(CSI[i].getReg());
353 // Insert the spill to the stack frame.
354 unsigned Reg = CSI[i].getReg();
355 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
356 TII.storeRegToStackSlot(*EntryBlock, I, Reg, true, CSI[i].getFrameIdx(),
361 // Restore using target interface.
362 for (unsigned ri = 0, re = ReturnBlocks.size(); ri != re; ++ri) {
363 MachineBasicBlock *MBB = ReturnBlocks[ri];
367 // Skip over all terminator instructions, which are part of the return
369 MachineBasicBlock::iterator I2 = I;
370 while (I2 != MBB->begin() && (--I2)->isTerminator())
373 bool AtStart = I == MBB->begin();
374 MachineBasicBlock::iterator BeforeI = I;
378 // Restore all registers immediately before the return and any
379 // terminators that precede it.
380 if (!TFI->restoreCalleeSavedRegisters(*MBB, I, CSI, TRI)) {
381 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
382 unsigned Reg = CSI[i].getReg();
383 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
384 TII.loadRegFromStackSlot(*MBB, I, Reg, CSI[i].getFrameIdx(), RC, TRI);
385 assert(I != MBB->begin() &&
386 "loadRegFromStackSlot didn't insert any code!");
387 // Insert in reverse order. loadRegFromStackSlot can insert
388 // multiple instructions.
400 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
402 AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
403 bool StackGrowsDown, int64_t &Offset,
404 unsigned &MaxAlign) {
405 // If the stack grows down, add the object size to find the lowest address.
407 Offset += MFI->getObjectSize(FrameIdx);
409 unsigned Align = MFI->getObjectAlignment(FrameIdx);
411 // If the alignment of this object is greater than that of the stack, then
412 // increase the stack alignment to match.
413 MaxAlign = std::max(MaxAlign, Align);
415 // Adjust to alignment boundary.
416 Offset = (Offset + Align - 1) / Align * Align;
418 if (StackGrowsDown) {
419 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
420 MFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
422 DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset << "]\n");
423 MFI->setObjectOffset(FrameIdx, Offset);
424 Offset += MFI->getObjectSize(FrameIdx);
428 /// AssignProtectedObjSet - Helper function to assign large stack objects (i.e.,
429 /// those required to be close to the Stack Protector) to stack offsets.
431 AssignProtectedObjSet(const StackObjSet &UnassignedObjs,
432 SmallSet<int, 16> &ProtectedObjs,
433 MachineFrameInfo *MFI, bool StackGrowsDown,
434 int64_t &Offset, unsigned &MaxAlign) {
436 for (StackObjSet::const_iterator I = UnassignedObjs.begin(),
437 E = UnassignedObjs.end(); I != E; ++I) {
439 AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
440 ProtectedObjs.insert(i);
444 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
445 /// abstract stack objects.
447 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
448 const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
449 StackProtector *SP = &getAnalysis<StackProtector>();
451 bool StackGrowsDown =
452 TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
454 // Loop over all of the stack objects, assigning sequential addresses...
455 MachineFrameInfo *MFI = Fn.getFrameInfo();
457 // Start at the beginning of the local area.
458 // The Offset is the distance from the stack top in the direction
459 // of stack growth -- so it's always nonnegative.
460 int LocalAreaOffset = TFI.getOffsetOfLocalArea();
462 LocalAreaOffset = -LocalAreaOffset;
463 assert(LocalAreaOffset >= 0
464 && "Local area offset should be in direction of stack growth");
465 int64_t Offset = LocalAreaOffset;
467 // If there are fixed sized objects that are preallocated in the local area,
468 // non-fixed objects can't be allocated right at the start of local area.
469 // We currently don't support filling in holes in between fixed sized
470 // objects, so we adjust 'Offset' to point to the end of last fixed sized
471 // preallocated object.
472 for (int i = MFI->getObjectIndexBegin(); i != 0; ++i) {
474 if (StackGrowsDown) {
475 // The maximum distance from the stack pointer is at lower address of
476 // the object -- which is given by offset. For down growing stack
477 // the offset is negative, so we negate the offset to get the distance.
478 FixedOff = -MFI->getObjectOffset(i);
480 // The maximum distance from the start pointer is at the upper
481 // address of the object.
482 FixedOff = MFI->getObjectOffset(i) + MFI->getObjectSize(i);
484 if (FixedOff > Offset) Offset = FixedOff;
487 // First assign frame offsets to stack objects that are used to spill
488 // callee saved registers.
489 if (StackGrowsDown) {
490 for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
491 // If the stack grows down, we need to add the size to find the lowest
492 // address of the object.
493 Offset += MFI->getObjectSize(i);
495 unsigned Align = MFI->getObjectAlignment(i);
496 // Adjust to alignment boundary
497 Offset = (Offset+Align-1)/Align*Align;
499 MFI->setObjectOffset(i, -Offset); // Set the computed offset
502 int MaxCSFI = MaxCSFrameIndex, MinCSFI = MinCSFrameIndex;
503 for (int i = MaxCSFI; i >= MinCSFI ; --i) {
504 unsigned Align = MFI->getObjectAlignment(i);
505 // Adjust to alignment boundary
506 Offset = (Offset+Align-1)/Align*Align;
508 MFI->setObjectOffset(i, Offset);
509 Offset += MFI->getObjectSize(i);
513 unsigned MaxAlign = MFI->getMaxAlignment();
515 // Make sure the special register scavenging spill slot is closest to the
516 // incoming stack pointer if a frame pointer is required and is closer
517 // to the incoming rather than the final stack pointer.
518 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
519 bool EarlyScavengingSlots = (TFI.hasFP(Fn) &&
520 TFI.isFPCloseToIncomingSP() &&
521 RegInfo->useFPForScavengingIndex(Fn) &&
522 !RegInfo->needsStackRealignment(Fn));
523 if (RS && EarlyScavengingSlots) {
524 SmallVector<int, 2> SFIs;
525 RS->getScavengingFrameIndices(SFIs);
526 for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
527 IE = SFIs.end(); I != IE; ++I)
528 AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign);
531 // FIXME: Once this is working, then enable flag will change to a target
532 // check for whether the frame is large enough to want to use virtual
533 // frame index registers. Functions which don't want/need this optimization
534 // will continue to use the existing code path.
535 if (MFI->getUseLocalStackAllocationBlock()) {
536 unsigned Align = MFI->getLocalFrameMaxAlign();
538 // Adjust to alignment boundary.
539 Offset = (Offset + Align - 1) / Align * Align;
541 DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
543 // Resolve offsets for objects in the local block.
544 for (unsigned i = 0, e = MFI->getLocalFrameObjectCount(); i != e; ++i) {
545 std::pair<int, int64_t> Entry = MFI->getLocalFrameObjectMap(i);
546 int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
547 DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" <<
549 MFI->setObjectOffset(Entry.first, FIOffset);
551 // Allocate the local block
552 Offset += MFI->getLocalFrameSize();
554 MaxAlign = std::max(Align, MaxAlign);
557 // Make sure that the stack protector comes before the local variables on the
559 SmallSet<int, 16> ProtectedObjs;
560 if (MFI->getStackProtectorIndex() >= 0) {
561 StackObjSet LargeArrayObjs;
562 StackObjSet SmallArrayObjs;
563 StackObjSet AddrOfObjs;
565 AdjustStackOffset(MFI, MFI->getStackProtectorIndex(), StackGrowsDown,
568 // Assign large stack objects first.
569 for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
570 if (MFI->isObjectPreAllocated(i) &&
571 MFI->getUseLocalStackAllocationBlock())
573 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
575 if (RS && RS->isScavengingFrameIndex((int)i))
577 if (MFI->isDeadObjectIndex(i))
579 if (MFI->getStackProtectorIndex() == (int)i)
582 switch (SP->getSSPLayout(MFI->getObjectAllocation(i))) {
583 case StackProtector::SSPLK_None:
585 case StackProtector::SSPLK_SmallArray:
586 SmallArrayObjs.insert(i);
588 case StackProtector::SSPLK_AddrOf:
589 AddrOfObjs.insert(i);
591 case StackProtector::SSPLK_LargeArray:
592 LargeArrayObjs.insert(i);
595 llvm_unreachable("Unexpected SSPLayoutKind.");
598 AssignProtectedObjSet(LargeArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
600 AssignProtectedObjSet(SmallArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
602 AssignProtectedObjSet(AddrOfObjs, ProtectedObjs, MFI, StackGrowsDown,
606 // Then assign frame offsets to stack objects that are not used to spill
607 // callee saved registers.
608 for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
609 if (MFI->isObjectPreAllocated(i) &&
610 MFI->getUseLocalStackAllocationBlock())
612 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
614 if (RS && RS->isScavengingFrameIndex((int)i))
616 if (MFI->isDeadObjectIndex(i))
618 if (MFI->getStackProtectorIndex() == (int)i)
620 if (ProtectedObjs.count(i))
623 AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
626 // Make sure the special register scavenging spill slot is closest to the
628 if (RS && !EarlyScavengingSlots) {
629 SmallVector<int, 2> SFIs;
630 RS->getScavengingFrameIndices(SFIs);
631 for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
632 IE = SFIs.end(); I != IE; ++I)
633 AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign);
636 if (!TFI.targetHandlesStackFrameRounding()) {
637 // If we have reserved argument space for call sites in the function
638 // immediately on entry to the current function, count it as part of the
639 // overall stack size.
640 if (MFI->adjustsStack() && TFI.hasReservedCallFrame(Fn))
641 Offset += MFI->getMaxCallFrameSize();
643 // Round up the size to a multiple of the alignment. If the function has
644 // any calls or alloca's, align to the target's StackAlignment value to
645 // ensure that the callee's frame or the alloca data is suitably aligned;
646 // otherwise, for leaf functions, align to the TransientStackAlignment
649 if (MFI->adjustsStack() || MFI->hasVarSizedObjects() ||
650 (RegInfo->needsStackRealignment(Fn) && MFI->getObjectIndexEnd() != 0))
651 StackAlign = TFI.getStackAlignment();
653 StackAlign = TFI.getTransientStackAlignment();
655 // If the frame pointer is eliminated, all frame offsets will be relative to
656 // SP not FP. Align to MaxAlign so this works.
657 StackAlign = std::max(StackAlign, MaxAlign);
658 unsigned AlignMask = StackAlign - 1;
659 Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
662 // Update frame info to pretend that this is part of the stack...
663 int64_t StackSize = Offset - LocalAreaOffset;
664 MFI->setStackSize(StackSize);
665 NumBytesStackSpace += StackSize;
668 /// insertPrologEpilogCode - Scan the function for modified callee saved
669 /// registers, insert spill code for these callee saved registers, then add
670 /// prolog and epilog code to the function.
672 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
673 const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
675 // Add prologue to the function...
676 TFI.emitPrologue(Fn);
678 // Add epilogue to restore the callee-save registers in each exiting block
679 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
680 // If last instruction is a return instruction, add an epilogue
681 if (!I->empty() && I->back().isReturn())
682 TFI.emitEpilogue(Fn, *I);
685 // Emit additional code that is required to support segmented stacks, if
686 // we've been asked for it. This, when linked with a runtime with support
687 // for segmented stacks (libgcc is one), will result in allocating stack
688 // space in small chunks instead of one large contiguous block.
689 if (Fn.shouldSplitStack())
690 TFI.adjustForSegmentedStacks(Fn);
692 // Emit additional code that is required to explicitly handle the stack in
693 // HiPE native code (if needed) when loaded in the Erlang/OTP runtime. The
694 // approach is rather similar to that of Segmented Stacks, but it uses a
695 // different conditional check and another BIF for allocating more stack
697 if (Fn.getFunction()->getCallingConv() == CallingConv::HiPE)
698 TFI.adjustForHiPEPrologue(Fn);
701 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
702 /// register references and actual offsets.
704 void PEI::replaceFrameIndices(MachineFunction &Fn) {
705 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
707 // Store SPAdj at exit of a basic block.
708 SmallVector<int, 8> SPState;
709 SPState.resize(Fn.getNumBlockIDs());
710 SmallPtrSet<MachineBasicBlock*, 8> Reachable;
712 // Iterate over the reachable blocks in DFS order.
713 for (df_ext_iterator<MachineFunction*, SmallPtrSet<MachineBasicBlock*, 8> >
714 DFI = df_ext_begin(&Fn, Reachable), DFE = df_ext_end(&Fn, Reachable);
717 // Check the exit state of the DFS stack predecessor.
718 if (DFI.getPathLength() >= 2) {
719 MachineBasicBlock *StackPred = DFI.getPath(DFI.getPathLength() - 2);
720 assert(Reachable.count(StackPred) &&
721 "DFS stack predecessor is already visited.\n");
722 SPAdj = SPState[StackPred->getNumber()];
724 MachineBasicBlock *BB = *DFI;
725 replaceFrameIndices(BB, Fn, SPAdj);
726 SPState[BB->getNumber()] = SPAdj;
729 // Handle the unreachable blocks.
730 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
731 if (Reachable.count(BB))
732 // Already handled in DFS traversal.
735 replaceFrameIndices(BB, Fn, SPAdj);
739 void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &Fn,
741 const TargetMachine &TM = Fn.getTarget();
742 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
743 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
744 const TargetRegisterInfo &TRI = *TM.getRegisterInfo();
745 const TargetFrameLowering *TFI = TM.getFrameLowering();
746 bool StackGrowsDown =
747 TFI->getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
748 int FrameSetupOpcode = TII.getCallFrameSetupOpcode();
749 int FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
751 if (RS && !FrameIndexVirtualScavenging) RS->enterBasicBlock(BB);
753 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
755 if (I->getOpcode() == FrameSetupOpcode ||
756 I->getOpcode() == FrameDestroyOpcode) {
757 // Remember how much SP has been adjusted to create the call
759 int Size = I->getOperand(0).getImm();
761 if ((!StackGrowsDown && I->getOpcode() == FrameSetupOpcode) ||
762 (StackGrowsDown && I->getOpcode() == FrameDestroyOpcode))
767 MachineBasicBlock::iterator PrevI = BB->end();
768 if (I != BB->begin()) PrevI = std::prev(I);
769 TFI->eliminateCallFramePseudoInstr(Fn, *BB, I);
771 // Visit the instructions created by eliminateCallFramePseudoInstr().
772 if (PrevI == BB->end())
773 I = BB->begin(); // The replaced instr was the first in the block.
775 I = std::next(PrevI);
779 MachineInstr *MI = I;
781 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
782 if (!MI->getOperand(i).isFI())
785 // Frame indicies in debug values are encoded in a target independent
786 // way with simply the frame index and offset rather than any
787 // target-specific addressing mode.
788 if (MI->isDebugValue()) {
789 assert(i == 0 && "Frame indicies can only appear as the first "
790 "operand of a DBG_VALUE machine instruction");
792 MachineOperand &Offset = MI->getOperand(1);
793 Offset.setImm(Offset.getImm() +
794 TFI->getFrameIndexReference(
795 Fn, MI->getOperand(0).getIndex(), Reg));
796 MI->getOperand(0).ChangeToRegister(Reg, false /*isDef*/);
800 // Some instructions (e.g. inline asm instructions) can have
801 // multiple frame indices and/or cause eliminateFrameIndex
802 // to insert more than one instruction. We need the register
803 // scavenger to go through all of these instructions so that
804 // it can update its register information. We keep the
805 // iterator at the point before insertion so that we can
806 // revisit them in full.
807 bool AtBeginning = (I == BB->begin());
808 if (!AtBeginning) --I;
810 // If this instruction has a FrameIndex operand, we need to
811 // use that target machine register info object to eliminate
813 TRI.eliminateFrameIndex(MI, SPAdj, i,
814 FrameIndexVirtualScavenging ? nullptr : RS);
816 // Reset the iterator if we were at the beginning of the BB.
826 if (DoIncr && I != BB->end()) ++I;
828 // Update register states.
829 if (RS && !FrameIndexVirtualScavenging && MI) RS->forward(MI);
833 /// scavengeFrameVirtualRegs - Replace all frame index virtual registers
834 /// with physical registers. Use the register scavenger to find an
835 /// appropriate register to use.
837 /// FIXME: Iterating over the instruction stream is unnecessary. We can simply
838 /// iterate over the vreg use list, which at this point only contains machine
839 /// operands for which eliminateFrameIndex need a new scratch reg.
840 void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
841 // Run through the instructions and find any virtual registers.
842 for (MachineFunction::iterator BB = Fn.begin(),
843 E = Fn.end(); BB != E; ++BB) {
844 RS->enterBasicBlock(BB);
848 // The instruction stream may change in the loop, so check BB->end()
850 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
851 // We might end up here again with a NULL iterator if we scavenged a
852 // register for which we inserted spill code for definition by what was
853 // originally the first instruction in BB.
854 if (I == MachineBasicBlock::iterator(nullptr))
857 MachineInstr *MI = I;
858 MachineBasicBlock::iterator J = std::next(I);
859 MachineBasicBlock::iterator P =
860 I == BB->begin() ? MachineBasicBlock::iterator(nullptr)
863 // RS should process this instruction before we might scavenge at this
864 // location. This is because we might be replacing a virtual register
865 // defined by this instruction, and if so, registers killed by this
866 // instruction are available, and defined registers are not.
869 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
870 if (MI->getOperand(i).isReg()) {
871 MachineOperand &MO = MI->getOperand(i);
872 unsigned Reg = MO.getReg();
875 if (!TargetRegisterInfo::isVirtualRegister(Reg))
878 // When we first encounter a new virtual register, it
879 // must be a definition.
880 assert(MI->getOperand(i).isDef() &&
881 "frame index virtual missing def!");
882 // Scavenge a new scratch register
883 const TargetRegisterClass *RC = Fn.getRegInfo().getRegClass(Reg);
884 unsigned ScratchReg = RS->scavengeRegister(RC, J, SPAdj);
888 // Replace this reference to the virtual register with the
890 assert (ScratchReg && "Missing scratch register!");
891 Fn.getRegInfo().replaceRegWith(Reg, ScratchReg);
893 // Because this instruction was processed by the RS before this
894 // register was allocated, make sure that the RS now records the
895 // register as being used.
896 RS->setUsed(ScratchReg);
900 // If the scavenger needed to use one of its spill slots, the
901 // spill code will have been inserted in between I and J. This is a
902 // problem because we need the spill code before I: Move I to just
904 if (I != std::prev(J)) {
905 BB->splice(J, BB, I);
907 // Before we move I, we need to prepare the RS to visit I again.
908 // Specifically, RS will assert if it sees uses of registers that
909 // it believes are undefined. Because we have already processed
910 // register kills in I, when it visits I again, it will believe that
911 // those registers are undefined. To avoid this situation, unprocess
912 // the instruction I.
913 assert(RS->getCurrentPosition() == I &&
914 "The register scavenger has an unexpected position");