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 // This pass provides an optional shrink wrapping variant of prolog/epilog
18 // insertion, enabled via --shrink-wrap. See ShrinkWrapping.cpp.
20 //===----------------------------------------------------------------------===//
22 #include "PrologEpilogInserter.h"
23 #include "llvm/CodeGen/MachineDominators.h"
24 #include "llvm/CodeGen/MachineLoopInfo.h"
25 #include "llvm/CodeGen/MachineInstr.h"
26 #include "llvm/CodeGen/MachineFrameInfo.h"
27 #include "llvm/CodeGen/MachineRegisterInfo.h"
28 #include "llvm/CodeGen/RegisterScavenging.h"
29 #include "llvm/Target/TargetMachine.h"
30 #include "llvm/Target/TargetRegisterInfo.h"
31 #include "llvm/Target/TargetFrameInfo.h"
32 #include "llvm/Target/TargetInstrInfo.h"
33 #include "llvm/Support/CommandLine.h"
34 #include "llvm/Support/Compiler.h"
35 #include "llvm/ADT/IndexedMap.h"
36 #include "llvm/ADT/SmallSet.h"
37 #include "llvm/ADT/STLExtras.h"
44 INITIALIZE_PASS(PEI, "prologepilog",
45 "Prologue/Epilogue Insertion", false, false);
47 /// createPrologEpilogCodeInserter - This function returns a pass that inserts
48 /// prolog and epilog code, and eliminates abstract frame references.
50 FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
52 /// runOnMachineFunction - Insert prolog/epilog code and replace abstract
53 /// frame indexes with appropriate references.
55 bool PEI::runOnMachineFunction(MachineFunction &Fn) {
56 const Function* F = Fn.getFunction();
57 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
58 RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : NULL;
59 FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(Fn);
60 FrameConstantRegMap.clear();
62 // Calculate the MaxCallFrameSize and AdjustsStack variables for the
63 // function's frame information. Also eliminates call frame pseudo
65 calculateCallsInformation(Fn);
67 // Allow the target machine to make some adjustments to the function
68 // e.g. UsedPhysRegs before calculateCalleeSavedRegisters.
69 TRI->processFunctionBeforeCalleeSavedScan(Fn, RS);
71 // Scan the function for modified callee saved registers and insert spill code
72 // for any callee saved registers that are modified.
73 calculateCalleeSavedRegisters(Fn);
75 // Determine placement of CSR spill/restore code:
76 // - With shrink wrapping, place spills and restores to tightly
77 // enclose regions in the Machine CFG of the function where
79 // - Without shink wrapping (default), place all spills in the
80 // entry block, all restores in return blocks.
81 placeCSRSpillsAndRestores(Fn);
83 // Add the code to save and restore the callee saved registers
84 if (!F->hasFnAttr(Attribute::Naked))
85 insertCSRSpillsAndRestores(Fn);
87 // Allow the target machine to make final modifications to the function
88 // before the frame layout is finalized.
89 TRI->processFunctionBeforeFrameFinalized(Fn);
91 // Calculate actual frame offsets for all abstract stack objects...
92 calculateFrameObjectOffsets(Fn);
94 // Add prolog and epilog code to the function. This function is required
95 // to align the stack frame as necessary for any stack variables or
96 // called functions. Because of this, calculateCalleeSavedRegisters()
97 // must be called before this function in order to set the AdjustsStack
98 // and MaxCallFrameSize variables.
99 if (!F->hasFnAttr(Attribute::Naked))
100 insertPrologEpilogCode(Fn);
102 // Replace all MO_FrameIndex operands with physical register references
103 // and actual offsets.
105 replaceFrameIndices(Fn);
107 // If register scavenging is needed, as we've enabled doing it as a
108 // post-pass, scavenge the virtual registers that frame index elimiation
110 if (TRI->requiresRegisterScavenging(Fn) && FrameIndexVirtualScavenging)
111 scavengeFrameVirtualRegs(Fn);
119 void PEI::getAnalysisUsage(AnalysisUsage &AU) const {
120 AU.setPreservesCFG();
121 if (ShrinkWrapping || ShrinkWrapFunc != "") {
122 AU.addRequired<MachineLoopInfo>();
123 AU.addRequired<MachineDominatorTree>();
125 AU.addPreserved<MachineLoopInfo>();
126 AU.addPreserved<MachineDominatorTree>();
127 MachineFunctionPass::getAnalysisUsage(AU);
131 /// calculateCallsInformation - Calculate the MaxCallFrameSize and AdjustsStack
132 /// variables for the function's frame information and eliminate call frame
133 /// pseudo instructions.
134 void PEI::calculateCallsInformation(MachineFunction &Fn) {
135 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
136 MachineFrameInfo *MFI = Fn.getFrameInfo();
138 unsigned MaxCallFrameSize = 0;
139 bool AdjustsStack = MFI->adjustsStack();
141 // Get the function call frame set-up and tear-down instruction opcode
142 int FrameSetupOpcode = RegInfo->getCallFrameSetupOpcode();
143 int FrameDestroyOpcode = RegInfo->getCallFrameDestroyOpcode();
145 // Early exit for targets which have no call frame setup/destroy pseudo
147 if (FrameSetupOpcode == -1 && FrameDestroyOpcode == -1)
150 std::vector<MachineBasicBlock::iterator> FrameSDOps;
151 for (MachineFunction::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB)
152 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
153 if (I->getOpcode() == FrameSetupOpcode ||
154 I->getOpcode() == FrameDestroyOpcode) {
155 assert(I->getNumOperands() >= 1 && "Call Frame Setup/Destroy Pseudo"
156 " instructions should have a single immediate argument!");
157 unsigned Size = I->getOperand(0).getImm();
158 if (Size > MaxCallFrameSize) MaxCallFrameSize = Size;
160 FrameSDOps.push_back(I);
161 } else if (I->isInlineAsm()) {
162 // Some inline asm's need a stack frame, as indicated by operand 1.
163 if (I->getOperand(1).getImm())
167 MFI->setAdjustsStack(AdjustsStack);
168 MFI->setMaxCallFrameSize(MaxCallFrameSize);
170 for (std::vector<MachineBasicBlock::iterator>::iterator
171 i = FrameSDOps.begin(), e = FrameSDOps.end(); i != e; ++i) {
172 MachineBasicBlock::iterator I = *i;
174 // If call frames are not being included as part of the stack frame, and
175 // the target doesn't indicate otherwise, remove the call frame pseudos
176 // here. The sub/add sp instruction pairs are still inserted, but we don't
177 // need to track the SP adjustment for frame index elimination.
178 if (RegInfo->canSimplifyCallFramePseudos(Fn))
179 RegInfo->eliminateCallFramePseudoInstr(Fn, *I->getParent(), I);
184 /// calculateCalleeSavedRegisters - Scan the function for modified callee saved
186 void PEI::calculateCalleeSavedRegisters(MachineFunction &Fn) {
187 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
188 const TargetFrameInfo *TFI = Fn.getTarget().getFrameInfo();
189 MachineFrameInfo *MFI = Fn.getFrameInfo();
191 // Get the callee saved register list...
192 const unsigned *CSRegs = RegInfo->getCalleeSavedRegs(&Fn);
194 // These are used to keep track the callee-save area. Initialize them.
195 MinCSFrameIndex = INT_MAX;
198 // Early exit for targets which have no callee saved registers.
199 if (CSRegs == 0 || CSRegs[0] == 0)
202 // In Naked functions we aren't going to save any registers.
203 if (Fn.getFunction()->hasFnAttr(Attribute::Naked))
206 std::vector<CalleeSavedInfo> CSI;
207 for (unsigned i = 0; CSRegs[i]; ++i) {
208 unsigned Reg = CSRegs[i];
209 if (Fn.getRegInfo().isPhysRegUsed(Reg)) {
210 // If the reg is modified, save it!
211 CSI.push_back(CalleeSavedInfo(Reg));
213 for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
214 *AliasSet; ++AliasSet) { // Check alias registers too.
215 if (Fn.getRegInfo().isPhysRegUsed(*AliasSet)) {
216 CSI.push_back(CalleeSavedInfo(Reg));
224 return; // Early exit if no callee saved registers are modified!
226 unsigned NumFixedSpillSlots;
227 const TargetFrameInfo::SpillSlot *FixedSpillSlots =
228 TFI->getCalleeSavedSpillSlots(NumFixedSpillSlots);
230 // Now that we know which registers need to be saved and restored, allocate
231 // stack slots for them.
232 for (std::vector<CalleeSavedInfo>::iterator
233 I = CSI.begin(), E = CSI.end(); I != E; ++I) {
234 unsigned Reg = I->getReg();
235 const TargetRegisterClass *RC = RegInfo->getMinimalPhysRegClass(Reg);
238 if (RegInfo->hasReservedSpillSlot(Fn, Reg, FrameIdx)) {
239 I->setFrameIdx(FrameIdx);
243 // Check to see if this physreg must be spilled to a particular stack slot
245 const TargetFrameInfo::SpillSlot *FixedSlot = FixedSpillSlots;
246 while (FixedSlot != FixedSpillSlots+NumFixedSpillSlots &&
247 FixedSlot->Reg != Reg)
250 if (FixedSlot == FixedSpillSlots + NumFixedSpillSlots) {
251 // Nope, just spill it anywhere convenient.
252 unsigned Align = RC->getAlignment();
253 unsigned StackAlign = TFI->getStackAlignment();
255 // We may not be able to satisfy the desired alignment specification of
256 // the TargetRegisterClass if the stack alignment is smaller. Use the
258 Align = std::min(Align, StackAlign);
259 FrameIdx = MFI->CreateStackObject(RC->getSize(), Align, true);
260 if ((unsigned)FrameIdx < MinCSFrameIndex) MinCSFrameIndex = FrameIdx;
261 if ((unsigned)FrameIdx > MaxCSFrameIndex) MaxCSFrameIndex = FrameIdx;
263 // Spill it to the stack where we must.
264 FrameIdx = MFI->CreateFixedObject(RC->getSize(), FixedSlot->Offset, true);
267 I->setFrameIdx(FrameIdx);
270 MFI->setCalleeSavedInfo(CSI);
273 /// insertCSRSpillsAndRestores - Insert spill and restore code for
274 /// callee saved registers used in the function, handling shrink wrapping.
276 void PEI::insertCSRSpillsAndRestores(MachineFunction &Fn) {
277 // Get callee saved register information.
278 MachineFrameInfo *MFI = Fn.getFrameInfo();
279 const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo();
281 MFI->setCalleeSavedInfoValid(true);
283 // Early exit if no callee saved registers are modified!
287 const TargetInstrInfo &TII = *Fn.getTarget().getInstrInfo();
288 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
289 MachineBasicBlock::iterator I;
291 if (! ShrinkWrapThisFunction) {
292 // Spill using target interface.
293 I = EntryBlock->begin();
294 if (!TII.spillCalleeSavedRegisters(*EntryBlock, I, CSI, TRI)) {
295 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
296 // Add the callee-saved register as live-in.
297 // It's killed at the spill.
298 EntryBlock->addLiveIn(CSI[i].getReg());
300 // Insert the spill to the stack frame.
301 unsigned Reg = CSI[i].getReg();
302 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
303 TII.storeRegToStackSlot(*EntryBlock, I, Reg, true,
304 CSI[i].getFrameIdx(), RC, TRI);
308 // Restore using target interface.
309 for (unsigned ri = 0, re = ReturnBlocks.size(); ri != re; ++ri) {
310 MachineBasicBlock* MBB = ReturnBlocks[ri];
313 // Skip over all terminator instructions, which are part of the return
315 MachineBasicBlock::iterator I2 = I;
316 while (I2 != MBB->begin() && (--I2)->getDesc().isTerminator())
319 bool AtStart = I == MBB->begin();
320 MachineBasicBlock::iterator BeforeI = I;
324 // Restore all registers immediately before the return and any
325 // terminators that preceed it.
326 if (!TII.restoreCalleeSavedRegisters(*MBB, I, CSI, TRI)) {
327 for (unsigned i = 0, e = CSI.size(); i != e; ++i) {
328 unsigned Reg = CSI[i].getReg();
329 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
330 TII.loadRegFromStackSlot(*MBB, I, Reg,
331 CSI[i].getFrameIdx(),
333 assert(I != MBB->begin() &&
334 "loadRegFromStackSlot didn't insert any code!");
335 // Insert in reverse order. loadRegFromStackSlot can insert
336 // multiple instructions.
350 std::vector<CalleeSavedInfo> blockCSI;
351 for (CSRegBlockMap::iterator BI = CSRSave.begin(),
352 BE = CSRSave.end(); BI != BE; ++BI) {
353 MachineBasicBlock* MBB = BI->first;
354 CSRegSet save = BI->second;
360 for (CSRegSet::iterator RI = save.begin(),
361 RE = save.end(); RI != RE; ++RI) {
362 blockCSI.push_back(CSI[*RI]);
364 assert(blockCSI.size() > 0 &&
365 "Could not collect callee saved register info");
369 // When shrink wrapping, use stack slot stores/loads.
370 for (unsigned i = 0, e = blockCSI.size(); i != e; ++i) {
371 // Add the callee-saved register as live-in.
372 // It's killed at the spill.
373 MBB->addLiveIn(blockCSI[i].getReg());
375 // Insert the spill to the stack frame.
376 unsigned Reg = blockCSI[i].getReg();
377 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
378 TII.storeRegToStackSlot(*MBB, I, Reg,
380 blockCSI[i].getFrameIdx(),
385 for (CSRegBlockMap::iterator BI = CSRRestore.begin(),
386 BE = CSRRestore.end(); BI != BE; ++BI) {
387 MachineBasicBlock* MBB = BI->first;
388 CSRegSet restore = BI->second;
394 for (CSRegSet::iterator RI = restore.begin(),
395 RE = restore.end(); RI != RE; ++RI) {
396 blockCSI.push_back(CSI[*RI]);
398 assert(blockCSI.size() > 0 &&
399 "Could not find callee saved register info");
401 // If MBB is empty and needs restores, insert at the _beginning_.
408 // Skip over all terminator instructions, which are part of the
410 if (! I->getDesc().isTerminator()) {
413 MachineBasicBlock::iterator I2 = I;
414 while (I2 != MBB->begin() && (--I2)->getDesc().isTerminator())
419 bool AtStart = I == MBB->begin();
420 MachineBasicBlock::iterator BeforeI = I;
424 // Restore all registers immediately before the return and any
425 // terminators that preceed it.
426 for (unsigned i = 0, e = blockCSI.size(); i != e; ++i) {
427 unsigned Reg = blockCSI[i].getReg();
428 const TargetRegisterClass *RC = TRI->getMinimalPhysRegClass(Reg);
429 TII.loadRegFromStackSlot(*MBB, I, Reg,
430 blockCSI[i].getFrameIdx(),
432 assert(I != MBB->begin() &&
433 "loadRegFromStackSlot didn't insert any code!");
434 // Insert in reverse order. loadRegFromStackSlot can insert
435 // multiple instructions.
446 /// AdjustStackOffset - Helper function used to adjust the stack frame offset.
448 AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
449 bool StackGrowsDown, int64_t &Offset,
450 unsigned &MaxAlign) {
451 // If the stack grows down, add the object size to find the lowest address.
453 Offset += MFI->getObjectSize(FrameIdx);
455 unsigned Align = MFI->getObjectAlignment(FrameIdx);
457 // If the alignment of this object is greater than that of the stack, then
458 // increase the stack alignment to match.
459 MaxAlign = std::max(MaxAlign, Align);
461 // Adjust to alignment boundary.
462 Offset = (Offset + Align - 1) / Align * Align;
464 if (StackGrowsDown) {
465 MFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
467 MFI->setObjectOffset(FrameIdx, Offset);
468 Offset += MFI->getObjectSize(FrameIdx);
472 /// calculateFrameObjectOffsets - Calculate actual frame offsets for all of the
473 /// abstract stack objects.
475 void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
476 const TargetFrameInfo &TFI = *Fn.getTarget().getFrameInfo();
478 bool StackGrowsDown =
479 TFI.getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
481 // Loop over all of the stack objects, assigning sequential addresses...
482 MachineFrameInfo *MFI = Fn.getFrameInfo();
484 // Start at the beginning of the local area.
485 // The Offset is the distance from the stack top in the direction
486 // of stack growth -- so it's always nonnegative.
487 int LocalAreaOffset = TFI.getOffsetOfLocalArea();
489 LocalAreaOffset = -LocalAreaOffset;
490 assert(LocalAreaOffset >= 0
491 && "Local area offset should be in direction of stack growth");
492 int64_t Offset = LocalAreaOffset;
494 // If there are fixed sized objects that are preallocated in the local area,
495 // non-fixed objects can't be allocated right at the start of local area.
496 // We currently don't support filling in holes in between fixed sized
497 // objects, so we adjust 'Offset' to point to the end of last fixed sized
498 // preallocated object.
499 for (int i = MFI->getObjectIndexBegin(); i != 0; ++i) {
501 if (StackGrowsDown) {
502 // The maximum distance from the stack pointer is at lower address of
503 // the object -- which is given by offset. For down growing stack
504 // the offset is negative, so we negate the offset to get the distance.
505 FixedOff = -MFI->getObjectOffset(i);
507 // The maximum distance from the start pointer is at the upper
508 // address of the object.
509 FixedOff = MFI->getObjectOffset(i) + MFI->getObjectSize(i);
511 if (FixedOff > Offset) Offset = FixedOff;
514 // First assign frame offsets to stack objects that are used to spill
515 // callee saved registers.
516 if (StackGrowsDown) {
517 for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
518 // If the stack grows down, we need to add the size to find the lowest
519 // address of the object.
520 Offset += MFI->getObjectSize(i);
522 unsigned Align = MFI->getObjectAlignment(i);
523 // Adjust to alignment boundary
524 Offset = (Offset+Align-1)/Align*Align;
526 MFI->setObjectOffset(i, -Offset); // Set the computed offset
529 int MaxCSFI = MaxCSFrameIndex, MinCSFI = MinCSFrameIndex;
530 for (int i = MaxCSFI; i >= MinCSFI ; --i) {
531 unsigned Align = MFI->getObjectAlignment(i);
532 // Adjust to alignment boundary
533 Offset = (Offset+Align-1)/Align*Align;
535 MFI->setObjectOffset(i, Offset);
536 Offset += MFI->getObjectSize(i);
540 unsigned MaxAlign = MFI->getMaxAlignment();
542 // Make sure the special register scavenging spill slot is closest to the
543 // frame pointer if a frame pointer is required.
544 const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
545 if (RS && RegInfo->hasFP(Fn) && !RegInfo->needsStackRealignment(Fn)) {
546 int SFI = RS->getScavengingFrameIndex();
548 AdjustStackOffset(MFI, SFI, StackGrowsDown, Offset, MaxAlign);
551 // Make sure that the stack protector comes before the local variables on the
553 SmallSet<int, 16> LargeStackObjs;
554 if (MFI->getStackProtectorIndex() >= 0) {
555 AdjustStackOffset(MFI, MFI->getStackProtectorIndex(), StackGrowsDown,
558 // Assign large stack objects first.
559 for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
560 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
562 if (RS && (int)i == RS->getScavengingFrameIndex())
564 if (MFI->isDeadObjectIndex(i))
566 if (MFI->getStackProtectorIndex() == (int)i)
568 if (!MFI->MayNeedStackProtector(i))
571 AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
572 LargeStackObjs.insert(i);
576 // Then assign frame offsets to stack objects that are not used to spill
577 // callee saved registers.
578 for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
579 if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
581 if (RS && (int)i == RS->getScavengingFrameIndex())
583 if (MFI->isDeadObjectIndex(i))
585 if (MFI->getStackProtectorIndex() == (int)i)
587 if (LargeStackObjs.count(i))
590 AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
593 // Make sure the special register scavenging spill slot is closest to the
595 if (RS && (!RegInfo->hasFP(Fn) || RegInfo->needsStackRealignment(Fn))) {
596 int SFI = RS->getScavengingFrameIndex();
598 AdjustStackOffset(MFI, SFI, StackGrowsDown, Offset, MaxAlign);
601 if (!RegInfo->targetHandlesStackFrameRounding()) {
602 // If we have reserved argument space for call sites in the function
603 // immediately on entry to the current function, count it as part of the
604 // overall stack size.
605 if (MFI->adjustsStack() && RegInfo->hasReservedCallFrame(Fn))
606 Offset += MFI->getMaxCallFrameSize();
608 // Round up the size to a multiple of the alignment. If the function has
609 // any calls or alloca's, align to the target's StackAlignment value to
610 // ensure that the callee's frame or the alloca data is suitably aligned;
611 // otherwise, for leaf functions, align to the TransientStackAlignment
614 if (MFI->adjustsStack() || MFI->hasVarSizedObjects() ||
615 (RegInfo->needsStackRealignment(Fn) && MFI->getObjectIndexEnd() != 0))
616 StackAlign = TFI.getStackAlignment();
618 StackAlign = TFI.getTransientStackAlignment();
620 // If the frame pointer is eliminated, all frame offsets will be relative to
621 // SP not FP. Align to MaxAlign so this works.
622 StackAlign = std::max(StackAlign, MaxAlign);
623 unsigned AlignMask = StackAlign - 1;
624 Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
627 // Update frame info to pretend that this is part of the stack...
628 MFI->setStackSize(Offset - LocalAreaOffset);
631 /// insertPrologEpilogCode - Scan the function for modified callee saved
632 /// registers, insert spill code for these callee saved registers, then add
633 /// prolog and epilog code to the function.
635 void PEI::insertPrologEpilogCode(MachineFunction &Fn) {
636 const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
638 // Add prologue to the function...
639 TRI->emitPrologue(Fn);
641 // Add epilogue to restore the callee-save registers in each exiting block
642 for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
643 // If last instruction is a return instruction, add an epilogue
644 if (!I->empty() && I->back().getDesc().isReturn())
645 TRI->emitEpilogue(Fn, *I);
649 /// replaceFrameIndices - Replace all MO_FrameIndex operands with physical
650 /// register references and actual offsets.
652 void PEI::replaceFrameIndices(MachineFunction &Fn) {
653 if (!Fn.getFrameInfo()->hasStackObjects()) return; // Nothing to do?
655 const TargetMachine &TM = Fn.getTarget();
656 assert(TM.getRegisterInfo() && "TM::getRegisterInfo() must be implemented!");
657 const TargetRegisterInfo &TRI = *TM.getRegisterInfo();
658 const TargetFrameInfo *TFI = TM.getFrameInfo();
659 bool StackGrowsDown =
660 TFI->getStackGrowthDirection() == TargetFrameInfo::StackGrowsDown;
661 int FrameSetupOpcode = TRI.getCallFrameSetupOpcode();
662 int FrameDestroyOpcode = TRI.getCallFrameDestroyOpcode();
664 for (MachineFunction::iterator BB = Fn.begin(),
665 E = Fn.end(); BB != E; ++BB) {
667 int SPAdjCount = 0; // frame setup / destroy count.
669 int SPAdj = 0; // SP offset due to call frame setup / destroy.
670 if (RS && !FrameIndexVirtualScavenging) RS->enterBasicBlock(BB);
672 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
674 if (I->getOpcode() == FrameSetupOpcode ||
675 I->getOpcode() == FrameDestroyOpcode) {
677 // Track whether we see even pairs of them
678 SPAdjCount += I->getOpcode() == FrameSetupOpcode ? 1 : -1;
680 // Remember how much SP has been adjusted to create the call
682 int Size = I->getOperand(0).getImm();
684 if ((!StackGrowsDown && I->getOpcode() == FrameSetupOpcode) ||
685 (StackGrowsDown && I->getOpcode() == FrameDestroyOpcode))
690 MachineBasicBlock::iterator PrevI = BB->end();
691 if (I != BB->begin()) PrevI = prior(I);
692 TRI.eliminateCallFramePseudoInstr(Fn, *BB, I);
694 // Visit the instructions created by eliminateCallFramePseudoInstr().
695 if (PrevI == BB->end())
696 I = BB->begin(); // The replaced instr was the first in the block.
698 I = llvm::next(PrevI);
702 MachineInstr *MI = I;
704 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
705 if (MI->getOperand(i).isFI()) {
706 // Some instructions (e.g. inline asm instructions) can have
707 // multiple frame indices and/or cause eliminateFrameIndex
708 // to insert more than one instruction. We need the register
709 // scavenger to go through all of these instructions so that
710 // it can update its register information. We keep the
711 // iterator at the point before insertion so that we can
712 // revisit them in full.
713 bool AtBeginning = (I == BB->begin());
714 if (!AtBeginning) --I;
716 // If this instruction has a FrameIndex operand, we need to
717 // use that target machine register info object to eliminate
719 TargetRegisterInfo::FrameIndexValue Value;
721 TRI.eliminateFrameIndex(MI, SPAdj, &Value,
722 FrameIndexVirtualScavenging ? NULL : RS);
724 assert (FrameIndexVirtualScavenging &&
725 "Not scavenging, but virtual returned from "
726 "eliminateFrameIndex()!");
727 FrameConstantRegMap[VReg] = FrameConstantEntry(Value, SPAdj);
730 // Reset the iterator if we were at the beginning of the BB.
740 if (DoIncr && I != BB->end()) ++I;
742 // Update register states.
743 if (RS && !FrameIndexVirtualScavenging && MI) RS->forward(MI);
746 // If we have evenly matched pairs of frame setup / destroy instructions,
747 // make sure the adjustments come out to zero. If we don't have matched
748 // pairs, we can't be sure the missing bit isn't in another basic block
749 // due to a custom inserter playing tricks, so just asserting SPAdj==0
750 // isn't sufficient. See tMOVCC on Thumb1, for example.
751 assert((SPAdjCount || SPAdj == 0) &&
752 "Unbalanced call frame setup / destroy pairs?");
756 /// findLastUseReg - find the killing use of the specified register within
757 /// the instruciton range. Return the operand number of the kill in Operand.
758 static MachineBasicBlock::iterator
759 findLastUseReg(MachineBasicBlock::iterator I, MachineBasicBlock::iterator ME,
761 // Scan forward to find the last use of this virtual register
762 for (++I; I != ME; ++I) {
763 MachineInstr *MI = I;
764 bool isDefInsn = false;
765 bool isKillInsn = false;
766 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
767 if (MI->getOperand(i).isReg()) {
768 unsigned OpReg = MI->getOperand(i).getReg();
769 if (OpReg == 0 || !TargetRegisterInfo::isVirtualRegister(OpReg))
772 && "overlapping use of scavenged index register!");
773 // If this is the killing use, we have a candidate.
774 if (MI->getOperand(i).isKill())
776 else if (MI->getOperand(i).isDef())
779 if (isKillInsn && !isDefInsn)
782 // If we hit the end of the basic block, there was no kill of
783 // the virtual register, which is wrong.
784 assert (0 && "scavenged index register never killed!");
788 /// scavengeFrameVirtualRegs - Replace all frame index virtual registers
789 /// with physical registers. Use the register scavenger to find an
790 /// appropriate register to use.
791 void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
792 // Run through the instructions and find any virtual registers.
793 for (MachineFunction::iterator BB = Fn.begin(),
794 E = Fn.end(); BB != E; ++BB) {
795 RS->enterBasicBlock(BB);
797 // FIXME: The logic flow in this function is still too convoluted.
798 // It needs a cleanup refactoring. Do that in preparation for tracking
799 // more than one scratch register value and using ranges to find
800 // available scratch registers.
801 unsigned CurrentVirtReg = 0;
802 unsigned CurrentScratchReg = 0;
803 bool havePrevValue = false;
804 TargetRegisterInfo::FrameIndexValue PrevValue(0,0);
805 TargetRegisterInfo::FrameIndexValue Value(0,0);
806 MachineInstr *PrevLastUseMI = NULL;
807 unsigned PrevLastUseOp = 0;
808 bool trackingCurrentValue = false;
811 // The instruction stream may change in the loop, so check BB->end()
813 for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ) {
814 MachineInstr *MI = I;
815 bool isDefInsn = false;
816 bool isKillInsn = false;
817 bool clobbersScratchReg = false;
819 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
820 if (MI->getOperand(i).isReg()) {
821 MachineOperand &MO = MI->getOperand(i);
822 unsigned Reg = MO.getReg();
825 if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
826 // If we have a previous scratch reg, check and see if anything
827 // here kills whatever value is in there.
828 if (Reg == CurrentScratchReg) {
830 // Two-address operands implicitly kill
831 if (MO.isKill() || MI->isRegTiedToDefOperand(i))
832 clobbersScratchReg = true;
835 clobbersScratchReg = true;
840 // If this is a def, remember that this insn defines the value.
841 // This lets us properly consider insns which re-use the scratch
842 // register, such as r2 = sub r2, #imm, in the middle of the
847 // Have we already allocated a scratch register for this virtual?
848 if (Reg != CurrentVirtReg) {
849 // When we first encounter a new virtual register, it
850 // must be a definition.
851 assert(MI->getOperand(i).isDef() &&
852 "frame index virtual missing def!");
853 // We can't have nested virtual register live ranges because
854 // there's only a guarantee of one scavenged register at a time.
855 assert (CurrentVirtReg == 0 &&
856 "overlapping frame index virtual registers!");
858 // If the target gave us information about what's in the register,
859 // we can use that to re-use scratch regs.
860 DenseMap<unsigned, FrameConstantEntry>::iterator Entry =
861 FrameConstantRegMap.find(Reg);
862 trackingCurrentValue = Entry != FrameConstantRegMap.end();
863 if (trackingCurrentValue) {
864 SPAdj = (*Entry).second.second;
865 Value = (*Entry).second.first;
872 // If the scratch register from the last allocation is still
873 // available, see if the value matches. If it does, just re-use it.
874 if (trackingCurrentValue && havePrevValue && PrevValue == Value) {
875 // FIXME: This assumes that the instructions in the live range
876 // for the virtual register are exclusively for the purpose
877 // of populating the value in the register. That's reasonable
878 // for these frame index registers, but it's still a very, very
879 // strong assumption. rdar://7322732. Better would be to
880 // explicitly check each instruction in the range for references
881 // to the virtual register. Only delete those insns that
882 // touch the virtual register.
884 // Find the last use of the new virtual register. Remove all
885 // instruction between here and there, and update the current
886 // instruction to reference the last use insn instead.
887 MachineBasicBlock::iterator LastUseMI =
888 findLastUseReg(I, BB->end(), Reg);
890 // Remove all instructions up 'til the last use, since they're
891 // just calculating the value we already have.
892 BB->erase(I, LastUseMI);
895 // Extend the live range of the scratch register
896 PrevLastUseMI->getOperand(PrevLastUseOp).setIsKill(false);
897 RS->setUsed(CurrentScratchReg);
898 CurrentVirtReg = Reg;
900 // We deleted the instruction we were scanning the operands of.
901 // Jump back to the instruction iterator loop. Don't increment
902 // past this instruction since we updated the iterator already.
907 // Scavenge a new scratch register
908 CurrentVirtReg = Reg;
909 const TargetRegisterClass *RC = Fn.getRegInfo().getRegClass(Reg);
910 CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj);
913 // replace this reference to the virtual register with the
915 assert (CurrentScratchReg && "Missing scratch register!");
916 MI->getOperand(i).setReg(CurrentScratchReg);
918 if (MI->getOperand(i).isKill()) {
925 // If this is the last use of the scratch, stop tracking it. The
926 // last use will be a kill operand in an instruction that does
927 // not also define the scratch register.
928 if (isKillInsn && !isDefInsn) {
930 havePrevValue = trackingCurrentValue;
932 // Similarly, notice if instruction clobbered the value in the
933 // register we're tracking for possible later reuse. This is noted
934 // above, but enforced here since the value is still live while we
935 // process the rest of the operands of the instruction.
936 if (clobbersScratchReg) {
937 havePrevValue = false;
938 CurrentScratchReg = 0;