1 //===-- BranchFolding.cpp - Fold machine code branch instructions ---------===//
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 forwards branches to unconditional branches to make them branch
11 // directly to the target block. This pass often results in dead MBB's, which
14 // Note that this pass must be run after register allocation, it cannot handle
17 //===----------------------------------------------------------------------===//
19 #define DEBUG_TYPE "branchfolding"
20 #include "BranchFolding.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/ADT/SmallSet.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/CodeGen/MachineFunctionPass.h"
25 #include "llvm/CodeGen/MachineJumpTableInfo.h"
26 #include "llvm/CodeGen/MachineModuleInfo.h"
27 #include "llvm/CodeGen/MachineRegisterInfo.h"
28 #include "llvm/CodeGen/Passes.h"
29 #include "llvm/CodeGen/RegisterScavenging.h"
30 #include "llvm/IR/Function.h"
31 #include "llvm/Support/CommandLine.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include "llvm/Support/raw_ostream.h"
35 #include "llvm/Target/TargetInstrInfo.h"
36 #include "llvm/Target/TargetMachine.h"
37 #include "llvm/Target/TargetRegisterInfo.h"
41 STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
42 STATISTIC(NumBranchOpts, "Number of branches optimized");
43 STATISTIC(NumTailMerge , "Number of block tails merged");
44 STATISTIC(NumHoist , "Number of times common instructions are hoisted");
46 static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
47 cl::init(cl::BOU_UNSET), cl::Hidden);
49 // Throttle for huge numbers of predecessors (compile speed problems)
50 static cl::opt<unsigned>
51 TailMergeThreshold("tail-merge-threshold",
52 cl::desc("Max number of predecessors to consider tail merging"),
53 cl::init(150), cl::Hidden);
55 // Heuristic for tail merging (and, inversely, tail duplication).
56 // TODO: This should be replaced with a target query.
57 static cl::opt<unsigned>
58 TailMergeSize("tail-merge-size",
59 cl::desc("Min number of instructions to consider tail merging"),
60 cl::init(3), cl::Hidden);
63 /// BranchFolderPass - Wrap branch folder in a machine function pass.
64 class BranchFolderPass : public MachineFunctionPass {
67 explicit BranchFolderPass(): MachineFunctionPass(ID) {}
69 virtual bool runOnMachineFunction(MachineFunction &MF);
71 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
72 AU.addRequired<TargetPassConfig>();
73 MachineFunctionPass::getAnalysisUsage(AU);
78 char BranchFolderPass::ID = 0;
79 char &llvm::BranchFolderPassID = BranchFolderPass::ID;
81 INITIALIZE_PASS(BranchFolderPass, "branch-folder",
82 "Control Flow Optimizer", false, false)
84 bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) {
85 TargetPassConfig *PassConfig = &getAnalysis<TargetPassConfig>();
86 BranchFolder Folder(PassConfig->getEnableTailMerge(), /*CommonHoist=*/true);
87 return Folder.OptimizeFunction(MF,
88 MF.getTarget().getInstrInfo(),
89 MF.getTarget().getRegisterInfo(),
90 getAnalysisIfAvailable<MachineModuleInfo>());
94 BranchFolder::BranchFolder(bool defaultEnableTailMerge, bool CommonHoist) {
95 switch (FlagEnableTailMerge) {
96 case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break;
97 case cl::BOU_TRUE: EnableTailMerge = true; break;
98 case cl::BOU_FALSE: EnableTailMerge = false; break;
101 EnableHoistCommonCode = CommonHoist;
104 /// RemoveDeadBlock - Remove the specified dead machine basic block from the
105 /// function, updating the CFG.
106 void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) {
107 assert(MBB->pred_empty() && "MBB must be dead!");
108 DEBUG(dbgs() << "\nRemoving MBB: " << *MBB);
110 MachineFunction *MF = MBB->getParent();
111 // drop all successors.
112 while (!MBB->succ_empty())
113 MBB->removeSuccessor(MBB->succ_end()-1);
115 // Avoid matching if this pointer gets reused.
116 TriedMerging.erase(MBB);
122 /// OptimizeImpDefsBlock - If a basic block is just a bunch of implicit_def
123 /// followed by terminators, and if the implicitly defined registers are not
124 /// used by the terminators, remove those implicit_def's. e.g.
126 /// r0 = implicit_def
127 /// r1 = implicit_def
129 /// This block can be optimized away later if the implicit instructions are
131 bool BranchFolder::OptimizeImpDefsBlock(MachineBasicBlock *MBB) {
132 SmallSet<unsigned, 4> ImpDefRegs;
133 MachineBasicBlock::iterator I = MBB->begin();
134 while (I != MBB->end()) {
135 if (!I->isImplicitDef())
137 unsigned Reg = I->getOperand(0).getReg();
138 ImpDefRegs.insert(Reg);
139 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
140 ImpDefRegs.insert(*SubRegs);
143 if (ImpDefRegs.empty())
146 MachineBasicBlock::iterator FirstTerm = I;
147 while (I != MBB->end()) {
148 if (!TII->isUnpredicatedTerminator(I))
150 // See if it uses any of the implicitly defined registers.
151 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
152 MachineOperand &MO = I->getOperand(i);
153 if (!MO.isReg() || !MO.isUse())
155 unsigned Reg = MO.getReg();
156 if (ImpDefRegs.count(Reg))
163 while (I != FirstTerm) {
164 MachineInstr *ImpDefMI = &*I;
166 MBB->erase(ImpDefMI);
172 /// OptimizeFunction - Perhaps branch folding, tail merging and other
173 /// CFG optimizations on the given function.
174 bool BranchFolder::OptimizeFunction(MachineFunction &MF,
175 const TargetInstrInfo *tii,
176 const TargetRegisterInfo *tri,
177 MachineModuleInfo *mmi) {
178 if (!tii) return false;
180 TriedMerging.clear();
187 // Use a RegScavenger to help update liveness when required.
188 MachineRegisterInfo &MRI = MF.getRegInfo();
189 if (MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF))
190 RS = new RegScavenger();
192 MRI.invalidateLiveness();
194 // Fix CFG. The later algorithms expect it to be right.
195 bool MadeChange = false;
196 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; I++) {
197 MachineBasicBlock *MBB = I, *TBB = 0, *FBB = 0;
198 SmallVector<MachineOperand, 4> Cond;
199 if (!TII->AnalyzeBranch(*MBB, TBB, FBB, Cond, true))
200 MadeChange |= MBB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
201 MadeChange |= OptimizeImpDefsBlock(MBB);
204 bool MadeChangeThisIteration = true;
205 while (MadeChangeThisIteration) {
206 MadeChangeThisIteration = TailMergeBlocks(MF);
207 MadeChangeThisIteration |= OptimizeBranches(MF);
208 if (EnableHoistCommonCode)
209 MadeChangeThisIteration |= HoistCommonCode(MF);
210 MadeChange |= MadeChangeThisIteration;
213 // See if any jump tables have become dead as the code generator
215 MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
221 // Walk the function to find jump tables that are live.
222 BitVector JTIsLive(JTI->getJumpTables().size());
223 for (MachineFunction::iterator BB = MF.begin(), E = MF.end();
225 for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end();
227 for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) {
228 MachineOperand &Op = I->getOperand(op);
229 if (!Op.isJTI()) continue;
231 // Remember that this JT is live.
232 JTIsLive.set(Op.getIndex());
236 // Finally, remove dead jump tables. This happens when the
237 // indirect jump was unreachable (and thus deleted).
238 for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i)
239 if (!JTIsLive.test(i)) {
240 JTI->RemoveJumpTable(i);
248 //===----------------------------------------------------------------------===//
249 // Tail Merging of Blocks
250 //===----------------------------------------------------------------------===//
252 /// HashMachineInstr - Compute a hash value for MI and its operands.
253 static unsigned HashMachineInstr(const MachineInstr *MI) {
254 unsigned Hash = MI->getOpcode();
255 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
256 const MachineOperand &Op = MI->getOperand(i);
258 // Merge in bits from the operand if easy.
259 unsigned OperandHash = 0;
260 switch (Op.getType()) {
261 case MachineOperand::MO_Register: OperandHash = Op.getReg(); break;
262 case MachineOperand::MO_Immediate: OperandHash = Op.getImm(); break;
263 case MachineOperand::MO_MachineBasicBlock:
264 OperandHash = Op.getMBB()->getNumber();
266 case MachineOperand::MO_FrameIndex:
267 case MachineOperand::MO_ConstantPoolIndex:
268 case MachineOperand::MO_JumpTableIndex:
269 OperandHash = Op.getIndex();
271 case MachineOperand::MO_GlobalAddress:
272 case MachineOperand::MO_ExternalSymbol:
273 // Global address / external symbol are too hard, don't bother, but do
274 // pull in the offset.
275 OperandHash = Op.getOffset();
280 Hash += ((OperandHash << 3) | Op.getType()) << (i&31);
285 /// HashEndOfMBB - Hash the last instruction in the MBB.
286 static unsigned HashEndOfMBB(const MachineBasicBlock *MBB) {
287 MachineBasicBlock::const_iterator I = MBB->end();
288 if (I == MBB->begin())
289 return 0; // Empty MBB.
292 // Skip debug info so it will not affect codegen.
293 while (I->isDebugValue()) {
295 return 0; // MBB empty except for debug info.
299 return HashMachineInstr(I);
302 /// ComputeCommonTailLength - Given two machine basic blocks, compute the number
303 /// of instructions they actually have in common together at their end. Return
304 /// iterators for the first shared instruction in each block.
305 static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
306 MachineBasicBlock *MBB2,
307 MachineBasicBlock::iterator &I1,
308 MachineBasicBlock::iterator &I2) {
312 unsigned TailLen = 0;
313 while (I1 != MBB1->begin() && I2 != MBB2->begin()) {
315 // Skip debugging pseudos; necessary to avoid changing the code.
316 while (I1->isDebugValue()) {
317 if (I1==MBB1->begin()) {
318 while (I2->isDebugValue()) {
319 if (I2==MBB2->begin())
320 // I1==DBG at begin; I2==DBG at begin
325 // I1==DBG at begin; I2==non-DBG, or first of DBGs not at begin
330 // I1==first (untested) non-DBG preceding known match
331 while (I2->isDebugValue()) {
332 if (I2==MBB2->begin()) {
334 // I1==non-DBG, or first of DBGs not at begin; I2==DBG at begin
339 // I1, I2==first (untested) non-DBGs preceding known match
340 if (!I1->isIdenticalTo(I2) ||
341 // FIXME: This check is dubious. It's used to get around a problem where
342 // people incorrectly expect inline asm directives to remain in the same
343 // relative order. This is untenable because normal compiler
344 // optimizations (like this one) may reorder and/or merge these
352 // Back past possible debugging pseudos at beginning of block. This matters
353 // when one block differs from the other only by whether debugging pseudos
354 // are present at the beginning. (This way, the various checks later for
355 // I1==MBB1->begin() work as expected.)
356 if (I1 == MBB1->begin() && I2 != MBB2->begin()) {
358 while (I2->isDebugValue()) {
359 if (I2 == MBB2->begin())
365 if (I2 == MBB2->begin() && I1 != MBB1->begin()) {
367 while (I1->isDebugValue()) {
368 if (I1 == MBB1->begin())
377 void BranchFolder::MaintainLiveIns(MachineBasicBlock *CurMBB,
378 MachineBasicBlock *NewMBB) {
380 RS->enterBasicBlock(CurMBB);
381 if (!CurMBB->empty())
382 RS->forward(prior(CurMBB->end()));
383 BitVector RegsLiveAtExit(TRI->getNumRegs());
384 RS->getRegsUsed(RegsLiveAtExit, false);
385 for (unsigned int i = 0, e = TRI->getNumRegs(); i != e; i++)
386 if (RegsLiveAtExit[i])
387 NewMBB->addLiveIn(i);
391 /// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything
392 /// after it, replacing it with an unconditional branch to NewDest.
393 void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
394 MachineBasicBlock *NewDest) {
395 MachineBasicBlock *CurMBB = OldInst->getParent();
397 TII->ReplaceTailWithBranchTo(OldInst, NewDest);
399 // For targets that use the register scavenger, we must maintain LiveIns.
400 MaintainLiveIns(CurMBB, NewDest);
405 /// SplitMBBAt - Given a machine basic block and an iterator into it, split the
406 /// MBB so that the part before the iterator falls into the part starting at the
407 /// iterator. This returns the new MBB.
408 MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
409 MachineBasicBlock::iterator BBI1) {
410 if (!TII->isLegalToSplitMBBAt(CurMBB, BBI1))
413 MachineFunction &MF = *CurMBB.getParent();
415 // Create the fall-through block.
416 MachineFunction::iterator MBBI = &CurMBB;
417 MachineBasicBlock *NewMBB =MF.CreateMachineBasicBlock(CurMBB.getBasicBlock());
418 CurMBB.getParent()->insert(++MBBI, NewMBB);
420 // Move all the successors of this block to the specified block.
421 NewMBB->transferSuccessors(&CurMBB);
423 // Add an edge from CurMBB to NewMBB for the fall-through.
424 CurMBB.addSuccessor(NewMBB);
426 // Splice the code over.
427 NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
429 // For targets that use the register scavenger, we must maintain LiveIns.
430 MaintainLiveIns(&CurMBB, NewMBB);
435 /// EstimateRuntime - Make a rough estimate for how long it will take to run
436 /// the specified code.
437 static unsigned EstimateRuntime(MachineBasicBlock::iterator I,
438 MachineBasicBlock::iterator E) {
440 for (; I != E; ++I) {
441 if (I->isDebugValue())
445 else if (I->mayLoad() || I->mayStore())
453 // CurMBB needs to add an unconditional branch to SuccMBB (we removed these
454 // branches temporarily for tail merging). In the case where CurMBB ends
455 // with a conditional branch to the next block, optimize by reversing the
456 // test and conditionally branching to SuccMBB instead.
457 static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB,
458 const TargetInstrInfo *TII) {
459 MachineFunction *MF = CurMBB->getParent();
460 MachineFunction::iterator I = llvm::next(MachineFunction::iterator(CurMBB));
461 MachineBasicBlock *TBB = 0, *FBB = 0;
462 SmallVector<MachineOperand, 4> Cond;
463 DebugLoc dl; // FIXME: this is nowhere
464 if (I != MF->end() &&
465 !TII->AnalyzeBranch(*CurMBB, TBB, FBB, Cond, true)) {
466 MachineBasicBlock *NextBB = I;
467 if (TBB == NextBB && !Cond.empty() && !FBB) {
468 if (!TII->ReverseBranchCondition(Cond)) {
469 TII->RemoveBranch(*CurMBB);
470 TII->InsertBranch(*CurMBB, SuccBB, NULL, Cond, dl);
475 TII->InsertBranch(*CurMBB, SuccBB, NULL,
476 SmallVector<MachineOperand, 0>(), dl);
480 BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const {
481 if (getHash() < o.getHash())
483 if (getHash() > o.getHash())
485 if (getBlock()->getNumber() < o.getBlock()->getNumber())
487 if (getBlock()->getNumber() > o.getBlock()->getNumber())
489 // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing
490 // an object with itself.
491 #ifndef _GLIBCXX_DEBUG
492 llvm_unreachable("Predecessor appears twice");
498 /// CountTerminators - Count the number of terminators in the given
499 /// block and set I to the position of the first non-terminator, if there
500 /// is one, or MBB->end() otherwise.
501 static unsigned CountTerminators(MachineBasicBlock *MBB,
502 MachineBasicBlock::iterator &I) {
504 unsigned NumTerms = 0;
506 if (I == MBB->begin()) {
511 if (!I->isTerminator()) break;
517 /// ProfitableToMerge - Check if two machine basic blocks have a common tail
518 /// and decide if it would be profitable to merge those tails. Return the
519 /// length of the common tail and iterators to the first common instruction
521 static bool ProfitableToMerge(MachineBasicBlock *MBB1,
522 MachineBasicBlock *MBB2,
523 unsigned minCommonTailLength,
524 unsigned &CommonTailLen,
525 MachineBasicBlock::iterator &I1,
526 MachineBasicBlock::iterator &I2,
527 MachineBasicBlock *SuccBB,
528 MachineBasicBlock *PredBB) {
529 CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2);
530 if (CommonTailLen == 0)
532 DEBUG(dbgs() << "Common tail length of BB#" << MBB1->getNumber()
533 << " and BB#" << MBB2->getNumber() << " is " << CommonTailLen
536 // It's almost always profitable to merge any number of non-terminator
537 // instructions with the block that falls through into the common successor.
538 if (MBB1 == PredBB || MBB2 == PredBB) {
539 MachineBasicBlock::iterator I;
540 unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I);
541 if (CommonTailLen > NumTerms)
545 // If one of the blocks can be completely merged and happens to be in
546 // a position where the other could fall through into it, merge any number
547 // of instructions, because it can be done without a branch.
548 // TODO: If the blocks are not adjacent, move one of them so that they are?
549 if (MBB1->isLayoutSuccessor(MBB2) && I2 == MBB2->begin())
551 if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin())
554 // If both blocks have an unconditional branch temporarily stripped out,
555 // count that as an additional common instruction for the following
557 unsigned EffectiveTailLen = CommonTailLen;
558 if (SuccBB && MBB1 != PredBB && MBB2 != PredBB &&
559 !MBB1->back().isBarrier() &&
560 !MBB2->back().isBarrier())
563 // Check if the common tail is long enough to be worthwhile.
564 if (EffectiveTailLen >= minCommonTailLength)
567 // If we are optimizing for code size, 2 instructions in common is enough if
568 // we don't have to split a block. At worst we will be introducing 1 new
569 // branch instruction, which is likely to be smaller than the 2
570 // instructions that would be deleted in the merge.
571 MachineFunction *MF = MBB1->getParent();
572 if (EffectiveTailLen >= 2 &&
573 MF->getFunction()->getAttributes().
574 hasAttribute(AttributeSet::FunctionIndex, Attribute::OptimizeForSize) &&
575 (I1 == MBB1->begin() || I2 == MBB2->begin()))
581 /// ComputeSameTails - Look through all the blocks in MergePotentials that have
582 /// hash CurHash (guaranteed to match the last element). Build the vector
583 /// SameTails of all those that have the (same) largest number of instructions
584 /// in common of any pair of these blocks. SameTails entries contain an
585 /// iterator into MergePotentials (from which the MachineBasicBlock can be
586 /// found) and a MachineBasicBlock::iterator into that MBB indicating the
587 /// instruction where the matching code sequence begins.
588 /// Order of elements in SameTails is the reverse of the order in which
589 /// those blocks appear in MergePotentials (where they are not necessarily
591 unsigned BranchFolder::ComputeSameTails(unsigned CurHash,
592 unsigned minCommonTailLength,
593 MachineBasicBlock *SuccBB,
594 MachineBasicBlock *PredBB) {
595 unsigned maxCommonTailLength = 0U;
597 MachineBasicBlock::iterator TrialBBI1, TrialBBI2;
598 MPIterator HighestMPIter = prior(MergePotentials.end());
599 for (MPIterator CurMPIter = prior(MergePotentials.end()),
600 B = MergePotentials.begin();
601 CurMPIter != B && CurMPIter->getHash() == CurHash;
603 for (MPIterator I = prior(CurMPIter); I->getHash() == CurHash ; --I) {
604 unsigned CommonTailLen;
605 if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(),
607 CommonTailLen, TrialBBI1, TrialBBI2,
609 if (CommonTailLen > maxCommonTailLength) {
611 maxCommonTailLength = CommonTailLen;
612 HighestMPIter = CurMPIter;
613 SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1));
615 if (HighestMPIter == CurMPIter &&
616 CommonTailLen == maxCommonTailLength)
617 SameTails.push_back(SameTailElt(I, TrialBBI2));
623 return maxCommonTailLength;
626 /// RemoveBlocksWithHash - Remove all blocks with hash CurHash from
627 /// MergePotentials, restoring branches at ends of blocks as appropriate.
628 void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
629 MachineBasicBlock *SuccBB,
630 MachineBasicBlock *PredBB) {
631 MPIterator CurMPIter, B;
632 for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin();
633 CurMPIter->getHash() == CurHash;
635 // Put the unconditional branch back, if we need one.
636 MachineBasicBlock *CurMBB = CurMPIter->getBlock();
637 if (SuccBB && CurMBB != PredBB)
638 FixTail(CurMBB, SuccBB, TII);
642 if (CurMPIter->getHash() != CurHash)
644 MergePotentials.erase(CurMPIter, MergePotentials.end());
647 /// CreateCommonTailOnlyBlock - None of the blocks to be tail-merged consist
648 /// only of the common tail. Create a block that does by splitting one.
649 bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
650 unsigned maxCommonTailLength,
651 unsigned &commonTailIndex) {
653 unsigned TimeEstimate = ~0U;
654 for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
655 // Use PredBB if possible; that doesn't require a new branch.
656 if (SameTails[i].getBlock() == PredBB) {
660 // Otherwise, make a (fairly bogus) choice based on estimate of
661 // how long it will take the various blocks to execute.
662 unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(),
663 SameTails[i].getTailStartPos());
664 if (t <= TimeEstimate) {
670 MachineBasicBlock::iterator BBI =
671 SameTails[commonTailIndex].getTailStartPos();
672 MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
674 // If the common tail includes any debug info we will take it pretty
675 // randomly from one of the inputs. Might be better to remove it?
676 DEBUG(dbgs() << "\nSplitting BB#" << MBB->getNumber() << ", size "
677 << maxCommonTailLength);
679 MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI);
681 DEBUG(dbgs() << "... failed!");
685 SameTails[commonTailIndex].setBlock(newMBB);
686 SameTails[commonTailIndex].setTailStartPos(newMBB->begin());
688 // If we split PredBB, newMBB is the new predecessor.
695 // See if any of the blocks in MergePotentials (which all have a common single
696 // successor, or all have no successor) can be tail-merged. If there is a
697 // successor, any blocks in MergePotentials that are not tail-merged and
698 // are not immediately before Succ must have an unconditional branch to
699 // Succ added (but the predecessor/successor lists need no adjustment).
700 // The lone predecessor of Succ that falls through into Succ,
701 // if any, is given in PredBB.
703 bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
704 MachineBasicBlock *PredBB) {
705 bool MadeChange = false;
707 // Except for the special cases below, tail-merge if there are at least
708 // this many instructions in common.
709 unsigned minCommonTailLength = TailMergeSize;
711 DEBUG(dbgs() << "\nTryTailMergeBlocks: ";
712 for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
713 dbgs() << "BB#" << MergePotentials[i].getBlock()->getNumber()
714 << (i == e-1 ? "" : ", ");
717 dbgs() << " with successor BB#" << SuccBB->getNumber() << '\n';
719 dbgs() << " which has fall-through from BB#"
720 << PredBB->getNumber() << "\n";
722 dbgs() << "Looking for common tails of at least "
723 << minCommonTailLength << " instruction"
724 << (minCommonTailLength == 1 ? "" : "s") << '\n';
727 // Sort by hash value so that blocks with identical end sequences sort
729 std::stable_sort(MergePotentials.begin(), MergePotentials.end());
731 // Walk through equivalence sets looking for actual exact matches.
732 while (MergePotentials.size() > 1) {
733 unsigned CurHash = MergePotentials.back().getHash();
735 // Build SameTails, identifying the set of blocks with this hash code
736 // and with the maximum number of instructions in common.
737 unsigned maxCommonTailLength = ComputeSameTails(CurHash,
741 // If we didn't find any pair that has at least minCommonTailLength
742 // instructions in common, remove all blocks with this hash code and retry.
743 if (SameTails.empty()) {
744 RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
748 // If one of the blocks is the entire common tail (and not the entry
749 // block, which we can't jump to), we can treat all blocks with this same
750 // tail at once. Use PredBB if that is one of the possibilities, as that
751 // will not introduce any extra branches.
752 MachineBasicBlock *EntryBB = MergePotentials.begin()->getBlock()->
753 getParent()->begin();
754 unsigned commonTailIndex = SameTails.size();
755 // If there are two blocks, check to see if one can be made to fall through
757 if (SameTails.size() == 2 &&
758 SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) &&
759 SameTails[1].tailIsWholeBlock())
761 else if (SameTails.size() == 2 &&
762 SameTails[1].getBlock()->isLayoutSuccessor(
763 SameTails[0].getBlock()) &&
764 SameTails[0].tailIsWholeBlock())
767 // Otherwise just pick one, favoring the fall-through predecessor if
769 for (unsigned i = 0, e = SameTails.size(); i != e; ++i) {
770 MachineBasicBlock *MBB = SameTails[i].getBlock();
771 if (MBB == EntryBB && SameTails[i].tailIsWholeBlock())
777 if (SameTails[i].tailIsWholeBlock())
782 if (commonTailIndex == SameTails.size() ||
783 (SameTails[commonTailIndex].getBlock() == PredBB &&
784 !SameTails[commonTailIndex].tailIsWholeBlock())) {
785 // None of the blocks consist entirely of the common tail.
786 // Split a block so that one does.
787 if (!CreateCommonTailOnlyBlock(PredBB,
788 maxCommonTailLength, commonTailIndex)) {
789 RemoveBlocksWithHash(CurHash, SuccBB, PredBB);
794 MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
795 // MBB is common tail. Adjust all other BB's to jump to this one.
796 // Traversal must be forwards so erases work.
797 DEBUG(dbgs() << "\nUsing common tail in BB#" << MBB->getNumber()
799 for (unsigned int i=0, e = SameTails.size(); i != e; ++i) {
800 if (commonTailIndex == i)
802 DEBUG(dbgs() << "BB#" << SameTails[i].getBlock()->getNumber()
803 << (i == e-1 ? "" : ", "));
804 // Hack the end off BB i, making it jump to BB commonTailIndex instead.
805 ReplaceTailWithBranchTo(SameTails[i].getTailStartPos(), MBB);
806 // BB i is no longer a predecessor of SuccBB; remove it from the worklist.
807 MergePotentials.erase(SameTails[i].getMPIter());
809 DEBUG(dbgs() << "\n");
810 // We leave commonTailIndex in the worklist in case there are other blocks
811 // that match it with a smaller number of instructions.
817 bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
818 bool MadeChange = false;
819 if (!EnableTailMerge) return MadeChange;
821 // First find blocks with no successors.
822 MergePotentials.clear();
823 for (MachineFunction::iterator I = MF.begin(), E = MF.end();
824 I != E && MergePotentials.size() < TailMergeThreshold; ++I) {
825 if (TriedMerging.count(I))
828 MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I), I));
831 // If this is a large problem, avoid visiting the same basic blocks
833 if (MergePotentials.size() == TailMergeThreshold)
834 for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
835 TriedMerging.insert(MergePotentials[i].getBlock());
837 // See if we can do any tail merging on those.
838 if (MergePotentials.size() >= 2)
839 MadeChange |= TryTailMergeBlocks(NULL, NULL);
841 // Look at blocks (IBB) with multiple predecessors (PBB).
842 // We change each predecessor to a canonical form, by
843 // (1) temporarily removing any unconditional branch from the predecessor
845 // (2) alter conditional branches so they branch to the other block
846 // not IBB; this may require adding back an unconditional branch to IBB
847 // later, where there wasn't one coming in. E.g.
849 // fallthrough to QBB
852 // with a conceptual B to IBB after that, which never actually exists.
853 // With those changes, we see whether the predecessors' tails match,
854 // and merge them if so. We change things out of canonical form and
855 // back to the way they were later in the process. (OptimizeBranches
856 // would undo some of this, but we can't use it, because we'd get into
857 // a compile-time infinite loop repeatedly doing and undoing the same
860 for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end();
862 if (I->pred_size() < 2) continue;
863 SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
864 MachineBasicBlock *IBB = I;
865 MachineBasicBlock *PredBB = prior(I);
866 MergePotentials.clear();
867 for (MachineBasicBlock::pred_iterator P = I->pred_begin(),
869 P != E2 && MergePotentials.size() < TailMergeThreshold; ++P) {
870 MachineBasicBlock *PBB = *P;
871 if (TriedMerging.count(PBB))
874 // Skip blocks that loop to themselves, can't tail merge these.
878 // Visit each predecessor only once.
879 if (!UniquePreds.insert(PBB))
882 // Skip blocks which may jump to a landing pad. Can't tail merge these.
883 if (PBB->getLandingPadSuccessor())
886 MachineBasicBlock *TBB = 0, *FBB = 0;
887 SmallVector<MachineOperand, 4> Cond;
888 if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond, true)) {
889 // Failing case: IBB is the target of a cbr, and we cannot reverse the
891 SmallVector<MachineOperand, 4> NewCond(Cond);
892 if (!Cond.empty() && TBB == IBB) {
893 if (TII->ReverseBranchCondition(NewCond))
895 // This is the QBB case described above
897 FBB = llvm::next(MachineFunction::iterator(PBB));
900 // Failing case: the only way IBB can be reached from PBB is via
901 // exception handling. Happens for landing pads. Would be nice to have
902 // a bit in the edge so we didn't have to do all this.
903 if (IBB->isLandingPad()) {
904 MachineFunction::iterator IP = PBB; IP++;
905 MachineBasicBlock *PredNextBB = NULL;
909 if (IBB != PredNextBB) // fallthrough
912 if (TBB != IBB && FBB != IBB) // cbr then ubr
914 } else if (Cond.empty()) {
915 if (TBB != IBB) // ubr
918 if (TBB != IBB && IBB != PredNextBB) // cbr
923 // Remove the unconditional branch at the end, if any.
924 if (TBB && (Cond.empty() || FBB)) {
925 DebugLoc dl; // FIXME: this is nowhere
926 TII->RemoveBranch(*PBB);
928 // reinsert conditional branch only, for now
929 TII->InsertBranch(*PBB, (TBB == IBB) ? FBB : TBB, 0, NewCond, dl);
932 MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB), *P));
936 // If this is a large problem, avoid visiting the same basic blocks multiple
938 if (MergePotentials.size() == TailMergeThreshold)
939 for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
940 TriedMerging.insert(MergePotentials[i].getBlock());
942 if (MergePotentials.size() >= 2)
943 MadeChange |= TryTailMergeBlocks(IBB, PredBB);
945 // Reinsert an unconditional branch if needed. The 1 below can occur as a
946 // result of removing blocks in TryTailMergeBlocks.
947 PredBB = prior(I); // this may have been changed in TryTailMergeBlocks
948 if (MergePotentials.size() == 1 &&
949 MergePotentials.begin()->getBlock() != PredBB)
950 FixTail(MergePotentials.begin()->getBlock(), IBB, TII);
956 //===----------------------------------------------------------------------===//
957 // Branch Optimization
958 //===----------------------------------------------------------------------===//
960 bool BranchFolder::OptimizeBranches(MachineFunction &MF) {
961 bool MadeChange = false;
963 // Make sure blocks are numbered in order
966 for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end();
968 MachineBasicBlock *MBB = I++;
969 MadeChange |= OptimizeBlock(MBB);
971 // If it is dead, remove it.
972 if (MBB->pred_empty()) {
973 RemoveDeadBlock(MBB);
981 // Blocks should be considered empty if they contain only debug info;
982 // else the debug info would affect codegen.
983 static bool IsEmptyBlock(MachineBasicBlock *MBB) {
986 for (MachineBasicBlock::iterator MBBI = MBB->begin(), MBBE = MBB->end();
987 MBBI!=MBBE; ++MBBI) {
988 if (!MBBI->isDebugValue())
994 // Blocks with only debug info and branches should be considered the same
995 // as blocks with only branches.
996 static bool IsBranchOnlyBlock(MachineBasicBlock *MBB) {
997 MachineBasicBlock::iterator MBBI, MBBE;
998 for (MBBI = MBB->begin(), MBBE = MBB->end(); MBBI!=MBBE; ++MBBI) {
999 if (!MBBI->isDebugValue())
1002 return (MBBI->isBranch());
1005 /// IsBetterFallthrough - Return true if it would be clearly better to
1006 /// fall-through to MBB1 than to fall through into MBB2. This has to return
1007 /// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
1008 /// result in infinite loops.
1009 static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
1010 MachineBasicBlock *MBB2) {
1011 // Right now, we use a simple heuristic. If MBB2 ends with a call, and
1012 // MBB1 doesn't, we prefer to fall through into MBB1. This allows us to
1013 // optimize branches that branch to either a return block or an assert block
1014 // into a fallthrough to the return.
1015 if (IsEmptyBlock(MBB1) || IsEmptyBlock(MBB2)) return false;
1017 // If there is a clear successor ordering we make sure that one block
1018 // will fall through to the next
1019 if (MBB1->isSuccessor(MBB2)) return true;
1020 if (MBB2->isSuccessor(MBB1)) return false;
1022 // Neither block consists entirely of debug info (per IsEmptyBlock check),
1023 // so we needn't test for falling off the beginning here.
1024 MachineBasicBlock::iterator MBB1I = --MBB1->end();
1025 while (MBB1I->isDebugValue())
1027 MachineBasicBlock::iterator MBB2I = --MBB2->end();
1028 while (MBB2I->isDebugValue())
1030 return MBB2I->isCall() && !MBB1I->isCall();
1033 /// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch
1034 /// instructions on the block. Always use the DebugLoc of the first
1035 /// branching instruction found unless its absent, in which case use the
1036 /// DebugLoc of the second if present.
1037 static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) {
1038 MachineBasicBlock::iterator I = MBB.end();
1039 if (I == MBB.begin())
1042 while (I->isDebugValue() && I != MBB.begin())
1045 return I->getDebugLoc();
1049 /// OptimizeBlock - Analyze and optimize control flow related to the specified
1050 /// block. This is never called on the entry block.
1051 bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
1052 bool MadeChange = false;
1053 MachineFunction &MF = *MBB->getParent();
1056 MachineFunction::iterator FallThrough = MBB;
1059 // If this block is empty, make everyone use its fall-through, not the block
1060 // explicitly. Landing pads should not do this since the landing-pad table
1061 // points to this block. Blocks with their addresses taken shouldn't be
1063 if (IsEmptyBlock(MBB) && !MBB->isLandingPad() && !MBB->hasAddressTaken()) {
1064 // Dead block? Leave for cleanup later.
1065 if (MBB->pred_empty()) return MadeChange;
1067 if (FallThrough == MF.end()) {
1068 // TODO: Simplify preds to not branch here if possible!
1070 // Rewrite all predecessors of the old block to go to the fallthrough
1072 while (!MBB->pred_empty()) {
1073 MachineBasicBlock *Pred = *(MBB->pred_end()-1);
1074 Pred->ReplaceUsesOfBlockWith(MBB, FallThrough);
1076 // If MBB was the target of a jump table, update jump tables to go to the
1077 // fallthrough instead.
1078 if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
1079 MJTI->ReplaceMBBInJumpTables(MBB, FallThrough);
1085 // Check to see if we can simplify the terminator of the block before this
1087 MachineBasicBlock &PrevBB = *prior(MachineFunction::iterator(MBB));
1089 MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
1090 SmallVector<MachineOperand, 4> PriorCond;
1091 bool PriorUnAnalyzable =
1092 TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true);
1093 if (!PriorUnAnalyzable) {
1094 // If the CFG for the prior block has extra edges, remove them.
1095 MadeChange |= PrevBB.CorrectExtraCFGEdges(PriorTBB, PriorFBB,
1096 !PriorCond.empty());
1098 // If the previous branch is conditional and both conditions go to the same
1099 // destination, remove the branch, replacing it with an unconditional one or
1101 if (PriorTBB && PriorTBB == PriorFBB) {
1102 DebugLoc dl = getBranchDebugLoc(PrevBB);
1103 TII->RemoveBranch(PrevBB);
1105 if (PriorTBB != MBB)
1106 TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond, dl);
1109 goto ReoptimizeBlock;
1112 // If the previous block unconditionally falls through to this block and
1113 // this block has no other predecessors, move the contents of this block
1114 // into the prior block. This doesn't usually happen when SimplifyCFG
1115 // has been used, but it can happen if tail merging splits a fall-through
1116 // predecessor of a block.
1117 // This has to check PrevBB->succ_size() because EH edges are ignored by
1119 if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 &&
1120 PrevBB.succ_size() == 1 &&
1121 !MBB->hasAddressTaken() && !MBB->isLandingPad()) {
1122 DEBUG(dbgs() << "\nMerging into block: " << PrevBB
1123 << "From MBB: " << *MBB);
1124 // Remove redundant DBG_VALUEs first.
1125 if (PrevBB.begin() != PrevBB.end()) {
1126 MachineBasicBlock::iterator PrevBBIter = PrevBB.end();
1128 MachineBasicBlock::iterator MBBIter = MBB->begin();
1129 // Check if DBG_VALUE at the end of PrevBB is identical to the
1130 // DBG_VALUE at the beginning of MBB.
1131 while (PrevBBIter != PrevBB.begin() && MBBIter != MBB->end()
1132 && PrevBBIter->isDebugValue() && MBBIter->isDebugValue()) {
1133 if (!MBBIter->isIdenticalTo(PrevBBIter))
1135 MachineInstr *DuplicateDbg = MBBIter;
1136 ++MBBIter; -- PrevBBIter;
1137 DuplicateDbg->eraseFromParent();
1140 PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end());
1141 PrevBB.removeSuccessor(PrevBB.succ_begin());
1142 assert(PrevBB.succ_empty());
1143 PrevBB.transferSuccessors(MBB);
1148 // If the previous branch *only* branches to *this* block (conditional or
1149 // not) remove the branch.
1150 if (PriorTBB == MBB && PriorFBB == 0) {
1151 TII->RemoveBranch(PrevBB);
1154 goto ReoptimizeBlock;
1157 // If the prior block branches somewhere else on the condition and here if
1158 // the condition is false, remove the uncond second branch.
1159 if (PriorFBB == MBB) {
1160 DebugLoc dl = getBranchDebugLoc(PrevBB);
1161 TII->RemoveBranch(PrevBB);
1162 TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond, dl);
1165 goto ReoptimizeBlock;
1168 // If the prior block branches here on true and somewhere else on false, and
1169 // if the branch condition is reversible, reverse the branch to create a
1171 if (PriorTBB == MBB) {
1172 SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
1173 if (!TII->ReverseBranchCondition(NewPriorCond)) {
1174 DebugLoc dl = getBranchDebugLoc(PrevBB);
1175 TII->RemoveBranch(PrevBB);
1176 TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond, dl);
1179 goto ReoptimizeBlock;
1183 // If this block has no successors (e.g. it is a return block or ends with
1184 // a call to a no-return function like abort or __cxa_throw) and if the pred
1185 // falls through into this block, and if it would otherwise fall through
1186 // into the block after this, move this block to the end of the function.
1188 // We consider it more likely that execution will stay in the function (e.g.
1189 // due to loops) than it is to exit it. This asserts in loops etc, moving
1190 // the assert condition out of the loop body.
1191 if (MBB->succ_empty() && !PriorCond.empty() && PriorFBB == 0 &&
1192 MachineFunction::iterator(PriorTBB) == FallThrough &&
1193 !MBB->canFallThrough()) {
1194 bool DoTransform = true;
1196 // We have to be careful that the succs of PredBB aren't both no-successor
1197 // blocks. If neither have successors and if PredBB is the second from
1198 // last block in the function, we'd just keep swapping the two blocks for
1199 // last. Only do the swap if one is clearly better to fall through than
1201 if (FallThrough == --MF.end() &&
1202 !IsBetterFallthrough(PriorTBB, MBB))
1203 DoTransform = false;
1206 // Reverse the branch so we will fall through on the previous true cond.
1207 SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
1208 if (!TII->ReverseBranchCondition(NewPriorCond)) {
1209 DEBUG(dbgs() << "\nMoving MBB: " << *MBB
1210 << "To make fallthrough to: " << *PriorTBB << "\n");
1212 DebugLoc dl = getBranchDebugLoc(PrevBB);
1213 TII->RemoveBranch(PrevBB);
1214 TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond, dl);
1216 // Move this block to the end of the function.
1217 MBB->moveAfter(--MF.end());
1226 // Analyze the branch in the current block.
1227 MachineBasicBlock *CurTBB = 0, *CurFBB = 0;
1228 SmallVector<MachineOperand, 4> CurCond;
1229 bool CurUnAnalyzable= TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true);
1230 if (!CurUnAnalyzable) {
1231 // If the CFG for the prior block has extra edges, remove them.
1232 MadeChange |= MBB->CorrectExtraCFGEdges(CurTBB, CurFBB, !CurCond.empty());
1234 // If this is a two-way branch, and the FBB branches to this block, reverse
1235 // the condition so the single-basic-block loop is faster. Instead of:
1236 // Loop: xxx; jcc Out; jmp Loop
1238 // Loop: xxx; jncc Loop; jmp Out
1239 if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) {
1240 SmallVector<MachineOperand, 4> NewCond(CurCond);
1241 if (!TII->ReverseBranchCondition(NewCond)) {
1242 DebugLoc dl = getBranchDebugLoc(*MBB);
1243 TII->RemoveBranch(*MBB);
1244 TII->InsertBranch(*MBB, CurFBB, CurTBB, NewCond, dl);
1247 goto ReoptimizeBlock;
1251 // If this branch is the only thing in its block, see if we can forward
1252 // other blocks across it.
1253 if (CurTBB && CurCond.empty() && CurFBB == 0 &&
1254 IsBranchOnlyBlock(MBB) && CurTBB != MBB &&
1255 !MBB->hasAddressTaken()) {
1256 DebugLoc dl = getBranchDebugLoc(*MBB);
1257 // This block may contain just an unconditional branch. Because there can
1258 // be 'non-branch terminators' in the block, try removing the branch and
1259 // then seeing if the block is empty.
1260 TII->RemoveBranch(*MBB);
1261 // If the only things remaining in the block are debug info, remove these
1262 // as well, so this will behave the same as an empty block in non-debug
1264 if (!MBB->empty()) {
1265 bool NonDebugInfoFound = false;
1266 for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
1268 if (!I->isDebugValue()) {
1269 NonDebugInfoFound = true;
1273 if (!NonDebugInfoFound)
1274 // Make the block empty, losing the debug info (we could probably
1275 // improve this in some cases.)
1276 MBB->erase(MBB->begin(), MBB->end());
1278 // If this block is just an unconditional branch to CurTBB, we can
1279 // usually completely eliminate the block. The only case we cannot
1280 // completely eliminate the block is when the block before this one
1281 // falls through into MBB and we can't understand the prior block's branch
1284 bool PredHasNoFallThrough = !PrevBB.canFallThrough();
1285 if (PredHasNoFallThrough || !PriorUnAnalyzable ||
1286 !PrevBB.isSuccessor(MBB)) {
1287 // If the prior block falls through into us, turn it into an
1288 // explicit branch to us to make updates simpler.
1289 if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) &&
1290 PriorTBB != MBB && PriorFBB != MBB) {
1291 if (PriorTBB == 0) {
1292 assert(PriorCond.empty() && PriorFBB == 0 &&
1293 "Bad branch analysis");
1296 assert(PriorFBB == 0 && "Machine CFG out of date!");
1299 DebugLoc pdl = getBranchDebugLoc(PrevBB);
1300 TII->RemoveBranch(PrevBB);
1301 TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, pdl);
1304 // Iterate through all the predecessors, revectoring each in-turn.
1306 bool DidChange = false;
1307 bool HasBranchToSelf = false;
1308 while(PI != MBB->pred_size()) {
1309 MachineBasicBlock *PMBB = *(MBB->pred_begin() + PI);
1311 // If this block has an uncond branch to itself, leave it.
1313 HasBranchToSelf = true;
1316 PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB);
1317 // If this change resulted in PMBB ending in a conditional
1318 // branch where both conditions go to the same destination,
1319 // change this to an unconditional branch (and fix the CFG).
1320 MachineBasicBlock *NewCurTBB = 0, *NewCurFBB = 0;
1321 SmallVector<MachineOperand, 4> NewCurCond;
1322 bool NewCurUnAnalyzable = TII->AnalyzeBranch(*PMBB, NewCurTBB,
1323 NewCurFBB, NewCurCond, true);
1324 if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) {
1325 DebugLoc pdl = getBranchDebugLoc(*PMBB);
1326 TII->RemoveBranch(*PMBB);
1328 TII->InsertBranch(*PMBB, NewCurTBB, 0, NewCurCond, pdl);
1331 PMBB->CorrectExtraCFGEdges(NewCurTBB, 0, false);
1336 // Change any jumptables to go to the new MBB.
1337 if (MachineJumpTableInfo *MJTI = MF.getJumpTableInfo())
1338 MJTI->ReplaceMBBInJumpTables(MBB, CurTBB);
1342 if (!HasBranchToSelf) return MadeChange;
1347 // Add the branch back if the block is more than just an uncond branch.
1348 TII->InsertBranch(*MBB, CurTBB, 0, CurCond, dl);
1352 // If the prior block doesn't fall through into this block, and if this
1353 // block doesn't fall through into some other block, see if we can find a
1354 // place to move this block where a fall-through will happen.
1355 if (!PrevBB.canFallThrough()) {
1357 // Now we know that there was no fall-through into this block, check to
1358 // see if it has a fall-through into its successor.
1359 bool CurFallsThru = MBB->canFallThrough();
1361 if (!MBB->isLandingPad()) {
1362 // Check all the predecessors of this block. If one of them has no fall
1363 // throughs, move this block right after it.
1364 for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
1365 E = MBB->pred_end(); PI != E; ++PI) {
1366 // Analyze the branch at the end of the pred.
1367 MachineBasicBlock *PredBB = *PI;
1368 MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough;
1369 MachineBasicBlock *PredTBB = 0, *PredFBB = 0;
1370 SmallVector<MachineOperand, 4> PredCond;
1371 if (PredBB != MBB && !PredBB->canFallThrough() &&
1372 !TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true)
1373 && (!CurFallsThru || !CurTBB || !CurFBB)
1374 && (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) {
1375 // If the current block doesn't fall through, just move it.
1376 // If the current block can fall through and does not end with a
1377 // conditional branch, we need to append an unconditional jump to
1378 // the (current) next block. To avoid a possible compile-time
1379 // infinite loop, move blocks only backward in this case.
1380 // Also, if there are already 2 branches here, we cannot add a third;
1381 // this means we have the case
1386 MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB));
1388 TII->InsertBranch(*MBB, NextBB, 0, CurCond, DebugLoc());
1390 MBB->moveAfter(PredBB);
1392 goto ReoptimizeBlock;
1397 if (!CurFallsThru) {
1398 // Check all successors to see if we can move this block before it.
1399 for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
1400 E = MBB->succ_end(); SI != E; ++SI) {
1401 // Analyze the branch at the end of the block before the succ.
1402 MachineBasicBlock *SuccBB = *SI;
1403 MachineFunction::iterator SuccPrev = SuccBB; --SuccPrev;
1405 // If this block doesn't already fall-through to that successor, and if
1406 // the succ doesn't already have a block that can fall through into it,
1407 // and if the successor isn't an EH destination, we can arrange for the
1408 // fallthrough to happen.
1409 if (SuccBB != MBB && &*SuccPrev != MBB &&
1410 !SuccPrev->canFallThrough() && !CurUnAnalyzable &&
1411 !SuccBB->isLandingPad()) {
1412 MBB->moveBefore(SuccBB);
1414 goto ReoptimizeBlock;
1418 // Okay, there is no really great place to put this block. If, however,
1419 // the block before this one would be a fall-through if this block were
1420 // removed, move this block to the end of the function.
1421 MachineBasicBlock *PrevTBB = 0, *PrevFBB = 0;
1422 SmallVector<MachineOperand, 4> PrevCond;
1423 if (FallThrough != MF.end() &&
1424 !TII->AnalyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) &&
1425 PrevBB.isSuccessor(FallThrough)) {
1426 MBB->moveAfter(--MF.end());
1436 //===----------------------------------------------------------------------===//
1437 // Hoist Common Code
1438 //===----------------------------------------------------------------------===//
1440 /// HoistCommonCode - Hoist common instruction sequences at the start of basic
1441 /// blocks to their common predecessor.
1442 bool BranchFolder::HoistCommonCode(MachineFunction &MF) {
1443 bool MadeChange = false;
1444 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ) {
1445 MachineBasicBlock *MBB = I++;
1446 MadeChange |= HoistCommonCodeInSuccs(MBB);
1452 /// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
1453 /// its 'true' successor.
1454 static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
1455 MachineBasicBlock *TrueBB) {
1456 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
1457 E = BB->succ_end(); SI != E; ++SI) {
1458 MachineBasicBlock *SuccBB = *SI;
1459 if (SuccBB != TrueBB)
1465 /// findHoistingInsertPosAndDeps - Find the location to move common instructions
1466 /// in successors to. The location is usually just before the terminator,
1467 /// however if the terminator is a conditional branch and its previous
1468 /// instruction is the flag setting instruction, the previous instruction is
1469 /// the preferred location. This function also gathers uses and defs of the
1470 /// instructions from the insertion point to the end of the block. The data is
1471 /// used by HoistCommonCodeInSuccs to ensure safety.
1473 MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
1474 const TargetInstrInfo *TII,
1475 const TargetRegisterInfo *TRI,
1476 SmallSet<unsigned,4> &Uses,
1477 SmallSet<unsigned,4> &Defs) {
1478 MachineBasicBlock::iterator Loc = MBB->getFirstTerminator();
1479 if (!TII->isUnpredicatedTerminator(Loc))
1482 for (unsigned i = 0, e = Loc->getNumOperands(); i != e; ++i) {
1483 const MachineOperand &MO = Loc->getOperand(i);
1486 unsigned Reg = MO.getReg();
1490 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
1492 } else if (!MO.isDead())
1493 // Don't try to hoist code in the rare case the terminator defines a
1494 // register that is later used.
1500 if (Loc == MBB->begin())
1503 // The terminator is probably a conditional branch, try not to separate the
1504 // branch from condition setting instruction.
1505 MachineBasicBlock::iterator PI = Loc;
1507 while (PI != MBB->begin() && Loc->isDebugValue())
1511 for (unsigned i = 0, e = PI->getNumOperands(); !IsDef && i != e; ++i) {
1512 const MachineOperand &MO = PI->getOperand(i);
1513 // If PI has a regmask operand, it is probably a call. Separate away.
1516 if (!MO.isReg() || MO.isUse())
1518 unsigned Reg = MO.getReg();
1521 if (Uses.count(Reg))
1525 // The condition setting instruction is not just before the conditional
1529 // Be conservative, don't insert instruction above something that may have
1530 // side-effects. And since it's potentially bad to separate flag setting
1531 // instruction from the conditional branch, just abort the optimization
1533 // Also avoid moving code above predicated instruction since it's hard to
1534 // reason about register liveness with predicated instruction.
1535 bool DontMoveAcrossStore = true;
1536 if (!PI->isSafeToMove(TII, 0, DontMoveAcrossStore) ||
1537 TII->isPredicated(PI))
1541 // Find out what registers are live. Note this routine is ignoring other live
1542 // registers which are only used by instructions in successor blocks.
1543 for (unsigned i = 0, e = PI->getNumOperands(); i != e; ++i) {
1544 const MachineOperand &MO = PI->getOperand(i);
1547 unsigned Reg = MO.getReg();
1551 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
1554 if (Uses.erase(Reg)) {
1555 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
1556 Uses.erase(*SubRegs); // Use sub-registers to be conservative
1558 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
1566 /// HoistCommonCodeInSuccs - If the successors of MBB has common instruction
1567 /// sequence at the start of the function, move the instructions before MBB
1568 /// terminator if it's legal.
1569 bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
1570 MachineBasicBlock *TBB = 0, *FBB = 0;
1571 SmallVector<MachineOperand, 4> Cond;
1572 if (TII->AnalyzeBranch(*MBB, TBB, FBB, Cond, true) || !TBB || Cond.empty())
1575 if (!FBB) FBB = findFalseBlock(MBB, TBB);
1577 // Malformed bcc? True and false blocks are the same?
1580 // Restrict the optimization to cases where MBB is the only predecessor,
1581 // it is an obvious win.
1582 if (TBB->pred_size() > 1 || FBB->pred_size() > 1)
1585 // Find a suitable position to hoist the common instructions to. Also figure
1586 // out which registers are used or defined by instructions from the insertion
1587 // point to the end of the block.
1588 SmallSet<unsigned, 4> Uses, Defs;
1589 MachineBasicBlock::iterator Loc =
1590 findHoistingInsertPosAndDeps(MBB, TII, TRI, Uses, Defs);
1591 if (Loc == MBB->end())
1594 bool HasDups = false;
1595 SmallVector<unsigned, 4> LocalDefs;
1596 SmallSet<unsigned, 4> LocalDefsSet;
1597 MachineBasicBlock::iterator TIB = TBB->begin();
1598 MachineBasicBlock::iterator FIB = FBB->begin();
1599 MachineBasicBlock::iterator TIE = TBB->end();
1600 MachineBasicBlock::iterator FIE = FBB->end();
1601 while (TIB != TIE && FIB != FIE) {
1602 // Skip dbg_value instructions. These do not count.
1603 if (TIB->isDebugValue()) {
1604 while (TIB != TIE && TIB->isDebugValue())
1609 if (FIB->isDebugValue()) {
1610 while (FIB != FIE && FIB->isDebugValue())
1615 if (!TIB->isIdenticalTo(FIB, MachineInstr::CheckKillDead))
1618 if (TII->isPredicated(TIB))
1619 // Hard to reason about register liveness with predicated instruction.
1623 for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) {
1624 MachineOperand &MO = TIB->getOperand(i);
1625 // Don't attempt to hoist instructions with register masks.
1626 if (MO.isRegMask()) {
1632 unsigned Reg = MO.getReg();
1636 if (Uses.count(Reg)) {
1637 // Avoid clobbering a register that's used by the instruction at
1638 // the point of insertion.
1643 if (Defs.count(Reg) && !MO.isDead()) {
1644 // Don't hoist the instruction if the def would be clobber by the
1645 // instruction at the point insertion. FIXME: This is overly
1646 // conservative. It should be possible to hoist the instructions
1647 // in BB2 in the following example:
1649 // r1, eflag = op1 r2, r3
1658 } else if (!LocalDefsSet.count(Reg)) {
1659 if (Defs.count(Reg)) {
1660 // Use is defined by the instruction at the point of insertion.
1665 if (MO.isKill() && Uses.count(Reg))
1666 // Kills a register that's read by the instruction at the point of
1667 // insertion. Remove the kill marker.
1668 MO.setIsKill(false);
1674 bool DontMoveAcrossStore = true;
1675 if (!TIB->isSafeToMove(TII, 0, DontMoveAcrossStore))
1678 // Remove kills from LocalDefsSet, these registers had short live ranges.
1679 for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) {
1680 MachineOperand &MO = TIB->getOperand(i);
1681 if (!MO.isReg() || !MO.isUse() || !MO.isKill())
1683 unsigned Reg = MO.getReg();
1684 if (!Reg || !LocalDefsSet.count(Reg))
1686 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
1687 LocalDefsSet.erase(*AI);
1690 // Track local defs so we can update liveins.
1691 for (unsigned i = 0, e = TIB->getNumOperands(); i != e; ++i) {
1692 MachineOperand &MO = TIB->getOperand(i);
1693 if (!MO.isReg() || !MO.isDef() || MO.isDead())
1695 unsigned Reg = MO.getReg();
1698 LocalDefs.push_back(Reg);
1699 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
1700 LocalDefsSet.insert(*AI);
1711 MBB->splice(Loc, TBB, TBB->begin(), TIB);
1712 FBB->erase(FBB->begin(), FIB);
1715 for (unsigned i = 0, e = LocalDefs.size(); i != e; ++i) {
1716 unsigned Def = LocalDefs[i];
1717 if (LocalDefsSet.count(Def)) {
1718 TBB->addLiveIn(Def);
1719 FBB->addLiveIn(Def);