diff options
Diffstat (limited to 'lib/CodeGen/BranchFolding.cpp')
| -rw-r--r-- | lib/CodeGen/BranchFolding.cpp | 689 |
1 files changed, 489 insertions, 200 deletions
diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp index baea9642d4fd..94bfb7204ba2 100644 --- a/lib/CodeGen/BranchFolding.cpp +++ b/lib/CodeGen/BranchFolding.cpp @@ -32,6 +32,7 @@ #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/raw_ostream.h" #include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SetVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/ADT/STLExtras.h" #include <algorithm> @@ -40,18 +41,38 @@ using namespace llvm; STATISTIC(NumDeadBlocks, "Number of dead blocks removed"); STATISTIC(NumBranchOpts, "Number of branches optimized"); STATISTIC(NumTailMerge , "Number of block tails merged"); -static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge", +static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge", cl::init(cl::BOU_UNSET), cl::Hidden); // Throttle for huge numbers of predecessors (compile speed problems) static cl::opt<unsigned> -TailMergeThreshold("tail-merge-threshold", +TailMergeThreshold("tail-merge-threshold", cl::desc("Max number of predecessors to consider tail merging"), cl::init(150), cl::Hidden); +// Heuristic for tail merging (and, inversely, tail duplication). +// TODO: This should be replaced with a target query. +static cl::opt<unsigned> +TailMergeSize("tail-merge-size", + cl::desc("Min number of instructions to consider tail merging"), + cl::init(3), cl::Hidden); + +namespace { + /// BranchFolderPass - Wrap branch folder in a machine function pass. + class BranchFolderPass : public MachineFunctionPass, + public BranchFolder { + public: + static char ID; + explicit BranchFolderPass(bool defaultEnableTailMerge) + : MachineFunctionPass(&ID), BranchFolder(defaultEnableTailMerge) {} + + virtual bool runOnMachineFunction(MachineFunction &MF); + virtual const char *getPassName() const { return "Control Flow Optimizer"; } + }; +} char BranchFolderPass::ID = 0; -FunctionPass *llvm::createBranchFoldingPass(bool DefaultEnableTailMerge) { +FunctionPass *llvm::createBranchFoldingPass(bool DefaultEnableTailMerge) { return new BranchFolderPass(DefaultEnableTailMerge); } @@ -63,7 +84,6 @@ bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) { } - BranchFolder::BranchFolder(bool defaultEnableTailMerge) { switch (FlagEnableTailMerge) { case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break; @@ -77,12 +97,12 @@ BranchFolder::BranchFolder(bool defaultEnableTailMerge) { void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) { assert(MBB->pred_empty() && "MBB must be dead!"); DEBUG(errs() << "\nRemoving MBB: " << *MBB); - + MachineFunction *MF = MBB->getParent(); // drop all successors. while (!MBB->succ_empty()) MBB->removeSuccessor(MBB->succ_end()-1); - + // If there are any labels in the basic block, unregister them from // MachineModuleInfo. if (MMI && !MBB->empty()) { @@ -93,7 +113,7 @@ void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) { MMI->InvalidateLabel(I->getOperand(0).getImm()); } } - + // Remove the block. MF->erase(MBB); } @@ -182,6 +202,11 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF, MadeChange |= MadeChangeThisIteration; } + // Do tail duplication once after tail merging is done. Otherwise it is + // tough to avoid situations where tail duplication and tail merging undo + // each other's transformations ad infinitum. + MadeChange |= TailDuplicateBlocks(MF); + // See if any jump tables have become mergable or dead as the code generator // did its thing. MachineJumpTableInfo *JTI = MF.getJumpTableInfo(); @@ -190,7 +215,7 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF, // Figure out how these jump tables should be merged. std::vector<unsigned> JTMapping; JTMapping.reserve(JTs.size()); - + // We always keep the 0th jump table. JTMapping.push_back(0); @@ -202,7 +227,7 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF, else JTMapping.push_back(JTI->getJumpTableIndex(JTs[i].MBBs)); } - + // If a jump table was merge with another one, walk the function rewriting // references to jump tables to reference the new JT ID's. Keep track of // whether we see a jump table idx, if not, we can delete the JT. @@ -221,7 +246,7 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF, JTIsLive.set(NewIdx); } } - + // Finally, remove dead jump tables. This happens either because the // indirect jump was unreachable (and thus deleted) or because the jump // table was merged with some other one. @@ -245,7 +270,7 @@ static unsigned HashMachineInstr(const MachineInstr *MI) { unsigned Hash = MI->getOpcode(); for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) { const MachineOperand &Op = MI->getOperand(i); - + // Merge in bits from the operand if easy. unsigned OperandHash = 0; switch (Op.getType()) { @@ -267,31 +292,30 @@ static unsigned HashMachineInstr(const MachineInstr *MI) { break; default: break; } - + Hash += ((OperandHash << 3) | Op.getType()) << (i&31); } return Hash; } /// HashEndOfMBB - Hash the last few instructions in the MBB. For blocks -/// with no successors, we hash two instructions, because cross-jumping -/// only saves code when at least two instructions are removed (since a +/// with no successors, we hash two instructions, because cross-jumping +/// only saves code when at least two instructions are removed (since a /// branch must be inserted). For blocks with a successor, one of the /// two blocks to be tail-merged will end with a branch already, so /// it gains to cross-jump even for one instruction. - static unsigned HashEndOfMBB(const MachineBasicBlock *MBB, unsigned minCommonTailLength) { MachineBasicBlock::const_iterator I = MBB->end(); if (I == MBB->begin()) return 0; // Empty MBB. - + --I; unsigned Hash = HashMachineInstr(I); - + if (I == MBB->begin() || minCommonTailLength == 1) return Hash; // Single instr MBB. - + --I; // Hash in the second-to-last instruction. Hash ^= HashMachineInstr(I) << 2; @@ -307,11 +331,11 @@ static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1, MachineBasicBlock::iterator &I2) { I1 = MBB1->end(); I2 = MBB2->end(); - + unsigned TailLen = 0; while (I1 != MBB1->begin() && I2 != MBB2->begin()) { --I1; --I2; - if (!I1->isIdenticalTo(I2) || + if (!I1->isIdenticalTo(I2) || // FIXME: This check is dubious. It's used to get around a problem where // people incorrectly expect inline asm directives to remain in the same // relative order. This is untenable because normal compiler @@ -332,11 +356,11 @@ static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1, void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst, MachineBasicBlock *NewDest) { MachineBasicBlock *OldBB = OldInst->getParent(); - + // Remove all the old successors of OldBB from the CFG. while (!OldBB->succ_empty()) OldBB->removeSuccessor(OldBB->succ_begin()); - + // Remove all the dead instructions from the end of OldBB. OldBB->erase(OldInst, OldBB->end()); @@ -361,10 +385,10 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, // Move all the successors of this block to the specified block. NewMBB->transferSuccessors(&CurMBB); - + // Add an edge from CurMBB to NewMBB for the fall-through. CurMBB.addSuccessor(NewMBB); - + // Splice the code over. NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end()); @@ -375,7 +399,7 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, RS->forward(prior(CurMBB.end())); BitVector RegsLiveAtExit(TRI->getNumRegs()); RS->getRegsUsed(RegsLiveAtExit, false); - for (unsigned int i=0, e=TRI->getNumRegs(); i!=e; i++) + for (unsigned int i = 0, e = TRI->getNumRegs(); i != e; i++) if (RegsLiveAtExit[i]) NewMBB->addLiveIn(i); } @@ -404,8 +428,7 @@ static unsigned EstimateRuntime(MachineBasicBlock::iterator I, // branches temporarily for tail merging). In the case where CurMBB ends // with a conditional branch to the next block, optimize by reversing the // test and conditionally branching to SuccMBB instead. - -static void FixTail(MachineBasicBlock* CurMBB, MachineBasicBlock *SuccBB, +static void FixTail(MachineBasicBlock *CurMBB, MachineBasicBlock *SuccBB, const TargetInstrInfo *TII) { MachineFunction *MF = CurMBB->getParent(); MachineFunction::iterator I = next(MachineFunction::iterator(CurMBB)); @@ -425,24 +448,43 @@ static void FixTail(MachineBasicBlock* CurMBB, MachineBasicBlock *SuccBB, TII->InsertBranch(*CurMBB, SuccBB, NULL, SmallVector<MachineOperand, 0>()); } -static bool MergeCompare(const std::pair<unsigned,MachineBasicBlock*> &p, - const std::pair<unsigned,MachineBasicBlock*> &q) { - if (p.first < q.first) - return true; - else if (p.first > q.first) - return false; - else if (p.second->getNumber() < q.second->getNumber()) - return true; - else if (p.second->getNumber() > q.second->getNumber()) - return false; - else { - // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing - // an object with itself. +bool +BranchFolder::MergePotentialsElt::operator<(const MergePotentialsElt &o) const { + if (getHash() < o.getHash()) + return true; + else if (getHash() > o.getHash()) + return false; + else if (getBlock()->getNumber() < o.getBlock()->getNumber()) + return true; + else if (getBlock()->getNumber() > o.getBlock()->getNumber()) + return false; + else { + // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing + // an object with itself. #ifndef _GLIBCXX_DEBUG - llvm_unreachable("Predecessor appears twice"); + llvm_unreachable("Predecessor appears twice"); #endif - return false; + return false; + } +} + +/// CountTerminators - Count the number of terminators in the given +/// block and set I to the position of the first non-terminator, if there +/// is one, or MBB->end() otherwise. +static unsigned CountTerminators(MachineBasicBlock *MBB, + MachineBasicBlock::iterator &I) { + I = MBB->end(); + unsigned NumTerms = 0; + for (;;) { + if (I == MBB->begin()) { + I = MBB->end(); + break; } + --I; + if (!I->getDesc().isTerminator()) break; + ++NumTerms; + } + return NumTerms; } /// ProfitableToMerge - Check if two machine basic blocks have a common tail @@ -454,21 +496,52 @@ static bool ProfitableToMerge(MachineBasicBlock *MBB1, unsigned minCommonTailLength, unsigned &CommonTailLen, MachineBasicBlock::iterator &I1, - MachineBasicBlock::iterator &I2) { + MachineBasicBlock::iterator &I2, + MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2); MachineFunction *MF = MBB1->getParent(); - if (CommonTailLen >= minCommonTailLength) - return true; - if (CommonTailLen == 0) return false; - // If we are optimizing for code size, 1 instruction in common is enough if - // we don't have to split a block. At worst we will be replacing a - // fallthrough into the common tail with a branch, which at worst breaks - // even with falling through into the duplicated common tail. - if (MF->getFunction()->hasFnAttr(Attribute::OptimizeForSize) && + // It's almost always profitable to merge any number of non-terminator + // instructions with the block that falls through into the common successor. + if (MBB1 == PredBB || MBB2 == PredBB) { + MachineBasicBlock::iterator I; + unsigned NumTerms = CountTerminators(MBB1 == PredBB ? MBB2 : MBB1, I); + if (CommonTailLen > NumTerms) + return true; + } + + // If one of the blocks can be completely merged and happens to be in + // a position where the other could fall through into it, merge any number + // of instructions, because it can be done without a branch. + // TODO: If the blocks are not adjacent, move one of them so that they are? + if (MBB1->isLayoutSuccessor(MBB2) && I2 == MBB2->begin()) + return true; + if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin()) + return true; + + // If both blocks have an unconditional branch temporarily stripped out, + // count that as an additional common instruction for the following + // heuristics. + unsigned EffectiveTailLen = CommonTailLen; + if (SuccBB && MBB1 != PredBB && MBB2 != PredBB && + !MBB1->back().getDesc().isBarrier() && + !MBB2->back().getDesc().isBarrier()) + ++EffectiveTailLen; + + // Check if the common tail is long enough to be worthwhile. + if (EffectiveTailLen >= minCommonTailLength) + return true; + + // If we are optimizing for code size, 2 instructions in common is enough if + // we don't have to split a block. At worst we will be introducing 1 new + // branch instruction, which is likely to be smaller than the 2 + // instructions that would be deleted in the merge. + if (EffectiveTailLen >= 2 && + MF->getFunction()->hasFnAttr(Attribute::OptimizeForSize) && (I1 == MBB1->begin() || I2 == MBB2->begin())) return true; @@ -476,40 +549,44 @@ static bool ProfitableToMerge(MachineBasicBlock *MBB1, } /// ComputeSameTails - Look through all the blocks in MergePotentials that have -/// hash CurHash (guaranteed to match the last element). Build the vector +/// hash CurHash (guaranteed to match the last element). Build the vector /// SameTails of all those that have the (same) largest number of instructions /// in common of any pair of these blocks. SameTails entries contain an -/// iterator into MergePotentials (from which the MachineBasicBlock can be -/// found) and a MachineBasicBlock::iterator into that MBB indicating the +/// iterator into MergePotentials (from which the MachineBasicBlock can be +/// found) and a MachineBasicBlock::iterator into that MBB indicating the /// instruction where the matching code sequence begins. /// Order of elements in SameTails is the reverse of the order in which /// those blocks appear in MergePotentials (where they are not necessarily /// consecutive). -unsigned BranchFolder::ComputeSameTails(unsigned CurHash, - unsigned minCommonTailLength) { +unsigned BranchFolder::ComputeSameTails(unsigned CurHash, + unsigned minCommonTailLength, + MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { unsigned maxCommonTailLength = 0U; SameTails.clear(); MachineBasicBlock::iterator TrialBBI1, TrialBBI2; MPIterator HighestMPIter = prior(MergePotentials.end()); for (MPIterator CurMPIter = prior(MergePotentials.end()), - B = MergePotentials.begin(); - CurMPIter!=B && CurMPIter->first==CurHash; + B = MergePotentials.begin(); + CurMPIter != B && CurMPIter->getHash() == CurHash; --CurMPIter) { - for (MPIterator I = prior(CurMPIter); I->first==CurHash ; --I) { + for (MPIterator I = prior(CurMPIter); I->getHash() == CurHash ; --I) { unsigned CommonTailLen; - if (ProfitableToMerge(CurMPIter->second, I->second, minCommonTailLength, - CommonTailLen, TrialBBI1, TrialBBI2)) { + if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(), + minCommonTailLength, + CommonTailLen, TrialBBI1, TrialBBI2, + SuccBB, PredBB)) { if (CommonTailLen > maxCommonTailLength) { SameTails.clear(); maxCommonTailLength = CommonTailLen; HighestMPIter = CurMPIter; - SameTails.push_back(std::make_pair(CurMPIter, TrialBBI1)); + SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1)); } if (HighestMPIter == CurMPIter && CommonTailLen == maxCommonTailLength) - SameTails.push_back(std::make_pair(I, TrialBBI2)); + SameTails.push_back(SameTailElt(I, TrialBBI2)); } - if (I==B) + if (I == B) break; } } @@ -518,21 +595,21 @@ unsigned BranchFolder::ComputeSameTails(unsigned CurHash, /// RemoveBlocksWithHash - Remove all blocks with hash CurHash from /// MergePotentials, restoring branches at ends of blocks as appropriate. -void BranchFolder::RemoveBlocksWithHash(unsigned CurHash, - MachineBasicBlock* SuccBB, - MachineBasicBlock* PredBB) { +void BranchFolder::RemoveBlocksWithHash(unsigned CurHash, + MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { MPIterator CurMPIter, B; - for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin(); - CurMPIter->first==CurHash; + for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin(); + CurMPIter->getHash() == CurHash; --CurMPIter) { // Put the unconditional branch back, if we need one. - MachineBasicBlock *CurMBB = CurMPIter->second; + MachineBasicBlock *CurMBB = CurMPIter->getBlock(); if (SuccBB && CurMBB != PredBB) FixTail(CurMBB, SuccBB, TII); - if (CurMPIter==B) + if (CurMPIter == B) break; } - if (CurMPIter->first!=CurHash) + if (CurMPIter->getHash() != CurHash) CurMPIter++; MergePotentials.erase(CurMPIter, MergePotentials.end()); } @@ -541,35 +618,37 @@ void BranchFolder::RemoveBlocksWithHash(unsigned CurHash, /// only of the common tail. Create a block that does by splitting one. unsigned BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB, unsigned maxCommonTailLength) { - unsigned i, commonTailIndex; + unsigned commonTailIndex = 0; unsigned TimeEstimate = ~0U; - for (i=0, commonTailIndex=0; i<SameTails.size(); i++) { + for (unsigned i = 0, e = SameTails.size(); i != e; ++i) { // Use PredBB if possible; that doesn't require a new branch. - if (SameTails[i].first->second==PredBB) { + if (SameTails[i].getBlock() == PredBB) { commonTailIndex = i; break; } // Otherwise, make a (fairly bogus) choice based on estimate of // how long it will take the various blocks to execute. - unsigned t = EstimateRuntime(SameTails[i].first->second->begin(), - SameTails[i].second); - if (t<=TimeEstimate) { + unsigned t = EstimateRuntime(SameTails[i].getBlock()->begin(), + SameTails[i].getTailStartPos()); + if (t <= TimeEstimate) { TimeEstimate = t; commonTailIndex = i; } } - MachineBasicBlock::iterator BBI = SameTails[commonTailIndex].second; - MachineBasicBlock *MBB = SameTails[commonTailIndex].first->second; + MachineBasicBlock::iterator BBI = + SameTails[commonTailIndex].getTailStartPos(); + MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); - DEBUG(errs() << "\nSplitting " << MBB->getNumber() << ", size " + DEBUG(errs() << "\nSplitting BB#" << MBB->getNumber() << ", size " << maxCommonTailLength); MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI); - SameTails[commonTailIndex].first->second = newMBB; - SameTails[commonTailIndex].second = newMBB->begin(); + SameTails[commonTailIndex].setBlock(newMBB); + SameTails[commonTailIndex].setTailStartPos(newMBB->begin()); + // If we split PredBB, newMBB is the new predecessor. - if (PredBB==MBB) + if (PredBB == MBB) PredBB = newMBB; return commonTailIndex; @@ -579,35 +658,49 @@ unsigned BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB, // successor, or all have no successor) can be tail-merged. If there is a // successor, any blocks in MergePotentials that are not tail-merged and // are not immediately before Succ must have an unconditional branch to -// Succ added (but the predecessor/successor lists need no adjustment). +// Succ added (but the predecessor/successor lists need no adjustment). // The lone predecessor of Succ that falls through into Succ, // if any, is given in PredBB. -bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, - MachineBasicBlock* PredBB) { +bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { bool MadeChange = false; - // It doesn't make sense to save a single instruction since tail merging - // will add a jump. - // FIXME: Ask the target to provide the threshold? - unsigned minCommonTailLength = (SuccBB ? 1 : 2) + 1; - - DEBUG(errs() << "\nTryMergeBlocks " << MergePotentials.size() << '\n'); + // Except for the special cases below, tail-merge if there are at least + // this many instructions in common. + unsigned minCommonTailLength = TailMergeSize; + + DEBUG(errs() << "\nTryTailMergeBlocks: "; + for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) + errs() << "BB#" << MergePotentials[i].getBlock()->getNumber() + << (i == e-1 ? "" : ", "); + errs() << "\n"; + if (SuccBB) { + errs() << " with successor BB#" << SuccBB->getNumber() << '\n'; + if (PredBB) + errs() << " which has fall-through from BB#" + << PredBB->getNumber() << "\n"; + } + errs() << "Looking for common tails of at least " + << minCommonTailLength << " instruction" + << (minCommonTailLength == 1 ? "" : "s") << '\n'; + ); // Sort by hash value so that blocks with identical end sequences sort // together. - std::stable_sort(MergePotentials.begin(), MergePotentials.end(),MergeCompare); + std::stable_sort(MergePotentials.begin(), MergePotentials.end()); // Walk through equivalence sets looking for actual exact matches. while (MergePotentials.size() > 1) { - unsigned CurHash = prior(MergePotentials.end())->first; - + unsigned CurHash = MergePotentials.back().getHash(); + // Build SameTails, identifying the set of blocks with this hash code // and with the maximum number of instructions in common. - unsigned maxCommonTailLength = ComputeSameTails(CurHash, - minCommonTailLength); + unsigned maxCommonTailLength = ComputeSameTails(CurHash, + minCommonTailLength, + SuccBB, PredBB); - // If we didn't find any pair that has at least minCommonTailLength + // If we didn't find any pair that has at least minCommonTailLength // instructions in common, remove all blocks with this hash code and retry. if (SameTails.empty()) { RemoveBlocksWithHash(CurHash, SuccBB, PredBB); @@ -618,36 +711,58 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, // block, which we can't jump to), we can treat all blocks with this same // tail at once. Use PredBB if that is one of the possibilities, as that // will not introduce any extra branches. - MachineBasicBlock *EntryBB = MergePotentials.begin()->second-> - getParent()->begin(); - unsigned int commonTailIndex, i; - for (commonTailIndex=SameTails.size(), i=0; i<SameTails.size(); i++) { - MachineBasicBlock *MBB = SameTails[i].first->second; - if (MBB->begin() == SameTails[i].second && MBB != EntryBB) { - commonTailIndex = i; - if (MBB==PredBB) + MachineBasicBlock *EntryBB = MergePotentials.begin()->getBlock()-> + getParent()->begin(); + unsigned commonTailIndex = SameTails.size(); + // If there are two blocks, check to see if one can be made to fall through + // into the other. + if (SameTails.size() == 2 && + SameTails[0].getBlock()->isLayoutSuccessor(SameTails[1].getBlock()) && + SameTails[1].tailIsWholeBlock()) + commonTailIndex = 1; + else if (SameTails.size() == 2 && + SameTails[1].getBlock()->isLayoutSuccessor( + SameTails[0].getBlock()) && + SameTails[0].tailIsWholeBlock()) + commonTailIndex = 0; + else { + // Otherwise just pick one, favoring the fall-through predecessor if + // there is one. + for (unsigned i = 0, e = SameTails.size(); i != e; ++i) { + MachineBasicBlock *MBB = SameTails[i].getBlock(); + if (MBB == EntryBB && SameTails[i].tailIsWholeBlock()) + continue; + if (MBB == PredBB) { + commonTailIndex = i; break; + } + if (SameTails[i].tailIsWholeBlock()) + commonTailIndex = i; } } - if (commonTailIndex==SameTails.size()) { + if (commonTailIndex == SameTails.size() || + (SameTails[commonTailIndex].getBlock() == PredBB && + !SameTails[commonTailIndex].tailIsWholeBlock())) { // None of the blocks consist entirely of the common tail. // Split a block so that one does. - commonTailIndex = CreateCommonTailOnlyBlock(PredBB, maxCommonTailLength); + commonTailIndex = CreateCommonTailOnlyBlock(PredBB, maxCommonTailLength); } - MachineBasicBlock *MBB = SameTails[commonTailIndex].first->second; + MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); // MBB is common tail. Adjust all other BB's to jump to this one. // Traversal must be forwards so erases work. - DEBUG(errs() << "\nUsing common tail " << MBB->getNumber() << " for "); - for (unsigned int i=0; i<SameTails.size(); ++i) { - if (commonTailIndex==i) + DEBUG(errs() << "\nUsing common tail in BB#" << MBB->getNumber() + << " for "); + for (unsigned int i=0, e = SameTails.size(); i != e; ++i) { + if (commonTailIndex == i) continue; - DEBUG(errs() << SameTails[i].first->second->getNumber() << ","); + DEBUG(errs() << "BB#" << SameTails[i].getBlock()->getNumber() + << (i == e-1 ? "" : ", ")); // Hack the end off BB i, making it jump to BB commonTailIndex instead. - ReplaceTailWithBranchTo(SameTails[i].second, MBB); + ReplaceTailWithBranchTo(SameTails[i].getTailStartPos(), MBB); // BB i is no longer a predecessor of SuccBB; remove it from the worklist. - MergePotentials.erase(SameTails[i].first); + MergePotentials.erase(SameTails[i].getMPIter()); } DEBUG(errs() << "\n"); // We leave commonTailIndex in the worklist in case there are other blocks @@ -660,26 +775,27 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { if (!EnableTailMerge) return false; - + bool MadeChange = false; // First find blocks with no successors. MergePotentials.clear(); for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) { if (I->succ_empty()) - MergePotentials.push_back(std::make_pair(HashEndOfMBB(I, 2U), I)); + MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I, 2U), I)); } + // See if we can do any tail merging on those. if (MergePotentials.size() < TailMergeThreshold && MergePotentials.size() >= 2) - MadeChange |= TryMergeBlocks(NULL, NULL); + MadeChange |= TryTailMergeBlocks(NULL, NULL); // Look at blocks (IBB) with multiple predecessors (PBB). // We change each predecessor to a canonical form, by // (1) temporarily removing any unconditional branch from the predecessor // to IBB, and // (2) alter conditional branches so they branch to the other block - // not IBB; this may require adding back an unconditional branch to IBB + // not IBB; this may require adding back an unconditional branch to IBB // later, where there wasn't one coming in. E.g. // Bcc IBB // fallthrough to QBB @@ -693,18 +809,19 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { // a compile-time infinite loop repeatedly doing and undoing the same // transformations.) - for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) { + for (MachineFunction::iterator I = next(MF.begin()), E = MF.end(); + I != E; ++I) { if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) { SmallPtrSet<MachineBasicBlock *, 8> UniquePreds; MachineBasicBlock *IBB = I; MachineBasicBlock *PredBB = prior(I); MergePotentials.clear(); - for (MachineBasicBlock::pred_iterator P = I->pred_begin(), + for (MachineBasicBlock::pred_iterator P = I->pred_begin(), E2 = I->pred_end(); P != E2; ++P) { - MachineBasicBlock* PBB = *P; + MachineBasicBlock *PBB = *P; // Skip blocks that loop to themselves, can't tail merge these. - if (PBB==IBB) + if (PBB == IBB) continue; // Visit each predecessor only once. if (!UniquePreds.insert(PBB)) @@ -715,7 +832,7 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { // Failing case: IBB is the target of a cbr, and // we cannot reverse the branch. SmallVector<MachineOperand, 4> NewCond(Cond); - if (!Cond.empty() && TBB==IBB) { + if (!Cond.empty() && TBB == IBB) { if (TII->ReverseBranchCondition(NewCond)) continue; // This is the QBB case described above @@ -727,20 +844,20 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { // to have a bit in the edge so we didn't have to do all this. if (IBB->isLandingPad()) { MachineFunction::iterator IP = PBB; IP++; - MachineBasicBlock* PredNextBB = NULL; - if (IP!=MF.end()) + MachineBasicBlock *PredNextBB = NULL; + if (IP != MF.end()) PredNextBB = IP; - if (TBB==NULL) { - if (IBB!=PredNextBB) // fallthrough + if (TBB == NULL) { + if (IBB != PredNextBB) // fallthrough continue; } else if (FBB) { - if (TBB!=IBB && FBB!=IBB) // cbr then ubr + if (TBB != IBB && FBB != IBB) // cbr then ubr continue; } else if (Cond.empty()) { - if (TBB!=IBB) // ubr + if (TBB != IBB) // ubr continue; } else { - if (TBB!=IBB && IBB!=PredNextBB) // cbr + if (TBB != IBB && IBB != PredNextBB) // cbr continue; } } @@ -749,19 +866,20 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { TII->RemoveBranch(*PBB); if (!Cond.empty()) // reinsert conditional branch only, for now - TII->InsertBranch(*PBB, (TBB==IBB) ? FBB : TBB, 0, NewCond); + TII->InsertBranch(*PBB, (TBB == IBB) ? FBB : TBB, 0, NewCond); } - MergePotentials.push_back(std::make_pair(HashEndOfMBB(PBB, 1U), *P)); + MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB, 1U), + *P)); } } - if (MergePotentials.size() >= 2) - MadeChange |= TryMergeBlocks(I, PredBB); - // Reinsert an unconditional branch if needed. - // The 1 below can occur as a result of removing blocks in TryMergeBlocks. - PredBB = prior(I); // this may have been changed in TryMergeBlocks - if (MergePotentials.size()==1 && - MergePotentials.begin()->second != PredBB) - FixTail(MergePotentials.begin()->second, I, TII); + if (MergePotentials.size() >= 2) + MadeChange |= TryTailMergeBlocks(IBB, PredBB); + // Reinsert an unconditional branch if needed. + // The 1 below can occur as a result of removing blocks in TryTailMergeBlocks. + PredBB = prior(I); // this may have been changed in TryTailMergeBlocks + if (MergePotentials.size() == 1 && + MergePotentials.begin()->getBlock() != PredBB) + FixTail(MergePotentials.begin()->getBlock(), IBB, TII); } } return MadeChange; @@ -773,14 +891,14 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { bool BranchFolder::OptimizeBranches(MachineFunction &MF) { bool MadeChange = false; - + // Make sure blocks are numbered in order MF.RenumberBlocks(); for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) { MachineBasicBlock *MBB = I++; MadeChange |= OptimizeBlock(MBB); - + // If it is dead, remove it. if (MBB->pred_empty()) { RemoveDeadBlock(MBB); @@ -801,7 +919,7 @@ bool BranchFolder::OptimizeBranches(MachineFunction &MF) { /// bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB, bool BranchUnAnalyzable, - MachineBasicBlock *TBB, + MachineBasicBlock *TBB, MachineBasicBlock *FBB, const SmallVectorImpl<MachineOperand> &Cond) { MachineFunction::iterator Fallthrough = CurBB; @@ -809,14 +927,22 @@ bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB, // If FallthroughBlock is off the end of the function, it can't fall through. if (Fallthrough == CurBB->getParent()->end()) return false; - + // If FallthroughBlock isn't a successor of CurBB, no fallthrough is possible. if (!CurBB->isSuccessor(Fallthrough)) return false; - - // If we couldn't analyze the branch, assume it could fall through. - if (BranchUnAnalyzable) return true; - + + // If we couldn't analyze the branch, examine the last instruction. + // If the block doesn't end in a known control barrier, assume fallthrough + // is possible. The isPredicable check is needed because this code can be + // called during IfConversion, where an instruction which is normally a + // Barrier is predicated and thus no longer an actual control barrier. This + // is over-conservative though, because if an instruction isn't actually + // predicated we could still treat it like a barrier. + if (BranchUnAnalyzable) + return CurBB->empty() || !CurBB->back().getDesc().isBarrier() || + CurBB->back().getDesc().isPredicable(); + // If there is no branch, control always falls through. if (TBB == 0) return true; @@ -825,11 +951,11 @@ bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB, if (MachineFunction::iterator(TBB) == Fallthrough || MachineFunction::iterator(FBB) == Fallthrough) return true; - - // If it's an unconditional branch to some block not the fall through, it + + // If it's an unconditional branch to some block not the fall through, it // doesn't fall through. if (Cond.empty()) return false; - + // Otherwise, if it is conditional and has no explicit false block, it falls // through. return FBB == 0; @@ -853,14 +979,14 @@ bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB) { /// fall-through to MBB1 than to fall through into MBB2. This has to return /// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will /// result in infinite loops. -static bool IsBetterFallthrough(MachineBasicBlock *MBB1, +static bool IsBetterFallthrough(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2) { // Right now, we use a simple heuristic. If MBB2 ends with a call, and // MBB1 doesn't, we prefer to fall through into MBB1. This allows us to // optimize branches that branch to either a return block or an assert block // into a fallthrough to the return. if (MBB1->empty() || MBB2->empty()) return false; - + // If there is a clear successor ordering we make sure that one block // will fall through to the next if (MBB1->isSuccessor(MBB2)) return true; @@ -871,14 +997,153 @@ static bool IsBetterFallthrough(MachineBasicBlock *MBB1, return MBB2I->getDesc().isCall() && !MBB1I->getDesc().isCall(); } +/// TailDuplicateBlocks - Look for small blocks that are unconditionally +/// branched to and do not fall through. Tail-duplicate their instructions +/// into their predecessors to eliminate (dynamic) branches. +bool BranchFolder::TailDuplicateBlocks(MachineFunction &MF) { + bool MadeChange = false; + + // Make sure blocks are numbered in order + MF.RenumberBlocks(); + + for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) { + MachineBasicBlock *MBB = I++; + + // Only duplicate blocks that end with unconditional branches. + if (CanFallThrough(MBB)) + continue; + + MadeChange |= TailDuplicate(MBB, MF); + + // If it is dead, remove it. + if (MBB->pred_empty()) { + RemoveDeadBlock(MBB); + MadeChange = true; + ++NumDeadBlocks; + } + } + return MadeChange; +} + +/// TailDuplicate - If it is profitable, duplicate TailBB's contents in each +/// of its predecessors. +bool BranchFolder::TailDuplicate(MachineBasicBlock *TailBB, + MachineFunction &MF) { + // Don't try to tail-duplicate single-block loops. + if (TailBB->isSuccessor(TailBB)) + return false; + + // Set the limit on the number of instructions to duplicate, with a default + // of one less than the tail-merge threshold. When optimizing for size, + // duplicate only one, because one branch instruction can be eliminated to + // compensate for the duplication. + unsigned MaxDuplicateCount = + MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize) ? + 1 : TII->TailDuplicationLimit(*TailBB, TailMergeSize - 1); + + // Check the instructions in the block to determine whether tail-duplication + // is invalid or unlikely to be profitable. + unsigned i = 0; + bool HasCall = false; + for (MachineBasicBlock::iterator I = TailBB->begin(); + I != TailBB->end(); ++I, ++i) { + // Non-duplicable things shouldn't be tail-duplicated. + if (I->getDesc().isNotDuplicable()) return false; + // Don't duplicate more than the threshold. + if (i == MaxDuplicateCount) return false; + // Remember if we saw a call. + if (I->getDesc().isCall()) HasCall = true; + } + // Heuristically, don't tail-duplicate calls if it would expand code size, + // as it's less likely to be worth the extra cost. + if (i > 1 && HasCall) + return false; + + // Iterate through all the unique predecessors and tail-duplicate this + // block into them, if possible. Copying the list ahead of time also + // avoids trouble with the predecessor list reallocating. + bool Changed = false; + SmallSetVector<MachineBasicBlock *, 8> Preds(TailBB->pred_begin(), + TailBB->pred_end()); + for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(), + PE = Preds.end(); PI != PE; ++PI) { + MachineBasicBlock *PredBB = *PI; + + assert(TailBB != PredBB && + "Single-block loop should have been rejected earlier!"); + if (PredBB->succ_size() > 1) continue; + + MachineBasicBlock *PredTBB, *PredFBB; + SmallVector<MachineOperand, 4> PredCond; + if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true)) + continue; + if (!PredCond.empty()) + continue; + // EH edges are ignored by AnalyzeBranch. + if (PredBB->succ_size() != 1) + continue; + // Don't duplicate into a fall-through predecessor (at least for now). + if (PredBB->isLayoutSuccessor(TailBB) && CanFallThrough(PredBB)) + continue; + + DEBUG(errs() << "\nTail-duplicating into PredBB: " << *PredBB + << "From Succ: " << *TailBB); + + // Remove PredBB's unconditional branch. + TII->RemoveBranch(*PredBB); + // Clone the contents of TailBB into PredBB. + for (MachineBasicBlock::iterator I = TailBB->begin(), E = TailBB->end(); + I != E; ++I) { + MachineInstr *NewMI = MF.CloneMachineInstr(I); + PredBB->insert(PredBB->end(), NewMI); + } + + // Update the CFG. + PredBB->removeSuccessor(PredBB->succ_begin()); + assert(PredBB->succ_empty() && + "TailDuplicate called on block with multiple successors!"); + for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(), + E = TailBB->succ_end(); I != E; ++I) + PredBB->addSuccessor(*I); + + Changed = true; + } + + // If TailBB was duplicated into all its predecessors except for the prior + // block, which falls through unconditionally, move the contents of this + // block into the prior block. + MachineBasicBlock &PrevBB = *prior(MachineFunction::iterator(TailBB)); + MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0; + SmallVector<MachineOperand, 4> PriorCond; + bool PriorUnAnalyzable = + TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true); + // This has to check PrevBB->succ_size() because EH edges are ignored by + // AnalyzeBranch. + if (!PriorUnAnalyzable && PriorCond.empty() && !PriorTBB && + TailBB->pred_size() == 1 && PrevBB.succ_size() == 1 && + !TailBB->hasAddressTaken()) { + DEBUG(errs() << "\nMerging into block: " << PrevBB + << "From MBB: " << *TailBB); + PrevBB.splice(PrevBB.end(), TailBB, TailBB->begin(), TailBB->end()); + PrevBB.removeSuccessor(PrevBB.succ_begin());; + assert(PrevBB.succ_empty()); + PrevBB.transferSuccessors(TailBB); + Changed = true; + } + + return Changed; +} + /// OptimizeBlock - Analyze and optimize control flow related to the specified /// block. This is never called on the entry block. bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { bool MadeChange = false; + MachineFunction &MF = *MBB->getParent(); +ReoptimizeBlock: MachineFunction::iterator FallThrough = MBB; ++FallThrough; - + // If this block is empty, make everyone use its fall-through, not the block // explicitly. Landing pads should not do this since the landing-pad table // points to this block. Blocks with their addresses taken shouldn't be @@ -886,8 +1151,8 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { if (MBB->empty() && !MBB->isLandingPad() && !MBB->hasAddressTaken()) { // Dead block? Leave for cleanup later. if (MBB->pred_empty()) return MadeChange; - - if (FallThrough == MBB->getParent()->end()) { + + if (FallThrough == MF.end()) { // TODO: Simplify preds to not branch here if possible! } else { // Rewrite all predecessors of the old block to go to the fallthrough @@ -898,8 +1163,7 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { } // If MBB was the target of a jump table, update jump tables to go to the // fallthrough instead. - MBB->getParent()->getJumpTableInfo()-> - ReplaceMBBInJumpTables(MBB, FallThrough); + MF.getJumpTableInfo()->ReplaceMBBInJumpTables(MBB, FallThrough); MadeChange = true; } return MadeChange; @@ -917,29 +1181,49 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // If the CFG for the prior block has extra edges, remove them. MadeChange |= PrevBB.CorrectExtraCFGEdges(PriorTBB, PriorFBB, !PriorCond.empty()); - + // If the previous branch is conditional and both conditions go to the same // destination, remove the branch, replacing it with an unconditional one or // a fall-through. if (PriorTBB && PriorTBB == PriorFBB) { TII->RemoveBranch(PrevBB); - PriorCond.clear(); + PriorCond.clear(); if (PriorTBB != MBB) TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } - + + // If the previous block unconditionally falls through to this block and + // this block has no other predecessors, move the contents of this block + // into the prior block. This doesn't usually happen when SimplifyCFG + // has been used, but it can happen if tail merging splits a fall-through + // predecessor of a block. + // This has to check PrevBB->succ_size() because EH edges are ignored by + // AnalyzeBranch. + if (PriorCond.empty() && !PriorTBB && MBB->pred_size() == 1 && + PrevBB.succ_size() == 1 && + !MBB->hasAddressTaken()) { + DEBUG(errs() << "\nMerging into block: " << PrevBB + << "From MBB: " << *MBB); + PrevBB.splice(PrevBB.end(), MBB, MBB->begin(), MBB->end()); + PrevBB.removeSuccessor(PrevBB.succ_begin());; + assert(PrevBB.succ_empty()); + PrevBB.transferSuccessors(MBB); + MadeChange = true; + return MadeChange; + } + // If the previous branch *only* branches to *this* block (conditional or // not) remove the branch. if (PriorTBB == MBB && PriorFBB == 0) { TII->RemoveBranch(PrevBB); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } - + // If the prior block branches somewhere else on the condition and here if // the condition is false, remove the uncond second branch. if (PriorFBB == MBB) { @@ -947,9 +1231,9 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } - + // If the prior block branches here on true and somewhere else on false, and // if the branch condition is reversible, reverse the branch to create a // fall-through. @@ -960,10 +1244,10 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } - + // If this block has no successors (e.g. it is a return block or ends with // a call to a no-return function like abort or __cxa_throw) and if the pred // falls through into this block, and if it would otherwise fall through @@ -976,13 +1260,13 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { MachineFunction::iterator(PriorTBB) == FallThrough && !CanFallThrough(MBB)) { bool DoTransform = true; - + // We have to be careful that the succs of PredBB aren't both no-successor // blocks. If neither have successors and if PredBB is the second from // last block in the function, we'd just keep swapping the two blocks for // last. Only do the swap if one is clearly better to fall through than // the other. - if (FallThrough == --MBB->getParent()->end() && + if (FallThrough == --MF.end() && !IsBetterFallthrough(PriorTBB, MBB)) DoTransform = false; @@ -1000,20 +1284,20 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { if (DoTransform && !MBB->succ_empty() && (!CanFallThrough(PriorTBB) || PriorTBB->empty())) DoTransform = false; - - + + if (DoTransform) { // Reverse the branch so we will fall through on the previous true cond. SmallVector<MachineOperand, 4> NewPriorCond(PriorCond); if (!TII->ReverseBranchCondition(NewPriorCond)) { DEBUG(errs() << "\nMoving MBB: " << *MBB << "To make fallthrough to: " << *PriorTBB << "\n"); - + TII->RemoveBranch(PrevBB); TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond); // Move this block to the end of the function. - MBB->moveAfter(--MBB->getParent()->end()); + MBB->moveAfter(--MF.end()); MadeChange = true; ++NumBranchOpts; return MadeChange; @@ -1021,7 +1305,7 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { } } } - + // Analyze the branch in the current block. MachineBasicBlock *CurTBB = 0, *CurFBB = 0; SmallVector<MachineOperand, 4> CurCond; @@ -1030,7 +1314,7 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // If the CFG for the prior block has extra edges, remove them. MadeChange |= MBB->CorrectExtraCFGEdges(CurTBB, CurFBB, !CurCond.empty()); - // If this is a two-way branch, and the FBB branches to this block, reverse + // If this is a two-way branch, and the FBB branches to this block, reverse // the condition so the single-basic-block loop is faster. Instead of: // Loop: xxx; jcc Out; jmp Loop // we want: @@ -1042,14 +1326,13 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { TII->InsertBranch(*MBB, CurFBB, CurTBB, NewCond); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } - - + // If this branch is the only thing in its block, see if we can forward // other blocks across it. - if (CurTBB && CurCond.empty() && CurFBB == 0 && + if (CurTBB && CurCond.empty() && CurFBB == 0 && MBB->begin()->getDesc().isBranch() && CurTBB != MBB && !MBB->hasAddressTaken()) { // This block may contain just an unconditional branch. Because there can @@ -1068,7 +1351,7 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { !PrevBB.isSuccessor(MBB)) { // If the prior block falls through into us, turn it into an // explicit branch to us to make updates simpler. - if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) && + if (!PredHasNoFallThrough && PrevBB.isSuccessor(MBB) && PriorTBB != MBB && PriorFBB != MBB) { if (PriorTBB == 0) { assert(PriorCond.empty() && PriorFBB == 0 && @@ -1104,18 +1387,17 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { NewCurFBB, NewCurCond, true); if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) { TII->RemoveBranch(*PMBB); - NewCurCond.clear(); + NewCurCond.clear(); TII->InsertBranch(*PMBB, NewCurTBB, 0, NewCurCond); MadeChange = true; ++NumBranchOpts; - PMBB->CorrectExtraCFGEdges(NewCurTBB, NewCurFBB, false); + PMBB->CorrectExtraCFGEdges(NewCurTBB, 0, false); } } } // Change any jumptables to go to the new MBB. - MBB->getParent()->getJumpTableInfo()-> - ReplaceMBBInJumpTables(MBB, CurTBB); + MF.getJumpTableInfo()->ReplaceMBBInJumpTables(MBB, CurTBB); if (DidChange) { ++NumBranchOpts; MadeChange = true; @@ -1123,7 +1405,7 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { } } } - + // Add the branch back if the block is more than just an uncond branch. TII->InsertBranch(*MBB, CurTBB, 0, CurCond); } @@ -1134,9 +1416,10 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // place to move this block where a fall-through will happen. if (!CanFallThrough(&PrevBB, PriorUnAnalyzable, PriorTBB, PriorFBB, PriorCond)) { + // Now we know that there was no fall-through into this block, check to // see if it has a fall-through into its successor. - bool CurFallsThru = CanFallThrough(MBB, CurUnAnalyzable, CurTBB, CurFBB, + bool CurFallsThru = CanFallThrough(MBB, CurUnAnalyzable, CurTBB, CurFBB, CurCond); if (!MBB->isLandingPad()) { @@ -1147,12 +1430,15 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // Analyze the branch at the end of the pred. MachineBasicBlock *PredBB = *PI; MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough; - if (PredBB != MBB && !CanFallThrough(PredBB) + MachineBasicBlock *PredTBB, *PredFBB; + SmallVector<MachineOperand, 4> PredCond; + if (PredBB != MBB && !CanFallThrough(PredBB) && + !TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true) && (!CurFallsThru || !CurTBB || !CurFBB) && (!CurFallsThru || MBB->getNumber() >= PredBB->getNumber())) { // If the current block doesn't fall through, just move it. // If the current block can fall through and does not end with a - // conditional branch, we need to append an unconditional jump to + // conditional branch, we need to append an unconditional jump to // the (current) next block. To avoid a possible compile-time // infinite loop, move blocks only backward in this case. // Also, if there are already 2 branches here, we cannot add a third; @@ -1167,11 +1453,11 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { } MBB->moveAfter(PredBB); MadeChange = true; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } } - + if (!CurFallsThru) { // Check all successors to see if we can move this block before it. for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(), @@ -1179,26 +1465,29 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { // Analyze the branch at the end of the block before the succ. MachineBasicBlock *SuccBB = *SI; MachineFunction::iterator SuccPrev = SuccBB; --SuccPrev; - std::vector<MachineOperand> SuccPrevCond; - + // If this block doesn't already fall-through to that successor, and if // the succ doesn't already have a block that can fall through into it, // and if the successor isn't an EH destination, we can arrange for the // fallthrough to happen. - if (SuccBB != MBB && !CanFallThrough(SuccPrev) && + if (SuccBB != MBB && &*SuccPrev != MBB && + !CanFallThrough(SuccPrev) && !CurUnAnalyzable && !SuccBB->isLandingPad()) { MBB->moveBefore(SuccBB); MadeChange = true; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } - + // Okay, there is no really great place to put this block. If, however, // the block before this one would be a fall-through if this block were // removed, move this block to the end of the function. - if (FallThrough != MBB->getParent()->end() && + MachineBasicBlock *PrevTBB, *PrevFBB; + SmallVector<MachineOperand, 4> PrevCond; + if (FallThrough != MF.end() && + !TII->AnalyzeBranch(PrevBB, PrevTBB, PrevFBB, PrevCond, true) && PrevBB.isSuccessor(FallThrough)) { - MBB->moveAfter(--MBB->getParent()->end()); + MBB->moveAfter(--MF.end()); MadeChange = true; return MadeChange; } |