X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FBranchFolding.cpp;h=dd17d881c51393f8d9121e93ee13928fb59e2f79;hb=b3bc115a2414a922caa40d5536d8a35ca54e40e3;hp=48f74d94c875de75a3383b747db9fa9027a12e70;hpb=a52dd151378eeaad1369829b1dc3164874774e04;p=oota-llvm.git diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp index 48f74d94c87..dd17d881c51 100644 --- a/lib/CodeGen/BranchFolding.cpp +++ b/lib/CodeGen/BranchFolding.cpp @@ -2,8 +2,8 @@ // // The LLVM Compiler Infrastructure // -// This file was developed by the LLVM research group and is distributed under -// the University of Illinois Open Source License. See LICENSE.TXT for details. +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // @@ -17,6 +17,8 @@ //===----------------------------------------------------------------------===// #define DEBUG_TYPE "branchfolding" +#include "BranchFolding.h" +#include "llvm/Function.h" #include "llvm/CodeGen/Passes.h" #include "llvm/CodeGen/MachineModuleInfo.h" #include "llvm/CodeGen/MachineFunctionPass.h" @@ -24,9 +26,13 @@ #include "llvm/CodeGen/RegisterScavenging.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetMachine.h" -#include "llvm/Target/MRegisterInfo.h" +#include "llvm/Target/TargetRegisterInfo.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" +#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 @@ -35,113 +41,165 @@ 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 FlagEnableTailMerge("enable-tail-merge", +static cl::opt FlagEnableTailMerge("enable-tail-merge", cl::init(cl::BOU_UNSET), cl::Hidden); +// Throttle for huge numbers of predecessors (compile speed problems) +static cl::opt +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 +TailMergeSize("tail-merge-size", + cl::desc("Min number of instructions to consider tail merging"), + cl::init(3), cl::Hidden); + namespace { - struct BranchFolder : public MachineFunctionPass { + /// BranchFolderPass - Wrap branch folder in a machine function pass. + class BranchFolderPass : public MachineFunctionPass, + public BranchFolder { + public: static char ID; - BranchFolder(bool defaultEnableTailMerge) : - MachineFunctionPass((intptr_t)&ID) { - switch (FlagEnableTailMerge) { - case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break; - case cl::BOU_TRUE: EnableTailMerge = true; break; - case cl::BOU_FALSE: EnableTailMerge = false; break; - } - } + explicit BranchFolderPass(bool defaultEnableTailMerge) + : MachineFunctionPass(&ID), BranchFolder(defaultEnableTailMerge) {} virtual bool runOnMachineFunction(MachineFunction &MF); virtual const char *getPassName() const { return "Control Flow Optimizer"; } - const TargetInstrInfo *TII; - MachineModuleInfo *MMI; - bool MadeChange; - private: - // Tail Merging. - bool EnableTailMerge; - bool TailMergeBlocks(MachineFunction &MF); - bool TryMergeBlocks(MachineBasicBlock* SuccBB, - MachineBasicBlock* PredBB); - void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst, - MachineBasicBlock *NewDest); - MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB, - MachineBasicBlock::iterator BBI1); - - std::vector > MergePotentials; - const MRegisterInfo *RegInfo; - RegScavenger *RS; - // Branch optzn. - bool OptimizeBranches(MachineFunction &MF); - void OptimizeBlock(MachineBasicBlock *MBB); - void RemoveDeadBlock(MachineBasicBlock *MBB); - - bool CanFallThrough(MachineBasicBlock *CurBB); - bool CanFallThrough(MachineBasicBlock *CurBB, bool BranchUnAnalyzable, - MachineBasicBlock *TBB, MachineBasicBlock *FBB, - const std::vector &Cond); }; - char BranchFolder::ID = 0; } -static bool CorrectExtraCFGEdges(MachineBasicBlock &MBB, - MachineBasicBlock *DestA, - MachineBasicBlock *DestB, - bool isCond, - MachineFunction::iterator FallThru); +char BranchFolderPass::ID = 0; -FunctionPass *llvm::createBranchFoldingPass(bool DefaultEnableTailMerge) { - return new BranchFolder(DefaultEnableTailMerge); } +FunctionPass *llvm::createBranchFoldingPass(bool DefaultEnableTailMerge) { + return new BranchFolderPass(DefaultEnableTailMerge); +} + +bool BranchFolderPass::runOnMachineFunction(MachineFunction &MF) { + return OptimizeFunction(MF, + MF.getTarget().getInstrInfo(), + MF.getTarget().getRegisterInfo(), + getAnalysisIfAvailable()); +} + + +BranchFolder::BranchFolder(bool defaultEnableTailMerge) { + switch (FlagEnableTailMerge) { + case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break; + case cl::BOU_TRUE: EnableTailMerge = true; break; + case cl::BOU_FALSE: EnableTailMerge = false; break; + } +} /// RemoveDeadBlock - Remove the specified dead machine basic block from the /// function, updating the CFG. void BranchFolder::RemoveDeadBlock(MachineBasicBlock *MBB) { assert(MBB->pred_empty() && "MBB must be dead!"); - DOUT << "\nRemoving MBB: " << *MBB; - + DEBUG(errs() << "\nRemoving MBB: " << *MBB); + MachineFunction *MF = MBB->getParent(); // drop all successors. while (!MBB->succ_empty()) MBB->removeSuccessor(MBB->succ_end()-1); - - // If there is DWARF info to active, check to see if there are any LABEL - // records in the basic block. If so, unregister them from MachineModuleInfo. + + // If there are any labels in the basic block, unregister them from + // MachineModuleInfo. if (MMI && !MBB->empty()) { for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E; ++I) { - if ((unsigned)I->getOpcode() == TargetInstrInfo::LABEL) { + if (I->isLabel()) // The label ID # is always operand #0, an immediate. MMI->InvalidateLabel(I->getOperand(0).getImm()); - } } } - + // Remove the block. - MF->getBasicBlockList().erase(MBB); + MF->erase(MBB); +} + +/// OptimizeImpDefsBlock - If a basic block is just a bunch of implicit_def +/// followed by terminators, and if the implicitly defined registers are not +/// used by the terminators, remove those implicit_def's. e.g. +/// BB1: +/// r0 = implicit_def +/// r1 = implicit_def +/// br +/// This block can be optimized away later if the implicit instructions are +/// removed. +bool BranchFolder::OptimizeImpDefsBlock(MachineBasicBlock *MBB) { + SmallSet ImpDefRegs; + MachineBasicBlock::iterator I = MBB->begin(); + while (I != MBB->end()) { + if (I->getOpcode() != TargetInstrInfo::IMPLICIT_DEF) + break; + unsigned Reg = I->getOperand(0).getReg(); + ImpDefRegs.insert(Reg); + for (const unsigned *SubRegs = TRI->getSubRegisters(Reg); + unsigned SubReg = *SubRegs; ++SubRegs) + ImpDefRegs.insert(SubReg); + ++I; + } + if (ImpDefRegs.empty()) + return false; + + MachineBasicBlock::iterator FirstTerm = I; + while (I != MBB->end()) { + if (!TII->isUnpredicatedTerminator(I)) + return false; + // See if it uses any of the implicitly defined registers. + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { + MachineOperand &MO = I->getOperand(i); + if (!MO.isReg() || !MO.isUse()) + continue; + unsigned Reg = MO.getReg(); + if (ImpDefRegs.count(Reg)) + return false; + } + ++I; + } + + I = MBB->begin(); + while (I != FirstTerm) { + MachineInstr *ImpDefMI = &*I; + ++I; + MBB->erase(ImpDefMI); + } + + return true; } -bool BranchFolder::runOnMachineFunction(MachineFunction &MF) { - TII = MF.getTarget().getInstrInfo(); - if (!TII) return false; +/// OptimizeFunction - Perhaps branch folding, tail merging and other +/// CFG optimizations on the given function. +bool BranchFolder::OptimizeFunction(MachineFunction &MF, + const TargetInstrInfo *tii, + const TargetRegisterInfo *tri, + MachineModuleInfo *mmi) { + if (!tii) return false; + + TII = tii; + TRI = tri; + MMI = mmi; + + RS = TRI->requiresRegisterScavenging(MF) ? new RegScavenger() : NULL; // Fix CFG. The later algorithms expect it to be right. - bool EverMadeChange = false; + bool MadeChange = false; for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; I++) { MachineBasicBlock *MBB = I, *TBB = 0, *FBB = 0; - std::vector Cond; - if (!TII->AnalyzeBranch(*MBB, TBB, FBB, Cond)) - EverMadeChange |= CorrectExtraCFGEdges(*MBB, TBB, FBB, - !Cond.empty(), next(I)); + SmallVector Cond; + if (!TII->AnalyzeBranch(*MBB, TBB, FBB, Cond, true)) + MadeChange |= MBB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty()); + MadeChange |= OptimizeImpDefsBlock(MBB); } - RegInfo = MF.getTarget().getRegisterInfo(); - RS = RegInfo->requiresRegisterScavenging(MF) ? new RegScavenger() : NULL; - - MMI = getAnalysisToUpdate(); bool MadeChangeThisIteration = true; while (MadeChangeThisIteration) { MadeChangeThisIteration = false; MadeChangeThisIteration |= TailMergeBlocks(MF); MadeChangeThisIteration |= OptimizeBranches(MF); - EverMadeChange |= MadeChangeThisIteration; + MadeChange |= MadeChangeThisIteration; } // See if any jump tables have become mergable or dead as the code generator @@ -152,47 +210,50 @@ bool BranchFolder::runOnMachineFunction(MachineFunction &MF) { // Figure out how these jump tables should be merged. std::vector JTMapping; JTMapping.reserve(JTs.size()); - + // We always keep the 0th jump table. JTMapping.push_back(0); // Scan the jump tables, seeing if there are any duplicates. Note that this // is N^2, which should be fixed someday. - for (unsigned i = 1, e = JTs.size(); i != e; ++i) - JTMapping.push_back(JTI->getJumpTableIndex(JTs[i].MBBs)); - + for (unsigned i = 1, e = JTs.size(); i != e; ++i) { + if (JTs[i].MBBs.empty()) + JTMapping.push_back(i); + 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. - std::vector JTIsLive; - JTIsLive.resize(JTs.size()); + BitVector JTIsLive(JTs.size()); for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); BB != E; ++BB) { for (MachineBasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op) { MachineOperand &Op = I->getOperand(op); - if (!Op.isJumpTableIndex()) continue; - unsigned NewIdx = JTMapping[Op.getJumpTableIndex()]; - Op.setJumpTableIndex(NewIdx); + if (!Op.isJTI()) continue; + unsigned NewIdx = JTMapping[Op.getIndex()]; + Op.setIndex(NewIdx); // Remember that this JT is live. - JTIsLive[NewIdx] = true; + 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. for (unsigned i = 0, e = JTIsLive.size(); i != e; ++i) - if (!JTIsLive[i]) { + if (!JTIsLive.test(i)) { JTI->RemoveJumpTable(i); - EverMadeChange = true; + MadeChange = true; } } - + delete RS; - return EverMadeChange; + return MadeChange; } //===----------------------------------------------------------------------===// @@ -204,21 +265,19 @@ 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()) { case MachineOperand::MO_Register: OperandHash = Op.getReg(); break; case MachineOperand::MO_Immediate: OperandHash = Op.getImm(); break; case MachineOperand::MO_MachineBasicBlock: - OperandHash = Op.getMachineBasicBlock()->getNumber(); + OperandHash = Op.getMBB()->getNumber(); break; - case MachineOperand::MO_FrameIndex: OperandHash = Op.getFrameIndex(); break; + case MachineOperand::MO_FrameIndex: case MachineOperand::MO_ConstantPoolIndex: - OperandHash = Op.getConstantPoolIndex(); - break; case MachineOperand::MO_JumpTableIndex: - OperandHash = Op.getJumpTableIndex(); + OperandHash = Op.getIndex(); break; case MachineOperand::MO_GlobalAddress: case MachineOperand::MO_ExternalSymbol: @@ -228,31 +287,30 @@ 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; @@ -268,11 +326,17 @@ 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 + // optimizations (like this one) may reorder and/or merge these + // directives. + I1->getOpcode() == TargetInstrInfo::INLINEASM) { ++I1; ++I2; break; } @@ -287,17 +351,17 @@ 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()); // If OldBB isn't immediately before OldBB, insert a branch to it. if (++MachineFunction::iterator(OldBB) != MachineFunction::iterator(NewDest)) - TII->InsertBranch(*OldBB, NewDest, 0, std::vector()); + TII->InsertBranch(*OldBB, NewDest, 0, SmallVector()); OldBB->addSuccessor(NewDest); ++NumTailMerge; } @@ -307,21 +371,19 @@ void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst, /// iterator. This returns the new MBB. MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, MachineBasicBlock::iterator BBI1) { + MachineFunction &MF = *CurMBB.getParent(); + // Create the fall-through block. MachineFunction::iterator MBBI = &CurMBB; - MachineBasicBlock *NewMBB = new MachineBasicBlock(CurMBB.getBasicBlock()); - CurMBB.getParent()->getBasicBlockList().insert(++MBBI, NewMBB); + MachineBasicBlock *NewMBB =MF.CreateMachineBasicBlock(CurMBB.getBasicBlock()); + CurMBB.getParent()->insert(++MBBI, NewMBB); // Move all the successors of this block to the specified block. - while (!CurMBB.succ_empty()) { - MachineBasicBlock *S = *(CurMBB.succ_end()-1); - NewMBB->addSuccessor(S); - CurMBB.removeSuccessor(S); - } - + 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()); @@ -330,9 +392,9 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, RS->enterBasicBlock(&CurMBB); if (!CurMBB.empty()) RS->forward(prior(CurMBB.end())); - BitVector RegsLiveAtExit(RegInfo->getNumRegs()); + BitVector RegsLiveAtExit(TRI->getNumRegs()); RS->getRegsUsed(RegsLiveAtExit, false); - for (unsigned int i=0, e=RegInfo->getNumRegs(); i!=e; i++) + for (unsigned int i = 0, e = TRI->getNumRegs(); i != e; i++) if (RegsLiveAtExit[i]) NewMBB->addLiveIn(i); } @@ -343,14 +405,13 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB, /// EstimateRuntime - Make a rough estimate for how long it will take to run /// the specified code. static unsigned EstimateRuntime(MachineBasicBlock::iterator I, - MachineBasicBlock::iterator E, - const TargetInstrInfo *TII) { + MachineBasicBlock::iterator E) { unsigned Time = 0; for (; I != E; ++I) { - const TargetInstrDescriptor &TID = TII->get(I->getOpcode()); - if (TID.Flags & M_CALL_FLAG) + const TargetInstrDesc &TID = I->getDesc(); + if (TID.isCall()) Time += 10; - else if (TID.Flags & (M_LOAD_FLAG|M_STORE_FLAG)) + else if (TID.mayLoad() || TID.mayStore()) Time += 2; else ++Time; @@ -358,58 +419,20 @@ static unsigned EstimateRuntime(MachineBasicBlock::iterator I, return Time; } -/// ShouldSplitFirstBlock - We need to either split MBB1 at MBB1I or MBB2 at -/// MBB2I and then insert an unconditional branch in the other block. Determine -/// which is the best to split -static bool ShouldSplitFirstBlock(MachineBasicBlock *MBB1, - MachineBasicBlock::iterator MBB1I, - MachineBasicBlock *MBB2, - MachineBasicBlock::iterator MBB2I, - const TargetInstrInfo *TII, - MachineBasicBlock *PredBB) { - // If one block is the entry block, split the other one; we can't generate - // a branch to the entry block, as its label is not emitted. - MachineBasicBlock *Entry = MBB1->getParent()->begin(); - if (MBB1 == Entry) - return false; - if (MBB2 == Entry) - return true; - - // If one block falls through into the common successor, choose that - // one to split; it is one instruction less to do that. - if (PredBB) { - if (MBB1 == PredBB) - return true; - else if (MBB2 == PredBB) - return false; - } - // TODO: if we had some notion of which block was hotter, we could split - // the hot block, so it is the fall-through. Since we don't have profile info - // make a decision based on which will hurt most to split. - unsigned MBB1Time = EstimateRuntime(MBB1->begin(), MBB1I, TII); - unsigned MBB2Time = EstimateRuntime(MBB2->begin(), MBB2I, TII); - - // If the MBB1 prefix takes "less time" to run than the MBB2 prefix, split the - // MBB1 block so it falls through. This will penalize the MBB2 path, but will - // have a lower overall impact on the program execution. - return MBB1Time < MBB2Time; -} - // CurMBB needs to add an unconditional branch to SuccMBB (we removed these // 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, const TargetInstrInfo *TII) { MachineFunction *MF = CurMBB->getParent(); MachineFunction::iterator I = next(MachineFunction::iterator(CurMBB)); MachineBasicBlock *TBB = 0, *FBB = 0; - std::vector Cond; + SmallVector Cond; if (I != MF->end() && - !TII->AnalyzeBranch(*CurMBB, TBB, FBB, Cond)) { + !TII->AnalyzeBranch(*CurMBB, TBB, FBB, Cond, true)) { MachineBasicBlock *NextBB = I; - if (TBB == NextBB && Cond.size() && !FBB) { + if (TBB == NextBB && !Cond.empty() && !FBB) { if (!TII->ReverseBranchCondition(Cond)) { TII->RemoveBranch(*CurMBB); TII->InsertBranch(*CurMBB, SuccBB, NULL, Cond); @@ -417,133 +440,358 @@ static void FixTail(MachineBasicBlock* CurMBB, MachineBasicBlock *SuccBB, } } } - TII->InsertBranch(*CurMBB, SuccBB, NULL, std::vector()); + TII->InsertBranch(*CurMBB, SuccBB, NULL, SmallVector()); } -static bool MergeCompare(const std::pair &p, - const std::pair &q) { - if (p.first < q.first) - return true; - else if (p.first > q.first) - return false; - else if (p.second->getNumber() < q.second->getNumber()) +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"); +#endif + 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 +/// and decide if it would be profitable to merge those tails. Return the +/// length of the common tail and iterators to the first common instruction +/// in each block. +static bool ProfitableToMerge(MachineBasicBlock *MBB1, + MachineBasicBlock *MBB2, + unsigned minCommonTailLength, + unsigned &CommonTailLen, + MachineBasicBlock::iterator &I1, + MachineBasicBlock::iterator &I2, + MachineBasicBlock *SuccBB, + MachineBasicBlock *PredBB) { + CommonTailLen = ComputeCommonTailLength(MBB1, MBB2, I1, I2); + MachineFunction *MF = MBB1->getParent(); + + if (CommonTailLen == 0) + return false; + + // 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; - else if (p.second->getNumber() > q.second->getNumber()) - return false; - else - assert(0 && "Predecessor appears twice"); + } + + // 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, + // treat that as an additional common instruction. + if (MBB1 != PredBB && MBB2 != PredBB && + !MBB1->back().getDesc().isBarrier() && + !MBB2->back().getDesc().isBarrier()) + --minCommonTailLength; + + // Check if the common tail is long enough to be worthwhile. + if (CommonTailLen >= minCommonTailLength) + return true; + + // 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) && + (I1 == MBB1->begin() || I2 == MBB2->begin())) + return true; + + return false; +} + +/// ComputeSameTails - Look through all the blocks in MergePotentials that have +/// 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 +/// 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, + 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->getHash() == CurHash; + --CurMPIter) { + for (MPIterator I = prior(CurMPIter); I->getHash() == CurHash ; --I) { + unsigned CommonTailLen; + if (ProfitableToMerge(CurMPIter->getBlock(), I->getBlock(), + minCommonTailLength, + CommonTailLen, TrialBBI1, TrialBBI2, + SuccBB, PredBB)) { + if (CommonTailLen > maxCommonTailLength) { + SameTails.clear(); + maxCommonTailLength = CommonTailLen; + HighestMPIter = CurMPIter; + SameTails.push_back(SameTailElt(CurMPIter, TrialBBI1)); + } + if (HighestMPIter == CurMPIter && + CommonTailLen == maxCommonTailLength) + SameTails.push_back(SameTailElt(I, TrialBBI2)); + } + if (I == B) + break; + } + } + return maxCommonTailLength; +} + +/// 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) { + MPIterator CurMPIter, B; + for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin(); + CurMPIter->getHash() == CurHash; + --CurMPIter) { + // Put the unconditional branch back, if we need one. + MachineBasicBlock *CurMBB = CurMPIter->getBlock(); + if (SuccBB && CurMBB != PredBB) + FixTail(CurMBB, SuccBB, TII); + if (CurMPIter == B) + break; + } + if (CurMPIter->getHash() != CurHash) + CurMPIter++; + MergePotentials.erase(CurMPIter, MergePotentials.end()); +} + +/// CreateCommonTailOnlyBlock - None of the blocks to be tail-merged consist +/// only of the common tail. Create a block that does by splitting one. +unsigned BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB, + unsigned maxCommonTailLength) { + unsigned commonTailIndex = 0; + unsigned TimeEstimate = ~0U; + for (unsigned i = 0, e = SameTails.size(); i != e; ++i) { + // Use PredBB if possible; that doesn't require a new branch. + 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].getBlock()->begin(), + SameTails[i].getTailStartPos()); + if (t <= TimeEstimate) { + TimeEstimate = t; + commonTailIndex = i; + } + } + + MachineBasicBlock::iterator BBI = + SameTails[commonTailIndex].getTailStartPos(); + MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock(); + + DEBUG(errs() << "\nSplitting BB#" << MBB->getNumber() << ", size " + << maxCommonTailLength); + + MachineBasicBlock *newMBB = SplitMBBAt(*MBB, BBI); + SameTails[commonTailIndex].setBlock(newMBB); + SameTails[commonTailIndex].setTailStartPos(newMBB->begin()); + + // If we split PredBB, newMBB is the new predecessor. + if (PredBB == MBB) + PredBB = newMBB; + + return commonTailIndex; } // See if any of the blocks in MergePotentials (which all have a common single // 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) { - unsigned minCommonTailLength = (SuccBB ? 1 : 2); - MadeChange = false; - +bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB, + MachineBasicBlock* PredBB) { + bool MadeChange = false; + + // Except for the special cases below, tail-merge if there are at least + // this many instructions in common. + unsigned minCommonTailLength = TailMergeSize; + + // If there's a successor block, there are some cases which don't require + // new branching and as such are very likely to be profitable. + if (SuccBB) { + if (SuccBB->pred_size() == MergePotentials.size() && + !MergePotentials[0].getBlock()->empty()) { + // If all the predecessors have at least one tail instruction in common, + // merging is very likely to be a win since it won't require an increase + // in static branches, and it will decrease the static instruction count. + bool AllPredsMatch = true; + MachineBasicBlock::iterator FirstNonTerm; + unsigned MinNumTerms = CountTerminators(MergePotentials[0].getBlock(), + FirstNonTerm); + if (FirstNonTerm != MergePotentials[0].getBlock()->end()) { + for (unsigned i = 1, e = MergePotentials.size(); i != e; ++i) { + MachineBasicBlock::iterator OtherFirstNonTerm; + unsigned NumTerms = CountTerminators(MergePotentials[0].getBlock(), + OtherFirstNonTerm); + if (NumTerms < MinNumTerms) + MinNumTerms = NumTerms; + if (OtherFirstNonTerm == MergePotentials[i].getBlock()->end() || + OtherFirstNonTerm->isIdenticalTo(FirstNonTerm)) { + AllPredsMatch = false; + break; + } + } + + // If they all have an instruction in common, do any amount of merging. + if (AllPredsMatch) + minCommonTailLength = MinNumTerms + 1; + } + } + } + + 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 = (MergePotentials.end()-1)->first; - unsigned PrevHash = (MergePotentials.end()-2)->first; - MachineBasicBlock *CurMBB = (MergePotentials.end()-1)->second; - - // If there is nothing that matches the hash of the current basic block, - // give up. - if (CurHash != PrevHash) { - if (SuccBB && CurMBB != PredBB) - FixTail(CurMBB, SuccBB, TII); - MergePotentials.pop_back(); - continue; - } - - // Look through all the blocks that have the same hash as this one, and - // find the one that has the largest number of instructions in common. - // Since instructions may get combined later (e.g. single stores into - // store multiple) this measure is not particularly accurate. - MachineBasicBlock::iterator BBI1, BBI2; - - unsigned FoundMatch = ~0U; - unsigned maxCommonTailLength = 0U; - for (int i = MergePotentials.size()-2; - i != -1 && MergePotentials[i].first == CurHash; --i) { - MachineBasicBlock::iterator TrialBBI1, TrialBBI2; - unsigned CommonTailLen = ComputeCommonTailLength(CurMBB, - MergePotentials[i].second, - TrialBBI1, TrialBBI2); - if (CommonTailLen >= minCommonTailLength && - CommonTailLen >= maxCommonTailLength) { - FoundMatch = i; - maxCommonTailLength = CommonTailLen; - BBI1 = TrialBBI1; - BBI2 = TrialBBI2; - } - } - - // If we didn't find anything that has at least minCommonTailLength - // instructions matching this one, bail out. - if (FoundMatch == ~0U) { - // Put the unconditional branch back, if we need one. - if (SuccBB && CurMBB != PredBB) - FixTail(CurMBB, SuccBB, TII); - MergePotentials.pop_back(); + 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, + SuccBB, PredBB); + + // 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); continue; } - - // Otherwise, move the matching block to the right position. - if (FoundMatch != MergePotentials.size()-2) - std::swap(MergePotentials[FoundMatch], *(MergePotentials.end()-2)); - - MachineBasicBlock *MBB2 = (MergePotentials.end()-2)->second; - - // If neither block is the entire common tail, split the tail of one block - // to make it redundant with the other tail. Also, we cannot jump to the - // entry block, so if one block is the entry block, split the other one. - MachineBasicBlock *Entry = CurMBB->getParent()->begin(); - if (CurMBB->begin() == BBI1 && CurMBB != Entry) - ; // CurMBB is common tail - else if (MBB2->begin() == BBI2 && MBB2 != Entry) - ; // MBB2 is common tail + + // If one of the blocks is the entire common tail (and not the entry + // 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()->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 { - if (0) { // Enable this to disable partial tail merges. - MergePotentials.pop_back(); - continue; - } - - // Decide whether we want to split CurMBB or MBB2. - if (ShouldSplitFirstBlock(CurMBB, BBI1, MBB2, BBI2, TII, PredBB)) { - CurMBB = SplitMBBAt(*CurMBB, BBI1); - BBI1 = CurMBB->begin(); - MergePotentials.back().second = CurMBB; - } else { - MBB2 = SplitMBBAt(*MBB2, BBI2); - BBI2 = MBB2->begin(); - (MergePotentials.end()-2)->second = MBB2; + // 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 (MBB2->begin() == BBI2 && MBB2 != Entry) { - // Hack the end off CurMBB, making it jump to MBBI@ instead. - ReplaceTailWithBranchTo(BBI1, MBB2); - // This modifies CurMBB, so remove it from the worklist. - MergePotentials.pop_back(); - } else { - assert(CurMBB->begin() == BBI1 && CurMBB != Entry && - "Didn't split block correctly?"); - // Hack the end off MBB2, making it jump to CurMBB instead. - ReplaceTailWithBranchTo(BBI2, CurMBB); - // This modifies MBB2, so remove it from the worklist. - MergePotentials.erase(MergePotentials.end()-2); + + 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); + } + + 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 in BB#" << MBB->getNumber() + << " for "); + for (unsigned int i=0, e = SameTails.size(); i != e; ++i) { + if (commonTailIndex == i) + continue; + 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].getTailStartPos(), MBB); + // BB i is no longer a predecessor of SuccBB; remove it from the worklist. + MergePotentials.erase(SameTails[i].getMPIter()); } + DEBUG(errs() << "\n"); + // We leave commonTailIndex in the worklist in case there are other blocks + // that match it with a smaller number of instructions. MadeChange = true; } return MadeChange; @@ -552,24 +800,27 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { if (!EnableTailMerge) return false; - - MadeChange = 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. - MadeChange |= TryMergeBlocks(NULL, NULL); + if (MergePotentials.size() < TailMergeThreshold && + MergePotentials.size() >= 2) + 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 @@ -583,49 +834,77 @@ 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) { - if (!I->succ_empty() && I->pred_size() >= 2) { + for (MachineFunction::iterator I = next(MF.begin()), E = MF.end(); + I != E; ++I) { + if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) { + SmallPtrSet UniquePreds; MachineBasicBlock *IBB = I; MachineBasicBlock *PredBB = prior(I); MergePotentials.clear(); - for (MachineBasicBlock::pred_iterator P = I->pred_begin(), E2 = I->pred_end(); + for (MachineBasicBlock::pred_iterator P = I->pred_begin(), + E2 = I->pred_end(); P != E2; ++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)) continue; MachineBasicBlock *TBB = 0, *FBB = 0; - std::vector Cond; - if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond)) { + SmallVector Cond; + if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond, true)) { // Failing case: IBB is the target of a cbr, and // we cannot reverse the branch. - std::vector NewCond(Cond); - if (Cond.size() && TBB==IBB) { + SmallVector NewCond(Cond); + if (!Cond.empty() && TBB == IBB) { if (TII->ReverseBranchCondition(NewCond)) continue; // This is the QBB case described above if (!FBB) FBB = next(MachineFunction::iterator(PBB)); } + // Failing case: the only way IBB can be reached from PBB is via + // exception handling. Happens for landing pads. Would be nice + // 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()) + PredNextBB = IP; + if (TBB == NULL) { + if (IBB != PredNextBB) // fallthrough + continue; + } else if (FBB) { + if (TBB != IBB && FBB != IBB) // cbr then ubr + continue; + } else if (Cond.empty()) { + if (TBB != IBB) // ubr + continue; + } else { + if (TBB != IBB && IBB != PredNextBB) // cbr + continue; + } + } // Remove the unconditional branch at the end, if any. - if (TBB && (Cond.size()==0 || FBB)) { + if (TBB && (Cond.empty() || FBB)) { TII->RemoveBranch(*PBB); - if (Cond.size()) + 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 be either an original single predecessor, or 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; @@ -636,15 +915,15 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { //===----------------------------------------------------------------------===// bool BranchFolder::OptimizeBranches(MachineFunction &MF) { - MadeChange = false; - + 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++; - OptimizeBlock(MBB); - + MadeChange |= OptimizeBlock(MBB); + // If it is dead, remove it. if (MBB->pred_empty()) { RemoveDeadBlock(MBB); @@ -656,109 +935,6 @@ bool BranchFolder::OptimizeBranches(MachineFunction &MF) { } -/// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the -/// CFG to be inserted. If we have proven that MBB can only branch to DestA and -/// DestB, remove any other MBB successors from the CFG. DestA and DestB can -/// be null. -static bool CorrectExtraCFGEdges(MachineBasicBlock &MBB, - MachineBasicBlock *DestA, - MachineBasicBlock *DestB, - bool isCond, - MachineFunction::iterator FallThru) { - bool MadeChange = false; - bool AddedFallThrough = false; - - // If this block ends with a conditional branch that falls through to its - // successor, set DestB as the successor. - if (isCond) { - if (DestB == 0 && FallThru != MBB.getParent()->end()) { - DestB = FallThru; - AddedFallThrough = true; - } - } else { - // If this is an unconditional branch with no explicit dest, it must just be - // a fallthrough into DestB. - if (DestA == 0 && FallThru != MBB.getParent()->end()) { - DestA = FallThru; - AddedFallThrough = true; - } - } - - MachineBasicBlock::succ_iterator SI = MBB.succ_begin(); - bool foundPad = false; - while (SI != MBB.succ_end()) { - if (*SI == DestA && DestA == DestB) { - DestA = DestB = 0; - if ((*SI)->isLandingPad()) - foundPad = true; - ++SI; - } else if (*SI == DestA) { - DestA = 0; - if ((*SI)->isLandingPad()) - foundPad = true; - ++SI; - } else if (*SI == DestB) { - DestB = 0; - if ((*SI)->isLandingPad()) - foundPad = true; - ++SI; - } else if ((*SI)->isLandingPad() && !foundPad) { - foundPad = true; - ++SI; - } else { - // Otherwise, this is a superfluous edge, remove it. - MBB.removeSuccessor(SI); - MadeChange = true; - } - } - if (!AddedFallThrough) { - assert(DestA == 0 && DestB == 0 && - "MachineCFG is missing edges!"); - } else if (isCond) { - assert(DestA == 0 && "MachineCFG is missing edges!"); - } - return MadeChange; -} - - -/// ReplaceUsesOfBlockWith - Given a machine basic block 'BB' that branched to -/// 'Old', change the code and CFG so that it branches to 'New' instead. -static void ReplaceUsesOfBlockWith(MachineBasicBlock *BB, - MachineBasicBlock *Old, - MachineBasicBlock *New, - const TargetInstrInfo *TII) { - assert(Old != New && "Cannot replace self with self!"); - - MachineBasicBlock::iterator I = BB->end(); - while (I != BB->begin()) { - --I; - if (!TII->isTerminatorInstr(I->getOpcode())) break; - - // Scan the operands of this machine instruction, replacing any uses of Old - // with New. - for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) - if (I->getOperand(i).isMachineBasicBlock() && - I->getOperand(i).getMachineBasicBlock() == Old) - I->getOperand(i).setMachineBasicBlock(New); - } - - // Update the successor information. If New was already a successor, just - // remove the link to Old instead of creating another one. PR 1444. - bool HadSuccessorNew = false; - std::vector Succs(BB->succ_begin(), BB->succ_end()); - for (int i = Succs.size()-1; i >= 0; --i) - if (Succs[i] == New) { - HadSuccessorNew = true; - break; - } - for (int i = Succs.size()-1; i >= 0; --i) - if (Succs[i] == Old) { - BB->removeSuccessor(Old); - if (!HadSuccessorNew) - BB->addSuccessor(New); - } -} - /// CanFallThrough - Return true if the specified block (with the specified /// branch condition) can implicitly transfer control to the block after it by /// falling off the end of it. This should return false if it can reach the @@ -768,20 +944,29 @@ static void ReplaceUsesOfBlockWith(MachineBasicBlock *BB, /// bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB, bool BranchUnAnalyzable, - MachineBasicBlock *TBB, MachineBasicBlock *FBB, - const std::vector &Cond) { + MachineBasicBlock *TBB, + MachineBasicBlock *FBB, + const SmallVectorImpl &Cond) { MachineFunction::iterator Fallthrough = CurBB; ++Fallthrough; // 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; @@ -791,11 +976,11 @@ 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; @@ -810,8 +995,8 @@ bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB, /// bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB) { MachineBasicBlock *TBB = 0, *FBB = 0; - std::vector Cond; - bool CurUnAnalyzable = TII->AnalyzeBranch(*CurBB, TBB, FBB, Cond); + SmallVector Cond; + bool CurUnAnalyzable = TII->AnalyzeBranch(*CurBB, TBB, FBB, Cond, true); return CanFallThrough(CurBB, CurUnAnalyzable, TBB, FBB, Cond); } @@ -819,50 +1004,153 @@ 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, - MachineBasicBlock *MBB2, - const TargetInstrInfo &TII) { +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; + if (MBB2->isSuccessor(MBB1)) return false; + MachineInstr *MBB1I = --MBB1->end(); MachineInstr *MBB2I = --MBB2->end(); - return TII.isCall(MBB2I->getOpcode()) && !TII.isCall(MBB1I->getOpcode()); + return MBB2I->getDesc().isCall() && !MBB1I->getDesc().isCall(); +} + +/// TailDuplicate - MBB unconditionally branches to SuccBB. If it is profitable, +/// duplicate SuccBB's contents in MBB to eliminate the branch. +bool BranchFolder::TailDuplicate(MachineBasicBlock *TailBB, + bool PrevFallsThrough, + MachineFunction &MF) { + // Don't try to tail-duplicate single-block loops. + if (TailBB->isSuccessor(TailBB)) + return false; + + // Don't tail-duplicate a block which will soon be folded into its successor. + if (TailBB->succ_size() == 1 && + TailBB->succ_begin()[0]->pred_size() == 1) + return false; + + // Duplicate up to one less that the tail-merge threshold, so that we don't + // get into an infinite loop between duplicating and merging. 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 : (TailMergeSize - 1); + + // Check the instructions in the block to determine whether tail-duplication + // is invalid or unlikely to be unprofitable. + 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 Preds(TailBB->pred_begin(), + TailBB->pred_end()); + for (SmallSetVector::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 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 unless its the + // only predecessor. + if (PredBB->isLayoutSuccessor(TailBB) && + PrevFallsThrough && + TailBB->pred_size() != 1) + 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; + } + + return Changed; } /// OptimizeBlock - Analyze and optimize control flow related to the specified /// block. This is never called on the entry block. -void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { +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. - if (MBB->empty() && !MBB->isLandingPad()) { + // points to this block. Blocks with their addresses taken shouldn't be + // optimized away. + if (MBB->empty() && !MBB->isLandingPad() && !MBB->hasAddressTaken()) { // Dead block? Leave for cleanup later. - if (MBB->pred_empty()) return; - - if (FallThrough == MBB->getParent()->end()) { + if (MBB->pred_empty()) return MadeChange; + + 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 // instead. while (!MBB->pred_empty()) { MachineBasicBlock *Pred = *(MBB->pred_end()-1); - ReplaceUsesOfBlockWith(Pred, MBB, FallThrough, TII); + Pred->ReplaceUsesOfBlockWith(MBB, FallThrough); } - // 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; + return MadeChange; } // Check to see if we can simplify the terminator of the block before this @@ -870,25 +1158,45 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { MachineBasicBlock &PrevBB = *prior(MachineFunction::iterator(MBB)); MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0; - std::vector PriorCond; + SmallVector PriorCond; bool PriorUnAnalyzable = - TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond); + TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, true); if (!PriorUnAnalyzable) { // If the CFG for the prior block has extra edges, remove them. - MadeChange |= CorrectExtraCFGEdges(PrevBB, PriorTBB, PriorFBB, - !PriorCond.empty(), MBB); - + 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 tail duplication eliminates all the + // non-branch predecessors of a block leaving only the fall-through edge. + // 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 @@ -897,9 +1205,9 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { 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) { @@ -907,43 +1215,43 @@ void 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. if (PriorTBB == MBB) { - std::vector NewPriorCond(PriorCond); + SmallVector NewPriorCond(PriorCond); if (!TII->ReverseBranchCondition(NewPriorCond)) { TII->RemoveBranch(PrevBB); TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond); MadeChange = true; ++NumBranchOpts; - return OptimizeBlock(MBB); + goto ReoptimizeBlock; } } - - // If this block doesn't fall through (e.g. it ends with an uncond branch or - // has no successors) and if the pred falls through into this block, and if - // it would otherwise fall through into the block after this, move this - // block to the end of the function. + + // 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 + // into the block after this, move this block to the end of the function. // // We consider it more likely that execution will stay in the function (e.g. // due to loops) than it is to exit it. This asserts in loops etc, moving // the assert condition out of the loop body. - if (!PriorCond.empty() && PriorFBB == 0 && + if (MBB->succ_empty() && !PriorCond.empty() && PriorFBB == 0 && 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() && - !IsBetterFallthrough(PriorTBB, MBB, *TII)) + if (FallThrough == --MF.end() && + !IsBetterFallthrough(PriorTBB, MBB)) DoTransform = false; // We don't want to do this transformation if we have control flow like: @@ -960,59 +1268,58 @@ void 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. - std::vector NewPriorCond(PriorCond); + SmallVector NewPriorCond(PriorCond); if (!TII->ReverseBranchCondition(NewPriorCond)) { - DOUT << "\nMoving MBB: " << *MBB; - DOUT << "To make fallthrough to: " << *PriorTBB << "\n"; - + 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; + return MadeChange; } } } } - + // Analyze the branch in the current block. MachineBasicBlock *CurTBB = 0, *CurFBB = 0; - std::vector CurCond; - bool CurUnAnalyzable = TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond); + SmallVector CurCond; + bool CurUnAnalyzable= TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond, true); if (!CurUnAnalyzable) { // If the CFG for the prior block has extra edges, remove them. - MadeChange |= CorrectExtraCFGEdges(*MBB, CurTBB, CurFBB, - !CurCond.empty(), - ++MachineFunction::iterator(MBB)); + 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: // Loop: xxx; jncc Loop; jmp Out if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) { - std::vector NewCond(CurCond); + SmallVector NewCond(CurCond); if (!TII->ReverseBranchCondition(NewCond)) { TII->RemoveBranch(*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 && - TII->isBranch(MBB->begin()->getOpcode()) && CurTBB != MBB) { + 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 // be 'non-branch terminators' in the block, try removing the branch and // then seeing if the block is empty. @@ -1029,7 +1336,7 @@ void 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 && @@ -1044,46 +1351,71 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) { } // Iterate through all the predecessors, revectoring each in-turn. - MachineBasicBlock::pred_iterator PI = MBB->pred_begin(); + size_t PI = 0; bool DidChange = false; bool HasBranchToSelf = false; - while (PI != MBB->pred_end()) { - if (*PI == MBB) { + while(PI != MBB->pred_size()) { + MachineBasicBlock *PMBB = *(MBB->pred_begin() + PI); + if (PMBB == MBB) { // If this block has an uncond branch to itself, leave it. ++PI; HasBranchToSelf = true; } else { DidChange = true; - ReplaceUsesOfBlockWith(*PI, MBB, CurTBB, TII); + PMBB->ReplaceUsesOfBlockWith(MBB, CurTBB); + // If this change resulted in PMBB ending in a conditional + // branch where both conditions go to the same destination, + // change this to an unconditional branch (and fix the CFG). + MachineBasicBlock *NewCurTBB = 0, *NewCurFBB = 0; + SmallVector NewCurCond; + bool NewCurUnAnalyzable = TII->AnalyzeBranch(*PMBB, NewCurTBB, + NewCurFBB, NewCurCond, true); + if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) { + TII->RemoveBranch(*PMBB); + NewCurCond.clear(); + TII->InsertBranch(*PMBB, NewCurTBB, 0, NewCurCond); + MadeChange = true; + ++NumBranchOpts; + 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; - if (!HasBranchToSelf) return; + if (!HasBranchToSelf) return MadeChange; } } } - + // Add the branch back if the block is more than just an uncond branch. TII->InsertBranch(*MBB, CurTBB, 0, CurCond); } } + // 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, + CurCond); + bool PrevFallsThru = CanFallThrough(&PrevBB, PriorUnAnalyzable, + PriorTBB, PriorFBB, PriorCond); + + // If this block is small, unconditionally branched to, and does not + // fall through, tail-duplicate its instructions into its predecessors + // to eliminate a (dynamic) branch. + if (!CurFallsThru) + if (TailDuplicate(MBB, PrevFallsThru, MF)) { + MadeChange = true; + return MadeChange; + } + // If the prior block doesn't fall through into this block, and if this // block doesn't fall through into some other block, see if we can find a // 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, - CurCond); - + if (!PrevFallsThru) { if (!MBB->isLandingPad()) { // Check all the predecessors of this block. If one of them has no fall // throughs, move this block right after it. @@ -1092,12 +1424,15 @@ void 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 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; @@ -1112,11 +1447,11 @@ void 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(), @@ -1124,29 +1459,34 @@ void 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 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 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; + return MadeChange; } } } + + return MadeChange; }