diff options
Diffstat (limited to 'lib/CodeGen/MachineBlockPlacement.cpp')
| -rw-r--r-- | lib/CodeGen/MachineBlockPlacement.cpp | 484 |
1 files changed, 253 insertions, 231 deletions
diff --git a/lib/CodeGen/MachineBlockPlacement.cpp b/lib/CodeGen/MachineBlockPlacement.cpp index aaa7d9156976..2969bad4ff98 100644 --- a/lib/CodeGen/MachineBlockPlacement.cpp +++ b/lib/CodeGen/MachineBlockPlacement.cpp @@ -33,6 +33,7 @@ #include "llvm/CodeGen/MachineBasicBlock.h" #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" #include "llvm/CodeGen/MachineBranchProbabilityInfo.h" +#include "llvm/CodeGen/MachineDominators.h" #include "llvm/CodeGen/MachineFunction.h" #include "llvm/CodeGen/MachineFunctionPass.h" #include "llvm/CodeGen/MachineLoopInfo.h" @@ -40,13 +41,14 @@ #include "llvm/Support/Allocator.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetLowering.h" #include "llvm/Target/TargetSubtargetInfo.h" #include <algorithm> using namespace llvm; -#define DEBUG_TYPE "block-placement2" +#define DEBUG_TYPE "block-placement" STATISTIC(NumCondBranches, "Number of conditional branches"); STATISTIC(NumUncondBranches, "Number of uncondittional branches"); @@ -61,11 +63,23 @@ static cl::opt<unsigned> AlignAllBlock("align-all-blocks", cl::init(0), cl::Hidden); // FIXME: Find a good default for this flag and remove the flag. -static cl::opt<unsigned> -ExitBlockBias("block-placement-exit-block-bias", - cl::desc("Block frequency percentage a loop exit block needs " - "over the original exit to be considered the new exit."), - cl::init(0), cl::Hidden); +static cl::opt<unsigned> ExitBlockBias( + "block-placement-exit-block-bias", + cl::desc("Block frequency percentage a loop exit block needs " + "over the original exit to be considered the new exit."), + cl::init(0), cl::Hidden); + +static cl::opt<bool> OutlineOptionalBranches( + "outline-optional-branches", + cl::desc("Put completely optional branches, i.e. branches with a common " + "post dominator, out of line."), + cl::init(false), cl::Hidden); + +static cl::opt<unsigned> OutlineOptionalThreshold( + "outline-optional-threshold", + cl::desc("Don't outline optional branches that are a single block with an " + "instruction count below this threshold"), + cl::init(4), cl::Hidden); namespace { class BlockChain; @@ -107,7 +121,7 @@ public: /// function. It also registers itself as the chain that block participates /// in with the BlockToChain mapping. BlockChain(BlockToChainMapType &BlockToChain, MachineBasicBlock *BB) - : Blocks(1, BB), BlockToChain(BlockToChain), LoopPredecessors(0) { + : Blocks(1, BB), BlockToChain(BlockToChain), LoopPredecessors(0) { assert(BB && "Cannot create a chain with a null basic block"); BlockToChain[BB] = this; } @@ -144,19 +158,18 @@ public: // Update the incoming blocks to point to this chain, and add them to the // chain structure. - for (BlockChain::iterator BI = Chain->begin(), BE = Chain->end(); - BI != BE; ++BI) { - Blocks.push_back(*BI); - assert(BlockToChain[*BI] == Chain && "Incoming blocks not in chain"); - BlockToChain[*BI] = this; + for (MachineBasicBlock *ChainBB : *Chain) { + Blocks.push_back(ChainBB); + assert(BlockToChain[ChainBB] == Chain && "Incoming blocks not in chain"); + BlockToChain[ChainBB] = this; } } #ifndef NDEBUG /// \brief Dump the blocks in this chain. LLVM_DUMP_METHOD void dump() { - for (iterator I = begin(), E = end(); I != E; ++I) - (*I)->dump(); + for (MachineBasicBlock *MBB : *this) + MBB->dump(); } #endif // NDEBUG @@ -188,6 +201,13 @@ class MachineBlockPlacement : public MachineFunctionPass { /// \brief A handle to the target's lowering info. const TargetLoweringBase *TLI; + /// \brief A handle to the post dominator tree. + MachineDominatorTree *MDT; + + /// \brief A set of blocks that are unavoidably execute, i.e. they dominate + /// all terminators of the MachineFunction. + SmallPtrSet<MachineBasicBlock *, 4> UnavoidableBlocks; + /// \brief Allocator and owner of BlockChain structures. /// /// We build BlockChains lazily while processing the loop structure of @@ -205,28 +225,26 @@ class MachineBlockPlacement : public MachineFunctionPass { /// between basic blocks. DenseMap<MachineBasicBlock *, BlockChain *> BlockToChain; - void markChainSuccessors(BlockChain &Chain, - MachineBasicBlock *LoopHeaderBB, + void markChainSuccessors(BlockChain &Chain, MachineBasicBlock *LoopHeaderBB, SmallVectorImpl<MachineBasicBlock *> &BlockWorkList, const BlockFilterSet *BlockFilter = nullptr); MachineBasicBlock *selectBestSuccessor(MachineBasicBlock *BB, BlockChain &Chain, const BlockFilterSet *BlockFilter); - MachineBasicBlock *selectBestCandidateBlock( - BlockChain &Chain, SmallVectorImpl<MachineBasicBlock *> &WorkList, - const BlockFilterSet *BlockFilter); - MachineBasicBlock *getFirstUnplacedBlock( - MachineFunction &F, - const BlockChain &PlacedChain, - MachineFunction::iterator &PrevUnplacedBlockIt, - const BlockFilterSet *BlockFilter); + MachineBasicBlock * + selectBestCandidateBlock(BlockChain &Chain, + SmallVectorImpl<MachineBasicBlock *> &WorkList, + const BlockFilterSet *BlockFilter); + MachineBasicBlock * + getFirstUnplacedBlock(MachineFunction &F, const BlockChain &PlacedChain, + MachineFunction::iterator &PrevUnplacedBlockIt, + const BlockFilterSet *BlockFilter); void buildChain(MachineBasicBlock *BB, BlockChain &Chain, SmallVectorImpl<MachineBasicBlock *> &BlockWorkList, const BlockFilterSet *BlockFilter = nullptr); MachineBasicBlock *findBestLoopTop(MachineLoop &L, const BlockFilterSet &LoopBlockSet); - MachineBasicBlock *findBestLoopExit(MachineFunction &F, - MachineLoop &L, + MachineBasicBlock *findBestLoopExit(MachineFunction &F, MachineLoop &L, const BlockFilterSet &LoopBlockSet); void buildLoopChains(MachineFunction &F, MachineLoop &L); void rotateLoop(BlockChain &LoopChain, MachineBasicBlock *ExitingBB, @@ -244,6 +262,7 @@ public: void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired<MachineBranchProbabilityInfo>(); AU.addRequired<MachineBlockFrequencyInfo>(); + AU.addRequired<MachineDominatorTree>(); AU.addRequired<MachineLoopInfo>(); MachineFunctionPass::getAnalysisUsage(AU); } @@ -252,12 +271,13 @@ public: char MachineBlockPlacement::ID = 0; char &llvm::MachineBlockPlacementID = MachineBlockPlacement::ID; -INITIALIZE_PASS_BEGIN(MachineBlockPlacement, "block-placement2", +INITIALIZE_PASS_BEGIN(MachineBlockPlacement, "block-placement", "Branch Probability Basic Block Placement", false, false) INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo) INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo) +INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo) -INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement2", +INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement", "Branch Probability Basic Block Placement", false, false) #ifndef NDEBUG @@ -267,8 +287,8 @@ INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement2", static std::string getBlockName(MachineBasicBlock *BB) { std::string Result; raw_string_ostream OS(Result); - OS << "BB#" << BB->getNumber() - << " (derived from LLVM BB '" << BB->getName() << "')"; + OS << "BB#" << BB->getNumber(); + OS << " (derived from LLVM BB '" << BB->getName() << "')"; OS.flush(); return Result; } @@ -292,26 +312,22 @@ static std::string getBlockNum(MachineBasicBlock *BB) { /// having one fewer active predecessor. It also adds any successors of this /// chain which reach the zero-predecessor state to the worklist passed in. void MachineBlockPlacement::markChainSuccessors( - BlockChain &Chain, - MachineBasicBlock *LoopHeaderBB, + BlockChain &Chain, MachineBasicBlock *LoopHeaderBB, SmallVectorImpl<MachineBasicBlock *> &BlockWorkList, const BlockFilterSet *BlockFilter) { // Walk all the blocks in this chain, marking their successors as having // a predecessor placed. - for (BlockChain::iterator CBI = Chain.begin(), CBE = Chain.end(); - CBI != CBE; ++CBI) { + for (MachineBasicBlock *MBB : Chain) { // Add any successors for which this is the only un-placed in-loop // predecessor to the worklist as a viable candidate for CFG-neutral // placement. No subsequent placement of this block will violate the CFG // shape, so we get to use heuristics to choose a favorable placement. - for (MachineBasicBlock::succ_iterator SI = (*CBI)->succ_begin(), - SE = (*CBI)->succ_end(); - SI != SE; ++SI) { - if (BlockFilter && !BlockFilter->count(*SI)) + for (MachineBasicBlock *Succ : MBB->successors()) { + if (BlockFilter && !BlockFilter->count(Succ)) continue; - BlockChain &SuccChain = *BlockToChain[*SI]; + BlockChain &SuccChain = *BlockToChain[Succ]; // Disregard edges within a fixed chain, or edges to the loop header. - if (&Chain == &SuccChain || *SI == LoopHeaderBB) + if (&Chain == &SuccChain || Succ == LoopHeaderBB) continue; // This is a cross-chain edge that is within the loop, so decrement the @@ -331,9 +347,10 @@ void MachineBlockPlacement::markChainSuccessors( /// very hot successor edges. /// /// \returns The best successor block found, or null if none are viable. -MachineBasicBlock *MachineBlockPlacement::selectBestSuccessor( - MachineBasicBlock *BB, BlockChain &Chain, - const BlockFilterSet *BlockFilter) { +MachineBasicBlock * +MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB, + BlockChain &Chain, + const BlockFilterSet *BlockFilter) { const BranchProbability HotProb(4, 5); // 80% MachineBasicBlock *BestSucc = nullptr; @@ -347,65 +364,85 @@ MachineBasicBlock *MachineBlockPlacement::selectBestSuccessor( uint32_t WeightScale = 0; uint32_t SumWeight = MBPI->getSumForBlock(BB, WeightScale); DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n"); - for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), - SE = BB->succ_end(); - SI != SE; ++SI) { - if (BlockFilter && !BlockFilter->count(*SI)) + for (MachineBasicBlock *Succ : BB->successors()) { + if (BlockFilter && !BlockFilter->count(Succ)) continue; - BlockChain &SuccChain = *BlockToChain[*SI]; + BlockChain &SuccChain = *BlockToChain[Succ]; if (&SuccChain == &Chain) { - DEBUG(dbgs() << " " << getBlockName(*SI) << " -> Already merged!\n"); + DEBUG(dbgs() << " " << getBlockName(Succ) << " -> Already merged!\n"); continue; } - if (*SI != *SuccChain.begin()) { - DEBUG(dbgs() << " " << getBlockName(*SI) << " -> Mid chain!\n"); + if (Succ != *SuccChain.begin()) { + DEBUG(dbgs() << " " << getBlockName(Succ) << " -> Mid chain!\n"); continue; } - uint32_t SuccWeight = MBPI->getEdgeWeight(BB, *SI); + uint32_t SuccWeight = MBPI->getEdgeWeight(BB, Succ); BranchProbability SuccProb(SuccWeight / WeightScale, SumWeight); + // If we outline optional branches, look whether Succ is unavoidable, i.e. + // dominates all terminators of the MachineFunction. If it does, other + // successors must be optional. Don't do this for cold branches. + if (OutlineOptionalBranches && SuccProb > HotProb.getCompl() && + UnavoidableBlocks.count(Succ) > 0) { + auto HasShortOptionalBranch = [&]() { + for (MachineBasicBlock *Pred : Succ->predecessors()) { + // Check whether there is an unplaced optional branch. + if (Pred == Succ || (BlockFilter && !BlockFilter->count(Pred)) || + BlockToChain[Pred] == &Chain) + continue; + // Check whether the optional branch has exactly one BB. + if (Pred->pred_size() > 1 || *Pred->pred_begin() != BB) + continue; + // Check whether the optional branch is small. + if (Pred->size() < OutlineOptionalThreshold) + return true; + } + return false; + }; + if (!HasShortOptionalBranch()) + return Succ; + } + // Only consider successors which are either "hot", or wouldn't violate // any CFG constraints. if (SuccChain.LoopPredecessors != 0) { if (SuccProb < HotProb) { - DEBUG(dbgs() << " " << getBlockName(*SI) << " -> " << SuccProb + DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb << " (prob) (CFG conflict)\n"); continue; } - // Make sure that a hot successor doesn't have a globally more important - // predecessor. - BlockFrequency CandidateEdgeFreq - = MBFI->getBlockFreq(BB) * SuccProb * HotProb.getCompl(); + // Make sure that a hot successor doesn't have a globally more + // important predecessor. + BlockFrequency CandidateEdgeFreq = + MBFI->getBlockFreq(BB) * SuccProb * HotProb.getCompl(); bool BadCFGConflict = false; - for (MachineBasicBlock::pred_iterator PI = (*SI)->pred_begin(), - PE = (*SI)->pred_end(); - PI != PE; ++PI) { - if (*PI == *SI || (BlockFilter && !BlockFilter->count(*PI)) || - BlockToChain[*PI] == &Chain) + for (MachineBasicBlock *Pred : Succ->predecessors()) { + if (Pred == Succ || (BlockFilter && !BlockFilter->count(Pred)) || + BlockToChain[Pred] == &Chain) continue; - BlockFrequency PredEdgeFreq - = MBFI->getBlockFreq(*PI) * MBPI->getEdgeProbability(*PI, *SI); + BlockFrequency PredEdgeFreq = + MBFI->getBlockFreq(Pred) * MBPI->getEdgeProbability(Pred, Succ); if (PredEdgeFreq >= CandidateEdgeFreq) { BadCFGConflict = true; break; } } if (BadCFGConflict) { - DEBUG(dbgs() << " " << getBlockName(*SI) << " -> " << SuccProb + DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb << " (prob) (non-cold CFG conflict)\n"); continue; } } - DEBUG(dbgs() << " " << getBlockName(*SI) << " -> " << SuccProb + DEBUG(dbgs() << " " << getBlockName(Succ) << " -> " << SuccProb << " (prob)" << (SuccChain.LoopPredecessors != 0 ? " (CFG break)" : "") << "\n"); if (BestSucc && BestWeight >= SuccWeight) continue; - BestSucc = *SI; + BestSucc = Succ; BestWeight = SuccWeight; } return BestSucc; @@ -430,29 +467,26 @@ MachineBasicBlock *MachineBlockPlacement::selectBestCandidateBlock( // some code complexity) into the loop below. WorkList.erase(std::remove_if(WorkList.begin(), WorkList.end(), [&](MachineBasicBlock *BB) { - return BlockToChain.lookup(BB) == &Chain; - }), + return BlockToChain.lookup(BB) == &Chain; + }), WorkList.end()); MachineBasicBlock *BestBlock = nullptr; BlockFrequency BestFreq; - for (SmallVectorImpl<MachineBasicBlock *>::iterator WBI = WorkList.begin(), - WBE = WorkList.end(); - WBI != WBE; ++WBI) { - BlockChain &SuccChain = *BlockToChain[*WBI]; + for (MachineBasicBlock *MBB : WorkList) { + BlockChain &SuccChain = *BlockToChain[MBB]; if (&SuccChain == &Chain) { - DEBUG(dbgs() << " " << getBlockName(*WBI) - << " -> Already merged!\n"); + DEBUG(dbgs() << " " << getBlockName(MBB) << " -> Already merged!\n"); continue; } assert(SuccChain.LoopPredecessors == 0 && "Found CFG-violating block"); - BlockFrequency CandidateFreq = MBFI->getBlockFreq(*WBI); - DEBUG(dbgs() << " " << getBlockName(*WBI) << " -> "; - MBFI->printBlockFreq(dbgs(), CandidateFreq) << " (freq)\n"); + BlockFrequency CandidateFreq = MBFI->getBlockFreq(MBB); + DEBUG(dbgs() << " " << getBlockName(MBB) << " -> "; + MBFI->printBlockFreq(dbgs(), CandidateFreq) << " (freq)\n"); if (BestBlock && BestFreq >= CandidateFreq) continue; - BestBlock = *WBI; + BestBlock = MBB; BestFreq = CandidateFreq; } return BestBlock; @@ -485,8 +519,7 @@ MachineBasicBlock *MachineBlockPlacement::getFirstUnplacedBlock( } void MachineBlockPlacement::buildChain( - MachineBasicBlock *BB, - BlockChain &Chain, + MachineBasicBlock *BB, BlockChain &Chain, SmallVectorImpl<MachineBasicBlock *> &BlockWorkList, const BlockFilterSet *BlockFilter) { assert(BB); @@ -513,8 +546,8 @@ void MachineBlockPlacement::buildChain( BestSucc = selectBestCandidateBlock(Chain, BlockWorkList, BlockFilter); if (!BestSucc) { - BestSucc = getFirstUnplacedBlock(F, Chain, PrevUnplacedBlockIt, - BlockFilter); + BestSucc = + getFirstUnplacedBlock(F, Chain, PrevUnplacedBlockIt, BlockFilter); if (!BestSucc) break; @@ -527,8 +560,8 @@ void MachineBlockPlacement::buildChain( // Zero out LoopPredecessors for the successor we're about to merge in case // we selected a successor that didn't fit naturally into the CFG. SuccChain.LoopPredecessors = 0; - DEBUG(dbgs() << "Merging from " << getBlockNum(BB) - << " to " << getBlockNum(BestSucc) << "\n"); + DEBUG(dbgs() << "Merging from " << getBlockNum(BB) << " to " + << getBlockNum(BestSucc) << "\n"); markChainSuccessors(SuccChain, LoopHeaderBB, BlockWorkList, BlockFilter); Chain.merge(BestSucc, &SuccChain); BB = *std::prev(Chain.end()); @@ -558,20 +591,17 @@ MachineBlockPlacement::findBestLoopTop(MachineLoop &L, if (!LoopBlockSet.count(*HeaderChain.begin())) return L.getHeader(); - DEBUG(dbgs() << "Finding best loop top for: " - << getBlockName(L.getHeader()) << "\n"); + DEBUG(dbgs() << "Finding best loop top for: " << getBlockName(L.getHeader()) + << "\n"); BlockFrequency BestPredFreq; MachineBasicBlock *BestPred = nullptr; - for (MachineBasicBlock::pred_iterator PI = L.getHeader()->pred_begin(), - PE = L.getHeader()->pred_end(); - PI != PE; ++PI) { - MachineBasicBlock *Pred = *PI; + for (MachineBasicBlock *Pred : L.getHeader()->predecessors()) { if (!LoopBlockSet.count(Pred)) continue; DEBUG(dbgs() << " header pred: " << getBlockName(Pred) << ", " << Pred->succ_size() << " successors, "; - MBFI->printBlockFreq(dbgs(), Pred) << " freq\n"); + MBFI->printBlockFreq(dbgs(), Pred) << " freq\n"); if (Pred->succ_size() > 1) continue; @@ -598,15 +628,13 @@ MachineBlockPlacement::findBestLoopTop(MachineLoop &L, return BestPred; } - /// \brief Find the best loop exiting block for layout. /// /// This routine implements the logic to analyze the loop looking for the best /// block to layout at the top of the loop. Typically this is done to maximize /// fallthrough opportunities. MachineBasicBlock * -MachineBlockPlacement::findBestLoopExit(MachineFunction &F, - MachineLoop &L, +MachineBlockPlacement::findBestLoopExit(MachineFunction &F, MachineLoop &L, const BlockFilterSet &LoopBlockSet) { // We don't want to layout the loop linearly in all cases. If the loop header // is just a normal basic block in the loop, we want to look for what block @@ -628,15 +656,13 @@ MachineBlockPlacement::findBestLoopExit(MachineFunction &F, // blocks where rotating to exit with that block will reach an outer loop. SmallPtrSet<MachineBasicBlock *, 4> BlocksExitingToOuterLoop; - DEBUG(dbgs() << "Finding best loop exit for: " - << getBlockName(L.getHeader()) << "\n"); - for (MachineLoop::block_iterator I = L.block_begin(), - E = L.block_end(); - I != E; ++I) { - BlockChain &Chain = *BlockToChain[*I]; + DEBUG(dbgs() << "Finding best loop exit for: " << getBlockName(L.getHeader()) + << "\n"); + for (MachineBasicBlock *MBB : L.getBlocks()) { + BlockChain &Chain = *BlockToChain[MBB]; // Ensure that this block is at the end of a chain; otherwise it could be - // mid-way through an inner loop or a successor of an analyzable branch. - if (*I != *std::prev(Chain.end())) + // mid-way through an inner loop or a successor of an unanalyzable branch. + if (MBB != *std::prev(Chain.end())) continue; // Now walk the successors. We need to establish whether this has a viable @@ -650,59 +676,56 @@ MachineBlockPlacement::findBestLoopExit(MachineFunction &F, // the MBPI analysis, we use the internal weights and manually compute the // probabilities to avoid quadratic behavior. uint32_t WeightScale = 0; - uint32_t SumWeight = MBPI->getSumForBlock(*I, WeightScale); - for (MachineBasicBlock::succ_iterator SI = (*I)->succ_begin(), - SE = (*I)->succ_end(); - SI != SE; ++SI) { - if ((*SI)->isLandingPad()) + uint32_t SumWeight = MBPI->getSumForBlock(MBB, WeightScale); + for (MachineBasicBlock *Succ : MBB->successors()) { + if (Succ->isLandingPad()) continue; - if (*SI == *I) + if (Succ == MBB) continue; - BlockChain &SuccChain = *BlockToChain[*SI]; + BlockChain &SuccChain = *BlockToChain[Succ]; // Don't split chains, either this chain or the successor's chain. if (&Chain == &SuccChain) { - DEBUG(dbgs() << " exiting: " << getBlockName(*I) << " -> " - << getBlockName(*SI) << " (chain conflict)\n"); + DEBUG(dbgs() << " exiting: " << getBlockName(MBB) << " -> " + << getBlockName(Succ) << " (chain conflict)\n"); continue; } - uint32_t SuccWeight = MBPI->getEdgeWeight(*I, *SI); - if (LoopBlockSet.count(*SI)) { - DEBUG(dbgs() << " looping: " << getBlockName(*I) << " -> " - << getBlockName(*SI) << " (" << SuccWeight << ")\n"); + uint32_t SuccWeight = MBPI->getEdgeWeight(MBB, Succ); + if (LoopBlockSet.count(Succ)) { + DEBUG(dbgs() << " looping: " << getBlockName(MBB) << " -> " + << getBlockName(Succ) << " (" << SuccWeight << ")\n"); HasLoopingSucc = true; continue; } unsigned SuccLoopDepth = 0; - if (MachineLoop *ExitLoop = MLI->getLoopFor(*SI)) { + if (MachineLoop *ExitLoop = MLI->getLoopFor(Succ)) { SuccLoopDepth = ExitLoop->getLoopDepth(); if (ExitLoop->contains(&L)) - BlocksExitingToOuterLoop.insert(*I); + BlocksExitingToOuterLoop.insert(MBB); } BranchProbability SuccProb(SuccWeight / WeightScale, SumWeight); - BlockFrequency ExitEdgeFreq = MBFI->getBlockFreq(*I) * SuccProb; - DEBUG(dbgs() << " exiting: " << getBlockName(*I) << " -> " - << getBlockName(*SI) << " [L:" << SuccLoopDepth - << "] ("; - MBFI->printBlockFreq(dbgs(), ExitEdgeFreq) << ")\n"); + BlockFrequency ExitEdgeFreq = MBFI->getBlockFreq(MBB) * SuccProb; + DEBUG(dbgs() << " exiting: " << getBlockName(MBB) << " -> " + << getBlockName(Succ) << " [L:" << SuccLoopDepth << "] ("; + MBFI->printBlockFreq(dbgs(), ExitEdgeFreq) << ")\n"); // Note that we bias this toward an existing layout successor to retain // incoming order in the absence of better information. The exit must have // a frequency higher than the current exit before we consider breaking // the layout. BranchProbability Bias(100 - ExitBlockBias, 100); - if (!ExitingBB || BestExitLoopDepth < SuccLoopDepth || + if (!ExitingBB || SuccLoopDepth > BestExitLoopDepth || ExitEdgeFreq > BestExitEdgeFreq || - ((*I)->isLayoutSuccessor(*SI) && + (MBB->isLayoutSuccessor(Succ) && !(ExitEdgeFreq < BestExitEdgeFreq * Bias))) { BestExitEdgeFreq = ExitEdgeFreq; - ExitingBB = *I; + ExitingBB = MBB; } } - // Restore the old exiting state, no viable looping successor was found. if (!HasLoopingSucc) { + // Restore the old exiting state, no viable looping successor was found. ExitingBB = OldExitingBB; BestExitEdgeFreq = OldBestExitEdgeFreq; continue; @@ -738,12 +761,10 @@ void MachineBlockPlacement::rotateLoop(BlockChain &LoopChain, MachineBasicBlock *Top = *LoopChain.begin(); bool ViableTopFallthrough = false; - for (MachineBasicBlock::pred_iterator PI = Top->pred_begin(), - PE = Top->pred_end(); - PI != PE; ++PI) { - BlockChain *PredChain = BlockToChain[*PI]; - if (!LoopBlockSet.count(*PI) && - (!PredChain || *PI == *std::prev(PredChain->end()))) { + for (MachineBasicBlock *Pred : Top->predecessors()) { + BlockChain *PredChain = BlockToChain[Pred]; + if (!LoopBlockSet.count(Pred) && + (!PredChain || Pred == *std::prev(PredChain->end()))) { ViableTopFallthrough = true; break; } @@ -754,18 +775,16 @@ void MachineBlockPlacement::rotateLoop(BlockChain &LoopChain, // introduce an unnecessary branch. if (ViableTopFallthrough) { MachineBasicBlock *Bottom = *std::prev(LoopChain.end()); - for (MachineBasicBlock::succ_iterator SI = Bottom->succ_begin(), - SE = Bottom->succ_end(); - SI != SE; ++SI) { - BlockChain *SuccChain = BlockToChain[*SI]; - if (!LoopBlockSet.count(*SI) && - (!SuccChain || *SI == *SuccChain->begin())) + for (MachineBasicBlock *Succ : Bottom->successors()) { + BlockChain *SuccChain = BlockToChain[Succ]; + if (!LoopBlockSet.count(Succ) && + (!SuccChain || Succ == *SuccChain->begin())) return; } } - BlockChain::iterator ExitIt = std::find(LoopChain.begin(), LoopChain.end(), - ExitingBB); + BlockChain::iterator ExitIt = + std::find(LoopChain.begin(), LoopChain.end(), ExitingBB); if (ExitIt == LoopChain.end()) return; @@ -782,8 +801,8 @@ void MachineBlockPlacement::buildLoopChains(MachineFunction &F, MachineLoop &L) { // First recurse through any nested loops, building chains for those inner // loops. - for (MachineLoop::iterator LI = L.begin(), LE = L.end(); LI != LE; ++LI) - buildLoopChains(F, **LI); + for (MachineLoop *InnerLoop : L) + buildLoopChains(F, *InnerLoop); SmallVector<MachineBasicBlock *, 16> BlockWorkList; BlockFilterSet LoopBlockSet(L.block_begin(), L.block_end()); @@ -809,21 +828,16 @@ void MachineBlockPlacement::buildLoopChains(MachineFunction &F, SmallPtrSet<BlockChain *, 4> UpdatedPreds; assert(LoopChain.LoopPredecessors == 0); UpdatedPreds.insert(&LoopChain); - for (MachineLoop::block_iterator BI = L.block_begin(), - BE = L.block_end(); - BI != BE; ++BI) { - BlockChain &Chain = *BlockToChain[*BI]; + for (MachineBasicBlock *LoopBB : L.getBlocks()) { + BlockChain &Chain = *BlockToChain[LoopBB]; if (!UpdatedPreds.insert(&Chain).second) continue; assert(Chain.LoopPredecessors == 0); - for (BlockChain::iterator BCI = Chain.begin(), BCE = Chain.end(); - BCI != BCE; ++BCI) { - assert(BlockToChain[*BCI] == &Chain); - for (MachineBasicBlock::pred_iterator PI = (*BCI)->pred_begin(), - PE = (*BCI)->pred_end(); - PI != PE; ++PI) { - if (BlockToChain[*PI] == &Chain || !LoopBlockSet.count(*PI)) + for (MachineBasicBlock *ChainBB : Chain) { + assert(BlockToChain[ChainBB] == &Chain); + for (MachineBasicBlock *Pred : ChainBB->predecessors()) { + if (BlockToChain[Pred] == &Chain || !LoopBlockSet.count(Pred)) continue; ++Chain.LoopPredecessors; } @@ -845,29 +859,26 @@ void MachineBlockPlacement::buildLoopChains(MachineFunction &F, << " Loop header: " << getBlockName(*L.block_begin()) << "\n" << " Chain header: " << getBlockName(*LoopChain.begin()) << "\n"; } - for (BlockChain::iterator BCI = LoopChain.begin(), BCE = LoopChain.end(); - BCI != BCE; ++BCI) { - dbgs() << " ... " << getBlockName(*BCI) << "\n"; - if (!LoopBlockSet.erase(*BCI)) { + for (MachineBasicBlock *ChainBB : LoopChain) { + dbgs() << " ... " << getBlockName(ChainBB) << "\n"; + if (!LoopBlockSet.erase(ChainBB)) { // We don't mark the loop as bad here because there are real situations // where this can occur. For example, with an unanalyzable fallthrough // from a loop block to a non-loop block or vice versa. dbgs() << "Loop chain contains a block not contained by the loop!\n" << " Loop header: " << getBlockName(*L.block_begin()) << "\n" << " Chain header: " << getBlockName(*LoopChain.begin()) << "\n" - << " Bad block: " << getBlockName(*BCI) << "\n"; + << " Bad block: " << getBlockName(ChainBB) << "\n"; } } if (!LoopBlockSet.empty()) { BadLoop = true; - for (BlockFilterSet::iterator LBI = LoopBlockSet.begin(), - LBE = LoopBlockSet.end(); - LBI != LBE; ++LBI) + for (MachineBasicBlock *LoopBB : LoopBlockSet) dbgs() << "Loop contains blocks never placed into a chain!\n" << " Loop header: " << getBlockName(*L.block_begin()) << "\n" << " Chain header: " << getBlockName(*LoopChain.begin()) << "\n" - << " Bad block: " << getBlockName(*LBI) << "\n"; + << " Bad block: " << getBlockName(LoopBB) << "\n"; } assert(!BadLoop && "Detected problems with the placement of this loop."); }); @@ -879,8 +890,8 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch. for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) { MachineBasicBlock *BB = FI; - BlockChain *Chain - = new (ChainAllocator.Allocate()) BlockChain(BlockToChain, BB); + BlockChain *Chain = + new (ChainAllocator.Allocate()) BlockChain(BlockToChain, BB); // Also, merge any blocks which we cannot reason about and must preserve // the exact fallthrough behavior for. for (;;) { @@ -903,28 +914,44 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { } } + if (OutlineOptionalBranches) { + // Find the nearest common dominator of all of F's terminators. + MachineBasicBlock *Terminator = nullptr; + for (MachineBasicBlock &MBB : F) { + if (MBB.succ_size() == 0) { + if (Terminator == nullptr) + Terminator = &MBB; + else + Terminator = MDT->findNearestCommonDominator(Terminator, &MBB); + } + } + + // MBBs dominating this common dominator are unavoidable. + UnavoidableBlocks.clear(); + for (MachineBasicBlock &MBB : F) { + if (MDT->dominates(&MBB, Terminator)) { + UnavoidableBlocks.insert(&MBB); + } + } + } + // Build any loop-based chains. - for (MachineLoopInfo::iterator LI = MLI->begin(), LE = MLI->end(); LI != LE; - ++LI) - buildLoopChains(F, **LI); + for (MachineLoop *L : *MLI) + buildLoopChains(F, *L); SmallVector<MachineBasicBlock *, 16> BlockWorkList; SmallPtrSet<BlockChain *, 4> UpdatedPreds; - for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) { - MachineBasicBlock *BB = &*FI; - BlockChain &Chain = *BlockToChain[BB]; + for (MachineBasicBlock &MBB : F) { + BlockChain &Chain = *BlockToChain[&MBB]; if (!UpdatedPreds.insert(&Chain).second) continue; assert(Chain.LoopPredecessors == 0); - for (BlockChain::iterator BCI = Chain.begin(), BCE = Chain.end(); - BCI != BCE; ++BCI) { - assert(BlockToChain[*BCI] == &Chain); - for (MachineBasicBlock::pred_iterator PI = (*BCI)->pred_begin(), - PE = (*BCI)->pred_end(); - PI != PE; ++PI) { - if (BlockToChain[*PI] == &Chain) + for (MachineBasicBlock *ChainBB : Chain) { + assert(BlockToChain[ChainBB] == &Chain); + for (MachineBasicBlock *Pred : ChainBB->predecessors()) { + if (BlockToChain[Pred] == &Chain) continue; ++Chain.LoopPredecessors; } @@ -944,46 +971,40 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { // Crash at the end so we get all of the debugging output first. bool BadFunc = false; FunctionBlockSetType FunctionBlockSet; - for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) - FunctionBlockSet.insert(FI); + for (MachineBasicBlock &MBB : F) + FunctionBlockSet.insert(&MBB); - for (BlockChain::iterator BCI = FunctionChain.begin(), - BCE = FunctionChain.end(); - BCI != BCE; ++BCI) - if (!FunctionBlockSet.erase(*BCI)) { + for (MachineBasicBlock *ChainBB : FunctionChain) + if (!FunctionBlockSet.erase(ChainBB)) { BadFunc = true; dbgs() << "Function chain contains a block not in the function!\n" - << " Bad block: " << getBlockName(*BCI) << "\n"; + << " Bad block: " << getBlockName(ChainBB) << "\n"; } if (!FunctionBlockSet.empty()) { BadFunc = true; - for (FunctionBlockSetType::iterator FBI = FunctionBlockSet.begin(), - FBE = FunctionBlockSet.end(); - FBI != FBE; ++FBI) + for (MachineBasicBlock *RemainingBB : FunctionBlockSet) dbgs() << "Function contains blocks never placed into a chain!\n" - << " Bad block: " << getBlockName(*FBI) << "\n"; + << " Bad block: " << getBlockName(RemainingBB) << "\n"; } assert(!BadFunc && "Detected problems with the block placement."); }); // Splice the blocks into place. MachineFunction::iterator InsertPos = F.begin(); - for (BlockChain::iterator BI = FunctionChain.begin(), - BE = FunctionChain.end(); - BI != BE; ++BI) { - DEBUG(dbgs() << (BI == FunctionChain.begin() ? "Placing chain " - : " ... ") - << getBlockName(*BI) << "\n"); - if (InsertPos != MachineFunction::iterator(*BI)) - F.splice(InsertPos, *BI); + for (MachineBasicBlock *ChainBB : FunctionChain) { + DEBUG(dbgs() << (ChainBB == *FunctionChain.begin() ? "Placing chain " + : " ... ") + << getBlockName(ChainBB) << "\n"); + if (InsertPos != MachineFunction::iterator(ChainBB)) + F.splice(InsertPos, ChainBB); else ++InsertPos; // Update the terminator of the previous block. - if (BI == FunctionChain.begin()) + if (ChainBB == *FunctionChain.begin()) continue; - MachineBasicBlock *PrevBB = std::prev(MachineFunction::iterator(*BI)); + MachineBasicBlock *PrevBB = std::prev(MachineFunction::iterator(ChainBB)); // FIXME: It would be awesome of updateTerminator would just return rather // than assert when the branch cannot be analyzed in order to remove this @@ -993,16 +1014,16 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { if (!TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond)) { // The "PrevBB" is not yet updated to reflect current code layout, so, // o. it may fall-through to a block without explict "goto" instruction - // before layout, and no longer fall-through it after layout; or + // before layout, and no longer fall-through it after layout; or // o. just opposite. - // + // // AnalyzeBranch() may return erroneous value for FBB when these two // situations take place. For the first scenario FBB is mistakenly set // NULL; for the 2nd scenario, the FBB, which is expected to be NULL, // is mistakenly pointing to "*BI". // bool needUpdateBr = true; - if (!Cond.empty() && (!FBB || FBB == *BI)) { + if (!Cond.empty() && (!FBB || FBB == ChainBB)) { PrevBB->updateTerminator(); needUpdateBr = false; Cond.clear(); @@ -1022,7 +1043,7 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { << getBlockName(PrevBB) << "\n"); DEBUG(dbgs() << " Edge weight: " << MBPI->getEdgeWeight(PrevBB, FBB) << " vs " << MBPI->getEdgeWeight(PrevBB, TBB) << "\n"); - DebugLoc dl; // FIXME: this is nowhere + DebugLoc dl; // FIXME: this is nowhere TII->RemoveBranch(*PrevBB); TII->InsertBranch(*PrevBB, FBB, TBB, Cond, dl); needUpdateBr = true; @@ -1043,33 +1064,33 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { // exclusively on the loop info here so that we can align backedges in // unnatural CFGs and backedges that were introduced purely because of the // loop rotations done during this layout pass. - if (F.getFunction()->getAttributes(). - hasAttribute(AttributeSet::FunctionIndex, Attribute::OptimizeForSize)) + if (F.getFunction()->hasFnAttribute(Attribute::OptimizeForSize)) return; if (FunctionChain.begin() == FunctionChain.end()) - return; // Empty chain. + return; // Empty chain. const BranchProbability ColdProb(1, 5); // 20% BlockFrequency EntryFreq = MBFI->getBlockFreq(F.begin()); BlockFrequency WeightedEntryFreq = EntryFreq * ColdProb; - for (BlockChain::iterator BI = std::next(FunctionChain.begin()), - BE = FunctionChain.end(); - BI != BE; ++BI) { + for (MachineBasicBlock *ChainBB : FunctionChain) { + if (ChainBB == *FunctionChain.begin()) + continue; + // Don't align non-looping basic blocks. These are unlikely to execute // enough times to matter in practice. Note that we'll still handle // unnatural CFGs inside of a natural outer loop (the common case) and // rotated loops. - MachineLoop *L = MLI->getLoopFor(*BI); + MachineLoop *L = MLI->getLoopFor(ChainBB); if (!L) continue; unsigned Align = TLI->getPrefLoopAlignment(L); if (!Align) - continue; // Don't care about loop alignment. + continue; // Don't care about loop alignment. // If the block is cold relative to the function entry don't waste space // aligning it. - BlockFrequency Freq = MBFI->getBlockFreq(*BI); + BlockFrequency Freq = MBFI->getBlockFreq(ChainBB); if (Freq < WeightedEntryFreq) continue; @@ -1082,12 +1103,13 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { // Check for the existence of a non-layout predecessor which would benefit // from aligning this block. - MachineBasicBlock *LayoutPred = *std::prev(BI); + MachineBasicBlock *LayoutPred = + &*std::prev(MachineFunction::iterator(ChainBB)); // Force alignment if all the predecessors are jumps. We already checked // that the block isn't cold above. - if (!LayoutPred->isSuccessor(*BI)) { - (*BI)->setAlignment(Align); + if (!LayoutPred->isSuccessor(ChainBB)) { + ChainBB->setAlignment(Align); continue; } @@ -1095,10 +1117,11 @@ void MachineBlockPlacement::buildCFGChains(MachineFunction &F) { // cold relative to the block. When this is true, other predecessors make up // all of the hot entries into the block and thus alignment is likely to be // important. - BranchProbability LayoutProb = MBPI->getEdgeProbability(LayoutPred, *BI); + BranchProbability LayoutProb = + MBPI->getEdgeProbability(LayoutPred, ChainBB); BlockFrequency LayoutEdgeFreq = MBFI->getBlockFreq(LayoutPred) * LayoutProb; if (LayoutEdgeFreq <= (Freq * ColdProb)) - (*BI)->setAlignment(Align); + ChainBB->setAlignment(Align); } } @@ -1115,6 +1138,7 @@ bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &F) { MLI = &getAnalysis<MachineLoopInfo>(); TII = F.getSubtarget().getInstrInfo(); TLI = F.getSubtarget().getTargetLowering(); + MDT = &getAnalysis<MachineDominatorTree>(); assert(BlockToChain.empty()); buildCFGChains(F); @@ -1124,9 +1148,8 @@ bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &F) { if (AlignAllBlock) // Align all of the blocks in the function to a specific alignment. - for (MachineFunction::iterator FI = F.begin(), FE = F.end(); - FI != FE; ++FI) - FI->setAlignment(AlignAllBlock); + for (MachineBasicBlock &MBB : F) + MBB.setAlignment(AlignAllBlock); // We always return true as we have no way to track whether the final order // differs from the original order. @@ -1181,20 +1204,19 @@ bool MachineBlockPlacementStats::runOnMachineFunction(MachineFunction &F) { MBPI = &getAnalysis<MachineBranchProbabilityInfo>(); MBFI = &getAnalysis<MachineBlockFrequencyInfo>(); - for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) { - BlockFrequency BlockFreq = MBFI->getBlockFreq(I); - Statistic &NumBranches = (I->succ_size() > 1) ? NumCondBranches - : NumUncondBranches; - Statistic &BranchTakenFreq = (I->succ_size() > 1) ? CondBranchTakenFreq - : UncondBranchTakenFreq; - for (MachineBasicBlock::succ_iterator SI = I->succ_begin(), - SE = I->succ_end(); - SI != SE; ++SI) { + for (MachineBasicBlock &MBB : F) { + BlockFrequency BlockFreq = MBFI->getBlockFreq(&MBB); + Statistic &NumBranches = + (MBB.succ_size() > 1) ? NumCondBranches : NumUncondBranches; + Statistic &BranchTakenFreq = + (MBB.succ_size() > 1) ? CondBranchTakenFreq : UncondBranchTakenFreq; + for (MachineBasicBlock *Succ : MBB.successors()) { // Skip if this successor is a fallthrough. - if (I->isLayoutSuccessor(*SI)) + if (MBB.isLayoutSuccessor(Succ)) continue; - BlockFrequency EdgeFreq = BlockFreq * MBPI->getEdgeProbability(I, *SI); + BlockFrequency EdgeFreq = + BlockFreq * MBPI->getEdgeProbability(&MBB, Succ); ++NumBranches; BranchTakenFreq += EdgeFreq.getFrequency(); } |