--- /dev/null
+//===-- MachineBlockPlacement.cpp - Basic Block Code Layout optimization --===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements basic block placement transformations using branch
+// probability estimates. It is based around "Algo2" from Profile Guided Code
+// Positioning [http://portal.acm.org/citation.cfm?id=989433].
+//
+// We combine the BlockFrequencyInfo with BranchProbabilityInfo to simulate
+// measured edge-weights. The BlockFrequencyInfo effectively summarizes the
+// probability of starting from any particular block, and the
+// BranchProbabilityInfo the probability of exiting the block via a particular
+// edge. Combined they form a function-wide ordering of the edges.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "block-placement2"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SCCIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include <algorithm>
+using namespace llvm;
+
+namespace {
+/// \brief A structure for storing a weighted edge.
+///
+/// This stores an edge and its weight, computed as the product of the
+/// frequency that the starting block is entered with the probability of
+/// a particular exit block.
+struct WeightedEdge {
+ BlockFrequency EdgeFrequency;
+ MachineBasicBlock *From, *To;
+
+ bool operator<(const WeightedEdge &RHS) const {
+ return EdgeFrequency < RHS.EdgeFrequency;
+ }
+};
+}
+
+namespace {
+struct BlockChain;
+/// \brief Type for our function-wide basic block -> block chain mapping.
+typedef DenseMap<MachineBasicBlock *, BlockChain *> BlockToChainMapType;
+}
+
+namespace {
+/// \brief A chain of blocks which will be laid out contiguously.
+///
+/// This is the datastructure representing a chain of consecutive blocks that
+/// are profitable to layout together in order to maximize fallthrough
+/// probabilities. We also can use a block chain to represent a sequence of
+/// basic blocks which have some external (correctness) requirement for
+/// sequential layout.
+///
+/// Eventually, the block chains will form a directed graph over the function.
+/// We provide an SCC-supporting-iterator in order to quicky build and walk the
+/// SCCs of block chains within a function.
+///
+/// The block chains also have support for calculating and caching probability
+/// information related to the chain itself versus other chains. This is used
+/// for ranking during the final layout of block chains.
+struct BlockChain {
+ class SuccIterator;
+
+ /// \brief The first and last basic block that from this chain.
+ ///
+ /// The chain is stored within the existing function ilist of basic blocks.
+ /// When merging chains or otherwise manipulating them, we splice the blocks
+ /// within this ilist, giving us very cheap storage here and constant time
+ /// merge operations.
+ ///
+ /// It is extremely important to note that LastBB is the iterator pointing
+ /// *at* the last basic block in the chain. That is, the chain consists of
+ /// the *closed* range [FirstBB, LastBB]. We cannot use half-open ranges
+ /// because the next basic block may get relocated to a different part of the
+ /// function at any time during the run of this pass.
+ MachineFunction::iterator FirstBB, LastBB;
+
+ /// \brief A handle to the function-wide basic block to block chain mapping.
+ ///
+ /// This is retained in each block chain to simplify the computation of child
+ /// block chains for SCC-formation and iteration. We store the edges to child
+ /// basic blocks, and map them back to their associated chains using this
+ /// structure.
+ BlockToChainMapType &BlockToChain;
+
+ /// \brief The weight used to rank two block chains in the same SCC.
+ ///
+ /// This is used during SCC layout of block chains to cache and rank the
+ /// chains. It is supposed to represent the expected frequency with which
+ /// control reaches a block within this chain, has the option of branching to
+ /// a block in some other chain participating in the SCC, but instead
+ /// continues within this chain. The higher this is, the more costly we
+ /// expect mis-predicted branches between this chain and other chains within
+ /// the SCC to be. Thus, since we expect branches between chains to be
+ /// predicted when backwards and not predicted when forwards, the higher this
+ /// is the more important that this chain is laid out first among those
+ /// chains in the same SCC as it.
+ BlockFrequency InChainEdgeFrequency;
+
+ /// \brief Construct a new BlockChain.
+ ///
+ /// This builds a new block chain representing a single basic block in the
+ /// function. It also registers itself as the chain that block participates
+ /// in with the BlockToChain mapping.
+ BlockChain(BlockToChainMapType &BlockToChain, MachineBasicBlock *BB)
+ : FirstBB(BB), LastBB(BB), BlockToChain(BlockToChain) {
+ assert(BB && "Cannot create a chain with a null basic block");
+ BlockToChain[BB] = this;
+ }
+
+ /// \brief Merge another block chain into this one.
+ ///
+ /// This routine merges a block chain into this one. It takes care of forming
+ /// a contiguous sequence of basic blocks, updating the edge list, and
+ /// updating the block -> chain mapping. It does not free or tear down the
+ /// old chain, but the old chain's block list is no longer valid.
+ void merge(BlockChain *Chain) {
+ assert(Chain && "Cannot merge a null chain");
+ MachineFunction::iterator EndBB = llvm::next(LastBB);
+ MachineFunction::iterator ChainEndBB = llvm::next(Chain->LastBB);
+
+ // Update the incoming blocks to point to this chain.
+ for (MachineFunction::iterator BI = Chain->FirstBB, BE = ChainEndBB;
+ BI != BE; ++BI) {
+ assert(BlockToChain[BI] == Chain && "Incoming blocks not in chain");
+ BlockToChain[BI] = this;
+ }
+
+ // We splice the blocks together within the function (unless they already
+ // are adjacent) so we can represent the new chain with a pair of pointers
+ // to basic blocks within the function. This is also useful as each chain
+ // of blocks will end up being laid out contiguously within the function.
+ if (EndBB != Chain->FirstBB)
+ FirstBB->getParent()->splice(EndBB, Chain->FirstBB, ChainEndBB);
+ LastBB = Chain->LastBB;
+ }
+};
+}
+
+namespace {
+/// \brief Successor iterator for BlockChains.
+///
+/// This is an iterator that walks over the successor block chains by looking
+/// through its blocks successors and mapping those back to block chains. This
+/// iterator is not a fully-functioning iterator, it is designed specifically
+/// to support the interface required by SCCIterator when forming and walking
+/// SCCs of BlockChains.
+///
+/// Note that this iterator cannot be used while the chains are still being
+/// formed and/or merged. Unlike the chains themselves, it does store end
+/// iterators which could be moved if the chains are re-ordered. Once we begin
+/// forming and iterating over an SCC of chains, the order of blocks within the
+/// function must not change until we finish using the SCC iterators.
+class BlockChain::SuccIterator
+ : public std::iterator<std::forward_iterator_tag,
+ BlockChain *, ptrdiff_t> {
+ BlockChain *Chain;
+ MachineFunction::iterator BI, BE;
+ MachineBasicBlock::succ_iterator SI;
+
+public:
+ explicit SuccIterator(BlockChain *Chain)
+ : Chain(Chain), BI(Chain->FirstBB), BE(llvm::next(Chain->LastBB)),
+ SI(BI->succ_begin()) {
+ while (BI != BE && BI->succ_begin() == BI->succ_end())
+ ++BI;
+ if (BI != BE)
+ SI = BI->succ_begin();
+ }
+
+ /// \brief Helper function to create an end iterator for a particular chain.
+ ///
+ /// The "end" state is extremely arbitrary. We chose to have BI == BE, and SI
+ /// == Chain->FirstBB->succ_begin(). The value of SI doesn't really make any
+ /// sense, but rather than try to rationalize SI and our increment, when we
+ /// detect an "end" state, we just immediately call this function to build
+ /// the canonical end iterator.
+ static SuccIterator CreateEnd(BlockChain *Chain) {
+ SuccIterator It(Chain);
+ It.BI = It.BE;
+ return It;
+ }
+
+ bool operator==(const SuccIterator &RHS) const {
+ return (Chain == RHS.Chain && BI == RHS.BI && SI == RHS.SI);
+ }
+ bool operator!=(const SuccIterator &RHS) const {
+ return !operator==(RHS);
+ }
+
+ SuccIterator& operator++() {
+ assert(*this != CreateEnd(Chain) && "Cannot increment the end iterator");
+ // There may be null successor pointers, skip over them.
+ // FIXME: I don't understand *why* there are null successor pointers.
+ do {
+ ++SI;
+ if (SI != BI->succ_end() && *SI)
+ return *this;
+
+ // There may be a basic block without successors. Skip over them.
+ do {
+ ++BI;
+ if (BI == BE)
+ return *this = CreateEnd(Chain);
+ } while (BI->succ_begin() == BI->succ_end());
+ SI = BI->succ_begin();
+ } while (!*SI);
+ return *this;
+ }
+ SuccIterator operator++(int) {
+ SuccIterator tmp = *this;
+ ++*this;
+ return tmp;
+ }
+
+ BlockChain *operator*() const {
+ assert(Chain->BlockToChain.lookup(*SI) && "Missing chain");
+ return Chain->BlockToChain.lookup(*SI);
+ }
+};
+}
+
+namespace {
+/// \brief Sorter used with containers of BlockChain pointers.
+///
+/// Sorts based on the \see BlockChain::InChainEdgeFrequency -- see its
+/// comments for details on what this ordering represents.
+struct ChainPtrPrioritySorter {
+ bool operator()(const BlockChain *LHS, const BlockChain *RHS) const {
+ assert(LHS && RHS && "Null chain entry");
+ return LHS->InChainEdgeFrequency < RHS->InChainEdgeFrequency;
+ }
+};
+}
+
+namespace {
+class MachineBlockPlacement : public MachineFunctionPass {
+ /// \brief A handle to the branch probability pass.
+ const MachineBranchProbabilityInfo *MBPI;
+
+ /// \brief A handle to the function-wide block frequency pass.
+ const MachineBlockFrequencyInfo *MBFI;
+
+ /// \brief A handle to the target's instruction info.
+ const TargetInstrInfo *TII;
+
+ /// \brief A prioritized list of edges in the BB-graph.
+ ///
+ /// For each function, we insert all control flow edges between BBs, along
+ /// with their "global" frequency. The Frequency of an edge being taken is
+ /// defined as the frequency of entering the source BB (from MBFI) times the
+ /// probability of taking a particular branch out of that block (from MBPI).
+ ///
+ /// Once built, this list is sorted in ascending frequency, making the last
+ /// edge the hottest one in the function.
+ SmallVector<WeightedEdge, 64> Edges;
+
+ /// \brief Allocator and owner of BlockChain structures.
+ ///
+ /// We build BlockChains lazily by merging together high probability BB
+ /// sequences acording to the "Algo2" in the paper mentioned at the top of
+ /// the file. To reduce malloc traffic, we allocate them using this slab-like
+ /// allocator, and destroy them after the pass completes.
+ SpecificBumpPtrAllocator<BlockChain> ChainAllocator;
+
+ /// \brief Function wide BasicBlock to BlockChain mapping.
+ ///
+ /// This mapping allows efficiently moving from any given basic block to the
+ /// BlockChain it participates in, if any. We use it to, among other things,
+ /// allow implicitly defining edges between chains as the existing edges
+ /// between basic blocks.
+ DenseMap<MachineBasicBlock *, BlockChain *> BlockToChain;
+
+ /// \brief A prioritized sequence of chains.
+ ///
+ /// We build up the ideal sequence of basic block chains in reverse order
+ /// here, and then walk backwards to arrange the final function ordering.
+ SmallVector<BlockChain *, 16> PChains;
+
+#ifndef NDEBUG
+ /// \brief A set of active chains used to sanity-check the pass algorithm.
+ ///
+ /// All operations on this member should be wrapped in an assert or NDEBUG.
+ SmallPtrSet<BlockChain *, 16> ActiveChains;
+#endif
+
+ BlockChain *CreateChain(MachineBasicBlock *BB);
+ void PrioritizeEdges(MachineFunction &F);
+ void BuildBlockChains();
+ void PrioritizeChains(MachineFunction &F);
+ void PlaceBlockChains(MachineFunction &F);
+
+public:
+ static char ID; // Pass identification, replacement for typeid
+ MachineBlockPlacement() : MachineFunctionPass(ID) {
+ initializeMachineBlockPlacementPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnMachineFunction(MachineFunction &F);
+
+ void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<MachineBranchProbabilityInfo>();
+ AU.addRequired<MachineBlockFrequencyInfo>();
+ MachineFunctionPass::getAnalysisUsage(AU);
+ }
+
+ const char *getPassName() const { return "Block Placement"; }
+};
+}
+
+char MachineBlockPlacement::ID = 0;
+INITIALIZE_PASS_BEGIN(MachineBlockPlacement, "block-placement2",
+ "Branch Probability Basic Block Placement", false, false)
+INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
+INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo)
+INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement2",
+ "Branch Probability Basic Block Placement", false, false)
+
+FunctionPass *llvm::createMachineBlockPlacementPass() {
+ return new MachineBlockPlacement();
+}
+
+namespace llvm {
+/// \brief GraphTraits specialization for our BlockChain graph.
+template <> struct GraphTraits<BlockChain *> {
+ typedef BlockChain NodeType;
+ typedef BlockChain::SuccIterator ChildIteratorType;
+
+ static NodeType *getEntryNode(NodeType *N) { return N; }
+ static BlockChain::SuccIterator child_begin(NodeType *N) {
+ return BlockChain::SuccIterator(N);
+ }
+ static BlockChain::SuccIterator child_end(NodeType *N) {
+ return BlockChain::SuccIterator::CreateEnd(N);
+ }
+};
+}
+
+/// \brief Helper to create a new chain for a single BB.
+///
+/// Takes care of growing the Chains, setting up the BlockChain object, and any
+/// debug checking logic.
+/// \returns A pointer to the new BlockChain.
+BlockChain *MachineBlockPlacement::CreateChain(MachineBasicBlock *BB) {
+ BlockChain *Chain =
+ new (ChainAllocator.Allocate()) BlockChain(BlockToChain, BB);
+ assert(ActiveChains.insert(Chain));
+ return Chain;
+}
+
+/// \brief Build a prioritized list of edges.
+///
+/// The priority is determined by the product of the block frequency (how
+/// likely it is to arrive at a particular block) times the probability of
+/// taking this particular edge out of the block. This provides a function-wide
+/// ordering of the edges.
+void MachineBlockPlacement::PrioritizeEdges(MachineFunction &F) {
+ assert(Edges.empty() && "Already have an edge list");
+ SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch.
+ BlockChain *RequiredChain = 0;
+ for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
+ MachineBasicBlock *From = &*FI;
+ // We only consider MBBs with analyzable branches. Even if the analysis
+ // fails, if there is no fallthrough, we can still work with the MBB.
+ MachineBasicBlock *TBB = 0, *FBB = 0;
+ Cond.clear();
+ if (TII->AnalyzeBranch(*From, TBB, FBB, Cond) && From->canFallThrough()) {
+ // We push all unanalyzed blocks onto a chain eagerly to prevent them
+ // from being split later. Create the chain if needed, otherwise just
+ // keep track that these blocks reside on it.
+ if (!RequiredChain)
+ RequiredChain = CreateChain(From);
+ else
+ BlockToChain[From] = RequiredChain;
+ } else {
+ // As soon as we find an analyzable branch, add that block to and
+ // finalize any required chain that has been started. The required chain
+ // is only modeling potentially inexplicable fallthrough, so the first
+ // block to have analyzable fallthrough is a known-safe stopping point.
+ if (RequiredChain) {
+ BlockToChain[From] = RequiredChain;
+ RequiredChain->LastBB = FI;
+ RequiredChain = 0;
+ }
+ }
+
+ BlockFrequency BaseFrequency = MBFI->getBlockFreq(From);
+ for (MachineBasicBlock::succ_iterator SI = From->succ_begin(),
+ SE = From->succ_end();
+ SI != SE; ++SI) {
+ MachineBasicBlock *To = *SI;
+ WeightedEdge WE = { BaseFrequency * MBPI->getEdgeProbability(From, To),
+ From, To };
+ Edges.push_back(WE);
+ }
+ }
+ assert(!RequiredChain && "Never found a terminator for a required chain");
+ std::stable_sort(Edges.begin(), Edges.end());
+}
+
+/// \brief Build chains of basic blocks along hot paths.
+///
+/// Build chains by trying to merge each pair of blocks from the mostly costly
+/// edge first. This is essentially "Algo2" from the Profile Guided Code
+/// Placement paper. While each node is considered a chain of one block, this
+/// routine lazily build the chain objects themselves so that when possible it
+/// can just merge a block into an existing chain.
+void MachineBlockPlacement::BuildBlockChains() {
+ for (SmallVectorImpl<WeightedEdge>::reverse_iterator EI = Edges.rbegin(),
+ EE = Edges.rend();
+ EI != EE; ++EI) {
+ MachineBasicBlock *SourceB = EI->From, *DestB = EI->To;
+ if (SourceB == DestB) continue;
+
+ BlockChain *SourceChain = BlockToChain.lookup(SourceB);
+ if (!SourceChain) SourceChain = CreateChain(SourceB);
+ BlockChain *DestChain = BlockToChain.lookup(DestB);
+ if (!DestChain) DestChain = CreateChain(DestB);
+ if (SourceChain == DestChain)
+ continue;
+
+ bool IsSourceTail =
+ SourceChain->LastBB == MachineFunction::iterator(SourceB);
+ bool IsDestHead =
+ DestChain->FirstBB == MachineFunction::iterator(DestB);
+
+ if (!IsSourceTail || !IsDestHead)
+ continue;
+
+ SourceChain->merge(DestChain);
+ assert(ActiveChains.erase(DestChain));
+ }
+}
+
+/// \brief Prioritize the chains to minimize back-edges between chains.
+///
+/// This is the trickiest part of the placement algorithm. Each chain is
+/// a hot-path through a sequence of basic blocks, but there are conditional
+/// branches away from this hot path, and to some other chain. Hardware branch
+/// predictors favor back edges over forward edges, and so it is desirable to
+/// arrange the targets of branches away from a hot path and to some other
+/// chain to come later in the function, making them forward branches, and
+/// helping the branch predictor to predict fallthrough.
+///
+/// In some cases, this is easy. simply topologically walking from the entry
+/// chain through its successors in order would work if there were no cycles
+/// between the chains of blocks, but often there are. In such a case, we first
+/// need to identify the participants in the cycle, and then rank them so that
+/// the linearizing of the chains has the lowest *probability* of causing
+/// a mispredicted branch. To compute the correct rank for a chain, we take the
+/// complement of the branch probability for each branch leading away from the
+/// chain and multiply it by the frequency of the source block for that branch.
+/// This gives us the probability of that particular branch *not* being taken
+/// in this function. The sum of these probabilities for each chain is used as
+/// a rank, so that we order the chain with the highest such sum first.
+/// FIXME: This seems like a good approximation, but there is probably a known
+/// technique for ordering of an SCC given edge weights. It would be good to
+/// use that, or even use its code if possible.
+///
+/// Also notable is that we prioritize the chains from the bottom up, and so
+/// all of the "first" and "before" relationships end up inverted in the code.
+void MachineBlockPlacement::PrioritizeChains(MachineFunction &F) {
+ MachineBasicBlock *EntryB = &F.front();
+ BlockChain *EntryChain = BlockToChain[EntryB];
+ assert(EntryChain && "Missing chain for entry block");
+ assert(EntryChain->FirstBB == F.begin() &&
+ "Entry block is not the head of the entry block chain");
+
+ // Form an SCC and walk it from the bottom up.
+ SmallPtrSet<BlockChain *, 4> IsInSCC;
+ for (scc_iterator<BlockChain *> I = scc_begin(EntryChain);
+ !I.isAtEnd(); ++I) {
+ const std::vector<BlockChain *> &SCC = *I;
+ PChains.insert(PChains.end(), SCC.begin(), SCC.end());
+
+ // If there is only one chain in the SCC, it's trivially sorted so just
+ // bail out early. Sorting the SCC is expensive.
+ if (SCC.size() == 1)
+ continue;
+
+ // We work strictly on the PChains range from here on out to maximize
+ // locality.
+ SmallVectorImpl<BlockChain *>::iterator SCCEnd = PChains.end(),
+ SCCBegin = SCCEnd - SCC.size();
+ IsInSCC.clear();
+ IsInSCC.insert(SCCBegin, SCCEnd);
+
+ // Compute the edge frequency of staying in a chain, despite the existency
+ // of an edge to some other chain within this SCC.
+ for (SmallVectorImpl<BlockChain *>::iterator SCCI = SCCBegin;
+ SCCI != SCCEnd; ++SCCI) {
+ BlockChain *Chain = *SCCI;
+
+ // Special case the entry chain. Regardless of the weights of other
+ // chains, the entry chain *must* come first, so move it to the end, and
+ // avoid processing that chain at all.
+ if (Chain == EntryChain) {
+ --SCCEnd;
+ if (SCCI == SCCEnd) break;
+ Chain = *SCCI = *SCCEnd;
+ *SCCEnd = EntryChain;
+ }
+
+ // Walk over every block in this chain looking for out-bound edges to
+ // other chains in this SCC.
+ for (MachineFunction::iterator BI = Chain->FirstBB,
+ BE = llvm::next(Chain->LastBB);
+ BI != BE; ++BI) {
+ MachineBasicBlock *From = &*BI;
+ for (MachineBasicBlock::succ_iterator SI = BI->succ_begin(),
+ SE = BI->succ_end();
+ SI != SE; ++SI) {
+ MachineBasicBlock *To = *SI;
+ if (!To || !IsInSCC.count(BlockToChain[To]))
+ continue;
+ BranchProbability ComplEdgeProb =
+ MBPI->getEdgeProbability(From, To).getCompl();
+ Chain->InChainEdgeFrequency +=
+ MBFI->getBlockFreq(From) * ComplEdgeProb;
+ }
+ }
+ }
+
+ // Sort the chains within the SCC according to their edge frequencies,
+ // which should make the least costly chain of blocks to mis-place be
+ // ordered first in the prioritized sequence.
+ std::stable_sort(SCCBegin, SCCEnd, ChainPtrPrioritySorter());
+ }
+}
+
+/// \brief Splice the function blocks together based on the chain priorities.
+///
+/// Each chain is already represented as a contiguous range of blocks in the
+/// function. Simply walk backwards down the prioritized chains and splice in
+/// any chains out of order. Note that the first chain we visit is necessarily
+/// the entry chain. It has no predecessors and so must be the top of the SCC.
+/// Also, we cannot splice any chain prior to the entry chain as we can't
+/// splice any blocks prior to the entry block.
+void MachineBlockPlacement::PlaceBlockChains(MachineFunction &F) {
+ assert(!PChains.empty() && "No chains were prioritized");
+ assert(PChains.back() == BlockToChain[&F.front()] &&
+ "The entry chain must always be the final chain");
+
+ MachineFunction::iterator InsertPos = F.begin();
+ for (SmallVectorImpl<BlockChain *>::reverse_iterator CI = PChains.rbegin(),
+ CE = PChains.rend();
+ CI != CE; ++CI) {
+ BlockChain *Chain = *CI;
+ // Check that we process this chain only once for debugging.
+ assert(ActiveChains.erase(Chain) && "Processed a chain twice");
+
+ // If this chain is already in the right position, just skip past it.
+ // Otherwise, splice it into position.
+ if (InsertPos == Chain->FirstBB)
+ InsertPos = llvm::next(Chain->LastBB);
+ else
+ F.splice(InsertPos, Chain->FirstBB, llvm::next(Chain->LastBB));
+ }
+
+ // Note that we can't assert this is empty as there may be unreachable blocks
+ // in the function.
+#ifndef NDEBUG
+ ActiveChains.clear();
+#endif
+
+ // Now that every block is in its final position, update all of the
+ // terminators.
+ SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch.
+ for (MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
+ // FIXME: It would be awesome of updateTerminator would just return rather
+ // than assert when the branch cannot be analyzed in order to remove this
+ // boiler plate.
+ Cond.clear();
+ MachineBasicBlock *TBB = 0, *FBB = 0; // For AnalyzeBranch.
+ if (!TII->AnalyzeBranch(*FI, TBB, FBB, Cond))
+ FI->updateTerminator();
+ }
+}
+
+bool MachineBlockPlacement::runOnMachineFunction(MachineFunction &F) {
+ // Check for single-block functions and skip them.
+ if (llvm::next(F.begin()) == F.end())
+ return false;
+
+ MBPI = &getAnalysis<MachineBranchProbabilityInfo>();
+ MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
+ TII = F.getTarget().getInstrInfo();
+ assert(Edges.empty());
+ assert(BlockToChain.empty());
+ assert(PChains.empty());
+ assert(ActiveChains.empty());
+
+ PrioritizeEdges(F);
+ BuildBlockChains();
+ PrioritizeChains(F);
+ PlaceBlockChains(F);
+
+ Edges.clear();
+ BlockToChain.clear();
+ PChains.clear();
+ ChainAllocator.DestroyAll();
+
+ // We always return true as we have no way to track whether the final order
+ // differs from the original order.
+ return true;
+}
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