diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/SampleProfile.cpp | 672 |
1 files changed, 605 insertions, 67 deletions
diff --git a/llvm/lib/Transforms/Scalar/SampleProfile.cpp b/llvm/lib/Transforms/Scalar/SampleProfile.cpp index 170a070aa5a..e3d290194cf 100644 --- a/llvm/lib/Transforms/Scalar/SampleProfile.cpp +++ b/llvm/lib/Transforms/Scalar/SampleProfile.cpp @@ -26,9 +26,14 @@ #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/OwningPtr.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/StringMap.h" #include "llvm/ADT/StringRef.h" -#include "llvm/DebugInfo/DIContext.h" +#include "llvm/Analysis/Dominators.h" +#include "llvm/Analysis/PostDominators.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/DebugInfo.h" #include "llvm/IR/Constants.h" #include "llvm/IR/Function.h" #include "llvm/IR/Instructions.h" @@ -52,11 +57,19 @@ using namespace llvm; static cl::opt<std::string> SampleProfileFile( "sample-profile-file", cl::init(""), cl::value_desc("filename"), cl::desc("Profile file loaded by -sample-profile"), cl::Hidden); +static cl::opt<unsigned> SampleProfileMaxPropagateIterations( + "sample-profile-max-propagate-iterations", cl::init(100), + cl::desc("Maximum number of iterations to go through when propagating " + "sample block/edge weights through the CFG.")); namespace { typedef DenseMap<uint32_t, uint32_t> BodySampleMap; typedef DenseMap<BasicBlock *, uint32_t> BlockWeightMap; +typedef DenseMap<BasicBlock *, BasicBlock *> EquivalenceClassMap; +typedef std::pair<BasicBlock *, BasicBlock *> Edge; +typedef DenseMap<Edge, uint32_t> EdgeWeightMap; +typedef DenseMap<BasicBlock *, SmallVector<BasicBlock *, 8> > BlockEdgeMap; /// \brief Representation of the runtime profile for a function. /// @@ -65,19 +78,34 @@ typedef DenseMap<BasicBlock *, uint32_t> BlockWeightMap; /// in the function and a map of samples collected in every statement. class SampleFunctionProfile { public: - SampleFunctionProfile() : TotalSamples(0), TotalHeadSamples(0) {} + SampleFunctionProfile() + : TotalSamples(0), TotalHeadSamples(0), HeaderLineno(0), DT(0), PDT(0), + LI(0) {} - bool emitAnnotations(Function &F); - uint32_t getInstWeight(Instruction &I, unsigned FirstLineno, - BodySampleMap &BodySamples); - uint32_t computeBlockWeight(BasicBlock *B, unsigned FirstLineno, - BodySampleMap &BodySamples); + unsigned getFunctionLoc(Function &F); + bool emitAnnotations(Function &F, DominatorTree *DomTree, + PostDominatorTree *PostDomTree, LoopInfo *Loops); + uint32_t getInstWeight(Instruction &I); + uint32_t getBlockWeight(BasicBlock *B); void addTotalSamples(unsigned Num) { TotalSamples += Num; } void addHeadSamples(unsigned Num) { TotalHeadSamples += Num; } void addBodySamples(unsigned LineOffset, unsigned Num) { BodySamples[LineOffset] += Num; } void print(raw_ostream &OS); + void printEdgeWeight(raw_ostream &OS, Edge E); + void printBlockWeight(raw_ostream &OS, BasicBlock *BB); + void printBlockEquivalence(raw_ostream &OS, BasicBlock *BB); + bool computeBlockWeights(Function &F); + void findEquivalenceClasses(Function &F); + void findEquivalencesFor(BasicBlock *BB1, + SmallVector<BasicBlock *, 8> Descendants, + DominatorTreeBase<BasicBlock> *DomTree); + void propagateWeights(Function &F); + uint32_t visitEdge(Edge E, unsigned *NumUnknownEdges, Edge *UnknownEdge); + void buildEdges(Function &F); + bool propagateThroughEdges(Function &F); + bool empty() { return BodySamples.empty(); } protected: /// \brief Total number of samples collected inside this function. @@ -86,9 +114,15 @@ protected: /// inside this function and all its inlined callees. unsigned TotalSamples; - // \brief Total number of samples collected at the head of the function. + /// \brief Total number of samples collected at the head of the function. unsigned TotalHeadSamples; + /// \brief Line number for the function header. Used to compute relative + /// line numbers from the absolute line LOCs found in instruction locations. + /// The relative line numbers are needed to address the samples from the + /// profile file. + unsigned HeaderLineno; + /// \brief Map line offsets to collected samples. /// /// Each entry in this map contains the number of samples @@ -101,6 +135,37 @@ protected: /// The weight of a basic block is defined to be the maximum /// of all the instruction weights in that block. BlockWeightMap BlockWeights; + + /// \brief Map edges to their computed weights. + /// + /// Edge weights are computed by propagating basic block weights in + /// SampleProfile::propagateWeights. + EdgeWeightMap EdgeWeights; + + /// \brief Set of visited blocks during propagation. + SmallPtrSet<BasicBlock *, 128> VisitedBlocks; + + /// \brief Set of visited edges during propagation. + SmallSet<Edge, 128> VisitedEdges; + + /// \brief Equivalence classes for block weights. + /// + /// Two blocks BB1 and BB2 are in the same equivalence class if they + /// dominate and post-dominate each other, and they are in the same loop + /// nest. When this happens, the two blocks are guaranteed to execute + /// the same number of times. + EquivalenceClassMap EquivalenceClass; + + /// \brief Dominance, post-dominance and loop information. + DominatorTree *DT; + PostDominatorTree *PDT; + LoopInfo *LI; + + /// \brief Predecessors for each basic block in the CFG. + BlockEdgeMap Predecessors; + + /// \brief Successors for each basic block in the CFG. + BlockEdgeMap Successors; }; /// \brief Sample-based profile reader. @@ -238,6 +303,9 @@ public: virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesCFG(); + AU.addRequired<LoopInfo>(); + AU.addRequired<DominatorTree>(); + AU.addRequired<PostDominatorTree>(); } protected: @@ -263,6 +331,34 @@ void SampleFunctionProfile::print(raw_ostream &OS) { OS << "\n"; } +/// \brief Print the weight of edge \p E on stream \p OS. +/// +/// \param OS Stream to emit the output to. +/// \param E Edge to print. +void SampleFunctionProfile::printEdgeWeight(raw_ostream &OS, Edge E) { + OS << "weight[" << E.first->getName() << "->" << E.second->getName() + << "]: " << EdgeWeights[E] << "\n"; +} + +/// \brief Print the equivalence class of block \p BB on stream \p OS. +/// +/// \param OS Stream to emit the output to. +/// \param BB Block to print. +void SampleFunctionProfile::printBlockEquivalence(raw_ostream &OS, + BasicBlock *BB) { + BasicBlock *Equiv = EquivalenceClass[BB]; + OS << "equivalence[" << BB->getName() + << "]: " << ((Equiv) ? EquivalenceClass[BB]->getName() : "NONE") << "\n"; +} + +/// \brief Print the weight of block \p BB on stream \p OS. +/// +/// \param OS Stream to emit the output to. +/// \param BB Block to print. +void SampleFunctionProfile::printBlockWeight(raw_ostream &OS, BasicBlock *BB) { + OS << "weight[" << BB->getName() << "]: " << BlockWeights[BB] << "\n"; +} + /// \brief Print the function profile for \p FName on stream \p OS. /// /// \param OS Stream to emit the output to. @@ -361,6 +457,12 @@ void SampleModuleProfile::loadText() { unsigned LineOffset, NumSamples; Matches[1].getAsInteger(10, LineOffset); Matches[2].getAsInteger(10, NumSamples); + // When dealing with instruction weights, we use the value + // zero to indicate the absence of a sample. If we read an + // actual zero from the profile file, return it as 1 to + // avoid the confusion later on. + if (NumSamples == 0) + NumSamples = 1; FProfile.addBodySamples(LineOffset, NumSamples); } @@ -369,59 +471,39 @@ void SampleModuleProfile::loadText() { } } -char SampleProfileLoader::ID = 0; -INITIALIZE_PASS(SampleProfileLoader, "sample-profile", "Sample Profile loader", - false, false) - -bool SampleProfileLoader::doInitialization(Module &M) { - Profiler.reset(new SampleModuleProfile(Filename)); - Profiler->loadText(); - return true; -} - -FunctionPass *llvm::createSampleProfileLoaderPass() { - return new SampleProfileLoader(SampleProfileFile); -} - -FunctionPass *llvm::createSampleProfileLoaderPass(StringRef Name) { - return new SampleProfileLoader(Name); -} - /// \brief Get the weight for an instruction. /// /// The "weight" of an instruction \p Inst is the number of samples /// collected on that instruction at runtime. To retrieve it, we /// need to compute the line number of \p Inst relative to the start of its -/// function. We use \p FirstLineno to compute the offset. We then -/// look up the samples collected for \p Inst using \p BodySamples. +/// function. We use HeaderLineno to compute the offset. We then +/// look up the samples collected for \p Inst using BodySamples. /// /// \param Inst Instruction to query. -/// \param FirstLineno Line number of the first instruction in the function. -/// \param BodySamples Map of relative source line locations to samples. /// /// \returns The profiled weight of I. -uint32_t SampleFunctionProfile::getInstWeight(Instruction &Inst, - unsigned FirstLineno, - BodySampleMap &BodySamples) { - unsigned LOffset = Inst.getDebugLoc().getLine() - FirstLineno + 1; - return BodySamples.lookup(LOffset); +uint32_t SampleFunctionProfile::getInstWeight(Instruction &Inst) { + unsigned Lineno = Inst.getDebugLoc().getLine(); + if (Lineno < HeaderLineno) + return 0; + unsigned LOffset = Lineno - HeaderLineno; + uint32_t Weight = BodySamples.lookup(LOffset); + DEBUG(dbgs() << " " << Lineno << ":" << Inst.getDebugLoc().getCol() << ":" + << Inst << " (line offset: " << LOffset + << " - weight: " << Weight << ")\n"); + return Weight; } /// \brief Compute the weight of a basic block. /// /// The weight of basic block \p B is the maximum weight of all the -/// instructions in B. +/// instructions in B. The weight of \p B is computed and cached in +/// the BlockWeights map. /// /// \param B The basic block to query. -/// \param FirstLineno The line number for the first line in the -/// function holding B. -/// \param BodySamples The map containing all the samples collected in that -/// function. /// /// \returns The computed weight of B. -uint32_t SampleFunctionProfile::computeBlockWeight(BasicBlock *B, - unsigned FirstLineno, - BodySampleMap &BodySamples) { +uint32_t SampleFunctionProfile::getBlockWeight(BasicBlock *B) { // If we've computed B's weight before, return it. std::pair<BlockWeightMap::iterator, bool> Entry = BlockWeights.insert(std::make_pair(B, 0)); @@ -431,7 +513,7 @@ uint32_t SampleFunctionProfile::computeBlockWeight(BasicBlock *B, // Otherwise, compute and cache B's weight. uint32_t Weight = 0; for (BasicBlock::iterator I = B->begin(), E = B->end(); I != E; ++I) { - uint32_t InstWeight = getInstWeight(*I, FirstLineno, BodySamples); + uint32_t InstWeight = getInstWeight(*I); if (InstWeight > Weight) Weight = InstWeight; } @@ -439,30 +521,344 @@ uint32_t SampleFunctionProfile::computeBlockWeight(BasicBlock *B, return Weight; } -/// \brief Generate branch weight metadata for all branches in \p F. +/// \brief Compute and store the weights of every basic block. +/// +/// This populates the BlockWeights map by computing +/// the weights of every basic block in the CFG. /// -/// For every branch instruction B in \p F, we compute the weight of the -/// target block for each of the edges out of B. This is the weight -/// that we associate with that branch. +/// \param F The function to query. +bool SampleFunctionProfile::computeBlockWeights(Function &F) { + bool Changed = false; + DEBUG(dbgs() << "Block weights\n"); + for (Function::iterator B = F.begin(), E = F.end(); B != E; ++B) { + uint32_t Weight = getBlockWeight(B); + Changed |= (Weight > 0); + DEBUG(printBlockWeight(dbgs(), B)); + } + + return Changed; +} + +/// \brief Find equivalence classes for the given block. /// -/// TODO - This weight assignment will most likely be wrong if the -/// target branch has more than two predecessors. This needs to be done -/// using some form of flow propagation. +/// This finds all the blocks that are guaranteed to execute the same +/// number of times as \p BB1. To do this, it traverses all the the +/// descendants of \p BB1 in the dominator or post-dominator tree. /// -/// Once all the branch weights are computed, we emit the MD_prof -/// metadata on B using the computed values. +/// A block BB2 will be in the same equivalence class as \p BB1 if +/// the following holds: +/// +/// 1- \p BB1 is a descendant of BB2 in the opposite tree. So, if BB2 +/// is a descendant of \p BB1 in the dominator tree, then BB2 should +/// dominate BB1 in the post-dominator tree. +/// +/// 2- Both BB2 and \p BB1 must be in the same loop. +/// +/// For every block BB2 that meets those two requirements, we set BB2's +/// equivalence class to \p BB1. +/// +/// \param BB1 Block to check. +/// \param Descendants Descendants of \p BB1 in either the dom or pdom tree. +/// \param DomTree Opposite dominator tree. If \p Descendants is filled +/// with blocks from \p BB1's dominator tree, then +/// this is the post-dominator tree, and vice versa. +void SampleFunctionProfile::findEquivalencesFor( + BasicBlock *BB1, SmallVector<BasicBlock *, 8> Descendants, + DominatorTreeBase<BasicBlock> *DomTree) { + for (SmallVectorImpl<BasicBlock *>::iterator I = Descendants.begin(), + E = Descendants.end(); + I != E; ++I) { + BasicBlock *BB2 = *I; + bool IsDomParent = DomTree->dominates(BB2, BB1); + bool IsInSameLoop = LI->getLoopFor(BB1) == LI->getLoopFor(BB2); + if (BB1 != BB2 && VisitedBlocks.insert(BB2) && IsDomParent && + IsInSameLoop) { + EquivalenceClass[BB2] = BB1; + + // If BB2 is heavier than BB1, make BB2 have the same weight + // as BB1. + // + // Note that we don't worry about the opposite situation here + // (when BB2 is lighter than BB1). We will deal with this + // during the propagation phase. Right now, we just want to + // make sure that BB1 has the largest weight of all the + // members of its equivalence set. + uint32_t &BB1Weight = BlockWeights[BB1]; + uint32_t &BB2Weight = BlockWeights[BB2]; + BB1Weight = std::max(BB1Weight, BB2Weight); + } + } +} + +/// \brief Find equivalence classes. +/// +/// Since samples may be missing from blocks, we can fill in the gaps by setting +/// the weights of all the blocks in the same equivalence class to the same +/// weight. To compute the concept of equivalence, we use dominance and loop +/// information. Two blocks B1 and B2 are in the same equivalence class if B1 +/// dominates B2, B2 post-dominates B1 and both are in the same loop. /// /// \param F The function to query. -bool SampleFunctionProfile::emitAnnotations(Function &F) { +void SampleFunctionProfile::findEquivalenceClasses(Function &F) { + SmallVector<BasicBlock *, 8> DominatedBBs; + DEBUG(dbgs() << "\nBlock equivalence classes\n"); + // Find equivalence sets based on dominance and post-dominance information. + for (Function::iterator B = F.begin(), E = F.end(); B != E; ++B) { + BasicBlock *BB1 = B; + + // Compute BB1's equivalence class once. + if (EquivalenceClass.count(BB1)) { + DEBUG(printBlockEquivalence(dbgs(), BB1)); + continue; + } + + // By default, blocks are in their own equivalence class. + EquivalenceClass[BB1] = BB1; + + // Traverse all the blocks dominated by BB1. We are looking for + // every basic block BB2 such that: + // + // 1- BB1 dominates BB2. + // 2- BB2 post-dominates BB1. + // 3- BB1 and BB2 are in the same loop nest. + // + // If all those conditions hold, it means that BB2 is executed + // as many times as BB1, so they are placed in the same equivalence + // class by making BB2's equivalence class be BB1. + DominatedBBs.clear(); + DT->getDescendants(BB1, DominatedBBs); + findEquivalencesFor(BB1, DominatedBBs, PDT->DT); + + // Repeat the same logic for all the blocks post-dominated by BB1. + // We are looking for every basic block BB2 such that: + // + // 1- BB1 post-dominates BB2. + // 2- BB2 dominates BB1. + // 3- BB1 and BB2 are in the same loop nest. + // + // If all those conditions hold, BB2's equivalence class is BB1. + DominatedBBs.clear(); + PDT->getDescendants(BB1, DominatedBBs); + findEquivalencesFor(BB1, DominatedBBs, DT->DT); + + DEBUG(printBlockEquivalence(dbgs(), BB1)); + } + + // Assign weights to equivalence classes. + // + // All the basic blocks in the same equivalence class will execute + // the same number of times. Since we know that the head block in + // each equivalence class has the largest weight, assign that weight + // to all the blocks in that equivalence class. + DEBUG(dbgs() << "\nAssign the same weight to all blocks in the same class\n"); + for (Function::iterator B = F.begin(), E = F.end(); B != E; ++B) { + BasicBlock *BB = B; + BasicBlock *EquivBB = EquivalenceClass[BB]; + if (BB != EquivBB) + BlockWeights[BB] = BlockWeights[EquivBB]; + DEBUG(printBlockWeight(dbgs(), BB)); + } +} + +/// \brief Visit the given edge to decide if it has a valid weight. +/// +/// If \p E has not been visited before, we copy to \p UnknownEdge +/// and increment the count of unknown edges. +/// +/// \param E Edge to visit. +/// \param NumUnknownEdges Current number of unknown edges. +/// \param UnknownEdge Set if E has not been visited before. +/// +/// \returns E's weight, if known. Otherwise, return 0. +uint32_t SampleFunctionProfile::visitEdge(Edge E, unsigned *NumUnknownEdges, + Edge *UnknownEdge) { + if (!VisitedEdges.count(E)) { + (*NumUnknownEdges)++; + *UnknownEdge = E; + return 0; + } + + return EdgeWeights[E]; +} + +/// \brief Propagate weights through incoming/outgoing edges. +/// +/// If the weight of a basic block is known, and there is only one edge +/// with an unknown weight, we can calculate the weight of that edge. +/// +/// Similarly, if all the edges have a known count, we can calculate the +/// count of the basic block, if needed. +/// +/// \param F Function to process. +/// +/// \returns True if new weights were assigned to edges or blocks. +bool SampleFunctionProfile::propagateThroughEdges(Function &F) { bool Changed = false; - unsigned FirstLineno = inst_begin(F)->getDebugLoc().getLine(); - MDBuilder MDB(F.getContext()); + DEBUG(dbgs() << "\nPropagation through edges\n"); + for (Function::iterator BI = F.begin(), EI = F.end(); BI != EI; ++BI) { + BasicBlock *BB = BI; + + // Visit all the predecessor and successor edges to determine + // which ones have a weight assigned already. Note that it doesn't + // matter that we only keep track of a single unknown edge. The + // only case we are interested in handling is when only a single + // edge is unknown (see setEdgeOrBlockWeight). + for (unsigned i = 0; i < 2; i++) { + uint32_t TotalWeight = 0; + unsigned NumUnknownEdges = 0; + Edge UnknownEdge, SelfReferentialEdge; + + if (i == 0) { + // First, visit all predecessor edges. + for (size_t I = 0; I < Predecessors[BB].size(); I++) { + Edge E = std::make_pair(Predecessors[BB][I], BB); + TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge); + if (E.first == E.second) + SelfReferentialEdge = E; + } + } else { + // On the second round, visit all successor edges. + for (size_t I = 0; I < Successors[BB].size(); I++) { + Edge E = std::make_pair(BB, Successors[BB][I]); + TotalWeight += visitEdge(E, &NumUnknownEdges, &UnknownEdge); + } + } + + // After visiting all the edges, there are three cases that we + // can handle immediately: + // + // - All the edge weights are known (i.e., NumUnknownEdges == 0). + // In this case, we simply check that the sum of all the edges + // is the same as BB's weight. If not, we change BB's weight + // to match. Additionally, if BB had not been visited before, + // we mark it visited. + // + // - Only one edge is unknown and BB has already been visited. + // In this case, we can compute the weight of the edge by + // subtracting the total block weight from all the known + // edge weights. If the edges weight more than BB, then the + // edge of the last remaining edge is set to zero. + // + // - There exists a self-referential edge and the weight of BB is + // known. In this case, this edge can be based on BB's weight. + // We add up all the other known edges and set the weight on + // the self-referential edge as we did in the previous case. + // + // In any other case, we must continue iterating. Eventually, + // all edges will get a weight, or iteration will stop when + // it reaches SampleProfileMaxPropagateIterations. + if (NumUnknownEdges <= 1) { + uint32_t &BBWeight = BlockWeights[BB]; + if (NumUnknownEdges == 0) { + // If we already know the weight of all edges, the weight of the + // basic block can be computed. It should be no larger than the sum + // of all edge weights. + if (TotalWeight > BBWeight) { + BBWeight = TotalWeight; + Changed = true; + DEBUG(dbgs() << "All edge weights for " << BB->getName() + << " known. Set weight for block: "; + printBlockWeight(dbgs(), BB);); + } + if (VisitedBlocks.insert(BB)) + Changed = true; + } else if (NumUnknownEdges == 1 && VisitedBlocks.count(BB)) { + // If there is a single unknown edge and the block has been + // visited, then we can compute E's weight. + if (BBWeight >= TotalWeight) + EdgeWeights[UnknownEdge] = BBWeight - TotalWeight; + else + EdgeWeights[UnknownEdge] = 0; + VisitedEdges.insert(UnknownEdge); + Changed = true; + DEBUG(dbgs() << "Set weight for edge: "; + printEdgeWeight(dbgs(), UnknownEdge)); + } + } else if (SelfReferentialEdge.first && VisitedBlocks.count(BB)) { + uint32_t &BBWeight = BlockWeights[BB]; + // We have a self-referential edge and the weight of BB is known. + if (BBWeight >= TotalWeight) + EdgeWeights[SelfReferentialEdge] = BBWeight - TotalWeight; + else + EdgeWeights[SelfReferentialEdge] = 0; + VisitedEdges.insert(SelfReferentialEdge); + Changed = true; + DEBUG(dbgs() << "Set self-referential edge weight to: "; + printEdgeWeight(dbgs(), SelfReferentialEdge)); + } + } + } + + return Changed; +} + +/// \brief Build in/out edge lists for each basic block in the CFG. +/// +/// We are interested in unique edges. If a block B1 has multiple +/// edges to another block B2, we only add a single B1->B2 edge. +void SampleFunctionProfile::buildEdges(Function &F) { + for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) { + BasicBlock *B1 = I; + + // Add predecessors for B1. + SmallPtrSet<BasicBlock *, 16> Visited; + if (!Predecessors[B1].empty()) + llvm_unreachable("Found a stale predecessors list in a basic block."); + for (pred_iterator PI = pred_begin(B1), PE = pred_end(B1); PI != PE; ++PI) { + BasicBlock *B2 = *PI; + if (Visited.insert(B2)) + Predecessors[B1].push_back(B2); + } + + // Add successors for B1. + Visited.clear(); + if (!Successors[B1].empty()) + llvm_unreachable("Found a stale successors list in a basic block."); + for (succ_iterator SI = succ_begin(B1), SE = succ_end(B1); SI != SE; ++SI) { + BasicBlock *B2 = *SI; + if (Visited.insert(B2)) + Successors[B1].push_back(B2); + } + } +} + +/// \brief Propagate weights into edges +/// +/// The following rules are applied to every block B in the CFG: +/// +/// - If B has a single predecessor/successor, then the weight +/// of that edge is the weight of the block. +/// +/// - If all incoming or outgoing edges are known except one, and the +/// weight of the block is already known, the weight of the unknown +/// edge will be the weight of the block minus the sum of all the known +/// edges. If the sum of all the known edges is larger than B's weight, +/// we set the unknown edge weight to zero. +/// +/// - If there is a self-referential edge, and the weight of the block is +/// known, the weight for that edge is set to the weight of the block +/// minus the weight of the other incoming edges to that block (if +/// known). +void SampleFunctionProfile::propagateWeights(Function &F) { + bool Changed = true; + unsigned i = 0; - // Clear the block weights cache. - BlockWeights.clear(); + // Before propagation starts, build, for each block, a list of + // unique predecessors and successors. This is necessary to handle + // identical edges in multiway branches. Since we visit all blocks and all + // edges of the CFG, it is cleaner to build these lists once at the start + // of the pass. + buildEdges(F); - // When we find a branch instruction: For each edge E out of the branch, - // the weight of E is the weight of the target block. + // Propagate until we converge or we go past the iteration limit. + while (Changed && i++ < SampleProfileMaxPropagateIterations) { + Changed = propagateThroughEdges(F); + } + + // Generate MD_prof metadata for every branch instruction using the + // edge weights computed during propagation. + DEBUG(dbgs() << "\nPropagation complete. Setting branch weights\n"); + MDBuilder MDB(F.getContext()); for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) { BasicBlock *B = I; TerminatorInst *TI = B->getTerminator(); @@ -471,22 +867,164 @@ bool SampleFunctionProfile::emitAnnotations(Function &F) { if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI)) continue; + DEBUG(dbgs() << "\nGetting weights for branch at line " + << TI->getDebugLoc().getLine() << ":" + << TI->getDebugLoc().getCol() << ".\n"); SmallVector<uint32_t, 4> Weights; - unsigned NSuccs = TI->getNumSuccessors(); - for (unsigned I = 0; I < NSuccs; ++I) { + bool AllWeightsZero = true; + for (unsigned I = 0; I < TI->getNumSuccessors(); ++I) { BasicBlock *Succ = TI->getSuccessor(I); - uint32_t Weight = computeBlockWeight(Succ, FirstLineno, BodySamples); + Edge E = std::make_pair(B, Succ); + uint32_t Weight = EdgeWeights[E]; + DEBUG(dbgs() << "\t"; printEdgeWeight(dbgs(), E)); Weights.push_back(Weight); + if (Weight != 0) + AllWeightsZero = false; + } + + // Only set weights if there is at least one non-zero weight. + // In any other case, let the analyzer set weights. + if (!AllWeightsZero) { + DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n"); + TI->setMetadata(llvm::LLVMContext::MD_prof, + MDB.createBranchWeights(Weights)); + } else { + DEBUG(dbgs() << "SKIPPED. All branch weights are zero.\n"); + } + } +} + +/// \brief Get the line number for the function header. +/// +/// This looks up function \p F in the current compilation unit and +/// retrieves the line number where the function is defined. This is +/// line 0 for all the samples read from the profile file. Every line +/// number is relative to this line. +/// +/// \param F Function object to query. +/// +/// \returns the line number where \p F is defined. +unsigned SampleFunctionProfile::getFunctionLoc(Function &F) { + NamedMDNode *CUNodes = F.getParent()->getNamedMetadata("llvm.dbg.cu"); + if (CUNodes) { + for (unsigned I = 0, E1 = CUNodes->getNumOperands(); I != E1; ++I) { + DICompileUnit CU(CUNodes->getOperand(I)); + DIArray Subprograms = CU.getSubprograms(); + for (unsigned J = 0, E2 = Subprograms.getNumElements(); J != E2; ++J) { + DISubprogram Subprogram(Subprograms.getElement(J)); + if (Subprogram.describes(&F)) + return Subprogram.getLineNumber(); + } } + } + + report_fatal_error("No debug information found in function " + F.getName() + + "\n"); +} + +/// \brief Generate branch weight metadata for all branches in \p F. +/// +/// Branch weights are computed out of instruction samples using a +/// propagation heuristic. Propagation proceeds in 3 phases: +/// +/// 1- Assignment of block weights. All the basic blocks in the function +/// are initial assigned the same weight as their most frequently +/// executed instruction. +/// +/// 2- Creation of equivalence classes. Since samples may be missing from +/// blocks, we can fill in the gaps by setting the weights of all the +/// blocks in the same equivalence class to the same weight. To compute +/// the concept of equivalence, we use dominance and loop information. +/// Two blocks B1 and B2 are in the same equivalence class if B1 +/// dominates B2, B2 post-dominates B1 and both are in the same loop. +/// +/// 3- Propagation of block weights into edges. This uses a simple +/// propagation heuristic. The following rules are applied to every +/// block B in the CFG: +/// +/// - If B has a single predecessor/successor, then the weight +/// of that edge is the weight of the block. +/// +/// - If all the edges are known except one, and the weight of the +/// block is already known, the weight of the unknown edge will +/// be the weight of the block minus the sum of all the known +/// edges. If the sum of all the known edges is larger than B's weight, +/// we set the unknown edge weight to zero. +/// +/// - If there is a self-referential edge, and the weight of the block is +/// known, the weight for that edge is set to the weight of the block +/// minus the weight of the other incoming edges to that block (if +/// known). +/// +/// Since this propagation is not guaranteed to finalize for every CFG, we +/// only allow it to proceed for a limited number of iterations (controlled +/// by -sample-profile-max-propagate-iterations). +/// +/// FIXME: Try to replace this propagation heuristic with a scheme +/// that is guaranteed to finalize. A work-list approach similar to +/// the standard value propagation algorithm used by SSA-CCP might +/// work here. +/// +/// Once all the branch weights are computed, we emit the MD_prof +/// metadata on B using the computed values for each of its branches. +/// +/// \param F The function to query. +bool SampleFunctionProfile::emitAnnotations(Function &F, DominatorTree *DomTree, + PostDominatorTree *PostDomTree, + LoopInfo *Loops) { + bool Changed = false; - TI->setMetadata(llvm::LLVMContext::MD_prof, - MDB.createBranchWeights(Weights)); - Changed = true; + // Initialize invariants used during computation and propagation. + HeaderLineno = getFunctionLoc(F); + DEBUG(dbgs() << "Line number for the first instruction in " << F.getName() + << ": " << HeaderLineno << "\n"); + DT = DomTree; + PDT = PostDomTree; + LI = Loops; + + // Compute basic block weights. + Changed |= computeBlockWeights(F); + + if (Changed) { + // Find equivalence classes. + findEquivalenceClasses(F); + + // Propagate weights to all edges. + propagateWeights(F); } return Changed; } +char SampleProfileLoader::ID = 0; +INITIALIZE_PASS_BEGIN(SampleProfileLoader, "sample-profile", + "Sample Profile loader", false, false) +INITIALIZE_PASS_DEPENDENCY(DominatorTree) +INITIALIZE_PASS_DEPENDENCY(PostDominatorTree) +INITIALIZE_PASS_DEPENDENCY(LoopInfo) +INITIALIZE_PASS_END(SampleProfileLoader, "sample-profile", + "Sample Profile loader", false, false) + +bool SampleProfileLoader::doInitialization(Module &M) { + Profiler.reset(new SampleModuleProfile(Filename)); + Profiler->loadText(); + return true; +} + +FunctionPass *llvm::createSampleProfileLoaderPass() { + return new SampleProfileLoader(SampleProfileFile); +} + +FunctionPass *llvm::createSampleProfileLoaderPass(StringRef Name) { + return new SampleProfileLoader(Name); +} + bool SampleProfileLoader::runOnFunction(Function &F) { - return Profiler->getProfile(F).emitAnnotations(F); + DominatorTree *DT = &getAnalysis<DominatorTree>(); + PostDominatorTree *PDT = &getAnalysis<PostDominatorTree>(); + LoopInfo *LI = &getAnalysis<LoopInfo>(); + SampleFunctionProfile &FunctionProfile = Profiler->getProfile(F); + if (!FunctionProfile.empty()) + return FunctionProfile.emitAnnotations(F, DT, PDT, LI); + return false; } |
