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Diffstat (limited to 'include/llvm/Analysis/BlockFrequencyImpl.h')
| -rw-r--r-- | include/llvm/Analysis/BlockFrequencyImpl.h | 349 |
1 files changed, 349 insertions, 0 deletions
diff --git a/include/llvm/Analysis/BlockFrequencyImpl.h b/include/llvm/Analysis/BlockFrequencyImpl.h new file mode 100644 index 0000000..6580fd1 --- /dev/null +++ b/include/llvm/Analysis/BlockFrequencyImpl.h @@ -0,0 +1,349 @@ +//===---- BlockFrequencyImpl.h - Machine Block Frequency Implementation ---===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// Shared implementation of BlockFrequency for IR and Machine Instructions. +// +//===----------------------------------------------------------------------===// + +#ifndef LLVM_ANALYSIS_BLOCKFREQUENCYIMPL_H +#define LLVM_ANALYSIS_BLOCKFREQUENCYIMPL_H + +#include "llvm/BasicBlock.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/PostOrderIterator.h" +#include "llvm/CodeGen/MachineBasicBlock.h" +#include "llvm/CodeGen/MachineFunction.h" +#include "llvm/Support/BranchProbability.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include <vector> +#include <sstream> +#include <string> + +namespace llvm { + + +class BlockFrequency; +class MachineBlockFrequency; + +/// BlockFrequencyImpl implements block frequency algorithm for IR and +/// Machine Instructions. Algorithm starts with value 1024 (START_FREQ) +/// for the entry block and then propagates frequencies using branch weights +/// from (Machine)BranchProbabilityInfo. LoopInfo is not required because +/// algorithm can find "backedges" by itself. +template<class BlockT, class FunctionT, class BlockProbInfoT> +class BlockFrequencyImpl { + + DenseMap<BlockT *, uint32_t> Freqs; + + BlockProbInfoT *BPI; + + FunctionT *Fn; + + typedef GraphTraits< Inverse<BlockT *> > GT; + + static const uint32_t START_FREQ = 1024; + + std::string getBlockName(BasicBlock *BB) const { + return BB->getNameStr(); + } + + std::string getBlockName(MachineBasicBlock *MBB) const { + std::stringstream ss; + ss << "BB#" << MBB->getNumber(); + + if (const BasicBlock *BB = MBB->getBasicBlock()) + ss << " derived from LLVM BB " << BB->getNameStr(); + + return ss.str(); + } + + void setBlockFreq(BlockT *BB, uint32_t Freq) { + Freqs[BB] = Freq; + DEBUG(dbgs() << "Frequency(" << getBlockName(BB) << ") = " << Freq << "\n"); + } + + /// getEdgeFreq - Return edge frequency based on SRC frequency and Src -> Dst + /// edge probability. + uint32_t getEdgeFreq(BlockT *Src, BlockT *Dst) const { + BranchProbability Prob = BPI->getEdgeProbability(Src, Dst); + uint64_t N = Prob.getNumerator(); + uint64_t D = Prob.getDenominator(); + uint64_t Res = (N * getBlockFreq(Src)) / D; + + assert(Res <= UINT32_MAX); + return (uint32_t) Res; + } + + /// incBlockFreq - Increase BB block frequency by FREQ. + /// + void incBlockFreq(BlockT *BB, uint32_t Freq) { + Freqs[BB] += Freq; + DEBUG(dbgs() << "Frequency(" << getBlockName(BB) << ") += " << Freq + << " --> " << Freqs[BB] << "\n"); + } + + /// divBlockFreq - Divide BB block frequency by PROB. If Prob = 0 do nothing. + /// + void divBlockFreq(BlockT *BB, BranchProbability Prob) { + uint64_t N = Prob.getNumerator(); + assert(N && "Illegal division by zero!"); + uint64_t D = Prob.getDenominator(); + uint64_t Freq = (Freqs[BB] * D) / N; + + // Should we assert it? + if (Freq > UINT32_MAX) + Freq = UINT32_MAX; + + Freqs[BB] = (uint32_t) Freq; + DEBUG(dbgs() << "Frequency(" << getBlockName(BB) << ") /= (" << Prob + << ") --> " << Freqs[BB] << "\n"); + } + + // All blocks in postorder. + std::vector<BlockT *> POT; + + // Map Block -> Position in reverse-postorder list. + DenseMap<BlockT *, unsigned> RPO; + + // Cycle Probability for each bloch. + DenseMap<BlockT *, uint32_t> CycleProb; + + // (reverse-)postorder traversal iterators. + typedef typename std::vector<BlockT *>::iterator pot_iterator; + typedef typename std::vector<BlockT *>::reverse_iterator rpot_iterator; + + pot_iterator pot_begin() { return POT.begin(); } + pot_iterator pot_end() { return POT.end(); } + + rpot_iterator rpot_begin() { return POT.rbegin(); } + rpot_iterator rpot_end() { return POT.rend(); } + + rpot_iterator rpot_at(BlockT *BB) { + rpot_iterator I = rpot_begin(); + unsigned idx = RPO[BB]; + assert(idx); + std::advance(I, idx - 1); + + assert(*I == BB); + return I; + } + + + /// Return a probability of getting to the DST block through SRC->DST edge. + /// + BranchProbability getBackEdgeProbability(BlockT *Src, BlockT *Dst) const { + uint32_t N = getEdgeFreq(Src, Dst); + uint32_t D = getBlockFreq(Dst); + + return BranchProbability(N, D); + } + + /// isReachable - Returns if BB block is reachable from the entry. + /// + bool isReachable(BlockT *BB) { + return RPO.count(BB); + } + + /// isBackedge - Return if edge Src -> Dst is a backedge. + /// + bool isBackedge(BlockT *Src, BlockT *Dst) { + assert(isReachable(Src)); + assert(isReachable(Dst)); + + unsigned a = RPO[Src]; + unsigned b = RPO[Dst]; + + return a > b; + } + + /// getSingleBlockPred - return single BB block predecessor or NULL if + /// BB has none or more predecessors. + BlockT *getSingleBlockPred(BlockT *BB) { + typename GT::ChildIteratorType + PI = GraphTraits< Inverse<BlockT *> >::child_begin(BB), + PE = GraphTraits< Inverse<BlockT *> >::child_end(BB); + + if (PI == PE) + return 0; + + BlockT *Pred = *PI; + + ++PI; + if (PI != PE) + return 0; + + return Pred; + } + + void doBlock(BlockT *BB, BlockT *LoopHead, + SmallPtrSet<BlockT *, 8> &BlocksInLoop) { + + DEBUG(dbgs() << "doBlock(" << getBlockName(BB) << ")\n"); + setBlockFreq(BB, 0); + + if (BB == LoopHead) { + setBlockFreq(BB, START_FREQ); + return; + } + + if(BlockT *Pred = getSingleBlockPred(BB)) { + if (BlocksInLoop.count(Pred)) + setBlockFreq(BB, getEdgeFreq(Pred, BB)); + // TODO: else? irreducible, ignore it for now. + return; + } + + bool isInLoop = false; + bool isLoopHead = false; + + for (typename GT::ChildIteratorType + PI = GraphTraits< Inverse<BlockT *> >::child_begin(BB), + PE = GraphTraits< Inverse<BlockT *> >::child_end(BB); + PI != PE; ++PI) { + BlockT *Pred = *PI; + + if (isReachable(Pred) && isBackedge(Pred, BB)) { + isLoopHead = true; + } else if (BlocksInLoop.count(Pred)) { + incBlockFreq(BB, getEdgeFreq(Pred, BB)); + isInLoop = true; + } + // TODO: else? irreducible. + } + + if (!isInLoop) + return; + + if (!isLoopHead) + return; + + assert(START_FREQ >= CycleProb[BB]); + uint32_t CProb = CycleProb[BB]; + uint32_t Numerator = START_FREQ - CProb ? START_FREQ - CProb : 1; + divBlockFreq(BB, BranchProbability(Numerator, START_FREQ)); + } + + /// doLoop - Propagate block frequency down throught the loop. + void doLoop(BlockT *Head, BlockT *Tail) { + DEBUG(dbgs() << "doLoop(" << getBlockName(Head) << ", " + << getBlockName(Tail) << ")\n"); + + SmallPtrSet<BlockT *, 8> BlocksInLoop; + + for (rpot_iterator I = rpot_at(Head), E = rpot_end(); I != E; ++I) { + BlockT *BB = *I; + doBlock(BB, Head, BlocksInLoop); + + BlocksInLoop.insert(BB); + } + + // Compute loop's cyclic probability using backedges probabilities. + for (typename GT::ChildIteratorType + PI = GraphTraits< Inverse<BlockT *> >::child_begin(Head), + PE = GraphTraits< Inverse<BlockT *> >::child_end(Head); + PI != PE; ++PI) { + BlockT *Pred = *PI; + assert(Pred); + if (isReachable(Pred) && isBackedge(Pred, Head)) { + BranchProbability Prob = getBackEdgeProbability(Pred, Head); + uint64_t N = Prob.getNumerator(); + uint64_t D = Prob.getDenominator(); + uint64_t Res = (N * START_FREQ) / D; + + assert(Res <= UINT32_MAX); + CycleProb[Head] += (uint32_t) Res; + } + } + } + + friend class BlockFrequency; + friend class MachineBlockFrequency; + + void doFunction(FunctionT *fn, BlockProbInfoT *bpi) { + Fn = fn; + BPI = bpi; + + // Clear everything. + RPO.clear(); + POT.clear(); + CycleProb.clear(); + Freqs.clear(); + + BlockT *EntryBlock = fn->begin(); + + copy(po_begin(EntryBlock), po_end(EntryBlock), back_inserter(POT)); + + unsigned RPOidx = 0; + for (rpot_iterator I = rpot_begin(), E = rpot_end(); I != E; ++I) { + BlockT *BB = *I; + RPO[BB] = ++RPOidx; + DEBUG(dbgs() << "RPO[" << getBlockName(BB) << "] = " << RPO[BB] << "\n"); + } + + // Travel over all blocks in postorder. + for (pot_iterator I = pot_begin(), E = pot_end(); I != E; ++I) { + BlockT *BB = *I; + BlockT *LastTail = 0; + DEBUG(dbgs() << "POT: " << getBlockName(BB) << "\n"); + + for (typename GT::ChildIteratorType + PI = GraphTraits< Inverse<BlockT *> >::child_begin(BB), + PE = GraphTraits< Inverse<BlockT *> >::child_end(BB); + PI != PE; ++PI) { + + BlockT *Pred = *PI; + if (isReachable(Pred) && isBackedge(Pred, BB) + && (!LastTail || RPO[Pred] > RPO[LastTail])) + LastTail = Pred; + } + + if (LastTail) + doLoop(BB, LastTail); + } + + // At the end assume the whole function as a loop, and travel over it once + // again. + doLoop(*(rpot_begin()), *(pot_begin())); + } + +public: + /// getBlockFreq - Return block frequency. Never return 0, value must be + /// positive. + uint32_t getBlockFreq(BlockT *BB) const { + typename DenseMap<BlockT *, uint32_t>::const_iterator I = Freqs.find(BB); + if (I != Freqs.end()) + return I->second ? I->second : 1; + return 1; + } + + void print(raw_ostream &OS) const { + OS << "\n\n---- Block Freqs ----\n"; + for (typename FunctionT::iterator I = Fn->begin(), E = Fn->end(); I != E;) { + BlockT *BB = I++; + OS << " " << getBlockName(BB) << " = " << getBlockFreq(BB) << "\n"; + + for (typename GraphTraits<BlockT *>::ChildIteratorType + SI = GraphTraits<BlockT *>::child_begin(BB), + SE = GraphTraits<BlockT *>::child_end(BB); SI != SE; ++SI) { + BlockT *Succ = *SI; + OS << " " << getBlockName(BB) << " -> " << getBlockName(Succ) + << " = " << getEdgeFreq(BB, Succ) << "\n"; + } + } + } + + void dump() const { + print(dbgs()); + } +}; + +} + +#endif |
