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Diffstat (limited to 'include/llvm/Analysis/LoopInfoImpl.h')
| -rw-r--r-- | include/llvm/Analysis/LoopInfoImpl.h | 570 |
1 files changed, 570 insertions, 0 deletions
diff --git a/include/llvm/Analysis/LoopInfoImpl.h b/include/llvm/Analysis/LoopInfoImpl.h new file mode 100644 index 0000000000000..c07fbf7aa8273 --- /dev/null +++ b/include/llvm/Analysis/LoopInfoImpl.h @@ -0,0 +1,570 @@ +//===- llvm/Analysis/LoopInfoImpl.h - Natural Loop Calculator ---*- C++ -*-===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This is the generic implementation of LoopInfo used for both Loops and +// MachineLoops. +// +//===----------------------------------------------------------------------===// + +#ifndef LLVM_ANALYSIS_LOOP_INFO_IMPL_H +#define LLVM_ANALYSIS_LOOP_INFO_IMPL_H + +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/ADT/PostOrderIterator.h" + +namespace llvm { + +//===----------------------------------------------------------------------===// +// APIs for simple analysis of the loop. See header notes. + +/// getExitingBlocks - Return all blocks inside the loop that have successors +/// outside of the loop. These are the blocks _inside of the current loop_ +/// which branch out. The returned list is always unique. +/// +template<class BlockT, class LoopT> +void LoopBase<BlockT, LoopT>:: +getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const { + // Sort the blocks vector so that we can use binary search to do quick + // lookups. + SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); + std::sort(LoopBBs.begin(), LoopBBs.end()); + + typedef GraphTraits<BlockT*> BlockTraits; + for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) + for (typename BlockTraits::ChildIteratorType I = + BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); + I != E; ++I) + if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) { + // Not in current loop? It must be an exit block. + ExitingBlocks.push_back(*BI); + break; + } +} + +/// getExitingBlock - If getExitingBlocks would return exactly one block, +/// return that block. Otherwise return null. +template<class BlockT, class LoopT> +BlockT *LoopBase<BlockT, LoopT>::getExitingBlock() const { + SmallVector<BlockT*, 8> ExitingBlocks; + getExitingBlocks(ExitingBlocks); + if (ExitingBlocks.size() == 1) + return ExitingBlocks[0]; + return 0; +} + +/// getExitBlocks - Return all of the successor blocks of this loop. These +/// are the blocks _outside of the current loop_ which are branched to. +/// +template<class BlockT, class LoopT> +void LoopBase<BlockT, LoopT>:: +getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const { + // Sort the blocks vector so that we can use binary search to do quick + // lookups. + SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); + std::sort(LoopBBs.begin(), LoopBBs.end()); + + typedef GraphTraits<BlockT*> BlockTraits; + for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) + for (typename BlockTraits::ChildIteratorType I = + BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); + I != E; ++I) + if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) + // Not in current loop? It must be an exit block. + ExitBlocks.push_back(*I); +} + +/// getExitBlock - If getExitBlocks would return exactly one block, +/// return that block. Otherwise return null. +template<class BlockT, class LoopT> +BlockT *LoopBase<BlockT, LoopT>::getExitBlock() const { + SmallVector<BlockT*, 8> ExitBlocks; + getExitBlocks(ExitBlocks); + if (ExitBlocks.size() == 1) + return ExitBlocks[0]; + return 0; +} + +/// getExitEdges - Return all pairs of (_inside_block_,_outside_block_). +template<class BlockT, class LoopT> +void LoopBase<BlockT, LoopT>:: +getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const { + // Sort the blocks vector so that we can use binary search to do quick + // lookups. + SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); + array_pod_sort(LoopBBs.begin(), LoopBBs.end()); + + typedef GraphTraits<BlockT*> BlockTraits; + for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) + for (typename BlockTraits::ChildIteratorType I = + BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI); + I != E; ++I) + if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) + // Not in current loop? It must be an exit block. + ExitEdges.push_back(Edge(*BI, *I)); +} + +/// getLoopPreheader - If there is a preheader for this loop, return it. A +/// loop has a preheader if there is only one edge to the header of the loop +/// from outside of the loop. If this is the case, the block branching to the +/// header of the loop is the preheader node. +/// +/// This method returns null if there is no preheader for the loop. +/// +template<class BlockT, class LoopT> +BlockT *LoopBase<BlockT, LoopT>::getLoopPreheader() const { + // Keep track of nodes outside the loop branching to the header... + BlockT *Out = getLoopPredecessor(); + if (!Out) return 0; + + // Make sure there is only one exit out of the preheader. + typedef GraphTraits<BlockT*> BlockTraits; + typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out); + ++SI; + if (SI != BlockTraits::child_end(Out)) + return 0; // Multiple exits from the block, must not be a preheader. + + // The predecessor has exactly one successor, so it is a preheader. + return Out; +} + +/// getLoopPredecessor - If the given loop's header has exactly one unique +/// predecessor outside the loop, return it. Otherwise return null. +/// This is less strict that the loop "preheader" concept, which requires +/// the predecessor to have exactly one successor. +/// +template<class BlockT, class LoopT> +BlockT *LoopBase<BlockT, LoopT>::getLoopPredecessor() const { + // Keep track of nodes outside the loop branching to the header... + BlockT *Out = 0; + + // Loop over the predecessors of the header node... + BlockT *Header = getHeader(); + typedef GraphTraits<BlockT*> BlockTraits; + typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; + for (typename InvBlockTraits::ChildIteratorType PI = + InvBlockTraits::child_begin(Header), + PE = InvBlockTraits::child_end(Header); PI != PE; ++PI) { + typename InvBlockTraits::NodeType *N = *PI; + if (!contains(N)) { // If the block is not in the loop... + if (Out && Out != N) + return 0; // Multiple predecessors outside the loop + Out = N; + } + } + + // Make sure there is only one exit out of the preheader. + assert(Out && "Header of loop has no predecessors from outside loop?"); + return Out; +} + +/// getLoopLatch - If there is a single latch block for this loop, return it. +/// A latch block is a block that contains a branch back to the header. +template<class BlockT, class LoopT> +BlockT *LoopBase<BlockT, LoopT>::getLoopLatch() const { + BlockT *Header = getHeader(); + typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; + typename InvBlockTraits::ChildIteratorType PI = + InvBlockTraits::child_begin(Header); + typename InvBlockTraits::ChildIteratorType PE = + InvBlockTraits::child_end(Header); + BlockT *Latch = 0; + for (; PI != PE; ++PI) { + typename InvBlockTraits::NodeType *N = *PI; + if (contains(N)) { + if (Latch) return 0; + Latch = N; + } + } + + return Latch; +} + +//===----------------------------------------------------------------------===// +// APIs for updating loop information after changing the CFG +// + +/// addBasicBlockToLoop - This method is used by other analyses to update loop +/// information. NewBB is set to be a new member of the current loop. +/// Because of this, it is added as a member of all parent loops, and is added +/// to the specified LoopInfo object as being in the current basic block. It +/// is not valid to replace the loop header with this method. +/// +template<class BlockT, class LoopT> +void LoopBase<BlockT, LoopT>:: +addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LIB) { + assert((Blocks.empty() || LIB[getHeader()] == this) && + "Incorrect LI specified for this loop!"); + assert(NewBB && "Cannot add a null basic block to the loop!"); + assert(LIB[NewBB] == 0 && "BasicBlock already in the loop!"); + + LoopT *L = static_cast<LoopT *>(this); + + // Add the loop mapping to the LoopInfo object... + LIB.BBMap[NewBB] = L; + + // Add the basic block to this loop and all parent loops... + while (L) { + L->Blocks.push_back(NewBB); + L = L->getParentLoop(); + } +} + +/// replaceChildLoopWith - This is used when splitting loops up. It replaces +/// the OldChild entry in our children list with NewChild, and updates the +/// parent pointer of OldChild to be null and the NewChild to be this loop. +/// This updates the loop depth of the new child. +template<class BlockT, class LoopT> +void LoopBase<BlockT, LoopT>:: +replaceChildLoopWith(LoopT *OldChild, LoopT *NewChild) { + assert(OldChild->ParentLoop == this && "This loop is already broken!"); + assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!"); + typename std::vector<LoopT *>::iterator I = + std::find(SubLoops.begin(), SubLoops.end(), OldChild); + assert(I != SubLoops.end() && "OldChild not in loop!"); + *I = NewChild; + OldChild->ParentLoop = 0; + NewChild->ParentLoop = static_cast<LoopT *>(this); +} + +/// verifyLoop - Verify loop structure +template<class BlockT, class LoopT> +void LoopBase<BlockT, LoopT>::verifyLoop() const { +#ifndef NDEBUG + assert(!Blocks.empty() && "Loop header is missing"); + + // Setup for using a depth-first iterator to visit every block in the loop. + SmallVector<BlockT*, 8> ExitBBs; + getExitBlocks(ExitBBs); + llvm::SmallPtrSet<BlockT*, 8> VisitSet; + VisitSet.insert(ExitBBs.begin(), ExitBBs.end()); + df_ext_iterator<BlockT*, llvm::SmallPtrSet<BlockT*, 8> > + BI = df_ext_begin(getHeader(), VisitSet), + BE = df_ext_end(getHeader(), VisitSet); + + // Keep track of the number of BBs visited. + unsigned NumVisited = 0; + + // Sort the blocks vector so that we can use binary search to do quick + // lookups. + SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end()); + std::sort(LoopBBs.begin(), LoopBBs.end()); + + // Check the individual blocks. + for ( ; BI != BE; ++BI) { + BlockT *BB = *BI; + bool HasInsideLoopSuccs = false; + bool HasInsideLoopPreds = false; + SmallVector<BlockT *, 2> OutsideLoopPreds; + + typedef GraphTraits<BlockT*> BlockTraits; + for (typename BlockTraits::ChildIteratorType SI = + BlockTraits::child_begin(BB), SE = BlockTraits::child_end(BB); + SI != SE; ++SI) + if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *SI)) { + HasInsideLoopSuccs = true; + break; + } + typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; + for (typename InvBlockTraits::ChildIteratorType PI = + InvBlockTraits::child_begin(BB), PE = InvBlockTraits::child_end(BB); + PI != PE; ++PI) { + BlockT *N = *PI; + if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), N)) + HasInsideLoopPreds = true; + else + OutsideLoopPreds.push_back(N); + } + + if (BB == getHeader()) { + assert(!OutsideLoopPreds.empty() && "Loop is unreachable!"); + } else if (!OutsideLoopPreds.empty()) { + // A non-header loop shouldn't be reachable from outside the loop, + // though it is permitted if the predecessor is not itself actually + // reachable. + BlockT *EntryBB = BB->getParent()->begin(); + for (df_iterator<BlockT *> NI = df_begin(EntryBB), + NE = df_end(EntryBB); NI != NE; ++NI) + for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i) + assert(*NI != OutsideLoopPreds[i] && + "Loop has multiple entry points!"); + } + assert(HasInsideLoopPreds && "Loop block has no in-loop predecessors!"); + assert(HasInsideLoopSuccs && "Loop block has no in-loop successors!"); + assert(BB != getHeader()->getParent()->begin() && + "Loop contains function entry block!"); + + NumVisited++; + } + + assert(NumVisited == getNumBlocks() && "Unreachable block in loop"); + + // Check the subloops. + for (iterator I = begin(), E = end(); I != E; ++I) + // Each block in each subloop should be contained within this loop. + for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end(); + BI != BE; ++BI) { + assert(std::binary_search(LoopBBs.begin(), LoopBBs.end(), *BI) && + "Loop does not contain all the blocks of a subloop!"); + } + + // Check the parent loop pointer. + if (ParentLoop) { + assert(std::find(ParentLoop->begin(), ParentLoop->end(), this) != + ParentLoop->end() && + "Loop is not a subloop of its parent!"); + } +#endif +} + +/// verifyLoop - Verify loop structure of this loop and all nested loops. +template<class BlockT, class LoopT> +void LoopBase<BlockT, LoopT>::verifyLoopNest( + DenseSet<const LoopT*> *Loops) const { + Loops->insert(static_cast<const LoopT *>(this)); + // Verify this loop. + verifyLoop(); + // Verify the subloops. + for (iterator I = begin(), E = end(); I != E; ++I) + (*I)->verifyLoopNest(Loops); +} + +template<class BlockT, class LoopT> +void LoopBase<BlockT, LoopT>::print(raw_ostream &OS, unsigned Depth) const { + OS.indent(Depth*2) << "Loop at depth " << getLoopDepth() + << " containing: "; + + for (unsigned i = 0; i < getBlocks().size(); ++i) { + if (i) OS << ","; + BlockT *BB = getBlocks()[i]; + WriteAsOperand(OS, BB, false); + if (BB == getHeader()) OS << "<header>"; + if (BB == getLoopLatch()) OS << "<latch>"; + if (isLoopExiting(BB)) OS << "<exiting>"; + } + OS << "\n"; + + for (iterator I = begin(), E = end(); I != E; ++I) + (*I)->print(OS, Depth+2); +} + +//===----------------------------------------------------------------------===// +/// Stable LoopInfo Analysis - Build a loop tree using stable iterators so the +/// result does / not depend on use list (block predecessor) order. +/// + +/// Discover a subloop with the specified backedges such that: All blocks within +/// this loop are mapped to this loop or a subloop. And all subloops within this +/// loop have their parent loop set to this loop or a subloop. +template<class BlockT, class LoopT> +static void discoverAndMapSubloop(LoopT *L, ArrayRef<BlockT*> Backedges, + LoopInfoBase<BlockT, LoopT> *LI, + DominatorTreeBase<BlockT> &DomTree) { + typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; + + unsigned NumBlocks = 0; + unsigned NumSubloops = 0; + + // Perform a backward CFG traversal using a worklist. + std::vector<BlockT *> ReverseCFGWorklist(Backedges.begin(), Backedges.end()); + while (!ReverseCFGWorklist.empty()) { + BlockT *PredBB = ReverseCFGWorklist.back(); + ReverseCFGWorklist.pop_back(); + + LoopT *Subloop = LI->getLoopFor(PredBB); + if (!Subloop) { + if (!DomTree.isReachableFromEntry(PredBB)) + continue; + + // This is an undiscovered block. Map it to the current loop. + LI->changeLoopFor(PredBB, L); + ++NumBlocks; + if (PredBB == L->getHeader()) + continue; + // Push all block predecessors on the worklist. + ReverseCFGWorklist.insert(ReverseCFGWorklist.end(), + InvBlockTraits::child_begin(PredBB), + InvBlockTraits::child_end(PredBB)); + } + else { + // This is a discovered block. Find its outermost discovered loop. + while (LoopT *Parent = Subloop->getParentLoop()) + Subloop = Parent; + + // If it is already discovered to be a subloop of this loop, continue. + if (Subloop == L) + continue; + + // Discover a subloop of this loop. + Subloop->setParentLoop(L); + ++NumSubloops; + NumBlocks += Subloop->getBlocks().capacity(); + PredBB = Subloop->getHeader(); + // Continue traversal along predecessors that are not loop-back edges from + // within this subloop tree itself. Note that a predecessor may directly + // reach another subloop that is not yet discovered to be a subloop of + // this loop, which we must traverse. + for (typename InvBlockTraits::ChildIteratorType PI = + InvBlockTraits::child_begin(PredBB), + PE = InvBlockTraits::child_end(PredBB); PI != PE; ++PI) { + if (LI->getLoopFor(*PI) != Subloop) + ReverseCFGWorklist.push_back(*PI); + } + } + } + L->getSubLoopsVector().reserve(NumSubloops); + L->getBlocksVector().reserve(NumBlocks); +} + +namespace { +/// Populate all loop data in a stable order during a single forward DFS. +template<class BlockT, class LoopT> +class PopulateLoopsDFS { + typedef GraphTraits<BlockT*> BlockTraits; + typedef typename BlockTraits::ChildIteratorType SuccIterTy; + + LoopInfoBase<BlockT, LoopT> *LI; + DenseSet<const BlockT *> VisitedBlocks; + std::vector<std::pair<BlockT*, SuccIterTy> > DFSStack; + +public: + PopulateLoopsDFS(LoopInfoBase<BlockT, LoopT> *li): + LI(li) {} + + void traverse(BlockT *EntryBlock); + +protected: + void insertIntoLoop(BlockT *Block); + + BlockT *dfsSource() { return DFSStack.back().first; } + SuccIterTy &dfsSucc() { return DFSStack.back().second; } + SuccIterTy dfsSuccEnd() { return BlockTraits::child_end(dfsSource()); } + + void pushBlock(BlockT *Block) { + DFSStack.push_back(std::make_pair(Block, BlockTraits::child_begin(Block))); + } +}; +} // anonymous + +/// Top-level driver for the forward DFS within the loop. +template<class BlockT, class LoopT> +void PopulateLoopsDFS<BlockT, LoopT>::traverse(BlockT *EntryBlock) { + pushBlock(EntryBlock); + VisitedBlocks.insert(EntryBlock); + while (!DFSStack.empty()) { + // Traverse the leftmost path as far as possible. + while (dfsSucc() != dfsSuccEnd()) { + BlockT *BB = *dfsSucc(); + ++dfsSucc(); + if (!VisitedBlocks.insert(BB).second) + continue; + + // Push the next DFS successor onto the stack. + pushBlock(BB); + } + // Visit the top of the stack in postorder and backtrack. + insertIntoLoop(dfsSource()); + DFSStack.pop_back(); + } +} + +/// Add a single Block to its ancestor loops in PostOrder. If the block is a +/// subloop header, add the subloop to its parent in PostOrder, then reverse the +/// Block and Subloop vectors of the now complete subloop to achieve RPO. +template<class BlockT, class LoopT> +void PopulateLoopsDFS<BlockT, LoopT>::insertIntoLoop(BlockT *Block) { + LoopT *Subloop = LI->getLoopFor(Block); + if (Subloop && Block == Subloop->getHeader()) { + // We reach this point once per subloop after processing all the blocks in + // the subloop. + if (Subloop->getParentLoop()) + Subloop->getParentLoop()->getSubLoopsVector().push_back(Subloop); + else + LI->addTopLevelLoop(Subloop); + + // For convenience, Blocks and Subloops are inserted in postorder. Reverse + // the lists, except for the loop header, which is always at the beginning. + std::reverse(Subloop->getBlocksVector().begin()+1, + Subloop->getBlocksVector().end()); + std::reverse(Subloop->getSubLoopsVector().begin(), + Subloop->getSubLoopsVector().end()); + + Subloop = Subloop->getParentLoop(); + } + for (; Subloop; Subloop = Subloop->getParentLoop()) + Subloop->getBlocksVector().push_back(Block); +} + +/// Analyze LoopInfo discovers loops during a postorder DominatorTree traversal +/// interleaved with backward CFG traversals within each subloop +/// (discoverAndMapSubloop). The backward traversal skips inner subloops, so +/// this part of the algorithm is linear in the number of CFG edges. Subloop and +/// Block vectors are then populated during a single forward CFG traversal +/// (PopulateLoopDFS). +/// +/// During the two CFG traversals each block is seen three times: +/// 1) Discovered and mapped by a reverse CFG traversal. +/// 2) Visited during a forward DFS CFG traversal. +/// 3) Reverse-inserted in the loop in postorder following forward DFS. +/// +/// The Block vectors are inclusive, so step 3 requires loop-depth number of +/// insertions per block. +template<class BlockT, class LoopT> +void LoopInfoBase<BlockT, LoopT>:: +Analyze(DominatorTreeBase<BlockT> &DomTree) { + + // Postorder traversal of the dominator tree. + DomTreeNodeBase<BlockT>* DomRoot = DomTree.getRootNode(); + for (po_iterator<DomTreeNodeBase<BlockT>*> DomIter = po_begin(DomRoot), + DomEnd = po_end(DomRoot); DomIter != DomEnd; ++DomIter) { + + BlockT *Header = DomIter->getBlock(); + SmallVector<BlockT *, 4> Backedges; + + // Check each predecessor of the potential loop header. + typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits; + for (typename InvBlockTraits::ChildIteratorType PI = + InvBlockTraits::child_begin(Header), + PE = InvBlockTraits::child_end(Header); PI != PE; ++PI) { + + BlockT *Backedge = *PI; + + // If Header dominates predBB, this is a new loop. Collect the backedges. + if (DomTree.dominates(Header, Backedge) + && DomTree.isReachableFromEntry(Backedge)) { + Backedges.push_back(Backedge); + } + } + // Perform a backward CFG traversal to discover and map blocks in this loop. + if (!Backedges.empty()) { + LoopT *L = new LoopT(Header); + discoverAndMapSubloop(L, ArrayRef<BlockT*>(Backedges), this, DomTree); + } + } + // Perform a single forward CFG traversal to populate block and subloop + // vectors for all loops. + PopulateLoopsDFS<BlockT, LoopT> DFS(this); + DFS.traverse(DomRoot->getBlock()); +} + +// Debugging +template<class BlockT, class LoopT> +void LoopInfoBase<BlockT, LoopT>::print(raw_ostream &OS) const { + for (unsigned i = 0; i < TopLevelLoops.size(); ++i) + TopLevelLoops[i]->print(OS); +#if 0 + for (DenseMap<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(), + E = BBMap.end(); I != E; ++I) + OS << "BB '" << I->first->getName() << "' level = " + << I->second->getLoopDepth() << "\n"; +#endif +} + +} // End llvm namespace + +#endif |