X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FLoopInfo.cpp;h=46c0eaabe1a3102e59ecc1b18f430800944b7dd4;hb=08f77a9f422e96110d8400e4caaf6a51be49a1f3;hp=20ca8929971ddf7be0dbb69598bf7c3a36f2e528;hpb=019b92a70c11319f5ab96c9f5e66e4e111a972f8;p=oota-llvm.git diff --git a/lib/Analysis/LoopInfo.cpp b/lib/Analysis/LoopInfo.cpp index 20ca8929971..46c0eaabe1a 100644 --- a/lib/Analysis/LoopInfo.cpp +++ b/lib/Analysis/LoopInfo.cpp @@ -2,8 +2,8 @@ // // The LLVM Compiler Infrastructure // -// This file was developed by the LLVM research group and is distributed under -// the University of Illinois Open Source License. See LICENSE.TXT for details. +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // @@ -15,271 +15,710 @@ //===----------------------------------------------------------------------===// #include "llvm/Analysis/LoopInfo.h" -#include "llvm/Constants.h" -#include "llvm/Instructions.h" -#include "llvm/Analysis/Dominators.h" -#include "llvm/Assembly/Writer.h" -#include "llvm/Support/CFG.h" -#include "llvm/Support/Streams.h" #include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/SmallPtrSet.h" +#include "llvm/Analysis/LoopInfoImpl.h" +#include "llvm/Analysis/LoopIterator.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/CFG.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/Metadata.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" #include -#include using namespace llvm; +// Explicitly instantiate methods in LoopInfoImpl.h for IR-level Loops. +template class llvm::LoopBase; +template class llvm::LoopInfoBase; + +// Always verify loopinfo if expensive checking is enabled. +#ifdef XDEBUG +static bool VerifyLoopInfo = true; +#else +static bool VerifyLoopInfo = false; +#endif +static cl::opt +VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo), + cl::desc("Verify loop info (time consuming)")); + char LoopInfo::ID = 0; -static RegisterPass -X("loops", "Natural Loop Construction", true); +INITIALIZE_PASS_BEGIN(LoopInfo, "loops", "Natural Loop Information", true, true) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_END(LoopInfo, "loops", "Natural Loop Information", true, true) + +// Loop identifier metadata name. +static const char *const LoopMDName = "llvm.loop"; //===----------------------------------------------------------------------===// // Loop implementation // -/// getNumBackEdges - Calculate the number of back edges to the loop header. +/// isLoopInvariant - Return true if the specified value is loop invariant /// - -//===----------------------------------------------------------------------===// -// LoopInfo implementation -// -bool LoopInfo::runOnFunction(Function &) { - releaseMemory(); - Calculate(getAnalysis()); // Update - return false; +bool Loop::isLoopInvariant(Value *V) const { + if (Instruction *I = dyn_cast(V)) + return !contains(I); + return true; // All non-instructions are loop invariant } -void LoopInfo::releaseMemory() { - for (std::vector::iterator I = TopLevelLoops.begin(), - E = TopLevelLoops.end(); I != E; ++I) - delete *I; // Delete all of the loops... +/// hasLoopInvariantOperands - Return true if all the operands of the +/// specified instruction are loop invariant. +bool Loop::hasLoopInvariantOperands(Instruction *I) const { + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) + if (!isLoopInvariant(I->getOperand(i))) + return false; - BBMap.clear(); // Reset internal state of analysis - TopLevelLoops.clear(); + return true; } -void LoopInfo::Calculate(DominatorTree &DT) { - BasicBlock *RootNode = DT.getRootNode()->getBlock(); +/// makeLoopInvariant - If the given value is an instruciton inside of the +/// loop and it can be hoisted, do so to make it trivially loop-invariant. +/// Return true if the value after any hoisting is loop invariant. This +/// function can be used as a slightly more aggressive replacement for +/// isLoopInvariant. +/// +/// If InsertPt is specified, it is the point to hoist instructions to. +/// If null, the terminator of the loop preheader is used. +/// +bool Loop::makeLoopInvariant(Value *V, bool &Changed, + Instruction *InsertPt) const { + if (Instruction *I = dyn_cast(V)) + return makeLoopInvariant(I, Changed, InsertPt); + return true; // All non-instructions are loop-invariant. +} - for (df_iterator NI = df_begin(RootNode), - NE = df_end(RootNode); NI != NE; ++NI) - if (Loop *L = ConsiderForLoop(*NI, DT)) - TopLevelLoops.push_back(L); +/// makeLoopInvariant - If the given instruction is inside of the +/// loop and it can be hoisted, do so to make it trivially loop-invariant. +/// Return true if the instruction after any hoisting is loop invariant. This +/// function can be used as a slightly more aggressive replacement for +/// isLoopInvariant. +/// +/// If InsertPt is specified, it is the point to hoist instructions to. +/// If null, the terminator of the loop preheader is used. +/// +bool Loop::makeLoopInvariant(Instruction *I, bool &Changed, + Instruction *InsertPt) const { + // Test if the value is already loop-invariant. + if (isLoopInvariant(I)) + return true; + if (!isSafeToSpeculativelyExecute(I)) + return false; + if (I->mayReadFromMemory()) + return false; + // The landingpad instruction is immobile. + if (isa(I)) + return false; + // Determine the insertion point, unless one was given. + if (!InsertPt) { + BasicBlock *Preheader = getLoopPreheader(); + // Without a preheader, hoisting is not feasible. + if (!Preheader) + return false; + InsertPt = Preheader->getTerminator(); + } + // Don't hoist instructions with loop-variant operands. + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) + if (!makeLoopInvariant(I->getOperand(i), Changed, InsertPt)) + return false; + + // Hoist. + I->moveBefore(InsertPt); + Changed = true; + return true; } -void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const { - AU.setPreservesAll(); - AU.addRequired(); +/// getCanonicalInductionVariable - Check to see if the loop has a canonical +/// induction variable: an integer recurrence that starts at 0 and increments +/// by one each time through the loop. If so, return the phi node that +/// corresponds to it. +/// +/// The IndVarSimplify pass transforms loops to have a canonical induction +/// variable. +/// +PHINode *Loop::getCanonicalInductionVariable() const { + BasicBlock *H = getHeader(); + + BasicBlock *Incoming = nullptr, *Backedge = nullptr; + pred_iterator PI = pred_begin(H); + assert(PI != pred_end(H) && + "Loop must have at least one backedge!"); + Backedge = *PI++; + if (PI == pred_end(H)) return nullptr; // dead loop + Incoming = *PI++; + if (PI != pred_end(H)) return nullptr; // multiple backedges? + + if (contains(Incoming)) { + if (contains(Backedge)) + return nullptr; + std::swap(Incoming, Backedge); + } else if (!contains(Backedge)) + return nullptr; + + // Loop over all of the PHI nodes, looking for a canonical indvar. + for (BasicBlock::iterator I = H->begin(); isa(I); ++I) { + PHINode *PN = cast(I); + if (ConstantInt *CI = + dyn_cast(PN->getIncomingValueForBlock(Incoming))) + if (CI->isNullValue()) + if (Instruction *Inc = + dyn_cast(PN->getIncomingValueForBlock(Backedge))) + if (Inc->getOpcode() == Instruction::Add && + Inc->getOperand(0) == PN) + if (ConstantInt *CI = dyn_cast(Inc->getOperand(1))) + if (CI->equalsInt(1)) + return PN; + } + return nullptr; } -void LoopInfo::print(std::ostream &OS, const Module* ) const { - for (unsigned i = 0; i < TopLevelLoops.size(); ++i) - TopLevelLoops[i]->print(OS); -#if 0 - for (std::map::const_iterator I = BBMap.begin(), - E = BBMap.end(); I != E; ++I) - OS << "BB '" << I->first->getName() << "' level = " - << I->second->getLoopDepth() << "\n"; -#endif +/// isLCSSAForm - Return true if the Loop is in LCSSA form +bool Loop::isLCSSAForm(DominatorTree &DT) const { + for (block_iterator BI = block_begin(), E = block_end(); BI != E; ++BI) { + BasicBlock *BB = *BI; + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;++I) + for (Use &U : I->uses()) { + Instruction *UI = cast(U.getUser()); + BasicBlock *UserBB = UI->getParent(); + if (PHINode *P = dyn_cast(UI)) + UserBB = P->getIncomingBlock(U); + + // Check the current block, as a fast-path, before checking whether + // the use is anywhere in the loop. Most values are used in the same + // block they are defined in. Also, blocks not reachable from the + // entry are special; uses in them don't need to go through PHIs. + if (UserBB != BB && + !contains(UserBB) && + DT.isReachableFromEntry(UserBB)) + return false; + } + } + + return true; } -static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) { - if (SubLoop == 0) return true; - if (SubLoop == ParentLoop) return false; - return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop); +/// isLoopSimplifyForm - Return true if the Loop is in the form that +/// the LoopSimplify form transforms loops to, which is sometimes called +/// normal form. +bool Loop::isLoopSimplifyForm() const { + // Normal-form loops have a preheader, a single backedge, and all of their + // exits have all their predecessors inside the loop. + return getLoopPreheader() && getLoopLatch() && hasDedicatedExits(); } -Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, DominatorTree &DT) { - if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node? - - std::vector TodoStack; - - // Scan the predecessors of BB, checking to see if BB dominates any of - // them. This identifies backedges which target this node... - for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) - if (DT.dominates(BB, *I)) // If BB dominates it's predecessor... - TodoStack.push_back(*I); - - if (TodoStack.empty()) return 0; // No backedges to this block... - - // Create a new loop to represent this basic block... - Loop *L = new Loop(BB); - BBMap[BB] = L; - - BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock(); - - while (!TodoStack.empty()) { // Process all the nodes in the loop - BasicBlock *X = TodoStack.back(); - TodoStack.pop_back(); - - if (!L->contains(X) && // As of yet unprocessed?? - DT.dominates(EntryBlock, X)) { // X is reachable from entry block? - // Check to see if this block already belongs to a loop. If this occurs - // then we have a case where a loop that is supposed to be a child of the - // current loop was processed before the current loop. When this occurs, - // this child loop gets added to a part of the current loop, making it a - // sibling to the current loop. We have to reparent this loop. - if (Loop *SubLoop = const_cast(getLoopFor(X))) - if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) { - // Remove the subloop from it's current parent... - assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L); - Loop *SLP = SubLoop->ParentLoop; // SubLoopParent - std::vector::iterator I = - std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop); - assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?"); - SLP->SubLoops.erase(I); // Remove from parent... - - // Add the subloop to THIS loop... - SubLoop->ParentLoop = L; - L->SubLoops.push_back(SubLoop); - } +/// isSafeToClone - Return true if the loop body is safe to clone in practice. +/// Routines that reform the loop CFG and split edges often fail on indirectbr. +bool Loop::isSafeToClone() const { + // Return false if any loop blocks contain indirectbrs, or there are any calls + // to noduplicate functions. + for (Loop::block_iterator I = block_begin(), E = block_end(); I != E; ++I) { + if (isa((*I)->getTerminator())) + return false; + + if (const InvokeInst *II = dyn_cast((*I)->getTerminator())) + if (II->cannotDuplicate()) + return false; + + for (BasicBlock::iterator BI = (*I)->begin(), BE = (*I)->end(); BI != BE; ++BI) { + if (const CallInst *CI = dyn_cast(BI)) { + if (CI->cannotDuplicate()) + return false; + } + } + } + return true; +} - // Normal case, add the block to our loop... - L->Blocks.push_back(X); +MDNode *Loop::getLoopID() const { + MDNode *LoopID = nullptr; + if (isLoopSimplifyForm()) { + LoopID = getLoopLatch()->getTerminator()->getMetadata(LoopMDName); + } else { + // Go through each predecessor of the loop header and check the + // terminator for the metadata. + BasicBlock *H = getHeader(); + for (block_iterator I = block_begin(), IE = block_end(); I != IE; ++I) { + TerminatorInst *TI = (*I)->getTerminator(); + MDNode *MD = nullptr; + + // Check if this terminator branches to the loop header. + for (unsigned i = 0, ie = TI->getNumSuccessors(); i != ie; ++i) { + if (TI->getSuccessor(i) == H) { + MD = TI->getMetadata(LoopMDName); + break; + } + } + if (!MD) + return nullptr; - // Add all of the predecessors of X to the end of the work stack... - TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X)); + if (!LoopID) + LoopID = MD; + else if (MD != LoopID) + return nullptr; } } + if (!LoopID || LoopID->getNumOperands() == 0 || + LoopID->getOperand(0) != LoopID) + return nullptr; + return LoopID; +} - // If there are any loops nested within this loop, create them now! - for (std::vector::iterator I = L->Blocks.begin(), - E = L->Blocks.end(); I != E; ++I) - if (Loop *NewLoop = ConsiderForLoop(*I, DT)) { - L->SubLoops.push_back(NewLoop); - NewLoop->ParentLoop = L; - } +void Loop::setLoopID(MDNode *LoopID) const { + assert(LoopID && "Loop ID should not be null"); + assert(LoopID->getNumOperands() > 0 && "Loop ID needs at least one operand"); + assert(LoopID->getOperand(0) == LoopID && "Loop ID should refer to itself"); - // Add the basic blocks that comprise this loop to the BBMap so that this - // loop can be found for them. - // - for (std::vector::iterator I = L->Blocks.begin(), - E = L->Blocks.end(); I != E; ++I) { - std::map::iterator BBMI = BBMap.lower_bound(*I); - if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet... - BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level + if (isLoopSimplifyForm()) { + getLoopLatch()->getTerminator()->setMetadata(LoopMDName, LoopID); + return; } - // Now that we have a list of all of the child loops of this loop, check to - // see if any of them should actually be nested inside of each other. We can - // accidentally pull loops our of their parents, so we must make sure to - // organize the loop nests correctly now. - { - std::map ContainingLoops; - for (unsigned i = 0; i != L->SubLoops.size(); ++i) { - Loop *Child = L->SubLoops[i]; - assert(Child->getParentLoop() == L && "Not proper child loop?"); - - if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) { - // If there is already a loop which contains this loop, move this loop - // into the containing loop. - MoveSiblingLoopInto(Child, ContainingLoop); - --i; // The loop got removed from the SubLoops list. - } else { - // This is currently considered to be a top-level loop. Check to see if - // any of the contained blocks are loop headers for subloops we have - // already processed. - for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) { - Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]]; - if (BlockLoop == 0) { // Child block not processed yet... - BlockLoop = Child; - } else if (BlockLoop != Child) { - Loop *SubLoop = BlockLoop; - // Reparent all of the blocks which used to belong to BlockLoops - for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j) - ContainingLoops[SubLoop->Blocks[j]] = Child; - - // There is already a loop which contains this block, that means - // that we should reparent the loop which the block is currently - // considered to belong to to be a child of this loop. - MoveSiblingLoopInto(SubLoop, Child); - --i; // We just shrunk the SubLoops list. - } + BasicBlock *H = getHeader(); + for (block_iterator I = block_begin(), IE = block_end(); I != IE; ++I) { + TerminatorInst *TI = (*I)->getTerminator(); + for (unsigned i = 0, ie = TI->getNumSuccessors(); i != ie; ++i) { + if (TI->getSuccessor(i) == H) + TI->setMetadata(LoopMDName, LoopID); + } + } +} + +bool Loop::isAnnotatedParallel() const { + MDNode *desiredLoopIdMetadata = getLoopID(); + + if (!desiredLoopIdMetadata) + return false; + + // The loop branch contains the parallel loop metadata. In order to ensure + // that any parallel-loop-unaware optimization pass hasn't added loop-carried + // dependencies (thus converted the loop back to a sequential loop), check + // that all the memory instructions in the loop contain parallelism metadata + // that point to the same unique "loop id metadata" the loop branch does. + for (block_iterator BB = block_begin(), BE = block_end(); BB != BE; ++BB) { + for (BasicBlock::iterator II = (*BB)->begin(), EE = (*BB)->end(); + II != EE; II++) { + + if (!II->mayReadOrWriteMemory()) + continue; + + // The memory instruction can refer to the loop identifier metadata + // directly or indirectly through another list metadata (in case of + // nested parallel loops). The loop identifier metadata refers to + // itself so we can check both cases with the same routine. + MDNode *loopIdMD = II->getMetadata("llvm.mem.parallel_loop_access"); + + if (!loopIdMD) + return false; + + bool loopIdMDFound = false; + for (unsigned i = 0, e = loopIdMD->getNumOperands(); i < e; ++i) { + if (loopIdMD->getOperand(i) == desiredLoopIdMetadata) { + loopIdMDFound = true; + break; } } + + if (!loopIdMDFound) + return false; } } + return true; +} - return L; + +/// hasDedicatedExits - Return true if no exit block for the loop +/// has a predecessor that is outside the loop. +bool Loop::hasDedicatedExits() const { + // Each predecessor of each exit block of a normal loop is contained + // within the loop. + SmallVector ExitBlocks; + getExitBlocks(ExitBlocks); + for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) + for (pred_iterator PI = pred_begin(ExitBlocks[i]), + PE = pred_end(ExitBlocks[i]); PI != PE; ++PI) + if (!contains(*PI)) + return false; + // All the requirements are met. + return true; } -/// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of -/// the NewParent Loop, instead of being a sibling of it. -void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) { - Loop *OldParent = NewChild->getParentLoop(); - assert(OldParent && OldParent == NewParent->getParentLoop() && - NewChild != NewParent && "Not sibling loops!"); - - // Remove NewChild from being a child of OldParent - std::vector::iterator I = - std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild); - assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??"); - OldParent->SubLoops.erase(I); // Remove from parent's subloops list - NewChild->ParentLoop = 0; - - InsertLoopInto(NewChild, NewParent); +/// getUniqueExitBlocks - Return all unique successor blocks of this loop. +/// These are the blocks _outside of the current loop_ which are branched to. +/// This assumes that loop exits are in canonical form. +/// +void +Loop::getUniqueExitBlocks(SmallVectorImpl &ExitBlocks) const { + assert(hasDedicatedExits() && + "getUniqueExitBlocks assumes the loop has canonical form exits!"); + + SmallVector switchExitBlocks; + + for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) { + + BasicBlock *current = *BI; + switchExitBlocks.clear(); + + for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I) { + // If block is inside the loop then it is not a exit block. + if (contains(*I)) + continue; + + pred_iterator PI = pred_begin(*I); + BasicBlock *firstPred = *PI; + + // If current basic block is this exit block's first predecessor + // then only insert exit block in to the output ExitBlocks vector. + // This ensures that same exit block is not inserted twice into + // ExitBlocks vector. + if (current != firstPred) + continue; + + // If a terminator has more then two successors, for example SwitchInst, + // then it is possible that there are multiple edges from current block + // to one exit block. + if (std::distance(succ_begin(current), succ_end(current)) <= 2) { + ExitBlocks.push_back(*I); + continue; + } + + // In case of multiple edges from current block to exit block, collect + // only one edge in ExitBlocks. Use switchExitBlocks to keep track of + // duplicate edges. + if (std::find(switchExitBlocks.begin(), switchExitBlocks.end(), *I) + == switchExitBlocks.end()) { + switchExitBlocks.push_back(*I); + ExitBlocks.push_back(*I); + } + } + } +} + +/// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one +/// block, return that block. Otherwise return null. +BasicBlock *Loop::getUniqueExitBlock() const { + SmallVector UniqueExitBlocks; + getUniqueExitBlocks(UniqueExitBlocks); + if (UniqueExitBlocks.size() == 1) + return UniqueExitBlocks[0]; + return nullptr; +} + +#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) +void Loop::dump() const { + print(dbgs()); } +#endif -/// InsertLoopInto - This inserts loop L into the specified parent loop. If the -/// parent loop contains a loop which should contain L, the loop gets inserted -/// into L instead. -void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) { - BasicBlock *LHeader = L->getHeader(); - assert(Parent->contains(LHeader) && "This loop should not be inserted here!"); - - // Check to see if it belongs in a child loop... - for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i) - if (Parent->SubLoops[i]->contains(LHeader)) { - InsertLoopInto(L, Parent->SubLoops[i]); - return; +//===----------------------------------------------------------------------===// +// UnloopUpdater implementation +// + +namespace { +/// Find the new parent loop for all blocks within the "unloop" whose last +/// backedges has just been removed. +class UnloopUpdater { + Loop *Unloop; + LoopInfo *LI; + + LoopBlocksDFS DFS; + + // Map unloop's immediate subloops to their nearest reachable parents. Nested + // loops within these subloops will not change parents. However, an immediate + // subloop's new parent will be the nearest loop reachable from either its own + // exits *or* any of its nested loop's exits. + DenseMap SubloopParents; + + // Flag the presence of an irreducible backedge whose destination is a block + // directly contained by the original unloop. + bool FoundIB; + +public: + UnloopUpdater(Loop *UL, LoopInfo *LInfo) : + Unloop(UL), LI(LInfo), DFS(UL), FoundIB(false) {} + + void updateBlockParents(); + + void removeBlocksFromAncestors(); + + void updateSubloopParents(); + +protected: + Loop *getNearestLoop(BasicBlock *BB, Loop *BBLoop); +}; +} // end anonymous namespace + +/// updateBlockParents - Update the parent loop for all blocks that are directly +/// contained within the original "unloop". +void UnloopUpdater::updateBlockParents() { + if (Unloop->getNumBlocks()) { + // Perform a post order CFG traversal of all blocks within this loop, + // propagating the nearest loop from sucessors to predecessors. + LoopBlocksTraversal Traversal(DFS, LI); + for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(), + POE = Traversal.end(); POI != POE; ++POI) { + + Loop *L = LI->getLoopFor(*POI); + Loop *NL = getNearestLoop(*POI, L); + + if (NL != L) { + // For reducible loops, NL is now an ancestor of Unloop. + assert((NL != Unloop && (!NL || NL->contains(Unloop))) && + "uninitialized successor"); + LI->changeLoopFor(*POI, NL); + } + else { + // Or the current block is part of a subloop, in which case its parent + // is unchanged. + assert((FoundIB || Unloop->contains(L)) && "uninitialized successor"); + } } + } + // Each irreducible loop within the unloop induces a round of iteration using + // the DFS result cached by Traversal. + bool Changed = FoundIB; + for (unsigned NIters = 0; Changed; ++NIters) { + assert(NIters < Unloop->getNumBlocks() && "runaway iterative algorithm"); + + // Iterate over the postorder list of blocks, propagating the nearest loop + // from successors to predecessors as before. + Changed = false; + for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(), + POE = DFS.endPostorder(); POI != POE; ++POI) { + + Loop *L = LI->getLoopFor(*POI); + Loop *NL = getNearestLoop(*POI, L); + if (NL != L) { + assert(NL != Unloop && (!NL || NL->contains(Unloop)) && + "uninitialized successor"); + LI->changeLoopFor(*POI, NL); + Changed = true; + } + } + } +} - // If not, insert it here! - Parent->SubLoops.push_back(L); - L->ParentLoop = Parent; +/// removeBlocksFromAncestors - Remove unloop's blocks from all ancestors below +/// their new parents. +void UnloopUpdater::removeBlocksFromAncestors() { + // Remove all unloop's blocks (including those in nested subloops) from + // ancestors below the new parent loop. + for (Loop::block_iterator BI = Unloop->block_begin(), + BE = Unloop->block_end(); BI != BE; ++BI) { + Loop *OuterParent = LI->getLoopFor(*BI); + if (Unloop->contains(OuterParent)) { + while (OuterParent->getParentLoop() != Unloop) + OuterParent = OuterParent->getParentLoop(); + OuterParent = SubloopParents[OuterParent]; + } + // Remove blocks from former Ancestors except Unloop itself which will be + // deleted. + for (Loop *OldParent = Unloop->getParentLoop(); OldParent != OuterParent; + OldParent = OldParent->getParentLoop()) { + assert(OldParent && "new loop is not an ancestor of the original"); + OldParent->removeBlockFromLoop(*BI); + } + } } -/// changeLoopFor - Change the top-level loop that contains BB to the -/// specified loop. This should be used by transformations that restructure -/// the loop hierarchy tree. -void LoopInfo::changeLoopFor(BasicBlock *BB, Loop *L) { - Loop *&OldLoop = BBMap[BB]; - assert(OldLoop && "Block not in a loop yet!"); - OldLoop = L; +/// updateSubloopParents - Update the parent loop for all subloops directly +/// nested within unloop. +void UnloopUpdater::updateSubloopParents() { + while (!Unloop->empty()) { + Loop *Subloop = *std::prev(Unloop->end()); + Unloop->removeChildLoop(std::prev(Unloop->end())); + + assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop"); + if (Loop *Parent = SubloopParents[Subloop]) + Parent->addChildLoop(Subloop); + else + LI->addTopLevelLoop(Subloop); + } } -/// changeTopLevelLoop - Replace the specified loop in the top-level loops -/// list with the indicated loop. -void LoopInfo::changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) { - std::vector::iterator I = std::find(TopLevelLoops.begin(), - TopLevelLoops.end(), OldLoop); - assert(I != TopLevelLoops.end() && "Old loop not at top level!"); - *I = NewLoop; - assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 && - "Loops already embedded into a subloop!"); +/// getNearestLoop - Return the nearest parent loop among this block's +/// successors. If a successor is a subloop header, consider its parent to be +/// the nearest parent of the subloop's exits. +/// +/// For subloop blocks, simply update SubloopParents and return NULL. +Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) { + + // Initially for blocks directly contained by Unloop, NearLoop == Unloop and + // is considered uninitialized. + Loop *NearLoop = BBLoop; + + Loop *Subloop = nullptr; + if (NearLoop != Unloop && Unloop->contains(NearLoop)) { + Subloop = NearLoop; + // Find the subloop ancestor that is directly contained within Unloop. + while (Subloop->getParentLoop() != Unloop) { + Subloop = Subloop->getParentLoop(); + assert(Subloop && "subloop is not an ancestor of the original loop"); + } + // Get the current nearest parent of the Subloop exits, initially Unloop. + NearLoop = + SubloopParents.insert(std::make_pair(Subloop, Unloop)).first->second; + } + + succ_iterator I = succ_begin(BB), E = succ_end(BB); + if (I == E) { + assert(!Subloop && "subloop blocks must have a successor"); + NearLoop = nullptr; // unloop blocks may now exit the function. + } + for (; I != E; ++I) { + if (*I == BB) + continue; // self loops are uninteresting + + Loop *L = LI->getLoopFor(*I); + if (L == Unloop) { + // This successor has not been processed. This path must lead to an + // irreducible backedge. + assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB"); + FoundIB = true; + } + if (L != Unloop && Unloop->contains(L)) { + // Successor is in a subloop. + if (Subloop) + continue; // Branching within subloops. Ignore it. + + // BB branches from the original into a subloop header. + assert(L->getParentLoop() == Unloop && "cannot skip into nested loops"); + + // Get the current nearest parent of the Subloop's exits. + L = SubloopParents[L]; + // L could be Unloop if the only exit was an irreducible backedge. + } + if (L == Unloop) { + continue; + } + // Handle critical edges from Unloop into a sibling loop. + if (L && !L->contains(Unloop)) { + L = L->getParentLoop(); + } + // Remember the nearest parent loop among successors or subloop exits. + if (NearLoop == Unloop || !NearLoop || NearLoop->contains(L)) + NearLoop = L; + } + if (Subloop) { + SubloopParents[Subloop] = NearLoop; + return BBLoop; + } + return NearLoop; } -/// removeLoop - This removes the specified top-level loop from this loop info -/// object. The loop is not deleted, as it will presumably be inserted into -/// another loop. -Loop *LoopInfo::removeLoop(iterator I) { - assert(I != end() && "Cannot remove end iterator!"); - Loop *L = *I; - assert(L->getParentLoop() == 0 && "Not a top-level loop!"); - TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin())); - return L; +//===----------------------------------------------------------------------===// +// LoopInfo implementation +// +bool LoopInfo::runOnFunction(Function &) { + releaseMemory(); + LI.Analyze(getAnalysis().getDomTree()); + return false; } -/// removeBlock - This method completely removes BB from all data structures, -/// including all of the Loop objects it is nested in and our mapping from -/// BasicBlocks to loops. -void LoopInfo::removeBlock(BasicBlock *BB) { - std::map::iterator I = BBMap.find(BB); - if (I != BBMap.end()) { - for (Loop *L = I->second; L; L = L->getParentLoop()) - L->removeBlockFromLoop(BB); +/// updateUnloop - The last backedge has been removed from a loop--now the +/// "unloop". Find a new parent for the blocks contained within unloop and +/// update the loop tree. We don't necessarily have valid dominators at this +/// point, but LoopInfo is still valid except for the removal of this loop. +/// +/// Note that Unloop may now be an empty loop. Calling Loop::getHeader without +/// checking first is illegal. +void LoopInfo::updateUnloop(Loop *Unloop) { + + // First handle the special case of no parent loop to simplify the algorithm. + if (!Unloop->getParentLoop()) { + // Since BBLoop had no parent, Unloop blocks are no longer in a loop. + for (Loop::block_iterator I = Unloop->block_begin(), + E = Unloop->block_end(); I != E; ++I) { + + // Don't reparent blocks in subloops. + if (getLoopFor(*I) != Unloop) + continue; + + // Blocks no longer have a parent but are still referenced by Unloop until + // the Unloop object is deleted. + LI.changeLoopFor(*I, nullptr); + } + + // Remove the loop from the top-level LoopInfo object. + for (LoopInfo::iterator I = LI.begin();; ++I) { + assert(I != LI.end() && "Couldn't find loop"); + if (*I == Unloop) { + LI.removeLoop(I); + break; + } + } + + // Move all of the subloops to the top-level. + while (!Unloop->empty()) + LI.addTopLevelLoop(Unloop->removeChildLoop(std::prev(Unloop->end()))); + + return; + } + + // Update the parent loop for all blocks within the loop. Blocks within + // subloops will not change parents. + UnloopUpdater Updater(Unloop, this); + Updater.updateBlockParents(); + + // Remove blocks from former ancestor loops. + Updater.removeBlocksFromAncestors(); + + // Add direct subloops as children in their new parent loop. + Updater.updateSubloopParents(); + + // Remove unloop from its parent loop. + Loop *ParentLoop = Unloop->getParentLoop(); + for (Loop::iterator I = ParentLoop->begin();; ++I) { + assert(I != ParentLoop->end() && "Couldn't find loop"); + if (*I == Unloop) { + ParentLoop->removeChildLoop(I); + break; + } + } +} - BBMap.erase(I); +void LoopInfo::verifyAnalysis() const { + // LoopInfo is a FunctionPass, but verifying every loop in the function + // each time verifyAnalysis is called is very expensive. The + // -verify-loop-info option can enable this. In order to perform some + // checking by default, LoopPass has been taught to call verifyLoop + // manually during loop pass sequences. + + if (!VerifyLoopInfo) return; + + DenseSet Loops; + for (iterator I = begin(), E = end(); I != E; ++I) { + assert(!(*I)->getParentLoop() && "Top-level loop has a parent!"); + (*I)->verifyLoopNest(&Loops); + } + + // Verify that blocks are mapped to valid loops. + for (DenseMap::const_iterator I = LI.BBMap.begin(), + E = LI.BBMap.end(); I != E; ++I) { + assert(Loops.count(I->second) && "orphaned loop"); + assert(I->second->contains(I->first) && "orphaned block"); } } -// Ensure this file gets linked when LoopInfo.h is used. -DEFINING_FILE_FOR(LoopInfo) +void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); + AU.addRequired(); +} + +void LoopInfo::print(raw_ostream &OS, const Module*) const { + LI.print(OS); +} + +//===----------------------------------------------------------------------===// +// LoopBlocksDFS implementation +// + +/// Traverse the loop blocks and store the DFS result. +/// Useful for clients that just want the final DFS result and don't need to +/// visit blocks during the initial traversal. +void LoopBlocksDFS::perform(LoopInfo *LI) { + LoopBlocksTraversal Traversal(*this, LI); + for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(), + POE = Traversal.end(); POI != POE; ++POI) ; +}