//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
-//
+//
// 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.
+//
//===----------------------------------------------------------------------===//
//
// This file defines the LoopInfo class that is used to identify natural loops
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopIterator.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CFG.h"
-#include "Support/DepthFirstIterator.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
#include <algorithm>
using namespace llvm;
-static RegisterAnalysis<LoopInfo>
-X("loops", "Natural Loop Construction", true);
+// Always verify loopinfo if expensive checking is enabled.
+#ifdef XDEBUG
+static bool VerifyLoopInfo = true;
+#else
+static bool VerifyLoopInfo = false;
+#endif
+static cl::opt<bool,true>
+VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
+ cl::desc("Verify loop info (time consuming)"));
+
+char LoopInfo::ID = 0;
+INITIALIZE_PASS_BEGIN(LoopInfo, "loops", "Natural Loop Information", true, true)
+INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_END(LoopInfo, "loops", "Natural Loop Information", true, true)
//===----------------------------------------------------------------------===//
// Loop implementation
//
-bool Loop::contains(const BasicBlock *BB) const {
- return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
-}
-
-bool Loop::isLoopExit(const BasicBlock *BB) const {
- for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
- SI != SE; ++SI) {
- if (!contains(*SI))
- return true;
- }
- return false;
-}
-/// getNumBackEdges - Calculate the number of back edges to the loop header.
+/// isLoopInvariant - Return true if the specified value is loop invariant
///
-unsigned Loop::getNumBackEdges() const {
- unsigned NumBackEdges = 0;
- BasicBlock *H = getHeader();
+bool Loop::isLoopInvariant(Value *V) const {
+ if (Instruction *I = dyn_cast<Instruction>(V))
+ return !contains(I);
+ return true; // All non-instructions are loop invariant
+}
- for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
- if (contains(*I))
- ++NumBackEdges;
+/// 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;
- return NumBackEdges;
+ return true;
}
-void Loop::print(std::ostream &OS, unsigned Depth) const {
- OS << std::string(Depth*2, ' ') << "Loop Containing: ";
+/// 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<Instruction>(V))
+ return makeLoopInvariant(I, Changed, InsertPt);
+ return true; // All non-instructions are loop-invariant.
+}
- for (unsigned i = 0; i < getBlocks().size(); ++i) {
- if (i) OS << ",";
- WriteAsOperand(OS, getBlocks()[i], false);
- }
- if (!ExitBlocks.empty()) {
- OS << "\tExitBlocks: ";
- for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
- if (i) OS << ",";
- WriteAsOperand(OS, getExitBlocks()[i], false);
- }
+/// 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<LandingPadInst>(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();
}
-
- OS << "\n";
-
- for (iterator I = begin(), E = end(); I != E; ++I)
- (*I)->print(OS, Depth+2);
+ // 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 Loop::dump() const {
- print(std::cerr);
-}
+/// 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 = 0, *Backedge = 0;
+ 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 0; // dead loop
+ Incoming = *PI++;
+ if (PI != pred_end(H)) return 0; // multiple backedges?
-//===----------------------------------------------------------------------===//
-// LoopInfo implementation
-//
-void LoopInfo::stub() {}
+ if (contains(Incoming)) {
+ if (contains(Backedge))
+ return 0;
+ std::swap(Incoming, Backedge);
+ } else if (!contains(Backedge))
+ return 0;
-bool LoopInfo::runOnFunction(Function &) {
- releaseMemory();
- Calculate(getAnalysis<DominatorSet>()); // Update
- return false;
+ // Loop over all of the PHI nodes, looking for a canonical indvar.
+ for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+ if (ConstantInt *CI =
+ dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
+ if (CI->isNullValue())
+ if (Instruction *Inc =
+ dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
+ if (Inc->getOpcode() == Instruction::Add &&
+ Inc->getOperand(0) == PN)
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
+ if (CI->equalsInt(1))
+ return PN;
+ }
+ return 0;
}
-void LoopInfo::releaseMemory() {
- for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
- E = TopLevelLoops.end(); I != E; ++I)
- delete *I; // Delete all of the loops...
+/// isLCSSAForm - Return true if the Loop is in LCSSA form
+bool Loop::isLCSSAForm(DominatorTree &DT) const {
+ // Sort the blocks vector so that we can use binary search to do quick
+ // lookups.
+ SmallPtrSet<BasicBlock*, 16> LoopBBs(block_begin(), block_end());
+
+ 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 (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
+ ++UI) {
+ User *U = *UI;
+ BasicBlock *UserBB = cast<Instruction>(U)->getParent();
+ if (PHINode *P = dyn_cast<PHINode>(U))
+ UserBB = P->getIncomingBlock(UI);
+
+ // 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 &&
+ !LoopBBs.count(UserBB) &&
+ DT.isReachableFromEntry(UserBB))
+ return false;
+ }
+ }
- BBMap.clear(); // Reset internal state of analysis
- TopLevelLoops.clear();
+ return true;
}
+/// 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();
+}
-void LoopInfo::Calculate(const DominatorSet &DS) {
- BasicBlock *RootNode = DS.getRoot();
-
- for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
- NE = df_end(RootNode); NI != NE; ++NI)
- if (Loop *L = ConsiderForLoop(*NI, DS))
- TopLevelLoops.push_back(L);
-
- for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
- TopLevelLoops[i]->setLoopDepth(1);
+/// hasDedicatedExits - Return true if no exit block for the loop
+/// has a predecessor that is outside the loop.
+bool Loop::hasDedicatedExits() const {
+ // Sort the blocks vector so that we can use binary search to do quick
+ // lookups.
+ SmallPtrSet<BasicBlock *, 16> LoopBBs(block_begin(), block_end());
+ // Each predecessor of each exit block of a normal loop is contained
+ // within the loop.
+ SmallVector<BasicBlock *, 4> 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 (!LoopBBs.count(*PI))
+ return false;
+ // All the requirements are met.
+ return true;
}
-void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesAll();
- AU.addRequired<DominatorSet>();
+/// 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<BasicBlock *> &ExitBlocks) const {
+ assert(hasDedicatedExits() &&
+ "getUniqueExitBlocks assumes the loop has canonical form exits!");
+
+ // Sort the blocks vector so that we can use binary search to do quick
+ // lookups.
+ SmallVector<BasicBlock *, 128> LoopBBs(block_begin(), block_end());
+ std::sort(LoopBBs.begin(), LoopBBs.end());
+
+ SmallVector<BasicBlock *, 32> 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 (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *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);
+ }
+ }
+ }
}
-void LoopInfo::print(std::ostream &OS) const {
- for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
- TopLevelLoops[i]->print(OS);
-#if 0
- for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
- E = BBMap.end(); I != E; ++I)
- OS << "BB '" << I->first->getName() << "' level = "
- << I->second->LoopDepth << "\n";
-#endif
+/// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one
+/// block, return that block. Otherwise return null.
+BasicBlock *Loop::getUniqueExitBlock() const {
+ SmallVector<BasicBlock *, 8> UniqueExitBlocks;
+ getUniqueExitBlocks(UniqueExitBlocks);
+ if (UniqueExitBlocks.size() == 1)
+ return UniqueExitBlocks[0];
+ return 0;
}
-static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
- if (SubLoop == 0) return true;
- if (SubLoop == ParentLoop) return false;
- return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
+void Loop::dump() const {
+ print(dbgs());
}
-Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
- if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
-
- std::vector<BasicBlock *> 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 (DS.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??
- DS.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<Loop*>(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<Loop*>::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);
- }
-
- // Normal case, add the block to our loop...
- L->Blocks.push_back(X);
-
- // Add all of the predecessors of X to the end of the work stack...
- TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
+//===----------------------------------------------------------------------===//
+// 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<Loop*, Loop*> 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");
+ }
}
}
-
- // If there are any loops nested within this loop, create them now!
- for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
- E = L->Blocks.end(); I != E; ++I)
- if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
- L->SubLoops.push_back(NewLoop);
- NewLoop->ParentLoop = L;
+ // 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;
+ }
}
-
- // Add the basic blocks that comprise this loop to the BBMap so that this
- // loop can be found for them.
- //
- for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
- E = L->Blocks.end(); I != E; ++I) {
- std::map<BasicBlock*, Loop*>::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
}
+}
- // 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<BasicBlock*, Loop*> 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.
- }
- }
- }
+/// 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);
}
}
-
- // Now that we know all of the blocks that make up this loop, see if there are
- // any branches to outside of the loop... building the ExitBlocks list.
- for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
- BE = L->Blocks.end(); BI != BE; ++BI)
- for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
- if (!L->contains(*I)) // Not in current loop?
- L->ExitBlocks.push_back(*I); // It must be an exit block...
-
- return L;
}
-/// 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<Loop*>::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);
+/// updateSubloopParents - Update the parent loop for all subloops directly
+/// nested within unloop.
+void UnloopUpdater::updateSubloopParents() {
+ while (!Unloop->empty()) {
+ Loop *Subloop = *llvm::prior(Unloop->end());
+ Unloop->removeChildLoop(llvm::prior(Unloop->end()));
+
+ assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop");
+ if (SubloopParents[Subloop])
+ SubloopParents[Subloop]->addChildLoop(Subloop);
+ else
+ LI->addTopLevelLoop(Subloop);
+ }
}
-/// 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;
- }
-
- // If not, insert it here!
- Parent->SubLoops.push_back(L);
- L->ParentLoop = Parent;
-}
+/// 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 = 0;
+ 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.
+ if (!SubloopParents.count(Subloop))
+ SubloopParents[Subloop] = Unloop;
+ NearLoop = SubloopParents[Subloop];
+ }
-/// 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;
-}
+ succ_iterator I = succ_begin(BB), E = succ_end(BB);
+ if (I == E) {
+ assert(!Subloop && "subloop blocks must have a successor");
+ NearLoop = 0; // 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.
-/// changeTopLevelLoop - Replace the specified loop in the top-level loops
-/// list with the indicated loop.
-void LoopInfo::changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
- std::vector<Loop*>::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!");
+ // 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;
}
//===----------------------------------------------------------------------===//
-// APIs for simple analysis of the loop.
+// LoopInfo implementation
//
+bool LoopInfo::runOnFunction(Function &) {
+ releaseMemory();
+ LI.Calculate(getAnalysis<DominatorTree>().getBase()); // Update
+ return false;
+}
-/// 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.
+/// 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.
///
-/// This method returns null if there is no preheader for the loop.
-///
-BasicBlock *Loop::getLoopPreheader() const {
- // Keep track of nodes outside the loop branching to the header...
- BasicBlock *Out = 0;
-
- // Loop over the predecessors of the header node...
- BasicBlock *Header = getHeader();
- for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
- PI != PE; ++PI)
- if (!contains(*PI)) { // If the block is not in the loop...
- if (Out && Out != *PI)
- return 0; // Multiple predecessors outside the loop
- Out = *PI;
+/// 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, 0);
}
-
- // Make sure there is only one exit out of the preheader...
- succ_iterator SI = succ_begin(Out);
- ++SI;
- if (SI != succ_end(Out))
- return 0; // Multiple exits from the block, must not be a preheader.
+ // 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;
+ }
+ }
- // If there is exactly one preheader, return it. If there was zero, then Out
- // is still null.
- return Out;
-}
+ // Move all of the subloops to the top-level.
+ while (!Unloop->empty())
+ LI.addTopLevelLoop(Unloop->removeChildLoop(llvm::prior(Unloop->end())));
-/// 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.
-///
-PHINode *Loop::getCanonicalInductionVariable() const {
- BasicBlock *H = getHeader();
-
- BasicBlock *Incoming = 0, *Backedge = 0;
- 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 0; // dead loop
- Incoming = *PI++;
- if (PI != pred_end(H)) return 0; // multiple backedges?
+ return;
+ }
- if (contains(Incoming)) {
- if (contains(Backedge))
- return 0;
- std::swap(Incoming, Backedge);
- } else if (!contains(Backedge))
- return 0;
+ // Update the parent loop for all blocks within the loop. Blocks within
+ // subloops will not change parents.
+ UnloopUpdater Updater(Unloop, this);
+ Updater.updateBlockParents();
- // Loop over all of the PHI nodes, looking for a canonical indvar.
- for (BasicBlock::iterator I = H->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I)
- if (Instruction *Inc =
- dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
- if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
- if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
- if (CI->equalsInt(1))
- return PN;
+ // Remove blocks from former ancestor loops.
+ Updater.removeBlocksFromAncestors();
- return 0;
-}
+ // Add direct subloops as children in their new parent loop.
+ Updater.updateSubloopParents();
-/// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
-/// the canonical induction variable value for the "next" iteration of the loop.
-/// This always succeeds if getCanonicalInductionVariable succeeds.
-///
-Instruction *Loop::getCanonicalInductionVariableIncrement() const {
- if (PHINode *PN = getCanonicalInductionVariable()) {
- bool P1InLoop = contains(PN->getIncomingBlock(1));
- return cast<Instruction>(PN->getIncomingValue(P1InLoop));
+ // 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;
+ }
}
- return 0;
-}
-
-/// getTripCount - Return a loop-invariant LLVM value indicating the number of
-/// times the loop will be executed. Note that this means that the backedge of
-/// the loop executes N-1 times. If the trip-count cannot be determined, this
-/// returns null.
-///
-Value *Loop::getTripCount() const {
- // Canonical loops will end with a 'setne I, V', where I is the incremented
- // canonical induction variable and V is the trip count of the loop.
- Instruction *Inc = getCanonicalInductionVariableIncrement();
- PHINode *IV = cast<PHINode>(Inc->getOperand(0));
-
- BasicBlock *BackedgeBlock =
- IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
-
- if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
- if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
- if (SCI->getOperand(0) == Inc)
- if (BI->getSuccessor(0) == getHeader()) {
- if (SCI->getOpcode() == Instruction::SetNE)
- return SCI->getOperand(1);
- } else if (SCI->getOpcode() == Instruction::SetEQ) {
- return SCI->getOperand(1);
- }
-
- return 0;
}
+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.
-//===-------------------------------------------------------------------===//
-// APIs for updating loop information after changing the CFG
-//
+ if (!VerifyLoopInfo) return;
-/// addBasicBlockToLoop - This function 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.
-///
-void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
- assert((Blocks.empty() || LI[getHeader()] == this) &&
- "Incorrect LI specified for this loop!");
- assert(NewBB && "Cannot add a null basic block to the loop!");
- assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
-
- // Add the loop mapping to the LoopInfo object...
- LI.BBMap[NewBB] = this;
-
- // Add the basic block to this loop and all parent loops...
- Loop *L = this;
- while (L) {
- L->Blocks.push_back(NewBB);
- L = L->getParentLoop();
+ DenseSet<const Loop*> Loops;
+ for (iterator I = begin(), E = end(); I != E; ++I) {
+ assert(!(*I)->getParentLoop() && "Top-level loop has a parent!");
+ (*I)->verifyLoopNest(&Loops);
}
-}
-/// changeExitBlock - This method is used to update loop information. All
-/// instances of the specified Old basic block are removed from the exit list
-/// and replaced with New.
-///
-void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
- assert(Old != New && "Cannot changeExitBlock to the same thing!");
- assert(Old && New && "Cannot changeExitBlock to or from a null node!");
- assert(hasExitBlock(Old) && "Old exit block not found!");
- std::vector<BasicBlock*>::iterator
- I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
- while (I != ExitBlocks.end()) {
- *I = New;
- I = std::find(I+1, ExitBlocks.end(), Old);
+ // Verify that blocks are mapped to valid loops.
+ //
+ // FIXME: With an up-to-date DFS (see LoopIterator.h) and DominatorTree, we
+ // could also verify that the blocks are still in the correct loops.
+ for (DenseMap<BasicBlock*, Loop*>::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");
}
}
-/// replaceChildLoopWith - This is used when splitting loops up. It replaces
-/// the OldChild entry in our children list with NewChild, and updates the
-/// parent pointers of the two loops as appropriate.
-void Loop::replaceChildLoopWith(Loop *OldChild, Loop *NewChild) {
- assert(OldChild->ParentLoop == this && "This loop is already broken!");
- assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
- std::vector<Loop*>::iterator I = std::find(SubLoops.begin(), SubLoops.end(),
- OldChild);
- assert(I != SubLoops.end() && "OldChild not in loop!");
- *I = NewChild;
- OldChild->ParentLoop = 0;
- NewChild->ParentLoop = this;
-
- // Update the loop depth of the new child.
- NewChild->setLoopDepth(LoopDepth+1);
-}
-
-/// addChildLoop - Add the specified loop to be a child of this loop.
-///
-void Loop::addChildLoop(Loop *NewChild) {
- assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
- NewChild->ParentLoop = this;
- SubLoops.push_back(NewChild);
-
- // Update the loop depth of the new child.
- NewChild->setLoopDepth(LoopDepth+1);
-}
-
-template<typename T>
-static void RemoveFromVector(std::vector<T*> &V, T *N) {
- typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N);
- assert(I != V.end() && "N is not in this list!");
- V.erase(I);
+void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesAll();
+ AU.addRequired<DominatorTree>();
}
-/// removeChildLoop - This removes the specified child from being a subloop of
-/// this loop. The loop is not deleted, as it will presumably be inserted
-/// into another loop.
-Loop *Loop::removeChildLoop(iterator I) {
- assert(I != SubLoops.end() && "Cannot remove end iterator!");
- Loop *Child = *I;
- assert(Child->ParentLoop == this && "Child is not a child of this loop!");
- SubLoops.erase(SubLoops.begin()+(I-begin()));
- Child->ParentLoop = 0;
- return Child;
+void LoopInfo::print(raw_ostream &OS, const Module*) const {
+ LI.print(OS);
}
+//===----------------------------------------------------------------------===//
+// LoopBlocksDFS implementation
+//
-/// removeBlockFromLoop - This removes the specified basic block from the
-/// current loop, updating the Blocks and ExitBlocks lists as appropriate. This
-/// does not update the mapping in the LoopInfo class.
-void Loop::removeBlockFromLoop(BasicBlock *BB) {
- RemoveFromVector(Blocks, BB);
-
- // If this block branched out of this loop, remove any exit blocks entries due
- // to it.
- for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
- if (!contains(*SI) && *SI != BB)
- RemoveFromVector(ExitBlocks, *SI);
-
- // If any blocks in this loop branch to BB, add it to the exit blocks set.
- for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
- if (contains(*PI))
- ExitBlocks.push_back(BB);
+/// 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) ;
}