#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CFG.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;
+// 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;
-static RegisterPass<LoopInfo>
-X("loops", "Natural Loop Information", true, true);
+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::isLoopInvariant(Value *V) const {
if (Instruction *I = dyn_cast<Instruction>(V))
- return isLoopInvariant(I);
+ return !contains(I);
return true; // All non-instructions are loop invariant
}
-/// isLoopInvariant - Return true if the specified instruction is
-/// loop-invariant.
-///
-bool Loop::isLoopInvariant(Instruction *I) const {
- return !contains(I->getParent());
+/// 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 true;
}
/// makeLoopInvariant - If the given value is an instruciton inside of the
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();
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;
BasicBlock *H = getHeader();
BasicBlock *Incoming = 0, *Backedge = 0;
- typedef GraphTraits<Inverse<BasicBlock*> > InvBlockTraits;
- InvBlockTraits::ChildIteratorType PI = InvBlockTraits::child_begin(H);
- assert(PI != InvBlockTraits::child_end(H) &&
+ pred_iterator PI = pred_begin(H);
+ assert(PI != pred_end(H) &&
"Loop must have at least one backedge!");
Backedge = *PI++;
- if (PI == InvBlockTraits::child_end(H)) return 0; // dead loop
+ if (PI == pred_end(H)) return 0; // dead loop
Incoming = *PI++;
- if (PI != InvBlockTraits::child_end(H)) return 0; // multiple backedges?
+ if (PI != pred_end(H)) return 0; // multiple backedges?
if (contains(Incoming)) {
if (contains(Backedge))
return 0;
}
-/// 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));
- }
- 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,
Value *Loop::getTripCount() const {
// Canonical loops will end with a 'cmp ne I, V', where I is the incremented
// canonical induction variable and V is the trip count of the loop.
- Instruction *Inc = getCanonicalInductionVariableIncrement();
- if (Inc == 0) return 0;
- PHINode *IV = cast<PHINode>(Inc->getOperand(0));
+ PHINode *IV = getCanonicalInductionVariable();
+ if (IV == 0 || IV->getNumIncomingValues() != 2) return 0;
- BasicBlock *BackedgeBlock =
- IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
+ bool P0InLoop = contains(IV->getIncomingBlock(0));
+ Value *Inc = IV->getIncomingValue(!P0InLoop);
+ BasicBlock *BackedgeBlock = IV->getIncomingBlock(!P0InLoop);
if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
if (BI->isConditional()) {
/// getSmallConstantTripCount - Returns the trip count of this loop as a
/// normal unsigned value, if possible. Returns 0 if the trip count is unknown
-/// of not constant. Will also return 0 if the trip count is very large
+/// or not constant. Will also return 0 if the trip count is very large
/// (>= 2^32)
unsigned Loop::getSmallConstantTripCount() const {
Value* TripCount = this->getTripCount();
case BinaryOperator::Mul:
Result = dyn_cast<ConstantInt>(BO->getOperand(1));
break;
+ case BinaryOperator::Shl:
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1)))
+ if (CI->getValue().getActiveBits() <= 5)
+ return 1u << CI->getZExtValue();
+ break;
default:
break;
}
}
/// isLCSSAForm - Return true if the Loop is in LCSSA form
-bool Loop::isLCSSAForm() const {
+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());
+ 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)
+ 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) {
- BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
- if (PHINode *P = dyn_cast<PHINode>(*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. Most values are used in
- // the same block they are defined in.
- if (UserBB != BB && !LoopBBs.count(UserBB))
+ // 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;
}
}
/// the LoopSimplify form transforms loops to, which is sometimes called
/// normal form.
bool Loop::isLoopSimplifyForm() const {
- // Normal-form loops have a preheader.
- if (!getLoopPreheader())
- return false;
- // Normal-form loops have a single backedge.
- if (!getLoopLatch())
- return false;
+ // 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();
+}
+
+/// 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;
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))
+ if (!LoopBBs.count(*PI))
return false;
// All the requirements are met.
return true;
/// 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 is in canonical form.
+/// This assumes that loop exits are in canonical form.
///
void
Loop::getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const {
- assert(isLoopSimplifyForm() &&
- "getUniqueExitBlocks assumes the loop is in canonical form!");
+ 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());
- std::vector<BasicBlock *> switchExitBlocks;
+ SmallVector<BasicBlock *, 32> switchExitBlocks;
for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI) {
BasicBlock *current = *BI;
switchExitBlocks.clear();
- typedef GraphTraits<BasicBlock *> BlockTraits;
- typedef GraphTraits<Inverse<BasicBlock *> > InvBlockTraits;
- for (BlockTraits::ChildIteratorType I =
- BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
- I != E; ++I) {
+ 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;
- InvBlockTraits::ChildIteratorType PI = InvBlockTraits::child_begin(*I);
+ pred_iterator PI = pred_begin(*I);
BasicBlock *firstPred = *PI;
// If current basic block is this exit block's first predecessor
// 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(BlockTraits::child_begin(current),
- BlockTraits::child_end(current)) <= 2) {
+ if (std::distance(succ_begin(current), succ_end(current)) <= 2) {
ExitBlocks.push_back(*I);
continue;
}
return 0;
}
+void Loop::dump() const {
+ print(dbgs());
+}
+
+//===----------------------------------------------------------------------===//
+// 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");
+ }
+ }
+ }
+ // 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;
+ }
+ }
+ }
+}
+
+/// removeBlocksFromAncestors - Remove unloop's blocks from all ancestors below
+/// their new parents.
+void UnloopUpdater::removeBlocksFromAncestors() {
+ // Remove unloop's blocks from all ancestors below their new parents.
+ for (Loop::block_iterator BI = Unloop->block_begin(),
+ BE = Unloop->block_end(); BI != BE; ++BI) {
+ Loop *NewParent = LI->getLoopFor(*BI);
+ // If this block is an immediate subloop, remove all blocks (including
+ // nested subloops) from ancestors below the new parent loop.
+ // Otherwise, if this block is in a nested subloop, skip it.
+ if (SubloopParents.count(NewParent))
+ NewParent = SubloopParents[NewParent];
+ else if (Unloop->contains(NewParent))
+ continue;
+
+ // Remove blocks from former Ancestors except Unloop itself which will be
+ // deleted.
+ for (Loop *OldParent = Unloop->getParentLoop(); OldParent != NewParent;
+ OldParent = OldParent->getParentLoop()) {
+ assert(OldParent && "new loop is not an ancestor of the original");
+ OldParent->removeBlockFromLoop(*BI);
+ }
+ }
+}
+
+/// 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);
+ }
+}
+
+/// 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];
+ }
+
+ 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.
+
+ // 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;
+}
+
//===----------------------------------------------------------------------===//
// LoopInfo implementation
//
return false;
}
+/// 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, 0);
+ }
+
+ // 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(llvm::prior(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;
+ }
+ }
+}
+
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<const Loop*> Loops;
for (iterator I = begin(), E = end(); I != E; ++I) {
assert(!(*I)->getParentLoop() && "Top-level loop has a parent!");
- (*I)->verifyLoop();
+ (*I)->verifyLoopNest(&Loops);
+ }
+
+ // 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");
}
}
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) ;
+}
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