-//===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
+//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// 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
// and determine the loop depth of various nodes of the CFG. Note that the
//===----------------------------------------------------------------------===//
#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 "Support/DepthFirstIterator.h"
+#include "llvm/Support/Streams.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
#include <algorithm>
+using namespace llvm;
-AnalysisID LoopInfo::ID(AnalysisID::create<LoopInfo>(), true);
+char LoopInfo::ID = 0;
+static RegisterPass<LoopInfo>
+X("loops", "Natural Loop Information", true, true);
//===----------------------------------------------------------------------===//
// Loop implementation
//
-bool Loop::contains(const BasicBlock *BB) const {
- return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
-}
-void LoopInfo::releaseMemory() {
- for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
- E = TopLevelLoops.end(); I != E; ++I)
- delete *I; // Delete all of the loops...
+/// isLoopInvariant - Return true if the specified value is loop invariant
+///
+bool Loop::isLoopInvariant(Value *V) const {
+ if (Instruction *I = dyn_cast<Instruction>(V))
+ return isLoopInvariant(I);
+ return true; // All non-instructions are loop invariant
+}
- BBMap.clear(); // Reset internal state of analysis
- TopLevelLoops.clear();
+/// isLoopInvariant - Return true if the specified instruction is
+/// loop-invariant.
+///
+bool Loop::isLoopInvariant(Instruction *I) const {
+ return !contains(I->getParent());
}
+/// 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, Instruction *InsertPt) const {
+ if (Instruction *I = dyn_cast<Instruction>(V))
+ return makeLoopInvariant(I);
+ return true; // All non-instructions are loop-invariant.
+}
-//===----------------------------------------------------------------------===//
-// LoopInfo implementation
-//
-bool LoopInfo::runOnFunction(Function *F) {
- releaseMemory();
- Calculate(getAnalysis<DominatorSet>()); // Update
- return 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, Instruction *InsertPt) const {
+ // Test if the value is already loop-invariant.
+ if (isLoopInvariant(I))
+ return true;
+ // Don't hoist instructions with side-effects.
+ if (I->isTrapping())
+ return false;
+ // Don't hoist PHI nodes.
+ if (isa<PHINode>(I))
+ return false;
+ // Don't hoist allocation instructions.
+ if (isa<AllocationInst>(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), InsertPt))
+ return false;
+ // Hoist.
+ I->moveBefore(InsertPt);
+ return true;
}
-void LoopInfo::Calculate(const DominatorSet &DS) {
- BasicBlock *RootNode = DS.getRoot();
+/// 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();
- 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);
+ BasicBlock *Incoming = 0, *Backedge = 0;
+ typedef GraphTraits<Inverse<BasicBlock*> > InvBlockTraits;
+ InvBlockTraits::ChildIteratorType PI = InvBlockTraits::child_begin(H);
+ assert(PI != InvBlockTraits::child_end(H) &&
+ "Loop must have at least one backedge!");
+ Backedge = *PI++;
+ if (PI == InvBlockTraits::child_end(H)) return 0; // dead loop
+ Incoming = *PI++;
+ if (PI != InvBlockTraits::child_end(H)) return 0; // multiple backedges?
- for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
- TopLevelLoops[i]->setLoopDepth(1);
+ if (contains(Incoming)) {
+ if (contains(Backedge))
+ return 0;
+ std::swap(Incoming, Backedge);
+ } else if (!contains(Backedge))
+ return 0;
+
+ // 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::getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesAll();
- AU.addRequired(DominatorSet::ID);
- AU.addProvided(ID);
+/// 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,
+/// this returns null.
+///
+/// The IndVarSimplify pass transforms loops to have a form that this
+/// function easily understands.
+///
+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));
-Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
- if (BBMap.find(BB) != BBMap.end()) return 0; // Havn't processed this node?
+ BasicBlock *BackedgeBlock =
+ IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
- std::vector<BasicBlock *> TodoStack;
+ if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
+ if (BI->isConditional()) {
+ if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) {
+ if (ICI->getOperand(0) == Inc) {
+ if (BI->getSuccessor(0) == getHeader()) {
+ if (ICI->getPredicate() == ICmpInst::ICMP_NE)
+ return ICI->getOperand(1);
+ } else if (ICI->getPredicate() == ICmpInst::ICMP_EQ) {
+ return ICI->getOperand(1);
+ }
+ }
+ }
+ }
- // Scan the predecessors of BB, checking to see if BB dominates any of
- // them.
- 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);
+ return 0;
+}
- if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
+/// 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
+/// (>= 2^32)
+unsigned Loop::getSmallConstantTripCount() const {
+ Value* TripCount = this->getTripCount();
+ if (TripCount) {
+ if (ConstantInt *TripCountC = dyn_cast<ConstantInt>(TripCount)) {
+ // Guard against huge trip counts.
+ if (TripCountC->getValue().getActiveBits() <= 32) {
+ return (unsigned)TripCountC->getZExtValue();
+ }
+ }
+ }
+ return 0;
+}
- // Create a new loop to represent this basic block...
- Loop *L = new Loop(BB);
- BBMap[BB] = L;
+/// getSmallConstantTripMultiple - Returns the largest constant divisor of the
+/// trip count of this loop as a normal unsigned value, if possible. This
+/// means that the actual trip count is always a multiple of the returned
+/// value (don't forget the trip count could very well be zero as well!).
+///
+/// Returns 1 if the trip count is unknown or not guaranteed to be the
+/// multiple of a constant (which is also the case if the trip count is simply
+/// constant, use getSmallConstantTripCount for that case), Will also return 1
+/// if the trip count is very large (>= 2^32).
+unsigned Loop::getSmallConstantTripMultiple() const {
+ Value* TripCount = this->getTripCount();
+ // This will hold the ConstantInt result, if any
+ ConstantInt *Result = NULL;
+ if (TripCount) {
+ // See if the trip count is constant itself
+ Result = dyn_cast<ConstantInt>(TripCount);
+ // if not, see if it is a multiplication
+ if (!Result)
+ if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TripCount)) {
+ switch (BO->getOpcode()) {
+ case BinaryOperator::Mul:
+ Result = dyn_cast<ConstantInt>(BO->getOperand(1));
+ break;
+ default:
+ break;
+ }
+ }
+ }
+ // Guard against huge trip counts.
+ if (Result && Result->getValue().getActiveBits() <= 32) {
+ return (unsigned)Result->getZExtValue();
+ } else {
+ return 1;
+ }
+}
- while (!TodoStack.empty()) { // Process all the nodes in the loop
- BasicBlock *X = TodoStack.back();
- TodoStack.pop_back();
+/// isLCSSAForm - Return true if the Loop is in LCSSA form
+bool Loop::isLCSSAForm() const {
+ // Sort the blocks vector so that we can use binary search to do quick
+ // lookups.
+ SmallPtrSet<BasicBlock *, 16> LoopBBs(block_begin(), block_end());
- if (!L->contains(X)) { // As of yet unprocessed??
- L->Blocks.push_back(X);
+ 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) {
+ BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
+ if (PHINode *P = dyn_cast<PHINode>(*UI)) {
+ UserBB = P->getIncomingBlock(UI);
+ }
- // Add all of the predecessors of X to the end of the work stack...
- TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
- }
+ // 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))
+ return false;
+ }
}
- // Add the basic blocks that comprise this loop to the BBMap so that this
- // loop can be found for them. Also check subsidary basic blocks to see if
- // they start subloops of their own.
- //
- for (std::vector<BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
- E = L->Blocks.rend(); I != E; ++I) {
-
- // Check to see if this block starts a new loop
- if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
- L->SubLoops.push_back(NewLoop);
- NewLoop->ParentLoop = L;
- }
-
- if (BBMap.find(*I) == BBMap.end())
- BBMap.insert(std::make_pair(*I, L));
- }
+ return true;
+}
+//===----------------------------------------------------------------------===//
+// LoopInfo implementation
+//
+bool LoopInfo::runOnFunction(Function &) {
+ releaseMemory();
+ LI.Calculate(getAnalysis<DominatorTree>().getBase()); // Update
+ return false;
+}
- return L;
+void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesAll();
+ AU.addRequired<DominatorTree>();
}
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