X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FLoopInfo.cpp;h=05831402f4092bcea8ccf670e5864f8fdab03f40;hb=12bf43bc4f86602a5677d5e1662cb4e40562351b;hp=e136f2930f6f92cca21260ceb78c54d43365cdfd;hpb=4ee451de366474b9c228b4e5fa573795a715216d;p=oota-llvm.git diff --git a/lib/Analysis/LoopInfo.cpp b/lib/Analysis/LoopInfo.cpp index e136f2930f6..05831402f40 100644 --- a/lib/Analysis/LoopInfo.cpp +++ b/lib/Analysis/LoopInfo.cpp @@ -20,37 +20,400 @@ #include "llvm/Analysis/Dominators.h" #include "llvm/Assembly/Writer.h" #include "llvm/Support/CFG.h" -#include "llvm/Support/Streams.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" #include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/SmallPtrSet.h" #include -#include 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 +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(DominatorTree) +INITIALIZE_PASS_END(LoopInfo, "loops", "Natural Loop Information", true, true) //===----------------------------------------------------------------------===// // Loop implementation // -/// getNumBackEdges - Calculate the number of back edges to the loop header. +/// isLoopInvariant - Return true if the specified value is loop invariant +/// +bool Loop::isLoopInvariant(Value *V) const { + if (Instruction *I = dyn_cast(V)) + return !contains(I); + return true; // All non-instructions are loop invariant +} + +/// 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 +/// 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. +} + +/// 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 (!I->isSafeToSpeculativelyExecute()) + return false; + if (I->mayReadFromMemory()) + 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; +} + +/// 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? + + 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(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 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. + PHINode *IV = getCanonicalInductionVariable(); + if (IV == 0 || IV->getNumIncomingValues() != 2) return 0; + + bool P0InLoop = contains(IV->getIncomingBlock(0)); + Value *Inc = IV->getIncomingValue(!P0InLoop); + BasicBlock *BackedgeBlock = IV->getIncomingBlock(!P0InLoop); + + if (BranchInst *BI = dyn_cast(BackedgeBlock->getTerminator())) + if (BI->isConditional()) { + if (ICmpInst *ICI = dyn_cast(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); + } + } + } + } + + return 0; +} + +/// getSmallConstantTripCount - Returns the trip count of this loop as a +/// normal unsigned value, if possible. Returns 0 if the trip count is unknown +/// or 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(TripCount)) { + // Guard against huge trip counts. + if (TripCountC->getValue().getActiveBits() <= 32) { + return (unsigned)TripCountC->getZExtValue(); + } + } + } + return 0; +} + +/// 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(TripCount); + // if not, see if it is a multiplication + if (!Result) + if (BinaryOperator *BO = dyn_cast(TripCount)) { + switch (BO->getOpcode()) { + case BinaryOperator::Mul: + Result = dyn_cast(BO->getOperand(1)); + break; + case BinaryOperator::Shl: + if (ConstantInt *CI = dyn_cast(BO->getOperand(1))) + if (CI->getValue().getActiveBits() <= 5) + return 1u << CI->getZExtValue(); + break; + default: + break; + } + } + } + // Guard against huge trip counts. + if (Result && Result->getValue().getActiveBits() <= 32) { + return (unsigned)Result->getZExtValue(); + } else { + return 1; + } +} + +/// 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 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(U)->getParent(); + if (PHINode *P = dyn_cast(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; + } + } + + 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(); +} + +/// 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 LoopBBs(block_begin(), block_end()); + // 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 (!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 exits are in canonical form. +/// +void +Loop::getUniqueExitBlocks(SmallVectorImpl &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 LoopBBs(block_begin(), block_end()); + std::sort(LoopBBs.begin(), LoopBBs.end()); + + 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 (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); + } + } + } +} + +/// 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 0; +} + +void Loop::dump() const { + print(dbgs()); +} //===----------------------------------------------------------------------===// // LoopInfo implementation // bool LoopInfo::runOnFunction(Function &) { releaseMemory(); - LI->Calculate(getAnalysis().getBase()); // Update + LI.Calculate(getAnalysis().getBase()); // Update return false; } +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; + + for (iterator I = begin(), E = end(); I != E; ++I) { + assert(!(*I)->getParentLoop() && "Top-level loop has a parent!"); + (*I)->verifyLoopNest(); + } + + // TODO: check BBMap consistency. +} + void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); AU.addRequired(); } -// Ensure this file gets linked when LoopInfo.h is used. -DEFINING_FILE_FOR(LoopInfo) +void LoopInfo::print(raw_ostream &OS, const Module*) const { + LI.print(OS); +} +