| //===-- LoopUnroll.cpp - Loop unroller pass -------------------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass implements a simple loop unroller. It works best when loops have |
| // been canonicalized by the -indvars pass, allowing it to determine the trip |
| // counts of loops easily. |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "loop-unroll" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Analysis/CodeMetrics.h" |
| #include "llvm/Analysis/LoopPass.h" |
| #include "llvm/Analysis/ScalarEvolution.h" |
| #include "llvm/DataLayout.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Utils/UnrollLoop.h" |
| #include <climits> |
| |
| using namespace llvm; |
| |
| static cl::opt<unsigned> |
| UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden, |
| cl::desc("The cut-off point for automatic loop unrolling")); |
| |
| static cl::opt<unsigned> |
| UnrollCount("unroll-count", cl::init(0), cl::Hidden, |
| cl::desc("Use this unroll count for all loops, for testing purposes")); |
| |
| static cl::opt<bool> |
| UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden, |
| cl::desc("Allows loops to be partially unrolled until " |
| "-unroll-threshold loop size is reached.")); |
| |
| static cl::opt<bool> |
| UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::init(false), cl::Hidden, |
| cl::desc("Unroll loops with run-time trip counts")); |
| |
| namespace { |
| class LoopUnroll : public LoopPass { |
| public: |
| static char ID; // Pass ID, replacement for typeid |
| LoopUnroll(int T = -1, int C = -1, int P = -1) : LoopPass(ID) { |
| CurrentThreshold = (T == -1) ? UnrollThreshold : unsigned(T); |
| CurrentCount = (C == -1) ? UnrollCount : unsigned(C); |
| CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P; |
| |
| UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0); |
| |
| initializeLoopUnrollPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| /// A magic value for use with the Threshold parameter to indicate |
| /// that the loop unroll should be performed regardless of how much |
| /// code expansion would result. |
| static const unsigned NoThreshold = UINT_MAX; |
| |
| // Threshold to use when optsize is specified (and there is no |
| // explicit -unroll-threshold). |
| static const unsigned OptSizeUnrollThreshold = 50; |
| |
| // Default unroll count for loops with run-time trip count if |
| // -unroll-count is not set |
| static const unsigned UnrollRuntimeCount = 8; |
| |
| unsigned CurrentCount; |
| unsigned CurrentThreshold; |
| bool CurrentAllowPartial; |
| bool UserThreshold; // CurrentThreshold is user-specified. |
| |
| bool runOnLoop(Loop *L, LPPassManager &LPM); |
| |
| /// This transformation requires natural loop information & requires that |
| /// loop preheaders be inserted into the CFG... |
| /// |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<LoopInfo>(); |
| AU.addPreserved<LoopInfo>(); |
| AU.addRequiredID(LoopSimplifyID); |
| AU.addPreservedID(LoopSimplifyID); |
| AU.addRequiredID(LCSSAID); |
| AU.addPreservedID(LCSSAID); |
| AU.addRequired<ScalarEvolution>(); |
| AU.addPreserved<ScalarEvolution>(); |
| // FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info. |
| // If loop unroll does not preserve dom info then LCSSA pass on next |
| // loop will receive invalid dom info. |
| // For now, recreate dom info, if loop is unrolled. |
| AU.addPreserved<DominatorTree>(); |
| } |
| }; |
| } |
| |
| char LoopUnroll::ID = 0; |
| INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false) |
| INITIALIZE_PASS_DEPENDENCY(LoopInfo) |
| INITIALIZE_PASS_DEPENDENCY(LoopSimplify) |
| INITIALIZE_PASS_DEPENDENCY(LCSSA) |
| INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) |
| INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false) |
| |
| Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial) { |
| return new LoopUnroll(Threshold, Count, AllowPartial); |
| } |
| |
| /// ApproximateLoopSize - Approximate the size of the loop. |
| static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, |
| bool &NotDuplicatable, const DataLayout *TD) { |
| CodeMetrics Metrics; |
| for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); |
| I != E; ++I) |
| Metrics.analyzeBasicBlock(*I, TD); |
| NumCalls = Metrics.NumInlineCandidates; |
| NotDuplicatable = Metrics.notDuplicatable; |
| |
| unsigned LoopSize = Metrics.NumInsts; |
| |
| // Don't allow an estimate of size zero. This would allows unrolling of loops |
| // with huge iteration counts, which is a compile time problem even if it's |
| // not a problem for code quality. |
| if (LoopSize == 0) LoopSize = 1; |
| |
| return LoopSize; |
| } |
| |
| bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { |
| LoopInfo *LI = &getAnalysis<LoopInfo>(); |
| ScalarEvolution *SE = &getAnalysis<ScalarEvolution>(); |
| |
| BasicBlock *Header = L->getHeader(); |
| DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName() |
| << "] Loop %" << Header->getName() << "\n"); |
| (void)Header; |
| |
| // Determine the current unrolling threshold. While this is normally set |
| // from UnrollThreshold, it is overridden to a smaller value if the current |
| // function is marked as optimize-for-size, and the unroll threshold was |
| // not user specified. |
| unsigned Threshold = CurrentThreshold; |
| if (!UserThreshold && |
| Header->getParent()->getAttributes(). |
| hasAttribute(AttributeSet::FunctionIndex, |
| Attribute::OptimizeForSize)) |
| Threshold = OptSizeUnrollThreshold; |
| |
| // Find trip count and trip multiple if count is not available |
| unsigned TripCount = 0; |
| unsigned TripMultiple = 1; |
| // Find "latch trip count". UnrollLoop assumes that control cannot exit |
| // via the loop latch on any iteration prior to TripCount. The loop may exit |
| // early via an earlier branch. |
| BasicBlock *LatchBlock = L->getLoopLatch(); |
| if (LatchBlock) { |
| TripCount = SE->getSmallConstantTripCount(L, LatchBlock); |
| TripMultiple = SE->getSmallConstantTripMultiple(L, LatchBlock); |
| } |
| // Use a default unroll-count if the user doesn't specify a value |
| // and the trip count is a run-time value. The default is different |
| // for run-time or compile-time trip count loops. |
| unsigned Count = CurrentCount; |
| if (UnrollRuntime && CurrentCount == 0 && TripCount == 0) |
| Count = UnrollRuntimeCount; |
| |
| if (Count == 0) { |
| // Conservative heuristic: if we know the trip count, see if we can |
| // completely unroll (subject to the threshold, checked below); otherwise |
| // try to find greatest modulo of the trip count which is still under |
| // threshold value. |
| if (TripCount == 0) |
| return false; |
| Count = TripCount; |
| } |
| |
| // Enforce the threshold. |
| if (Threshold != NoThreshold) { |
| const DataLayout *TD = getAnalysisIfAvailable<DataLayout>(); |
| unsigned NumInlineCandidates; |
| bool notDuplicatable; |
| unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates, |
| notDuplicatable, TD); |
| DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); |
| if (notDuplicatable) { |
| DEBUG(dbgs() << " Not unrolling loop which contains non duplicatable" |
| << " instructions.\n"); |
| return false; |
| } |
| if (NumInlineCandidates != 0) { |
| DEBUG(dbgs() << " Not unrolling loop with inlinable calls.\n"); |
| return false; |
| } |
| uint64_t Size = (uint64_t)LoopSize*Count; |
| if (TripCount != 1 && Size > Threshold) { |
| DEBUG(dbgs() << " Too large to fully unroll with count: " << Count |
| << " because size: " << Size << ">" << Threshold << "\n"); |
| if (!CurrentAllowPartial && !(UnrollRuntime && TripCount == 0)) { |
| DEBUG(dbgs() << " will not try to unroll partially because " |
| << "-unroll-allow-partial not given\n"); |
| return false; |
| } |
| if (TripCount) { |
| // Reduce unroll count to be modulo of TripCount for partial unrolling |
| Count = Threshold / LoopSize; |
| while (Count != 0 && TripCount%Count != 0) |
| Count--; |
| } |
| else if (UnrollRuntime) { |
| // Reduce unroll count to be a lower power-of-two value |
| while (Count != 0 && Size > Threshold) { |
| Count >>= 1; |
| Size = LoopSize*Count; |
| } |
| } |
| if (Count < 2) { |
| DEBUG(dbgs() << " could not unroll partially\n"); |
| return false; |
| } |
| DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n"); |
| } |
| } |
| |
| // Unroll the loop. |
| if (!UnrollLoop(L, Count, TripCount, UnrollRuntime, TripMultiple, LI, &LPM)) |
| return false; |
| |
| return true; |
| } |