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Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp | 260 |
1 files changed, 260 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp new file mode 100644 index 000000000000..08ac38dec5dd --- /dev/null +++ b/contrib/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp @@ -0,0 +1,260 @@ +//===-- 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/Analysis/TargetTransformInfo.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/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, int R = -1) : LoopPass(ID) { + CurrentThreshold = (T == -1) ? UnrollThreshold : unsigned(T); + CurrentCount = (C == -1) ? UnrollCount : unsigned(C); + CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P; + CurrentRuntime = (R == -1) ? UnrollRuntime : (bool)R; + + UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0); + UserAllowPartial = (P != -1) || + (UnrollAllowPartial.getNumOccurrences() > 0); + UserRuntime = (R != -1) || (UnrollRuntime.getNumOccurrences() > 0); + UserCount = (C != -1) || (UnrollCount.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 CurrentRuntime; + bool UserCount; // CurrentCount is user-specified. + bool UserThreshold; // CurrentThreshold is user-specified. + bool UserAllowPartial; // CurrentAllowPartial is user-specified. + bool UserRuntime; // CurrentRuntime 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>(); + AU.addRequired<TargetTransformInfo>(); + // 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_AG_DEPENDENCY(TargetTransformInfo) +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, + int Runtime) { + return new LoopUnroll(Threshold, Count, AllowPartial, Runtime); +} + +/// ApproximateLoopSize - Approximate the size of the loop. +static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls, + bool &NotDuplicatable, + const TargetTransformInfo &TTI) { + CodeMetrics Metrics; + for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); + I != E; ++I) + Metrics.analyzeBasicBlock(*I, TTI); + 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>(); + const TargetTransformInfo &TTI = getAnalysis<TargetTransformInfo>(); + + BasicBlock *Header = L->getHeader(); + DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName() + << "] Loop %" << Header->getName() << "\n"); + (void)Header; + + TargetTransformInfo::UnrollingPreferences UP; + UP.Threshold = CurrentThreshold; + UP.OptSizeThreshold = OptSizeUnrollThreshold; + UP.Count = CurrentCount; + UP.Partial = CurrentAllowPartial; + UP.Runtime = CurrentRuntime; + TTI.getUnrollingPreferences(L, UP); + + // 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 = UserThreshold ? CurrentThreshold : UP.Threshold; + if (!UserThreshold && + Header->getParent()->getAttributes(). + hasAttribute(AttributeSet::FunctionIndex, + Attribute::OptimizeForSize)) + Threshold = UP.OptSizeThreshold; + + // 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); + } + + bool Runtime = UserRuntime ? CurrentRuntime : UP.Runtime; + + // 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 = UserCount ? CurrentCount : UP.Count; + if (Runtime && Count == 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) { + unsigned NumInlineCandidates; + bool notDuplicatable; + unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates, + notDuplicatable, TTI); + 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"); + bool AllowPartial = UserAllowPartial ? CurrentAllowPartial : UP.Partial; + if (!AllowPartial && !(Runtime && 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 (Runtime) { + // 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, Runtime, TripMultiple, LI, &LPM)) + return false; + + return true; +} |