X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopUnrollPass.cpp;h=e0f915b445fa03baeda40bf9f6aa7cd1f28fb053;hb=0b8c9a80f20772c3793201ab5b251d3520b9cea3;hp=1b4583d0b355fe5e3a06b48cb885be9bd8d44b93;hpb=d13db2c59cc94162d6cf0a04187d408bfef6d4a7;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/LoopUnrollPass.cpp b/lib/Transforms/Scalar/LoopUnrollPass.cpp index 1b4583d0b35..e0f915b445f 100644 --- a/lib/Transforms/Scalar/LoopUnrollPass.cpp +++ b/lib/Transforms/Scalar/LoopUnrollPass.cpp @@ -13,10 +13,12 @@ //===----------------------------------------------------------------------===// #define DEBUG_TYPE "loop-unroll" -#include "llvm/IntrinsicInst.h" #include "llvm/Transforms/Scalar.h" +#include "llvm/Analysis/CodeMetrics.h" #include "llvm/Analysis/LoopPass.h" -#include "llvm/Analysis/InlineCost.h" +#include "llvm/Analysis/ScalarEvolution.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" @@ -26,7 +28,7 @@ using namespace llvm; static cl::opt -UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden, +UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden, cl::desc("The cut-off point for automatic loop unrolling")); static cl::opt @@ -38,66 +40,135 @@ 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 +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() : LoopPass(&ID) {} + 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(); + AU.addPreserved(); AU.addRequiredID(LoopSimplifyID); + AU.addPreservedID(LoopSimplifyID); AU.addRequiredID(LCSSAID); - AU.addRequired(); AU.addPreservedID(LCSSAID); - AU.addPreserved(); + AU.addRequired(); + AU.addPreserved(); // 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(); - AU.addPreserved(); } }; } char LoopUnroll::ID = 0; -INITIALIZE_PASS(LoopUnroll, "loop-unroll", "Unroll loops", false, false); - -Pass *llvm::createLoopUnrollPass() { return new LoopUnroll(); } +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) { +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); - NumCalls = Metrics.NumCalls; - return Metrics.NumInsts; + 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(); + ScalarEvolution *SE = &getAnalysis(); BasicBlock *Header = L->getHeader(); DEBUG(dbgs() << "Loop Unroll: F[" << Header->getParent()->getName() << "] Loop %" << Header->getName() << "\n"); (void)Header; - // Find trip count - unsigned TripCount = L->getSmallConstantTripCount(); - unsigned Count = UnrollCount; + // 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; - // Automatically select an unroll count. if (Count == 0) { // Conservative heuristic: if we know the trip count, see if we can // completely unroll (subject to the threshold, checked below); otherwise @@ -109,27 +180,43 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { } // Enforce the threshold. - if (UnrollThreshold != NoThreshold) { - unsigned NumCalls; - unsigned LoopSize = ApproximateLoopSize(L, NumCalls); + if (Threshold != NoThreshold) { + const DataLayout *TD = getAnalysisIfAvailable(); + unsigned NumInlineCandidates; + bool notDuplicatable; + unsigned LoopSize = ApproximateLoopSize(L, NumInlineCandidates, + notDuplicatable, TD); DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n"); - if (NumCalls != 0) { - DEBUG(dbgs() << " Not unrolling loop with function calls.\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 > UnrollThreshold) { + if (TripCount != 1 && Size > Threshold) { DEBUG(dbgs() << " Too large to fully unroll with count: " << Count - << " because size: " << Size << ">" << UnrollThreshold << "\n"); - if (!UnrollAllowPartial) { + << " 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; } - // Reduce unroll count to be modulo of TripCount for partial unrolling - Count = UnrollThreshold / LoopSize; - while (Count != 0 && TripCount%Count != 0) { - Count--; + 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"); @@ -140,17 +227,8 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { } // Unroll the loop. - Function *F = L->getHeader()->getParent(); - if (!UnrollLoop(L, Count, LI, &LPM)) + if (!UnrollLoop(L, Count, TripCount, UnrollRuntime, TripMultiple, LI, &LPM)) return false; - // FIXME: Reconstruct dom info, because it is not preserved properly. - DominatorTree *DT = getAnalysisIfAvailable(); - if (DT) { - DT->runOnFunction(*F); - DominanceFrontier *DF = getAnalysisIfAvailable(); - if (DF) - DF->runOnFunction(*F); - } return true; }