// counts of loops easily.
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "loop-unroll"
-#include "llvm/IntrinsicInst.h"
#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/LoopPass.h"
-#include "llvm/Analysis/InlineCost.h"
#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Metadata.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/UnrollLoop.h"
+#include "llvm/IR/InstVisitor.h"
+#include "llvm/Analysis/InstructionSimplify.h"
#include <climits>
using namespace llvm;
+#define DEBUG_TYPE "loop-unroll"
+
static cl::opt<unsigned>
-UnrollThreshold("unroll-threshold", cl::init(200), cl::Hidden,
+UnrollThreshold("unroll-threshold", cl::init(150), cl::Hidden,
cl::desc("The cut-off point for automatic loop unrolling"));
+static cl::opt<unsigned> UnrollMaxIterationsCountToAnalyze(
+ "unroll-max-iteration-count-to-analyze", cl::init(1000), cl::Hidden,
+ cl::desc("Don't allow loop unrolling to simulate more than this number of"
+ "iterations when checking full unroll profitability"));
+
+static cl::opt<unsigned> UnrollMinPercentOfOptimized(
+ "unroll-percent-of-optimized-for-complete-unroll", cl::init(20), cl::Hidden,
+ cl::desc("If complete unrolling could trigger further optimizations, and, "
+ "by that, remove the given percent of instructions, perform the "
+ "complete unroll even if it's beyond the threshold"));
+
+static cl::opt<unsigned> UnrollAbsoluteThreshold(
+ "unroll-absolute-threshold", cl::init(2000), cl::Hidden,
+ cl::desc("Don't unroll if the unrolled size is bigger than this threshold,"
+ " even if we can remove big portion of instructions later."));
+
static cl::opt<unsigned>
UnrollCount("unroll-count", cl::init(0), cl::Hidden,
- cl::desc("Use this unroll count for all loops, for testing purposes"));
+ cl::desc("Use this unroll count for all loops including those with "
+ "unroll_count pragma values, 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"));
+
+static cl::opt<unsigned>
+PragmaUnrollThreshold("pragma-unroll-threshold", cl::init(16 * 1024), cl::Hidden,
+ cl::desc("Unrolled size limit for loops with an unroll(full) or "
+ "unroll_count pragma."));
+
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, int R = -1) : LoopPass(ID) {
+ CurrentThreshold = (T == -1) ? UnrollThreshold : unsigned(T);
+ CurrentAbsoluteThreshold = UnrollAbsoluteThreshold;
+ CurrentMinPercentOfOptimized = UnrollMinPercentOfOptimized;
+ CurrentCount = (C == -1) ? UnrollCount : unsigned(C);
+ CurrentAllowPartial = (P == -1) ? UnrollAllowPartial : (bool)P;
+ CurrentRuntime = (R == -1) ? UnrollRuntime : (bool)R;
+
+ UserThreshold = (T != -1) || (UnrollThreshold.getNumOccurrences() > 0);
+ UserAbsoluteThreshold = (UnrollAbsoluteThreshold.getNumOccurrences() > 0);
+ UserPercentOfOptimized =
+ (UnrollMinPercentOfOptimized.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;
- bool runOnLoop(Loop *L, LPPassManager &LPM);
+ // 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;
+ unsigned CurrentAbsoluteThreshold;
+ unsigned CurrentMinPercentOfOptimized;
+ bool CurrentAllowPartial;
+ bool CurrentRuntime;
+ bool UserCount; // CurrentCount is user-specified.
+ bool UserThreshold; // CurrentThreshold is user-specified.
+ bool UserAbsoluteThreshold; // CurrentAbsoluteThreshold is
+ // user-specified.
+ bool UserPercentOfOptimized; // CurrentMinPercentOfOptimized is
+ // user-specified.
+ bool UserAllowPartial; // CurrentAllowPartial is user-specified.
+ bool UserRuntime; // CurrentRuntime is user-specified.
+
+ bool runOnLoop(Loop *L, LPPassManager &LPM) override;
/// 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>();
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<AssumptionCacheTracker>();
+ AU.addRequired<LoopInfoWrapperPass>();
+ AU.addPreserved<LoopInfoWrapperPass>();
AU.addRequiredID(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
+ AU.addRequired<ScalarEvolution>();
+ AU.addPreserved<ScalarEvolution>();
+ AU.addRequired<TargetTransformInfoWrapperPass>();
// 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>();
- AU.addPreserved<DominanceFrontier>();
- AU.addPreserved<ScalarEvolution>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
+ }
+
+ // Fill in the UnrollingPreferences parameter with values from the
+ // TargetTransformationInfo.
+ void getUnrollingPreferences(Loop *L, const TargetTransformInfo &TTI,
+ TargetTransformInfo::UnrollingPreferences &UP) {
+ UP.Threshold = CurrentThreshold;
+ UP.AbsoluteThreshold = CurrentAbsoluteThreshold;
+ UP.MinPercentOfOptimized = CurrentMinPercentOfOptimized;
+ UP.OptSizeThreshold = OptSizeUnrollThreshold;
+ UP.PartialThreshold = CurrentThreshold;
+ UP.PartialOptSizeThreshold = OptSizeUnrollThreshold;
+ UP.Count = CurrentCount;
+ UP.MaxCount = UINT_MAX;
+ UP.Partial = CurrentAllowPartial;
+ UP.Runtime = CurrentRuntime;
+ TTI.getUnrollingPreferences(L, UP);
+ }
+
+ // Select and return an unroll count based on parameters from
+ // user, unroll preferences, unroll pragmas, or a heuristic.
+ // SetExplicitly is set to true if the unroll count is is set by
+ // the user or a pragma rather than selected heuristically.
+ unsigned
+ selectUnrollCount(const Loop *L, unsigned TripCount, bool PragmaFullUnroll,
+ unsigned PragmaCount,
+ const TargetTransformInfo::UnrollingPreferences &UP,
+ bool &SetExplicitly);
+
+ // Select threshold values used to limit unrolling based on a
+ // total unrolled size. Parameters Threshold and PartialThreshold
+ // are set to the maximum unrolled size for fully and partially
+ // unrolled loops respectively.
+ void selectThresholds(const Loop *L, bool HasPragma,
+ const TargetTransformInfo::UnrollingPreferences &UP,
+ unsigned &Threshold, unsigned &PartialThreshold,
+ unsigned NumberOfOptimizedInstructions) {
+ // 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.
+ Threshold = UserThreshold ? CurrentThreshold : UP.Threshold;
+
+ // If we are allowed to completely unroll if we can remove M% of
+ // instructions, and we know that with complete unrolling we'll be able
+ // to kill N instructions, then we can afford to completely unroll loops
+ // with unrolled size up to N*100/M.
+ // Adjust the threshold according to that:
+ unsigned PercentOfOptimizedForCompleteUnroll =
+ UserPercentOfOptimized ? CurrentMinPercentOfOptimized
+ : UP.MinPercentOfOptimized;
+ unsigned AbsoluteThreshold = UserAbsoluteThreshold
+ ? CurrentAbsoluteThreshold
+ : UP.AbsoluteThreshold;
+ if (PercentOfOptimizedForCompleteUnroll)
+ Threshold = std::max<unsigned>(Threshold,
+ NumberOfOptimizedInstructions * 100 /
+ PercentOfOptimizedForCompleteUnroll);
+ // But don't allow unrolling loops bigger than absolute threshold.
+ Threshold = std::min<unsigned>(Threshold, AbsoluteThreshold);
+
+ PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold;
+ if (!UserThreshold &&
+ L->getHeader()->getParent()->getAttributes().
+ hasAttribute(AttributeSet::FunctionIndex,
+ Attribute::OptimizeForSize)) {
+ Threshold = UP.OptSizeThreshold;
+ PartialThreshold = UP.PartialOptSizeThreshold;
+ }
+ if (HasPragma) {
+ // If the loop has an unrolling pragma, we want to be more
+ // aggressive with unrolling limits. Set thresholds to at
+ // least the PragmaTheshold value which is larger than the
+ // default limits.
+ if (Threshold != NoThreshold)
+ Threshold = std::max<unsigned>(Threshold, PragmaUnrollThreshold);
+ if (PartialThreshold != NoThreshold)
+ PartialThreshold =
+ std::max<unsigned>(PartialThreshold, PragmaUnrollThreshold);
+ }
}
};
}
char LoopUnroll::ID = 0;
-INITIALIZE_PASS(LoopUnroll, "loop-unroll", "Unroll loops", false, false);
+INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+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);
+}
+
+Pass *llvm::createSimpleLoopUnrollPass() {
+ return llvm::createLoopUnrollPass(-1, -1, 0, 0);
+}
+
+static bool isLoadFromConstantInitializer(Value *V) {
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
+ if (GV->isConstant() && GV->hasDefinitiveInitializer())
+ return GV->getInitializer();
+ return false;
+}
+
+struct FindConstantPointers {
+ bool LoadCanBeConstantFolded;
+ bool IndexIsConstant;
+ APInt Step;
+ APInt StartValue;
+ Value *BaseAddress;
+ const Loop *L;
+ ScalarEvolution &SE;
+ FindConstantPointers(const Loop *loop, ScalarEvolution &SE)
+ : LoadCanBeConstantFolded(true), IndexIsConstant(true), L(loop), SE(SE) {}
+
+ bool follow(const SCEV *S) {
+ if (const SCEVUnknown *SC = dyn_cast<SCEVUnknown>(S)) {
+ // We've reached the leaf node of SCEV, it's most probably just a
+ // variable. Now it's time to see if it corresponds to a global constant
+ // global (in which case we can eliminate the load), or not.
+ BaseAddress = SC->getValue();
+ LoadCanBeConstantFolded =
+ IndexIsConstant && isLoadFromConstantInitializer(BaseAddress);
+ return false;
+ }
+ if (isa<SCEVConstant>(S))
+ return true;
+ if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+ // If the current SCEV expression is AddRec, and its loop isn't the loop
+ // we are about to unroll, then we won't get a constant address after
+ // unrolling, and thus, won't be able to eliminate the load.
+ if (AR->getLoop() != L)
+ return IndexIsConstant = false;
+ // If the step isn't constant, we won't get constant addresses in unrolled
+ // version. Bail out.
+ if (const SCEVConstant *StepSE =
+ dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
+ Step = StepSE->getValue()->getValue();
+ else
+ return IndexIsConstant = false;
+
+ return IndexIsConstant;
+ }
+ // If Result is true, continue traversal.
+ // Otherwise, we have found something that prevents us from (possible) load
+ // elimination.
+ return IndexIsConstant;
+ }
+ bool isDone() const { return !IndexIsConstant; }
+};
-Pass *llvm::createLoopUnrollPass() { return new LoopUnroll(); }
+// This class is used to get an estimate of the optimization effects that we
+// could get from complete loop unrolling. It comes from the fact that some
+// loads might be replaced with concrete constant values and that could trigger
+// a chain of instruction simplifications.
+//
+// E.g. we might have:
+// int a[] = {0, 1, 0};
+// v = 0;
+// for (i = 0; i < 3; i ++)
+// v += b[i]*a[i];
+// If we completely unroll the loop, we would get:
+// v = b[0]*a[0] + b[1]*a[1] + b[2]*a[2]
+// Which then will be simplified to:
+// v = b[0]* 0 + b[1]* 1 + b[2]* 0
+// And finally:
+// v = b[1]
+class UnrollAnalyzer : public InstVisitor<UnrollAnalyzer, bool> {
+ typedef InstVisitor<UnrollAnalyzer, bool> Base;
+ friend class InstVisitor<UnrollAnalyzer, bool>;
+
+ const Loop *L;
+ unsigned TripCount;
+ ScalarEvolution &SE;
+ const TargetTransformInfo &TTI;
+
+ DenseMap<Value *, Constant *> SimplifiedValues;
+ DenseMap<LoadInst *, Value *> LoadBaseAddresses;
+ SmallPtrSet<Instruction *, 32> CountedInstructions;
+
+ /// \brief Count the number of optimized instructions.
+ unsigned NumberOfOptimizedInstructions;
+
+ // Provide base case for our instruction visit.
+ bool visitInstruction(Instruction &I) { return false; };
+ // TODO: We should also visit ICmp, FCmp, GetElementPtr, Trunc, ZExt, SExt,
+ // FPTrunc, FPExt, FPToUI, FPToSI, UIToFP, SIToFP, BitCast, Select,
+ // ExtractElement, InsertElement, ShuffleVector, ExtractValue, InsertValue.
+ //
+ // Probaly it's worth to hoist the code for estimating the simplifications
+ // effects to a separate class, since we have a very similar code in
+ // InlineCost already.
+ bool visitBinaryOperator(BinaryOperator &I) {
+ Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
+ if (!isa<Constant>(LHS))
+ if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS))
+ LHS = SimpleLHS;
+ if (!isa<Constant>(RHS))
+ if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS))
+ RHS = SimpleRHS;
+ Value *SimpleV = nullptr;
+ if (auto FI = dyn_cast<FPMathOperator>(&I))
+ SimpleV =
+ SimplifyFPBinOp(I.getOpcode(), LHS, RHS, FI->getFastMathFlags());
+ else
+ SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS);
+
+ if (SimpleV && CountedInstructions.insert(&I).second)
+ NumberOfOptimizedInstructions += TTI.getUserCost(&I);
+
+ if (Constant *C = dyn_cast_or_null<Constant>(SimpleV)) {
+ SimplifiedValues[&I] = C;
+ return true;
+ }
+ return false;
+ }
+
+ Constant *computeLoadValue(LoadInst *LI, unsigned Iteration) {
+ if (!LI)
+ return nullptr;
+ Value *BaseAddr = LoadBaseAddresses[LI];
+ if (!BaseAddr)
+ return nullptr;
+
+ auto GV = dyn_cast<GlobalVariable>(BaseAddr);
+ if (!GV)
+ return nullptr;
+
+ ConstantDataSequential *CDS =
+ dyn_cast<ConstantDataSequential>(GV->getInitializer());
+ if (!CDS)
+ return nullptr;
+
+ const SCEV *BaseAddrSE = SE.getSCEV(BaseAddr);
+ const SCEV *S = SE.getSCEV(LI->getPointerOperand());
+ const SCEV *OffSE = SE.getMinusSCEV(S, BaseAddrSE);
+
+ APInt StepC, StartC;
+ const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(OffSE);
+ if (!AR)
+ return nullptr;
+
+ if (const SCEVConstant *StepSE =
+ dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
+ StepC = StepSE->getValue()->getValue();
+ else
+ return nullptr;
+
+ if (const SCEVConstant *StartSE = dyn_cast<SCEVConstant>(AR->getStart()))
+ StartC = StartSE->getValue()->getValue();
+ else
+ return nullptr;
+
+ unsigned ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
+ unsigned Start = StartC.getLimitedValue();
+ unsigned Step = StepC.getLimitedValue();
+
+ unsigned Index = (Start + Step * Iteration) / ElemSize;
+ if (Index >= CDS->getNumElements())
+ return nullptr;
+
+ Constant *CV = CDS->getElementAsConstant(Index);
+
+ return CV;
+ }
+
+public:
+ UnrollAnalyzer(const Loop *L, unsigned TripCount, ScalarEvolution &SE,
+ const TargetTransformInfo &TTI)
+ : L(L), TripCount(TripCount), SE(SE), TTI(TTI),
+ NumberOfOptimizedInstructions(0) {}
+
+ // Visit all loads the loop L, and for those that, after complete loop
+ // unrolling, would have a constant address and it will point to a known
+ // constant initializer, record its base address for future use. It is used
+ // when we estimate number of potentially simplified instructions.
+ void findConstFoldableLoads() {
+ for (auto BB : L->getBlocks()) {
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+ if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
+ if (!LI->isSimple())
+ continue;
+ Value *AddrOp = LI->getPointerOperand();
+ const SCEV *S = SE.getSCEV(AddrOp);
+ FindConstantPointers Visitor(L, SE);
+ SCEVTraversal<FindConstantPointers> T(Visitor);
+ T.visitAll(S);
+ if (Visitor.IndexIsConstant && Visitor.LoadCanBeConstantFolded) {
+ LoadBaseAddresses[LI] = Visitor.BaseAddress;
+ }
+ }
+ }
+ }
+ }
+
+ // Given a list of loads that could be constant-folded (LoadBaseAddresses),
+ // estimate number of optimized instructions after substituting the concrete
+ // values for the given Iteration. Also track how many instructions become
+ // dead through this process.
+ unsigned estimateNumberOfOptimizedInstructions(unsigned Iteration) {
+ // We keep a set vector for the worklist so that we don't wast space in the
+ // worklist queuing up the same instruction repeatedly. This can happen due
+ // to multiple operands being the same instruction or due to the same
+ // instruction being an operand of lots of things that end up dead or
+ // simplified.
+ SmallSetVector<Instruction *, 8> Worklist;
+
+ // Clear the simplified values and counts for this iteration.
+ SimplifiedValues.clear();
+ CountedInstructions.clear();
+ NumberOfOptimizedInstructions = 0;
+
+ // We start by adding all loads to the worklist.
+ for (auto &LoadDescr : LoadBaseAddresses) {
+ LoadInst *LI = LoadDescr.first;
+ SimplifiedValues[LI] = computeLoadValue(LI, Iteration);
+ if (CountedInstructions.insert(LI).second)
+ NumberOfOptimizedInstructions += TTI.getUserCost(LI);
+
+ for (User *U : LI->users())
+ Worklist.insert(cast<Instruction>(U));
+ }
+
+ // And then we try to simplify every user of every instruction from the
+ // worklist. If we do simplify a user, add it to the worklist to process
+ // its users as well.
+ while (!Worklist.empty()) {
+ Instruction *I = Worklist.pop_back_val();
+ if (!L->contains(I))
+ continue;
+ if (!visit(I))
+ continue;
+ for (User *U : I->users())
+ Worklist.insert(cast<Instruction>(U));
+ }
+
+ // Now that we know the potentially simplifed instructions, estimate number
+ // of instructions that would become dead if we do perform the
+ // simplification.
+
+ // The dead instructions are held in a separate set. This is used to
+ // prevent us from re-examining instructions and make sure we only count
+ // the benifit once. The worklist's internal set handles insertion
+ // deduplication.
+ SmallPtrSet<Instruction *, 16> DeadInstructions;
+
+ // Lambda to enque operands onto the worklist.
+ auto EnqueueOperands = [&](Instruction &I) {
+ for (auto *Op : I.operand_values())
+ if (auto *OpI = dyn_cast<Instruction>(Op))
+ if (!OpI->use_empty())
+ Worklist.insert(OpI);
+ };
+
+ // Start by initializing worklist with simplified instructions.
+ for (auto &FoldedKeyValue : SimplifiedValues)
+ if (auto *FoldedInst = dyn_cast<Instruction>(FoldedKeyValue.first)) {
+ DeadInstructions.insert(FoldedInst);
+
+ // Add each instruction operand of this dead instruction to the
+ // worklist.
+ EnqueueOperands(*FoldedInst);
+ }
+
+ // If a definition of an insn is only used by simplified or dead
+ // instructions, it's also dead. Check defs of all instructions from the
+ // worklist.
+ while (!Worklist.empty()) {
+ Instruction *I = Worklist.pop_back_val();
+ if (!L->contains(I))
+ continue;
+ if (DeadInstructions.count(I))
+ continue;
+
+ if (std::all_of(I->user_begin(), I->user_end(), [&](User *U) {
+ return DeadInstructions.count(cast<Instruction>(U));
+ })) {
+ NumberOfOptimizedInstructions += TTI.getUserCost(I);
+ DeadInstructions.insert(I);
+ EnqueueOperands(*I);
+ }
+ }
+ return NumberOfOptimizedInstructions;
+ }
+};
+
+// Complete loop unrolling can make some loads constant, and we need to know if
+// that would expose any further optimization opportunities.
+// This routine estimates this optimization effect and returns the number of
+// instructions, that potentially might be optimized away.
+static unsigned
+approximateNumberOfOptimizedInstructions(const Loop *L, ScalarEvolution &SE,
+ unsigned TripCount,
+ const TargetTransformInfo &TTI) {
+ if (!TripCount || !UnrollMaxIterationsCountToAnalyze)
+ return 0;
+
+ UnrollAnalyzer UA(L, TripCount, SE, TTI);
+ UA.findConstFoldableLoads();
+
+ // Estimate number of instructions, that could be simplified if we replace a
+ // load with the corresponding constant. Since the same load will take
+ // different values on different iterations, we have to go through all loop's
+ // iterations here. To limit ourselves here, we check only first N
+ // iterations, and then scale the found number, if necessary.
+ unsigned IterationsNumberForEstimate =
+ std::min<unsigned>(UnrollMaxIterationsCountToAnalyze, TripCount);
+ unsigned NumberOfOptimizedInstructions = 0;
+ for (unsigned i = 0; i < IterationsNumberForEstimate; ++i)
+ NumberOfOptimizedInstructions +=
+ UA.estimateNumberOfOptimizedInstructions(i);
+
+ NumberOfOptimizedInstructions *= TripCount / IterationsNumberForEstimate;
+
+ return NumberOfOptimizedInstructions;
+}
/// 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 TargetTransformInfo &TTI,
+ AssumptionCache *AC) {
+ SmallPtrSet<const Value *, 32> EphValues;
+ CodeMetrics::collectEphemeralValues(L, AC, EphValues);
+
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, TTI, EphValues);
+ 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. Also, the code using this size may assume
+ // that each loop has at least three instructions (likely a conditional
+ // branch, a comparison feeding that branch, and some kind of loop increment
+ // feeding that comparison instruction).
+ LoopSize = std::max(LoopSize, 3u);
+
+ return LoopSize;
+}
+
+// Returns the loop hint metadata node with the given name (for example,
+// "llvm.loop.unroll.count"). If no such metadata node exists, then nullptr is
+// returned.
+static MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) {
+ if (MDNode *LoopID = L->getLoopID())
+ return GetUnrollMetadata(LoopID, Name);
+ return nullptr;
+}
+
+// Returns true if the loop has an unroll(full) pragma.
+static bool HasUnrollFullPragma(const Loop *L) {
+ return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.full");
+}
+
+// Returns true if the loop has an unroll(disable) pragma.
+static bool HasUnrollDisablePragma(const Loop *L) {
+ return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.disable");
+}
+
+// If loop has an unroll_count pragma return the (necessarily
+// positive) value from the pragma. Otherwise return 0.
+static unsigned UnrollCountPragmaValue(const Loop *L) {
+ MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count");
+ if (MD) {
+ assert(MD->getNumOperands() == 2 &&
+ "Unroll count hint metadata should have two operands.");
+ unsigned Count =
+ mdconst::extract<ConstantInt>(MD->getOperand(1))->getZExtValue();
+ assert(Count >= 1 && "Unroll count must be positive.");
+ return Count;
+ }
+ return 0;
+}
+
+// Remove existing unroll metadata and add unroll disable metadata to
+// indicate the loop has already been unrolled. This prevents a loop
+// from being unrolled more than is directed by a pragma if the loop
+// unrolling pass is run more than once (which it generally is).
+static void SetLoopAlreadyUnrolled(Loop *L) {
+ MDNode *LoopID = L->getLoopID();
+ if (!LoopID) return;
+
+ // First remove any existing loop unrolling metadata.
+ SmallVector<Metadata *, 4> MDs;
+ // Reserve first location for self reference to the LoopID metadata node.
+ MDs.push_back(nullptr);
+ for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
+ bool IsUnrollMetadata = false;
+ MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
+ if (MD) {
+ const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
+ IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll.");
+ }
+ if (!IsUnrollMetadata)
+ MDs.push_back(LoopID->getOperand(i));
+ }
+
+ // Add unroll(disable) metadata to disable future unrolling.
+ LLVMContext &Context = L->getHeader()->getContext();
+ SmallVector<Metadata *, 1> DisableOperands;
+ DisableOperands.push_back(MDString::get(Context, "llvm.loop.unroll.disable"));
+ MDNode *DisableNode = MDNode::get(Context, DisableOperands);
+ MDs.push_back(DisableNode);
+
+ MDNode *NewLoopID = MDNode::get(Context, MDs);
+ // Set operand 0 to refer to the loop id itself.
+ NewLoopID->replaceOperandWith(0, NewLoopID);
+ L->setLoopID(NewLoopID);
+}
+
+unsigned LoopUnroll::selectUnrollCount(
+ const Loop *L, unsigned TripCount, bool PragmaFullUnroll,
+ unsigned PragmaCount, const TargetTransformInfo::UnrollingPreferences &UP,
+ bool &SetExplicitly) {
+ SetExplicitly = true;
+
+ // User-specified count (either as a command-line option or
+ // constructor parameter) has highest precedence.
+ unsigned Count = UserCount ? CurrentCount : 0;
+
+ // If there is no user-specified count, unroll pragmas have the next
+ // highest precendence.
+ if (Count == 0) {
+ if (PragmaCount) {
+ Count = PragmaCount;
+ } else if (PragmaFullUnroll) {
+ Count = TripCount;
+ }
+ }
+
+ if (Count == 0)
+ Count = UP.Count;
+
+ if (Count == 0) {
+ SetExplicitly = false;
+ if (TripCount == 0)
+ // Runtime trip count.
+ Count = UnrollRuntimeCount;
+ else
+ // 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.
+ Count = TripCount;
+ }
+ if (TripCount && Count > TripCount)
+ return TripCount;
+ return Count;
}
bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
- LoopInfo *LI = &getAnalysis<LoopInfo>();
+ if (skipOptnoneFunction(L))
+ return false;
+
+ Function &F = *L->getHeader()->getParent();
+
+ LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ ScalarEvolution *SE = &getAnalysis<ScalarEvolution>();
+ const TargetTransformInfo &TTI =
+ getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
+ auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
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;
+ if (HasUnrollDisablePragma(L)) {
+ return false;
+ }
+ bool PragmaFullUnroll = HasUnrollFullPragma(L);
+ unsigned PragmaCount = UnrollCountPragmaValue(L);
+ bool HasPragma = PragmaFullUnroll || PragmaCount > 0;
- // 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
- // try to find greatest modulo of the trip count which is still under
- // threshold value.
- if (TripCount == 0)
- return false;
- Count = TripCount;
+ TargetTransformInfo::UnrollingPreferences UP;
+ getUnrollingPreferences(L, TTI, UP);
+
+ // Find trip count and trip multiple if count is not available
+ unsigned TripCount = 0;
+ unsigned TripMultiple = 1;
+ // If there are multiple exiting blocks but one of them is the latch, use the
+ // latch for the trip count estimation. Otherwise insist on a single exiting
+ // block for the trip count estimation.
+ BasicBlock *ExitingBlock = L->getLoopLatch();
+ if (!ExitingBlock || !L->isLoopExiting(ExitingBlock))
+ ExitingBlock = L->getExitingBlock();
+ if (ExitingBlock) {
+ TripCount = SE->getSmallConstantTripCount(L, ExitingBlock);
+ TripMultiple = SE->getSmallConstantTripMultiple(L, ExitingBlock);
+ }
+
+ // Select an initial unroll count. This may be reduced later based
+ // on size thresholds.
+ bool CountSetExplicitly;
+ unsigned Count = selectUnrollCount(L, TripCount, PragmaFullUnroll,
+ PragmaCount, UP, CountSetExplicitly);
+
+ unsigned NumInlineCandidates;
+ bool notDuplicatable;
+ unsigned LoopSize =
+ ApproximateLoopSize(L, NumInlineCandidates, notDuplicatable, TTI, &AC);
+ DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n");
+
+ // When computing the unrolled size, note that the conditional branch on the
+ // backedge and the comparison feeding it are not replicated like the rest of
+ // the loop body (which is why 2 is subtracted).
+ uint64_t UnrolledSize = (uint64_t)(LoopSize-2) * Count + 2;
+ 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;
+ }
+
+ unsigned NumberOfOptimizedInstructions =
+ approximateNumberOfOptimizedInstructions(L, *SE, TripCount, TTI);
+ DEBUG(dbgs() << " Complete unrolling could save: "
+ << NumberOfOptimizedInstructions << "\n");
- // Enforce the threshold.
- if (UnrollThreshold != NoThreshold) {
- unsigned NumCalls;
- unsigned LoopSize = ApproximateLoopSize(L, NumCalls);
- DEBUG(dbgs() << " Loop Size = " << LoopSize << "\n");
- if (NumCalls != 0) {
- DEBUG(dbgs() << " Not unrolling loop with function calls.\n");
+ unsigned Threshold, PartialThreshold;
+ selectThresholds(L, HasPragma, UP, Threshold, PartialThreshold,
+ NumberOfOptimizedInstructions);
+
+ // Given Count, TripCount and thresholds determine the type of
+ // unrolling which is to be performed.
+ enum { Full = 0, Partial = 1, Runtime = 2 };
+ int Unrolling;
+ if (TripCount && Count == TripCount) {
+ if (Threshold != NoThreshold && UnrolledSize > Threshold) {
+ DEBUG(dbgs() << " Too large to fully unroll with count: " << Count
+ << " because size: " << UnrolledSize << ">" << Threshold
+ << "\n");
+ Unrolling = Partial;
+ } else {
+ Unrolling = Full;
+ }
+ } else if (TripCount && Count < TripCount) {
+ Unrolling = Partial;
+ } else {
+ Unrolling = Runtime;
+ }
+
+ // Reduce count based on the type of unrolling and the threshold values.
+ unsigned OriginalCount = Count;
+ bool AllowRuntime = UserRuntime ? CurrentRuntime : UP.Runtime;
+ if (Unrolling == Partial) {
+ bool AllowPartial = UserAllowPartial ? CurrentAllowPartial : UP.Partial;
+ if (!AllowPartial && !CountSetExplicitly) {
+ DEBUG(dbgs() << " will not try to unroll partially because "
+ << "-unroll-allow-partial not given\n");
return false;
}
- uint64_t Size = (uint64_t)LoopSize*Count;
- if (TripCount != 1 && Size > UnrollThreshold) {
- DEBUG(dbgs() << " Too large to fully unroll with count: " << Count
- << " because size: " << Size << ">" << UnrollThreshold << "\n");
- if (!UnrollAllowPartial) {
- 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) {
+ if (PartialThreshold != NoThreshold && UnrolledSize > PartialThreshold) {
+ // Reduce unroll count to be modulo of TripCount for partial unrolling.
+ Count = (std::max(PartialThreshold, 3u)-2) / (LoopSize-2);
+ while (Count != 0 && TripCount % Count != 0)
Count--;
+ }
+ } else if (Unrolling == Runtime) {
+ if (!AllowRuntime && !CountSetExplicitly) {
+ DEBUG(dbgs() << " will not try to unroll loop with runtime trip count "
+ << "-unroll-runtime not given\n");
+ return false;
+ }
+ // Reduce unroll count to be the largest power-of-two factor of
+ // the original count which satisfies the threshold limit.
+ while (Count != 0 && UnrolledSize > PartialThreshold) {
+ Count >>= 1;
+ UnrolledSize = (LoopSize-2) * Count + 2;
+ }
+ if (Count > UP.MaxCount)
+ Count = UP.MaxCount;
+ DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n");
+ }
+
+ if (HasPragma) {
+ if (PragmaCount != 0)
+ // If loop has an unroll count pragma mark loop as unrolled to prevent
+ // unrolling beyond that requested by the pragma.
+ SetLoopAlreadyUnrolled(L);
+
+ // Emit optimization remarks if we are unable to unroll the loop
+ // as directed by a pragma.
+ DebugLoc LoopLoc = L->getStartLoc();
+ Function *F = Header->getParent();
+ LLVMContext &Ctx = F->getContext();
+ if (PragmaFullUnroll && PragmaCount == 0) {
+ if (TripCount && Count != TripCount) {
+ emitOptimizationRemarkMissed(
+ Ctx, DEBUG_TYPE, *F, LoopLoc,
+ "Unable to fully unroll loop as directed by unroll(full) pragma "
+ "because unrolled size is too large.");
+ } else if (!TripCount) {
+ emitOptimizationRemarkMissed(
+ Ctx, DEBUG_TYPE, *F, LoopLoc,
+ "Unable to fully unroll loop as directed by unroll(full) pragma "
+ "because loop has a runtime trip count.");
}
- if (Count < 2) {
- DEBUG(dbgs() << " could not unroll partially\n");
- return false;
- }
- DEBUG(dbgs() << " partially unrolling with count: " << Count << "\n");
+ } else if (PragmaCount > 0 && Count != OriginalCount) {
+ emitOptimizationRemarkMissed(
+ Ctx, DEBUG_TYPE, *F, LoopLoc,
+ "Unable to unroll loop the number of times directed by "
+ "unroll_count pragma because unrolled size is too large.");
}
}
+ if (Unrolling != Full && Count < 2) {
+ // Partial unrolling by 1 is a nop. For full unrolling, a factor
+ // of 1 makes sense because loop control can be eliminated.
+ return false;
+ }
+
// Unroll the loop.
- Function *F = L->getHeader()->getParent();
- if (!UnrollLoop(L, Count, LI, &LPM))
+ if (!UnrollLoop(L, Count, TripCount, AllowRuntime, TripMultiple, LI, this,
+ &LPM, &AC))
return false;
- // FIXME: Reconstruct dom info, because it is not preserved properly.
- DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
- if (DT) {
- DT->runOnFunction(*F);
- DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
- if (DF)
- DF->runOnFunction(*F);
- }
return true;
}
projects / oota-llvm.git / blobdiff