| //===- llvm/Transforms/Vectorize/LoopVectorizationLegality.h ----*- C++ -*-===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| /// \file |
| /// This file defines the LoopVectorizationLegality class. Original code |
| /// in Loop Vectorizer has been moved out to its own file for modularity |
| /// and reusability. |
| /// |
| /// Currently, it works for innermost loop vectorization. Extending this to |
| /// outer loop vectorization is a TODO item. |
| /// |
| /// Also provides: |
| /// 1) LoopVectorizeHints class which keeps a number of loop annotations |
| /// locally for easy look up. It has the ability to write them back as |
| /// loop metadata, upon request. |
| /// 2) LoopVectorizationRequirements class for lazy bail out for the purpose |
| /// of reporting useful failure to vectorize message. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZATIONLEGALITY_H |
| #define LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZATIONLEGALITY_H |
| |
| #include "llvm/ADT/MapVector.h" |
| #include "llvm/Analysis/LoopAccessAnalysis.h" |
| #include "llvm/Analysis/OptimizationRemarkEmitter.h" |
| #include "llvm/Transforms/Utils/LoopUtils.h" |
| |
| namespace llvm { |
| |
| /// Create an analysis remark that explains why vectorization failed |
| /// |
| /// \p PassName is the name of the pass (e.g. can be AlwaysPrint). \p |
| /// RemarkName is the identifier for the remark. If \p I is passed it is an |
| /// instruction that prevents vectorization. Otherwise \p TheLoop is used for |
| /// the location of the remark. \return the remark object that can be |
| /// streamed to. |
| OptimizationRemarkAnalysis createLVMissedAnalysis(const char *PassName, |
| StringRef RemarkName, |
| Loop *TheLoop, |
| Instruction *I = nullptr); |
| |
| /// Utility class for getting and setting loop vectorizer hints in the form |
| /// of loop metadata. |
| /// This class keeps a number of loop annotations locally (as member variables) |
| /// and can, upon request, write them back as metadata on the loop. It will |
| /// initially scan the loop for existing metadata, and will update the local |
| /// values based on information in the loop. |
| /// We cannot write all values to metadata, as the mere presence of some info, |
| /// for example 'force', means a decision has been made. So, we need to be |
| /// careful NOT to add them if the user hasn't specifically asked so. |
| class LoopVectorizeHints { |
| enum HintKind { HK_WIDTH, HK_UNROLL, HK_FORCE, HK_ISVECTORIZED }; |
| |
| /// Hint - associates name and validation with the hint value. |
| struct Hint { |
| const char *Name; |
| unsigned Value; // This may have to change for non-numeric values. |
| HintKind Kind; |
| |
| Hint(const char *Name, unsigned Value, HintKind Kind) |
| : Name(Name), Value(Value), Kind(Kind) {} |
| |
| bool validate(unsigned Val); |
| }; |
| |
| /// Vectorization width. |
| Hint Width; |
| |
| /// Vectorization interleave factor. |
| Hint Interleave; |
| |
| /// Vectorization forced |
| Hint Force; |
| |
| /// Already Vectorized |
| Hint IsVectorized; |
| |
| /// Return the loop metadata prefix. |
| static StringRef Prefix() { return "llvm.loop."; } |
| |
| /// True if there is any unsafe math in the loop. |
| bool PotentiallyUnsafe = false; |
| |
| public: |
| enum ForceKind { |
| FK_Undefined = -1, ///< Not selected. |
| FK_Disabled = 0, ///< Forcing disabled. |
| FK_Enabled = 1, ///< Forcing enabled. |
| }; |
| |
| LoopVectorizeHints(const Loop *L, bool InterleaveOnlyWhenForced, |
| OptimizationRemarkEmitter &ORE); |
| |
| /// Mark the loop L as already vectorized by setting the width to 1. |
| void setAlreadyVectorized(); |
| |
| bool allowVectorization(Function *F, Loop *L, |
| bool VectorizeOnlyWhenForced) const; |
| |
| /// Dumps all the hint information. |
| void emitRemarkWithHints() const; |
| |
| unsigned getWidth() const { return Width.Value; } |
| unsigned getInterleave() const { return Interleave.Value; } |
| unsigned getIsVectorized() const { return IsVectorized.Value; } |
| enum ForceKind getForce() const { |
| if ((ForceKind)Force.Value == FK_Undefined && |
| hasDisableAllTransformsHint(TheLoop)) |
| return FK_Disabled; |
| return (ForceKind)Force.Value; |
| } |
| |
| /// If hints are provided that force vectorization, use the AlwaysPrint |
| /// pass name to force the frontend to print the diagnostic. |
| const char *vectorizeAnalysisPassName() const; |
| |
| bool allowReordering() const { |
| // When enabling loop hints are provided we allow the vectorizer to change |
| // the order of operations that is given by the scalar loop. This is not |
| // enabled by default because can be unsafe or inefficient. For example, |
| // reordering floating-point operations will change the way round-off |
| // error accumulates in the loop. |
| return getForce() == LoopVectorizeHints::FK_Enabled || getWidth() > 1; |
| } |
| |
| bool isPotentiallyUnsafe() const { |
| // Avoid FP vectorization if the target is unsure about proper support. |
| // This may be related to the SIMD unit in the target not handling |
| // IEEE 754 FP ops properly, or bad single-to-double promotions. |
| // Otherwise, a sequence of vectorized loops, even without reduction, |
| // could lead to different end results on the destination vectors. |
| return getForce() != LoopVectorizeHints::FK_Enabled && PotentiallyUnsafe; |
| } |
| |
| void setPotentiallyUnsafe() { PotentiallyUnsafe = true; } |
| |
| private: |
| /// Find hints specified in the loop metadata and update local values. |
| void getHintsFromMetadata(); |
| |
| /// Checks string hint with one operand and set value if valid. |
| void setHint(StringRef Name, Metadata *Arg); |
| |
| /// The loop these hints belong to. |
| const Loop *TheLoop; |
| |
| /// Interface to emit optimization remarks. |
| OptimizationRemarkEmitter &ORE; |
| }; |
| |
| /// This holds vectorization requirements that must be verified late in |
| /// the process. The requirements are set by legalize and costmodel. Once |
| /// vectorization has been determined to be possible and profitable the |
| /// requirements can be verified by looking for metadata or compiler options. |
| /// For example, some loops require FP commutativity which is only allowed if |
| /// vectorization is explicitly specified or if the fast-math compiler option |
| /// has been provided. |
| /// Late evaluation of these requirements allows helpful diagnostics to be |
| /// composed that tells the user what need to be done to vectorize the loop. For |
| /// example, by specifying #pragma clang loop vectorize or -ffast-math. Late |
| /// evaluation should be used only when diagnostics can generated that can be |
| /// followed by a non-expert user. |
| class LoopVectorizationRequirements { |
| public: |
| LoopVectorizationRequirements(OptimizationRemarkEmitter &ORE) : ORE(ORE) {} |
| |
| void addUnsafeAlgebraInst(Instruction *I) { |
| // First unsafe algebra instruction. |
| if (!UnsafeAlgebraInst) |
| UnsafeAlgebraInst = I; |
| } |
| |
| void addRuntimePointerChecks(unsigned Num) { NumRuntimePointerChecks = Num; } |
| |
| bool doesNotMeet(Function *F, Loop *L, const LoopVectorizeHints &Hints); |
| |
| private: |
| unsigned NumRuntimePointerChecks = 0; |
| Instruction *UnsafeAlgebraInst = nullptr; |
| |
| /// Interface to emit optimization remarks. |
| OptimizationRemarkEmitter &ORE; |
| }; |
| |
| /// LoopVectorizationLegality checks if it is legal to vectorize a loop, and |
| /// to what vectorization factor. |
| /// This class does not look at the profitability of vectorization, only the |
| /// legality. This class has two main kinds of checks: |
| /// * Memory checks - The code in canVectorizeMemory checks if vectorization |
| /// will change the order of memory accesses in a way that will change the |
| /// correctness of the program. |
| /// * Scalars checks - The code in canVectorizeInstrs and canVectorizeMemory |
| /// checks for a number of different conditions, such as the availability of a |
| /// single induction variable, that all types are supported and vectorize-able, |
| /// etc. This code reflects the capabilities of InnerLoopVectorizer. |
| /// This class is also used by InnerLoopVectorizer for identifying |
| /// induction variable and the different reduction variables. |
| class LoopVectorizationLegality { |
| public: |
| LoopVectorizationLegality( |
| Loop *L, PredicatedScalarEvolution &PSE, DominatorTree *DT, |
| TargetTransformInfo *TTI, TargetLibraryInfo *TLI, AliasAnalysis *AA, |
| Function *F, std::function<const LoopAccessInfo &(Loop &)> *GetLAA, |
| LoopInfo *LI, OptimizationRemarkEmitter *ORE, |
| LoopVectorizationRequirements *R, LoopVectorizeHints *H, DemandedBits *DB, |
| AssumptionCache *AC) |
| : TheLoop(L), LI(LI), PSE(PSE), TTI(TTI), TLI(TLI), DT(DT), |
| GetLAA(GetLAA), ORE(ORE), Requirements(R), Hints(H), DB(DB), AC(AC) {} |
| |
| /// ReductionList contains the reduction descriptors for all |
| /// of the reductions that were found in the loop. |
| using ReductionList = DenseMap<PHINode *, RecurrenceDescriptor>; |
| |
| /// InductionList saves induction variables and maps them to the |
| /// induction descriptor. |
| using InductionList = MapVector<PHINode *, InductionDescriptor>; |
| |
| /// RecurrenceSet contains the phi nodes that are recurrences other than |
| /// inductions and reductions. |
| using RecurrenceSet = SmallPtrSet<const PHINode *, 8>; |
| |
| /// Returns true if it is legal to vectorize this loop. |
| /// This does not mean that it is profitable to vectorize this |
| /// loop, only that it is legal to do so. |
| /// Temporarily taking UseVPlanNativePath parameter. If true, take |
| /// the new code path being implemented for outer loop vectorization |
| /// (should be functional for inner loop vectorization) based on VPlan. |
| /// If false, good old LV code. |
| bool canVectorize(bool UseVPlanNativePath); |
| |
| /// Return true if we can vectorize this loop while folding its tail by |
| /// masking. |
| bool canFoldTailByMasking(); |
| |
| /// Returns the primary induction variable. |
| PHINode *getPrimaryInduction() { return PrimaryInduction; } |
| |
| /// Returns the reduction variables found in the loop. |
| ReductionList *getReductionVars() { return &Reductions; } |
| |
| /// Returns the induction variables found in the loop. |
| InductionList *getInductionVars() { return &Inductions; } |
| |
| /// Return the first-order recurrences found in the loop. |
| RecurrenceSet *getFirstOrderRecurrences() { return &FirstOrderRecurrences; } |
| |
| /// Return the set of instructions to sink to handle first-order recurrences. |
| DenseMap<Instruction *, Instruction *> &getSinkAfter() { return SinkAfter; } |
| |
| /// Returns the widest induction type. |
| Type *getWidestInductionType() { return WidestIndTy; } |
| |
| /// Returns True if V is a Phi node of an induction variable in this loop. |
| bool isInductionPhi(const Value *V); |
| |
| /// Returns True if V is a cast that is part of an induction def-use chain, |
| /// and had been proven to be redundant under a runtime guard (in other |
| /// words, the cast has the same SCEV expression as the induction phi). |
| bool isCastedInductionVariable(const Value *V); |
| |
| /// Returns True if V can be considered as an induction variable in this |
| /// loop. V can be the induction phi, or some redundant cast in the def-use |
| /// chain of the inducion phi. |
| bool isInductionVariable(const Value *V); |
| |
| /// Returns True if PN is a reduction variable in this loop. |
| bool isReductionVariable(PHINode *PN) { return Reductions.count(PN); } |
| |
| /// Returns True if Phi is a first-order recurrence in this loop. |
| bool isFirstOrderRecurrence(const PHINode *Phi); |
| |
| /// Return true if the block BB needs to be predicated in order for the loop |
| /// to be vectorized. |
| bool blockNeedsPredication(BasicBlock *BB); |
| |
| /// Check if this pointer is consecutive when vectorizing. This happens |
| /// when the last index of the GEP is the induction variable, or that the |
| /// pointer itself is an induction variable. |
| /// This check allows us to vectorize A[idx] into a wide load/store. |
| /// Returns: |
| /// 0 - Stride is unknown or non-consecutive. |
| /// 1 - Address is consecutive. |
| /// -1 - Address is consecutive, and decreasing. |
| /// NOTE: This method must only be used before modifying the original scalar |
| /// loop. Do not use after invoking 'createVectorizedLoopSkeleton' (PR34965). |
| int isConsecutivePtr(Value *Ptr); |
| |
| /// Returns true if the value V is uniform within the loop. |
| bool isUniform(Value *V); |
| |
| /// Returns the information that we collected about runtime memory check. |
| const RuntimePointerChecking *getRuntimePointerChecking() const { |
| return LAI->getRuntimePointerChecking(); |
| } |
| |
| const LoopAccessInfo *getLAI() const { return LAI; } |
| |
| unsigned getMaxSafeDepDistBytes() { return LAI->getMaxSafeDepDistBytes(); } |
| |
| uint64_t getMaxSafeRegisterWidth() const { |
| return LAI->getDepChecker().getMaxSafeRegisterWidth(); |
| } |
| |
| bool hasStride(Value *V) { return LAI->hasStride(V); } |
| |
| /// Returns true if vector representation of the instruction \p I |
| /// requires mask. |
| bool isMaskRequired(const Instruction *I) { return (MaskedOp.count(I) != 0); } |
| |
| unsigned getNumStores() const { return LAI->getNumStores(); } |
| unsigned getNumLoads() const { return LAI->getNumLoads(); } |
| |
| // Returns true if the NoNaN attribute is set on the function. |
| bool hasFunNoNaNAttr() const { return HasFunNoNaNAttr; } |
| |
| private: |
| /// Return true if the pre-header, exiting and latch blocks of \p Lp and all |
| /// its nested loops are considered legal for vectorization. These legal |
| /// checks are common for inner and outer loop vectorization. |
| /// Temporarily taking UseVPlanNativePath parameter. If true, take |
| /// the new code path being implemented for outer loop vectorization |
| /// (should be functional for inner loop vectorization) based on VPlan. |
| /// If false, good old LV code. |
| bool canVectorizeLoopNestCFG(Loop *Lp, bool UseVPlanNativePath); |
| |
| /// Set up outer loop inductions by checking Phis in outer loop header for |
| /// supported inductions (int inductions). Return false if any of these Phis |
| /// is not a supported induction or if we fail to find an induction. |
| bool setupOuterLoopInductions(); |
| |
| /// Return true if the pre-header, exiting and latch blocks of \p Lp |
| /// (non-recursive) are considered legal for vectorization. |
| /// Temporarily taking UseVPlanNativePath parameter. If true, take |
| /// the new code path being implemented for outer loop vectorization |
| /// (should be functional for inner loop vectorization) based on VPlan. |
| /// If false, good old LV code. |
| bool canVectorizeLoopCFG(Loop *Lp, bool UseVPlanNativePath); |
| |
| /// Check if a single basic block loop is vectorizable. |
| /// At this point we know that this is a loop with a constant trip count |
| /// and we only need to check individual instructions. |
| bool canVectorizeInstrs(); |
| |
| /// When we vectorize loops we may change the order in which |
| /// we read and write from memory. This method checks if it is |
| /// legal to vectorize the code, considering only memory constrains. |
| /// Returns true if the loop is vectorizable |
| bool canVectorizeMemory(); |
| |
| /// Return true if we can vectorize this loop using the IF-conversion |
| /// transformation. |
| bool canVectorizeWithIfConvert(); |
| |
| /// Return true if we can vectorize this outer loop. The method performs |
| /// specific checks for outer loop vectorization. |
| bool canVectorizeOuterLoop(); |
| |
| /// Return true if all of the instructions in the block can be speculatively |
| /// executed. \p SafePtrs is a list of addresses that are known to be legal |
| /// and we know that we can read from them without segfault. |
| bool blockCanBePredicated(BasicBlock *BB, SmallPtrSetImpl<Value *> &SafePtrs); |
| |
| /// Updates the vectorization state by adding \p Phi to the inductions list. |
| /// This can set \p Phi as the main induction of the loop if \p Phi is a |
| /// better choice for the main induction than the existing one. |
| void addInductionPhi(PHINode *Phi, const InductionDescriptor &ID, |
| SmallPtrSetImpl<Value *> &AllowedExit); |
| |
| /// If an access has a symbolic strides, this maps the pointer value to |
| /// the stride symbol. |
| const ValueToValueMap *getSymbolicStrides() { |
| // FIXME: Currently, the set of symbolic strides is sometimes queried before |
| // it's collected. This happens from canVectorizeWithIfConvert, when the |
| // pointer is checked to reference consecutive elements suitable for a |
| // masked access. |
| return LAI ? &LAI->getSymbolicStrides() : nullptr; |
| } |
| |
| /// Reports a vectorization illegality: print \p DebugMsg for debugging |
| /// purposes along with the corresponding optimization remark \p RemarkName. |
| /// If \p I is passed it is an instruction that prevents vectorization. |
| /// Otherwise the loop is used for the location of the remark. |
| void reportVectorizationFailure(const StringRef DebugMsg, |
| const StringRef OREMsg, const StringRef ORETag, |
| Instruction *I = nullptr) const; |
| |
| /// The loop that we evaluate. |
| Loop *TheLoop; |
| |
| /// Loop Info analysis. |
| LoopInfo *LI; |
| |
| /// A wrapper around ScalarEvolution used to add runtime SCEV checks. |
| /// Applies dynamic knowledge to simplify SCEV expressions in the context |
| /// of existing SCEV assumptions. The analysis will also add a minimal set |
| /// of new predicates if this is required to enable vectorization and |
| /// unrolling. |
| PredicatedScalarEvolution &PSE; |
| |
| /// Target Transform Info. |
| TargetTransformInfo *TTI; |
| |
| /// Target Library Info. |
| TargetLibraryInfo *TLI; |
| |
| /// Dominator Tree. |
| DominatorTree *DT; |
| |
| // LoopAccess analysis. |
| std::function<const LoopAccessInfo &(Loop &)> *GetLAA; |
| |
| // And the loop-accesses info corresponding to this loop. This pointer is |
| // null until canVectorizeMemory sets it up. |
| const LoopAccessInfo *LAI = nullptr; |
| |
| /// Interface to emit optimization remarks. |
| OptimizationRemarkEmitter *ORE; |
| |
| // --- vectorization state --- // |
| |
| /// Holds the primary induction variable. This is the counter of the |
| /// loop. |
| PHINode *PrimaryInduction = nullptr; |
| |
| /// Holds the reduction variables. |
| ReductionList Reductions; |
| |
| /// Holds all of the induction variables that we found in the loop. |
| /// Notice that inductions don't need to start at zero and that induction |
| /// variables can be pointers. |
| InductionList Inductions; |
| |
| /// Holds all the casts that participate in the update chain of the induction |
| /// variables, and that have been proven to be redundant (possibly under a |
| /// runtime guard). These casts can be ignored when creating the vectorized |
| /// loop body. |
| SmallPtrSet<Instruction *, 4> InductionCastsToIgnore; |
| |
| /// Holds the phi nodes that are first-order recurrences. |
| RecurrenceSet FirstOrderRecurrences; |
| |
| /// Holds instructions that need to sink past other instructions to handle |
| /// first-order recurrences. |
| DenseMap<Instruction *, Instruction *> SinkAfter; |
| |
| /// Holds the widest induction type encountered. |
| Type *WidestIndTy = nullptr; |
| |
| /// Allowed outside users. This holds the induction and reduction |
| /// vars which can be accessed from outside the loop. |
| SmallPtrSet<Value *, 4> AllowedExit; |
| |
| /// Can we assume the absence of NaNs. |
| bool HasFunNoNaNAttr = false; |
| |
| /// Vectorization requirements that will go through late-evaluation. |
| LoopVectorizationRequirements *Requirements; |
| |
| /// Used to emit an analysis of any legality issues. |
| LoopVectorizeHints *Hints; |
| |
| /// The demanded bits analysis is used to compute the minimum type size in |
| /// which a reduction can be computed. |
| DemandedBits *DB; |
| |
| /// The assumption cache analysis is used to compute the minimum type size in |
| /// which a reduction can be computed. |
| AssumptionCache *AC; |
| |
| /// While vectorizing these instructions we have to generate a |
| /// call to the appropriate masked intrinsic |
| SmallPtrSet<const Instruction *, 8> MaskedOp; |
| }; |
| |
| } // namespace llvm |
| |
| #endif // LLVM_TRANSFORMS_VECTORIZE_LOOPVECTORIZATIONLEGALITY_H |