| //===- llvm/Transforms/Utils/LoopUtils.h - Loop utilities -------*- 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file defines some loop transformation utilities. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_TRANSFORMS_UTILS_LOOPUTILS_H |
| #define LLVM_TRANSFORMS_UTILS_LOOPUTILS_H |
| |
| #include "llvm/ADT/StringRef.h" |
| #include "llvm/Analysis/IVDescriptors.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/Transforms/Utils/ValueMapper.h" |
| |
| namespace llvm { |
| |
| template <typename T> class DomTreeNodeBase; |
| using DomTreeNode = DomTreeNodeBase<BasicBlock>; |
| class AAResults; |
| class AliasSet; |
| class AliasSetTracker; |
| class BasicBlock; |
| class BlockFrequencyInfo; |
| class IRBuilderBase; |
| class Loop; |
| class LoopInfo; |
| class MemoryAccess; |
| class MemorySSA; |
| class MemorySSAUpdater; |
| class OptimizationRemarkEmitter; |
| class PredIteratorCache; |
| class ScalarEvolution; |
| class SCEV; |
| class SCEVExpander; |
| class TargetLibraryInfo; |
| class LPPassManager; |
| class Instruction; |
| struct RuntimeCheckingPtrGroup; |
| typedef std::pair<const RuntimeCheckingPtrGroup *, |
| const RuntimeCheckingPtrGroup *> |
| RuntimePointerCheck; |
| |
| template <typename T> class Optional; |
| template <typename T, unsigned N> class SmallSetVector; |
| template <typename T, unsigned N> class SmallVector; |
| template <typename T> class SmallVectorImpl; |
| template <typename T, unsigned N> class SmallPriorityWorklist; |
| |
| BasicBlock *InsertPreheaderForLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, |
| MemorySSAUpdater *MSSAU, bool PreserveLCSSA); |
| |
| /// Ensure that all exit blocks of the loop are dedicated exits. |
| /// |
| /// For any loop exit block with non-loop predecessors, we split the loop |
| /// predecessors to use a dedicated loop exit block. We update the dominator |
| /// tree and loop info if provided, and will preserve LCSSA if requested. |
| bool formDedicatedExitBlocks(Loop *L, DominatorTree *DT, LoopInfo *LI, |
| MemorySSAUpdater *MSSAU, bool PreserveLCSSA); |
| |
| /// Ensures LCSSA form for every instruction from the Worklist in the scope of |
| /// innermost containing loop. |
| /// |
| /// For the given instruction which have uses outside of the loop, an LCSSA PHI |
| /// node is inserted and the uses outside the loop are rewritten to use this |
| /// node. |
| /// |
| /// LoopInfo and DominatorTree are required and, since the routine makes no |
| /// changes to CFG, preserved. |
| /// |
| /// Returns true if any modifications are made. |
| /// |
| /// This function may introduce unused PHI nodes. If \p PHIsToRemove is not |
| /// nullptr, those are added to it (before removing, the caller has to check if |
| /// they still do not have any uses). Otherwise the PHIs are directly removed. |
| bool formLCSSAForInstructions( |
| SmallVectorImpl<Instruction *> &Worklist, const DominatorTree &DT, |
| const LoopInfo &LI, ScalarEvolution *SE, IRBuilderBase &Builder, |
| SmallVectorImpl<PHINode *> *PHIsToRemove = nullptr); |
| |
| /// Put loop into LCSSA form. |
| /// |
| /// Looks at all instructions in the loop which have uses outside of the |
| /// current loop. For each, an LCSSA PHI node is inserted and the uses outside |
| /// the loop are rewritten to use this node. Sub-loops must be in LCSSA form |
| /// already. |
| /// |
| /// LoopInfo and DominatorTree are required and preserved. |
| /// |
| /// If ScalarEvolution is passed in, it will be preserved. |
| /// |
| /// Returns true if any modifications are made to the loop. |
| bool formLCSSA(Loop &L, const DominatorTree &DT, const LoopInfo *LI, |
| ScalarEvolution *SE); |
| |
| /// Put a loop nest into LCSSA form. |
| /// |
| /// This recursively forms LCSSA for a loop nest. |
| /// |
| /// LoopInfo and DominatorTree are required and preserved. |
| /// |
| /// If ScalarEvolution is passed in, it will be preserved. |
| /// |
| /// Returns true if any modifications are made to the loop. |
| bool formLCSSARecursively(Loop &L, const DominatorTree &DT, const LoopInfo *LI, |
| ScalarEvolution *SE); |
| |
| struct SinkAndHoistLICMFlags { |
| bool NoOfMemAccTooLarge; |
| unsigned LicmMssaOptCounter; |
| unsigned LicmMssaOptCap; |
| unsigned LicmMssaNoAccForPromotionCap; |
| bool IsSink; |
| }; |
| |
| /// Walk the specified region of the CFG (defined by all blocks |
| /// dominated by the specified block, and that are in the current loop) in |
| /// reverse depth first order w.r.t the DominatorTree. This allows us to visit |
| /// uses before definitions, allowing us to sink a loop body in one pass without |
| /// iteration. Takes DomTreeNode, AAResults, LoopInfo, DominatorTree, |
| /// BlockFrequencyInfo, TargetLibraryInfo, Loop, AliasSet information for all |
| /// instructions of the loop and loop safety information as |
| /// arguments. Diagnostics is emitted via \p ORE. It returns changed status. |
| bool sinkRegion(DomTreeNode *, AAResults *, LoopInfo *, DominatorTree *, |
| BlockFrequencyInfo *, TargetLibraryInfo *, |
| TargetTransformInfo *, Loop *, AliasSetTracker *, |
| MemorySSAUpdater *, ICFLoopSafetyInfo *, |
| SinkAndHoistLICMFlags &, OptimizationRemarkEmitter *); |
| |
| /// Walk the specified region of the CFG (defined by all blocks |
| /// dominated by the specified block, and that are in the current loop) in depth |
| /// first order w.r.t the DominatorTree. This allows us to visit definitions |
| /// before uses, allowing us to hoist a loop body in one pass without iteration. |
| /// Takes DomTreeNode, AAResults, LoopInfo, DominatorTree, |
| /// BlockFrequencyInfo, TargetLibraryInfo, Loop, AliasSet information for all |
| /// instructions of the loop and loop safety information as arguments. |
| /// Diagnostics is emitted via \p ORE. It returns changed status. |
| bool hoistRegion(DomTreeNode *, AAResults *, LoopInfo *, DominatorTree *, |
| BlockFrequencyInfo *, TargetLibraryInfo *, Loop *, |
| AliasSetTracker *, MemorySSAUpdater *, ScalarEvolution *, |
| ICFLoopSafetyInfo *, SinkAndHoistLICMFlags &, |
| OptimizationRemarkEmitter *); |
| |
| /// This function deletes dead loops. The caller of this function needs to |
| /// guarantee that the loop is infact dead. |
| /// The function requires a bunch or prerequisites to be present: |
| /// - The loop needs to be in LCSSA form |
| /// - The loop needs to have a Preheader |
| /// - A unique dedicated exit block must exist |
| /// |
| /// This also updates the relevant analysis information in \p DT, \p SE, \p LI |
| /// and \p MSSA if pointers to those are provided. |
| /// It also updates the loop PM if an updater struct is provided. |
| |
| void deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE, |
| LoopInfo *LI, MemorySSA *MSSA = nullptr); |
| |
| /// Try to promote memory values to scalars by sinking stores out of |
| /// the loop and moving loads to before the loop. We do this by looping over |
| /// the stores in the loop, looking for stores to Must pointers which are |
| /// loop invariant. It takes a set of must-alias values, Loop exit blocks |
| /// vector, loop exit blocks insertion point vector, PredIteratorCache, |
| /// LoopInfo, DominatorTree, Loop, AliasSet information for all instructions |
| /// of the loop and loop safety information as arguments. |
| /// Diagnostics is emitted via \p ORE. It returns changed status. |
| bool promoteLoopAccessesToScalars( |
| const SmallSetVector<Value *, 8> &, SmallVectorImpl<BasicBlock *> &, |
| SmallVectorImpl<Instruction *> &, SmallVectorImpl<MemoryAccess *> &, |
| PredIteratorCache &, LoopInfo *, DominatorTree *, const TargetLibraryInfo *, |
| Loop *, AliasSetTracker *, MemorySSAUpdater *, ICFLoopSafetyInfo *, |
| OptimizationRemarkEmitter *); |
| |
| /// Does a BFS from a given node to all of its children inside a given loop. |
| /// The returned vector of nodes includes the starting point. |
| SmallVector<DomTreeNode *, 16> collectChildrenInLoop(DomTreeNode *N, |
| const Loop *CurLoop); |
| |
| /// Returns the instructions that use values defined in the loop. |
| SmallVector<Instruction *, 8> findDefsUsedOutsideOfLoop(Loop *L); |
| |
| /// Find string metadata for loop |
| /// |
| /// If it has a value (e.g. {"llvm.distribute", 1} return the value as an |
| /// operand or null otherwise. If the string metadata is not found return |
| /// Optional's not-a-value. |
| Optional<const MDOperand *> findStringMetadataForLoop(const Loop *TheLoop, |
| StringRef Name); |
| |
| /// Find named metadata for a loop with an integer value. |
| llvm::Optional<int> getOptionalIntLoopAttribute(Loop *TheLoop, StringRef Name); |
| |
| /// Create a new loop identifier for a loop created from a loop transformation. |
| /// |
| /// @param OrigLoopID The loop ID of the loop before the transformation. |
| /// @param FollowupAttrs List of attribute names that contain attributes to be |
| /// added to the new loop ID. |
| /// @param InheritOptionsAttrsPrefix Selects which attributes should be inherited |
| /// from the original loop. The following values |
| /// are considered: |
| /// nullptr : Inherit all attributes from @p OrigLoopID. |
| /// "" : Do not inherit any attribute from @p OrigLoopID; only use |
| /// those specified by a followup attribute. |
| /// "<prefix>": Inherit all attributes except those which start with |
| /// <prefix>; commonly used to remove metadata for the |
| /// applied transformation. |
| /// @param AlwaysNew If true, do not try to reuse OrigLoopID and never return |
| /// None. |
| /// |
| /// @return The loop ID for the after-transformation loop. The following values |
| /// can be returned: |
| /// None : No followup attribute was found; it is up to the |
| /// transformation to choose attributes that make sense. |
| /// @p OrigLoopID: The original identifier can be reused. |
| /// nullptr : The new loop has no attributes. |
| /// MDNode* : A new unique loop identifier. |
| Optional<MDNode *> |
| makeFollowupLoopID(MDNode *OrigLoopID, ArrayRef<StringRef> FollowupAttrs, |
| const char *InheritOptionsAttrsPrefix = "", |
| bool AlwaysNew = false); |
| |
| /// Look for the loop attribute that disables all transformation heuristic. |
| bool hasDisableAllTransformsHint(const Loop *L); |
| |
| /// Look for the loop attribute that disables the LICM transformation heuristics. |
| bool hasDisableLICMTransformsHint(const Loop *L); |
| |
| /// The mode sets how eager a transformation should be applied. |
| enum TransformationMode { |
| /// The pass can use heuristics to determine whether a transformation should |
| /// be applied. |
| TM_Unspecified, |
| |
| /// The transformation should be applied without considering a cost model. |
| TM_Enable, |
| |
| /// The transformation should not be applied. |
| TM_Disable, |
| |
| /// Force is a flag and should not be used alone. |
| TM_Force = 0x04, |
| |
| /// The transformation was directed by the user, e.g. by a #pragma in |
| /// the source code. If the transformation could not be applied, a |
| /// warning should be emitted. |
| TM_ForcedByUser = TM_Enable | TM_Force, |
| |
| /// The transformation must not be applied. For instance, `#pragma clang loop |
| /// unroll(disable)` explicitly forbids any unrolling to take place. Unlike |
| /// general loop metadata, it must not be dropped. Most passes should not |
| /// behave differently under TM_Disable and TM_SuppressedByUser. |
| TM_SuppressedByUser = TM_Disable | TM_Force |
| }; |
| |
| /// @{ |
| /// Get the mode for LLVM's supported loop transformations. |
| TransformationMode hasUnrollTransformation(Loop *L); |
| TransformationMode hasUnrollAndJamTransformation(Loop *L); |
| TransformationMode hasVectorizeTransformation(Loop *L); |
| TransformationMode hasDistributeTransformation(Loop *L); |
| TransformationMode hasLICMVersioningTransformation(Loop *L); |
| /// @} |
| |
| /// Set input string into loop metadata by keeping other values intact. |
| /// If the string is already in loop metadata update value if it is |
| /// different. |
| void addStringMetadataToLoop(Loop *TheLoop, const char *MDString, |
| unsigned V = 0); |
| |
| /// Returns a loop's estimated trip count based on branch weight metadata. |
| /// In addition if \p EstimatedLoopInvocationWeight is not null it is |
| /// initialized with weight of loop's latch leading to the exit. |
| /// Returns 0 when the count is estimated to be 0, or None when a meaningful |
| /// estimate can not be made. |
| Optional<unsigned> |
| getLoopEstimatedTripCount(Loop *L, |
| unsigned *EstimatedLoopInvocationWeight = nullptr); |
| |
| /// Set a loop's branch weight metadata to reflect that loop has \p |
| /// EstimatedTripCount iterations and \p EstimatedLoopInvocationWeight exits |
| /// through latch. Returns true if metadata is successfully updated, false |
| /// otherwise. Note that loop must have a latch block which controls loop exit |
| /// in order to succeed. |
| bool setLoopEstimatedTripCount(Loop *L, unsigned EstimatedTripCount, |
| unsigned EstimatedLoopInvocationWeight); |
| |
| /// Check inner loop (L) backedge count is known to be invariant on all |
| /// iterations of its outer loop. If the loop has no parent, this is trivially |
| /// true. |
| bool hasIterationCountInvariantInParent(Loop *L, ScalarEvolution &SE); |
| |
| /// Helper to consistently add the set of standard passes to a loop pass's \c |
| /// AnalysisUsage. |
| /// |
| /// All loop passes should call this as part of implementing their \c |
| /// getAnalysisUsage. |
| void getLoopAnalysisUsage(AnalysisUsage &AU); |
| |
| /// Returns true if is legal to hoist or sink this instruction disregarding the |
| /// possible introduction of faults. Reasoning about potential faulting |
| /// instructions is the responsibility of the caller since it is challenging to |
| /// do efficiently from within this routine. |
| /// \p TargetExecutesOncePerLoop is true only when it is guaranteed that the |
| /// target executes at most once per execution of the loop body. This is used |
| /// to assess the legality of duplicating atomic loads. Generally, this is |
| /// true when moving out of loop and not true when moving into loops. |
| /// If \p ORE is set use it to emit optimization remarks. |
| bool canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT, |
| Loop *CurLoop, AliasSetTracker *CurAST, |
| MemorySSAUpdater *MSSAU, bool TargetExecutesOncePerLoop, |
| SinkAndHoistLICMFlags *LICMFlags = nullptr, |
| OptimizationRemarkEmitter *ORE = nullptr); |
| |
| /// Returns a Min/Max operation corresponding to MinMaxRecurrenceKind. |
| Value *createMinMaxOp(IRBuilderBase &Builder, |
| RecurrenceDescriptor::MinMaxRecurrenceKind RK, |
| Value *Left, Value *Right); |
| |
| /// Generates an ordered vector reduction using extracts to reduce the value. |
| Value * |
| getOrderedReduction(IRBuilderBase &Builder, Value *Acc, Value *Src, unsigned Op, |
| RecurrenceDescriptor::MinMaxRecurrenceKind MinMaxKind = |
| RecurrenceDescriptor::MRK_Invalid, |
| ArrayRef<Value *> RedOps = None); |
| |
| /// Generates a vector reduction using shufflevectors to reduce the value. |
| /// Fast-math-flags are propagated using the IRBuilder's setting. |
| Value *getShuffleReduction(IRBuilderBase &Builder, Value *Src, unsigned Op, |
| RecurrenceDescriptor::MinMaxRecurrenceKind |
| MinMaxKind = RecurrenceDescriptor::MRK_Invalid, |
| ArrayRef<Value *> RedOps = None); |
| |
| /// Create a target reduction of the given vector. The reduction operation |
| /// is described by the \p Opcode parameter. min/max reductions require |
| /// additional information supplied in \p Flags. |
| /// The target is queried to determine if intrinsics or shuffle sequences are |
| /// required to implement the reduction. |
| /// Fast-math-flags are propagated using the IRBuilder's setting. |
| Value *createSimpleTargetReduction(IRBuilderBase &B, |
| const TargetTransformInfo *TTI, |
| unsigned Opcode, Value *Src, |
| TargetTransformInfo::ReductionFlags Flags = |
| TargetTransformInfo::ReductionFlags(), |
| ArrayRef<Value *> RedOps = None); |
| |
| /// Create a generic target reduction using a recurrence descriptor \p Desc |
| /// The target is queried to determine if intrinsics or shuffle sequences are |
| /// required to implement the reduction. |
| /// Fast-math-flags are propagated using the RecurrenceDescriptor. |
| Value *createTargetReduction(IRBuilderBase &B, const TargetTransformInfo *TTI, |
| RecurrenceDescriptor &Desc, Value *Src, |
| bool NoNaN = false); |
| |
| /// Get the intersection (logical and) of all of the potential IR flags |
| /// of each scalar operation (VL) that will be converted into a vector (I). |
| /// If OpValue is non-null, we only consider operations similar to OpValue |
| /// when intersecting. |
| /// Flag set: NSW, NUW, exact, and all of fast-math. |
| void propagateIRFlags(Value *I, ArrayRef<Value *> VL, Value *OpValue = nullptr); |
| |
| /// Returns true if we can prove that \p S is defined and always negative in |
| /// loop \p L. |
| bool isKnownNegativeInLoop(const SCEV *S, const Loop *L, ScalarEvolution &SE); |
| |
| /// Returns true if we can prove that \p S is defined and always non-negative in |
| /// loop \p L. |
| bool isKnownNonNegativeInLoop(const SCEV *S, const Loop *L, |
| ScalarEvolution &SE); |
| |
| /// Returns true if \p S is defined and never is equal to signed/unsigned max. |
| bool cannotBeMaxInLoop(const SCEV *S, const Loop *L, ScalarEvolution &SE, |
| bool Signed); |
| |
| /// Returns true if \p S is defined and never is equal to signed/unsigned min. |
| bool cannotBeMinInLoop(const SCEV *S, const Loop *L, ScalarEvolution &SE, |
| bool Signed); |
| |
| enum ReplaceExitVal { NeverRepl, OnlyCheapRepl, NoHardUse, AlwaysRepl }; |
| |
| /// If the final value of any expressions that are recurrent in the loop can |
| /// be computed, substitute the exit values from the loop into any instructions |
| /// outside of the loop that use the final values of the current expressions. |
| /// Return the number of loop exit values that have been replaced, and the |
| /// corresponding phi node will be added to DeadInsts. |
| int rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI, |
| ScalarEvolution *SE, const TargetTransformInfo *TTI, |
| SCEVExpander &Rewriter, DominatorTree *DT, |
| ReplaceExitVal ReplaceExitValue, |
| SmallVector<WeakTrackingVH, 16> &DeadInsts); |
| |
| /// Set weights for \p UnrolledLoop and \p RemainderLoop based on weights for |
| /// \p OrigLoop and the following distribution of \p OrigLoop iteration among \p |
| /// UnrolledLoop and \p RemainderLoop. \p UnrolledLoop receives weights that |
| /// reflect TC/UF iterations, and \p RemainderLoop receives weights that reflect |
| /// the remaining TC%UF iterations. |
| /// |
| /// Note that \p OrigLoop may be equal to either \p UnrolledLoop or \p |
| /// RemainderLoop in which case weights for \p OrigLoop are updated accordingly. |
| /// Note also behavior is undefined if \p UnrolledLoop and \p RemainderLoop are |
| /// equal. \p UF must be greater than zero. |
| /// If \p OrigLoop has no profile info associated nothing happens. |
| /// |
| /// This utility may be useful for such optimizations as unroller and |
| /// vectorizer as it's typical transformation for them. |
| void setProfileInfoAfterUnrolling(Loop *OrigLoop, Loop *UnrolledLoop, |
| Loop *RemainderLoop, uint64_t UF); |
| |
| /// Utility that implements appending of loops onto a worklist given a range. |
| /// We want to process loops in postorder, but the worklist is a LIFO data |
| /// structure, so we append to it in *reverse* postorder. |
| /// For trees, a preorder traversal is a viable reverse postorder, so we |
| /// actually append using a preorder walk algorithm. |
| template <typename RangeT> |
| void appendLoopsToWorklist(RangeT &&, SmallPriorityWorklist<Loop *, 4> &); |
| /// Utility that implements appending of loops onto a worklist given a range. |
| /// It has the same behavior as appendLoopsToWorklist, but assumes the range of |
| /// loops has already been reversed, so it processes loops in the given order. |
| template <typename RangeT> |
| void appendReversedLoopsToWorklist(RangeT &&, |
| SmallPriorityWorklist<Loop *, 4> &); |
| |
| /// Utility that implements appending of loops onto a worklist given LoopInfo. |
| /// Calls the templated utility taking a Range of loops, handing it the Loops |
| /// in LoopInfo, iterated in reverse. This is because the loops are stored in |
| /// RPO w.r.t. the control flow graph in LoopInfo. For the purpose of unrolling, |
| /// loop deletion, and LICM, we largely want to work forward across the CFG so |
| /// that we visit defs before uses and can propagate simplifications from one |
| /// loop nest into the next. Calls appendReversedLoopsToWorklist with the |
| /// already reversed loops in LI. |
| /// FIXME: Consider changing the order in LoopInfo. |
| void appendLoopsToWorklist(LoopInfo &, SmallPriorityWorklist<Loop *, 4> &); |
| |
| /// Recursively clone the specified loop and all of its children, |
| /// mapping the blocks with the specified map. |
| Loop *cloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM, |
| LoopInfo *LI, LPPassManager *LPM); |
| |
| /// Add code that checks at runtime if the accessed arrays in \p PointerChecks |
| /// overlap. |
| /// |
| /// Returns a pair of instructions where the first element is the first |
| /// instruction generated in possibly a sequence of instructions and the |
| /// second value is the final comparator value or NULL if no check is needed. |
| std::pair<Instruction *, Instruction *> |
| addRuntimeChecks(Instruction *Loc, Loop *TheLoop, |
| const SmallVectorImpl<RuntimePointerCheck> &PointerChecks, |
| ScalarEvolution *SE); |
| |
| } // end namespace llvm |
| |
| #endif // LLVM_TRANSFORMS_UTILS_LOOPUTILS_H |