Split the LoopVectorizer into H and CPP.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169771 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Vectorize/LoopVectorize.h

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+//===- LoopVectorize.h --- A Loop Vectorizer ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This is the LLVM loop vectorizer. This pass modifies 'vectorizable' loops
+// and generates target-independent LLVM-IR. Legalization of the IR is done
+// in the codegen. However, the vectorizes uses (will use) the codegen
+// interfaces to generate IR that is likely to result in an optimal binary.
+//
+// The loop vectorizer combines consecutive loop iteration into a single
+// 'wide' iteration. After this transformation the index is incremented
+// by the SIMD vector width, and not by one.
+//
+// This pass has three parts:
+// 1. The main loop pass that drives the different parts.
+// 2. LoopVectorizationLegality - A unit that checks for the legality
+//    of the vectorization.
+// 3. InnerLoopVectorizer - A unit that performs the actual
+//    widening of instructions.
+// 4. LoopVectorizationCostModel - A unit that checks for the profitability
+//    of vectorization. It decides on the optimal vector width, which
+//    can be one, if vectorization is not profitable.
+//
+//===----------------------------------------------------------------------===//
+//
+// The reduction-variable vectorization is based on the paper:
+//  D. Nuzman and R. Henderson. Multi-platform Auto-vectorization.
+//
+// Variable uniformity checks are inspired by:
+// Karrenberg, R. and Hack, S. Whole Function Vectorization.
+//
+// Other ideas/concepts are from:
+//  A. Zaks and D. Nuzman. Autovectorization in GCC-two years later.
+//
+//  S. Maleki, Y. Gao, M. Garzaran, T. Wong and D. Padua.  An Evaluation of
+//  Vectorizing Compilers.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_TRANSFORM_VECTORIZE_LOOP_VECTORIZE_H
+#define LLVM_TRANSFORM_VECTORIZE_LOOP_VECTORIZE_H
+
+#define LV_NAME "loop-vectorize"
+#define DEBUG_TYPE LV_NAME
+
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/IRBuilder.h" 
+
+#include <algorithm>
+using namespace llvm;
+
+/// We don't vectorize loops with a known constant trip count below this number.
+const unsigned TinyTripCountThreshold = 16;
+
+/// When performing a runtime memory check, do not check more than this
+/// number of pointers. Notice that the check is quadratic!
+const unsigned RuntimeMemoryCheckThreshold = 4;
+
+/// This is the highest vector width that we try to generate.
+const unsigned MaxVectorSize = 8;
+
+namespace llvm {
+
+// Forward declarations.
+class LoopVectorizationLegality;
+class LoopVectorizationCostModel;
+class VectorTargetTransformInfo;
+
+/// InnerLoopVectorizer vectorizes loops which contain only one basic
+/// block to a specified vectorization factor (VF).
+/// This class performs the widening of scalars into vectors, or multiple
+/// scalars. This class also implements the following features:
+/// * It inserts an epilogue loop for handling loops that don't have iteration
+///   counts that are known to be a multiple of the vectorization factor.
+/// * It handles the code generation for reduction variables.
+/// * Scalarization (implementation using scalars) of un-vectorizable
+///   instructions.
+/// InnerLoopVectorizer does not perform any vectorization-legality
+/// checks, and relies on the caller to check for the different legality
+/// aspects. The InnerLoopVectorizer relies on the
+/// LoopVectorizationLegality class to provide information about the induction
+/// and reduction variables that were found to a given vectorization factor.
+class InnerLoopVectorizer {
+public:
+  /// Ctor.
+  InnerLoopVectorizer(Loop *Orig, ScalarEvolution *Se, LoopInfo *Li,
+                      DominatorTree *Dt, DataLayout *Dl, unsigned VecWidth):
+  OrigLoop(Orig), SE(Se), LI(Li), DT(Dt), DL(Dl), VF(VecWidth),
+  Builder(Se->getContext()), Induction(0), OldInduction(0) { }
+
+  // Perform the actual loop widening (vectorization).
+  void vectorize(LoopVectorizationLegality *Legal) {
+    // Create a new empty loop. Unlink the old loop and connect the new one.
+    createEmptyLoop(Legal);
+    // Widen each instruction in the old loop to a new one in the new loop.
+    // Use the Legality module to find the induction and reduction variables.
+    vectorizeLoop(Legal);
+    // Register the new loop and update the analysis passes.
+    updateAnalysis();
+  }
+
+private:
+  /// A small list of PHINodes.
+  typedef SmallVector<PHINode*, 4> PhiVector;
+
+  /// Add code that checks at runtime if the accessed arrays overlap.
+  /// Returns the comparator value or NULL if no check is needed.
+  Value *addRuntimeCheck(LoopVectorizationLegality *Legal,
+                         Instruction *Loc);
+  /// Create an empty loop, based on the loop ranges of the old loop.
+  void createEmptyLoop(LoopVectorizationLegality *Legal);
+  /// Copy and widen the instructions from the old loop.
+  void vectorizeLoop(LoopVectorizationLegality *Legal);
+
+  /// A helper function that computes the predicate of the block BB, assuming
+  /// that the header block of the loop is set to True. It returns the *entry*
+  /// mask for the block BB.
+  Value *createBlockInMask(BasicBlock *BB);
+  /// A helper function that computes the predicate of the edge between SRC
+  /// and DST.
+  Value *createEdgeMask(BasicBlock *Src, BasicBlock *Dst);
+
+  /// A helper function to vectorize a single BB within the innermost loop.
+  void vectorizeBlockInLoop(LoopVectorizationLegality *Legal, BasicBlock *BB,
+                            PhiVector *PV);
+
+  /// Insert the new loop to the loop hierarchy and pass manager
+  /// and update the analysis passes.
+  void updateAnalysis();
+
+  /// This instruction is un-vectorizable. Implement it as a sequence
+  /// of scalars.
+  void scalarizeInstruction(Instruction *Instr);
+
+  /// Create a broadcast instruction. This method generates a broadcast
+  /// instruction (shuffle) for loop invariant values and for the induction
+  /// value. If this is the induction variable then we extend it to N, N+1, ...
+  /// this is needed because each iteration in the loop corresponds to a SIMD
+  /// element.
+  Value *getBroadcastInstrs(Value *V);
+
+  /// This function adds 0, 1, 2 ... to each vector element, starting at zero.
+  /// If Negate is set then negative numbers are added e.g. (0, -1, -2, ...).
+  Value *getConsecutiveVector(Value* Val, bool Negate = false);
+
+  /// When we go over instructions in the basic block we rely on previous
+  /// values within the current basic block or on loop invariant values.
+  /// When we widen (vectorize) values we place them in the map. If the values
+  /// are not within the map, they have to be loop invariant, so we simply
+  /// broadcast them into a vector.
+  Value *getVectorValue(Value *V);
+
+  /// Get a uniform vector of constant integers. We use this to get
+  /// vectors of ones and zeros for the reduction code.
+  Constant* getUniformVector(unsigned Val, Type* ScalarTy);
+
+  typedef DenseMap<Value*, Value*> ValueMap;
+
+  /// The original loop.
+  Loop *OrigLoop;
+  // Scev analysis to use.
+  ScalarEvolution *SE;
+  // Loop Info.
+  LoopInfo *LI;
+  // Dominator Tree.
+  DominatorTree *DT;
+  // Data Layout.
+  DataLayout *DL;
+  // The vectorization factor to use.
+  unsigned VF;
+
+  // The builder that we use
+  IRBuilder<> Builder;
+
+  // --- Vectorization state ---
+
+  /// The vector-loop preheader.
+  BasicBlock *LoopVectorPreHeader;
+  /// The scalar-loop preheader.
+  BasicBlock *LoopScalarPreHeader;
+  /// Middle Block between the vector and the scalar.
+  BasicBlock *LoopMiddleBlock;
+  ///The ExitBlock of the scalar loop.
+  BasicBlock *LoopExitBlock;
+  ///The vector loop body.
+  BasicBlock *LoopVectorBody;
+  ///The scalar loop body.
+  BasicBlock *LoopScalarBody;
+  ///The first bypass block.
+  BasicBlock *LoopBypassBlock;
+
+  /// The new Induction variable which was added to the new block.
+  PHINode *Induction;
+  /// The induction variable of the old basic block.
+  PHINode *OldInduction;
+  // Maps scalars to widened vectors.
+  ValueMap WidenMap;
+};
+
+/// 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 *Lp, ScalarEvolution *Se, DataLayout *Dl,
+                            DominatorTree *Dt):
+  TheLoop(Lp), SE(Se), DL(Dl), DT(Dt), Induction(0) { }
+
+  /// This enum represents the kinds of reductions that we support.
+  enum ReductionKind {
+    NoReduction, /// Not a reduction.
+    IntegerAdd,  /// Sum of numbers.
+    IntegerMult, /// Product of numbers.
+    IntegerOr,   /// Bitwise or logical OR of numbers.
+    IntegerAnd,  /// Bitwise or logical AND of numbers.
+    IntegerXor   /// Bitwise or logical XOR of numbers.
+  };
+
+  /// This enum represents the kinds of inductions that we support.
+  enum InductionKind {
+    NoInduction,         /// Not an induction variable.
+    IntInduction,        /// Integer induction variable. Step = 1.
+    ReverseIntInduction, /// Reverse int induction variable. Step = -1.
+    PtrInduction         /// Pointer induction variable. Step = sizeof(elem).
+  };
+
+  /// This POD struct holds information about reduction variables.
+  struct ReductionDescriptor {
+    // Default C'tor
+    ReductionDescriptor():
+    StartValue(0), LoopExitInstr(0), Kind(NoReduction) {}
+
+    // C'tor.
+    ReductionDescriptor(Value *Start, Instruction *Exit, ReductionKind K):
+    StartValue(Start), LoopExitInstr(Exit), Kind(K) {}
+
+    // The starting value of the reduction.
+    // It does not have to be zero!
+    Value *StartValue;
+    // The instruction who's value is used outside the loop.
+    Instruction *LoopExitInstr;
+    // The kind of the reduction.
+    ReductionKind Kind;
+  };
+
+  // This POD struct holds information about the memory runtime legality
+  // check that a group of pointers do not overlap.
+  struct RuntimePointerCheck {
+    RuntimePointerCheck(): Need(false) {}
+
+    /// Reset the state of the pointer runtime information.
+    void reset() {
+      Need = false;
+      Pointers.clear();
+      Starts.clear();
+      Ends.clear();
+    }
+
+    /// Insert a pointer and calculate the start and end SCEVs.
+    void insert(ScalarEvolution *SE, Loop *Lp, Value *Ptr);
+
+    /// This flag indicates if we need to add the runtime check.
+    bool Need;
+    /// Holds the pointers that we need to check.
+    SmallVector<Value*, 2> Pointers;
+    /// Holds the pointer value at the beginning of the loop.
+    SmallVector<const SCEV*, 2> Starts;
+    /// Holds the pointer value at the end of the loop.
+    SmallVector<const SCEV*, 2> Ends;
+  };
+
+  /// A POD for saving information about induction variables.
+  struct InductionInfo {
+    /// Ctors.
+    InductionInfo(Value *Start, InductionKind K):
+    StartValue(Start), IK(K) {};
+    InductionInfo(): StartValue(0), IK(NoInduction) {};
+    /// Start value.
+    Value *StartValue;
+    /// Induction kind.
+    InductionKind IK;
+  };
+
+  /// ReductionList contains the reduction descriptors for all
+  /// of the reductions that were found in the loop.
+  typedef DenseMap<PHINode*, ReductionDescriptor> ReductionList;
+
+  /// InductionList saves induction variables and maps them to the
+  /// induction descriptor.
+  typedef DenseMap<PHINode*, InductionInfo> InductionList;
+
+  /// 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.
+  bool canVectorize();
+
+  /// Returns the Induction variable.
+  PHINode *getInduction() {return Induction;}
+
+  /// 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 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.
+  bool isConsecutivePtr(Value *Ptr);
+
+  /// Returns true if the value V is uniform within the loop.
+  bool isUniform(Value *V);
+
+  /// Returns true if this instruction will remain scalar after vectorization.
+  bool isUniformAfterVectorization(Instruction* I) {return Uniforms.count(I);}
+
+  /// Returns the information that we collected about runtime memory check.
+  RuntimePointerCheck *getRuntimePointerCheck() {return &PtrRtCheck; }
+private:
+  /// 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();
+
+  /// Collect the variables that need to stay uniform after vectorization.
+  void collectLoopUniforms();
+
+  /// Return true if all of the instructions in the block can be speculatively
+  /// executed.
+  bool blockCanBePredicated(BasicBlock *BB);
+
+  /// Returns True, if 'Phi' is the kind of reduction variable for type
+  /// 'Kind'. If this is a reduction variable, it adds it to ReductionList.
+  bool AddReductionVar(PHINode *Phi, ReductionKind Kind);
+  /// Returns true if the instruction I can be a reduction variable of type
+  /// 'Kind'.
+  bool isReductionInstr(Instruction *I, ReductionKind Kind);
+  /// Returns the induction kind of Phi. This function may return NoInduction
+  /// if the PHI is not an induction variable.
+  InductionKind isInductionVariable(PHINode *Phi);
+  /// Return true if can compute the address bounds of Ptr within the loop.
+  bool hasComputableBounds(Value *Ptr);
+
+  /// The loop that we evaluate.
+  Loop *TheLoop;
+  /// Scev analysis.
+  ScalarEvolution *SE;
+  /// DataLayout analysis.
+  DataLayout *DL;
+  // Dominators.
+  DominatorTree *DT;
+
+  //  ---  vectorization state --- //
+
+  /// Holds the integer induction variable. This is the counter of the
+  /// loop.
+  PHINode *Induction;
+  /// 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;
+
+  /// Allowed outside users. This holds the reduction
+  /// vars which can be accessed from outside the loop.
+  SmallPtrSet<Value*, 4> AllowedExit;
+  /// This set holds the variables which are known to be uniform after
+  /// vectorization.
+  SmallPtrSet<Instruction*, 4> Uniforms;
+  /// We need to check that all of the pointers in this list are disjoint
+  /// at runtime.
+  RuntimePointerCheck PtrRtCheck;
+};
+
+/// LoopVectorizationCostModel - estimates the expected speedups due to
+/// vectorization.
+/// In many cases vectorization is not profitable. This can happen because
+/// of a number of reasons. In this class we mainly attempt to predict
+/// the expected speedup/slowdowns due to the supported instruction set.
+/// We use the VectorTargetTransformInfo to query the different backends
+/// for the cost of different operations.
+class LoopVectorizationCostModel {
+public:
+  /// C'tor.
+  LoopVectorizationCostModel(Loop *Lp, ScalarEvolution *Se,
+                             LoopVectorizationLegality *Leg,
+                             const VectorTargetTransformInfo *Vtti):
+  TheLoop(Lp), SE(Se), Legal(Leg), VTTI(Vtti) { }
+
+  /// Returns the most profitable vectorization factor for the loop that is
+  /// smaller or equal to the VF argument. This method checks every power
+  /// of two up to VF.
+  unsigned findBestVectorizationFactor(unsigned VF = MaxVectorSize);
+
+private:
+  /// Returns the expected execution cost. The unit of the cost does
+  /// not matter because we use the 'cost' units to compare different
+  /// vector widths. The cost that is returned is *not* normalized by
+  /// the factor width.
+  unsigned expectedCost(unsigned VF);
+
+  /// Returns the execution time cost of an instruction for a given vector
+  /// width. Vector width of one means scalar.
+  unsigned getInstructionCost(Instruction *I, unsigned VF);
+
+  /// A helper function for converting Scalar types to vector types.
+  /// If the incoming type is void, we return void. If the VF is 1, we return
+  /// the scalar type.
+  static Type* ToVectorTy(Type *Scalar, unsigned VF);
+
+  /// The loop that we evaluate.
+  Loop *TheLoop;
+  /// Scev analysis.
+  ScalarEvolution *SE;
+
+  /// Vectorization legality.
+  LoopVectorizationLegality *Legal;
+  /// Vector target information.
+  const VectorTargetTransformInfo *VTTI;
+};
+
+}// namespace llvm
+
+#endif //LLVM_TRANSFORM_VECTORIZE_LOOP_VECTORIZE_H
+