[oota-llvm.git] / include / llvm / Analysis / ValueTracking.h

//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains routines that help analyze properties that chains of
// computations have.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_VALUETRACKING_H
#define LLVM_ANALYSIS_VALUETRACKING_H

#include "llvm/ADT/ArrayRef.h"
#include "llvm/IR/Instruction.h"
#include "llvm/Support/DataTypes.h"

namespace llvm {
  class Value;
  class Instruction;
  class APInt;
  class DataLayout;
  class StringRef;
  class MDNode;
  class AssumptionCache;
  class DominatorTree;
  class TargetLibraryInfo;
  class LoopInfo;
  class Loop;

  /// Determine which bits of V are known to be either zero or one and return
  /// them in the KnownZero/KnownOne bit sets.
  ///
  /// This function is defined on values with integer type, values with pointer
  /// type, and vectors of integers.  In the case
  /// where V is a vector, the known zero and known one values are the
  /// same width as the vector element, and the bit is set only if it is true
  /// for all of the elements in the vector.
  void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
                        const DataLayout &DL, unsigned Depth = 0,
                        AssumptionCache *AC = nullptr,
                        const Instruction *CxtI = nullptr,
                        const DominatorTree *DT = nullptr);
  /// Compute known bits from the range metadata.
  /// \p KnownZero the set of bits that are known to be zero
  void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
                                         APInt &KnownZero);
  /// Return true if LHS and RHS have no common bits set.
  bool haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL,
                           AssumptionCache *AC = nullptr,
                           const Instruction *CxtI = nullptr,
                           const DominatorTree *DT = nullptr);

  /// ComputeSignBit - Determine whether the sign bit is known to be zero or
  /// one.  Convenience wrapper around computeKnownBits.
  void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
                      const DataLayout &DL, unsigned Depth = 0,
                      AssumptionCache *AC = nullptr,
                      const Instruction *CxtI = nullptr,
                      const DominatorTree *DT = nullptr);

  /// isKnownToBeAPowerOfTwo - Return true if the given value is known to have
  /// exactly one bit set when defined. For vectors return true if every
  /// element is known to be a power of two when defined.  Supports values with
  /// integer or pointer type and vectors of integers.  If 'OrZero' is set then
  /// return true if the given value is either a power of two or zero.
  bool isKnownToBeAPowerOfTwo(Value *V, const DataLayout &DL,
                              bool OrZero = false, unsigned Depth = 0,
                              AssumptionCache *AC = nullptr,
                              const Instruction *CxtI = nullptr,
                              const DominatorTree *DT = nullptr);

  /// isKnownNonZero - Return true if the given value is known to be non-zero
  /// when defined.  For vectors return true if every element is known to be
  /// non-zero when defined.  Supports values with integer or pointer type and
  /// vectors of integers.
  bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth = 0,
                      AssumptionCache *AC = nullptr,
                      const Instruction *CxtI = nullptr,
                      const DominatorTree *DT = nullptr);

  /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.  We use
  /// this predicate to simplify operations downstream.  Mask is known to be
  /// zero for bits that V cannot have.
  ///
  /// This function is defined on values with integer type, values with pointer
  /// type, and vectors of integers.  In the case
  /// where V is a vector, the mask, known zero, and known one values are the
  /// same width as the vector element, and the bit is set only if it is true
  /// for all of the elements in the vector.
  bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
                         unsigned Depth = 0, AssumptionCache *AC = nullptr,
                         const Instruction *CxtI = nullptr,
                         const DominatorTree *DT = nullptr);

  /// ComputeNumSignBits - Return the number of times the sign bit of the
  /// register is replicated into the other bits.  We know that at least 1 bit
  /// is always equal to the sign bit (itself), but other cases can give us
  /// information.  For example, immediately after an "ashr X, 2", we know that
  /// the top 3 bits are all equal to each other, so we return 3.
  ///
  /// 'Op' must have a scalar integer type.
  ///
  unsigned ComputeNumSignBits(Value *Op, const DataLayout &DL,
                              unsigned Depth = 0, AssumptionCache *AC = nullptr,
                              const Instruction *CxtI = nullptr,
                              const DominatorTree *DT = nullptr);

  /// ComputeMultiple - This function computes the integer multiple of Base that
  /// equals V.  If successful, it returns true and returns the multiple in
  /// Multiple.  If unsuccessful, it returns false.  Also, if V can be
  /// simplified to an integer, then the simplified V is returned in Val.  Look
  /// through sext only if LookThroughSExt=true.
  bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
                       bool LookThroughSExt = false,
                       unsigned Depth = 0);

  /// CannotBeNegativeZero - Return true if we can prove that the specified FP 
  /// value is never equal to -0.0.
  ///
  bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);

  /// CannotBeOrderedLessThanZero - Return true if we can prove that the 
  /// specified FP value is either a NaN or never less than 0.0.
  ///
  bool CannotBeOrderedLessThanZero(const Value *V, unsigned Depth = 0);

  /// isBytewiseValue - If the specified value can be set by repeating the same
  /// byte in memory, return the i8 value that it is represented with.  This is
  /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
  /// i16 0xF0F0, double 0.0 etc.  If the value can't be handled with a repeated
  /// byte store (e.g. i16 0x1234), return null.
  Value *isBytewiseValue(Value *V);
    
  /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
  /// the scalar value indexed is already around as a register, for example if
  /// it were inserted directly into the aggregrate.
  ///
  /// If InsertBefore is not null, this function will duplicate (modified)
  /// insertvalues when a part of a nested struct is extracted.
  Value *FindInsertedValue(Value *V,
                           ArrayRef<unsigned> idx_range,
                           Instruction *InsertBefore = nullptr);

  /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
  /// it can be expressed as a base pointer plus a constant offset.  Return the
  /// base and offset to the caller.
  Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
                                          const DataLayout &DL);
  static inline const Value *
  GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
                                   const DataLayout &DL) {
    return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset,
                                            DL);
  }
  
  /// getConstantStringInfo - This function computes the length of a
  /// null-terminated C string pointed to by V.  If successful, it returns true
  /// and returns the string in Str.  If unsuccessful, it returns false.  This
  /// does not include the trailing nul character by default.  If TrimAtNul is
  /// set to false, then this returns any trailing nul characters as well as any
  /// other characters that come after it.
  bool getConstantStringInfo(const Value *V, StringRef &Str,
                             uint64_t Offset = 0, bool TrimAtNul = true);

  /// GetStringLength - If we can compute the length of the string pointed to by
  /// the specified pointer, return 'len+1'.  If we can't, return 0.
  uint64_t GetStringLength(Value *V);

  /// GetUnderlyingObject - This method strips off any GEP address adjustments
  /// and pointer casts from the specified value, returning the original object
  /// being addressed.  Note that the returned value has pointer type if the
  /// specified value does.  If the MaxLookup value is non-zero, it limits the
  /// number of instructions to be stripped off.
  Value *GetUnderlyingObject(Value *V, const DataLayout &DL,
                             unsigned MaxLookup = 6);
  static inline const Value *GetUnderlyingObject(const Value *V,
                                                 const DataLayout &DL,
                                                 unsigned MaxLookup = 6) {
    return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup);
  }

  /// \brief This method is similar to GetUnderlyingObject except that it can
  /// look through phi and select instructions and return multiple objects.
  ///
  /// If LoopInfo is passed, loop phis are further analyzed.  If a pointer
  /// accesses different objects in each iteration, we don't look through the
  /// phi node. E.g. consider this loop nest:
  ///
  ///   int **A;
  ///   for (i)
  ///     for (j) {
  ///        A[i][j] = A[i-1][j] * B[j]
  ///     }
  ///
  /// This is transformed by Load-PRE to stash away A[i] for the next iteration
  /// of the outer loop:
  ///
  ///   Curr = A[0];          // Prev_0
  ///   for (i: 1..N) {
  ///     Prev = Curr;        // Prev = PHI (Prev_0, Curr)
  ///     Curr = A[i];
  ///     for (j: 0..N) {
  ///        Curr[j] = Prev[j] * B[j]
  ///     }
  ///   }
  ///
  /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects
  /// should not assume that Curr and Prev share the same underlying object thus
  /// it shouldn't look through the phi above.
  void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
                            const DataLayout &DL, LoopInfo *LI = nullptr,
                            unsigned MaxLookup = 6);

  /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
  /// are lifetime markers.
  bool onlyUsedByLifetimeMarkers(const Value *V);

  /// isDereferenceablePointer - Return true if this is always a dereferenceable
  /// pointer. If the context instruction is specified perform context-sensitive
  /// analysis and return true if the pointer is dereferenceable at the
  /// specified instruction.
  bool isDereferenceablePointer(const Value *V, const DataLayout &DL,
                                const Instruction *CtxI = nullptr,
                                const DominatorTree *DT = nullptr,
                                const TargetLibraryInfo *TLI = nullptr);
  
  /// isSafeToSpeculativelyExecute - Return true if the instruction does not
  /// have any effects besides calculating the result and does not have
  /// undefined behavior.
  ///
  /// This method never returns true for an instruction that returns true for
  /// mayHaveSideEffects; however, this method also does some other checks in
  /// addition. It checks for undefined behavior, like dividing by zero or
  /// loading from an invalid pointer (but not for undefined results, like a
  /// shift with a shift amount larger than the width of the result). It checks
  /// for malloc and alloca because speculatively executing them might cause a
  /// memory leak. It also returns false for instructions related to control
  /// flow, specifically terminators and PHI nodes.
  ///
  /// If the CtxI is specified this method performs context-sensitive analysis
  /// and returns true if it is safe to execute the instruction immediately
  /// before the CtxI.
  ///
  /// If the CtxI is NOT specified this method only looks at the instruction
  /// itself and its operands, so if this method returns true, it is safe to
  /// move the instruction as long as the correct dominance relationships for
  /// the operands and users hold.
  ///
  /// This method can return true for instructions that read memory;
  /// for such instructions, moving them may change the resulting value.
  bool isSafeToSpeculativelyExecute(const Value *V,
                                    const Instruction *CtxI = nullptr,
                                    const DominatorTree *DT = nullptr,
                                    const TargetLibraryInfo *TLI = nullptr);

  /// isKnownNonNull - Return true if this pointer couldn't possibly be null by
  /// its definition.  This returns true for allocas, non-extern-weak globals
  /// and byval arguments.
  bool isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI = nullptr);

  /// isKnownNonNullAt - Return true if this pointer couldn't possibly be null.
  /// If the context instruction is specified perform context-sensitive analysis
  /// and return true if the pointer couldn't possibly be null at the specified
  /// instruction.
  bool isKnownNonNullAt(const Value *V,
                        const Instruction *CtxI = nullptr,
                        const DominatorTree *DT  = nullptr,
                        const TargetLibraryInfo *TLI = nullptr);

  /// Return true if it is valid to use the assumptions provided by an
  /// assume intrinsic, I, at the point in the control-flow identified by the
  /// context instruction, CxtI.
  bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
                               const DominatorTree *DT = nullptr);

  enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
  OverflowResult computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
                                               const DataLayout &DL,
                                               AssumptionCache *AC,
                                               const Instruction *CxtI,
                                               const DominatorTree *DT);
  OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
                                               const DataLayout &DL,
                                               AssumptionCache *AC,
                                               const Instruction *CxtI,
                                               const DominatorTree *DT);

  /// Return true if this function can prove that the instruction I will
  /// always transfer execution to one of its successors (including the next
  /// instruction that follows within a basic block). E.g. this is not
  /// guaranteed for function calls that could loop infinitely.
  ///
  /// In other words, this function returns false for instructions that may
  /// transfer execution or fail to transfer execution in a way that is not
  /// captured in the CFG nor in the sequence of instructions within a basic
  /// block.
  ///
  /// Undefined behavior is assumed not to happen, so e.g. division is
  /// guaranteed to transfer execution to the following instruction even
  /// though division by zero might cause undefined behavior.
  bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I);

  /// Return true if this function can prove that the instruction I
  /// is executed for every iteration of the loop L.
  ///
  /// Note that this currently only considers the loop header.
  bool isGuaranteedToExecuteForEveryIteration(const Instruction *I,
                                              const Loop *L);

  /// Return true if this function can prove that I is guaranteed to yield
  /// full-poison (all bits poison) if at least one of its operands are
  /// full-poison (all bits poison).
  ///
  /// The exact rules for how poison propagates through instructions have
  /// not been settled as of 2015-07-10, so this function is conservative
  /// and only considers poison to be propagated in uncontroversial
  /// cases. There is no attempt to track values that may be only partially
  /// poison.
  bool propagatesFullPoison(const Instruction *I);

  /// Return either nullptr or an operand of I such that I will trigger
  /// undefined behavior if I is executed and that operand has a full-poison
  /// value (all bits poison).
  const Value *getGuaranteedNonFullPoisonOp(const Instruction *I);

  /// Return true if this function can prove that if PoisonI is executed
  /// and yields a full-poison value (all bits poison), then that will
  /// trigger undefined behavior.
  ///
  /// Note that this currently only considers the basic block that is
  /// the parent of I.
  bool isKnownNotFullPoison(const Instruction *PoisonI);

  /// \brief Specific patterns of select instructions we can match.
  enum SelectPatternFlavor {
    SPF_UNKNOWN = 0,
    SPF_SMIN,                   // Signed minimum
    SPF_UMIN,                   // Unsigned minimum
    SPF_SMAX,                   // Signed maximum
    SPF_UMAX,                   // Unsigned maximum
    SPF_ABS,                    // Absolute value
    SPF_NABS                    // Negated absolute value
  };
  /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind
  /// and providing the out parameter results if we successfully match.
  ///
  /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does
  /// not match that of the original select. If this is the case, the cast
  /// operation (one of Trunc,SExt,Zext) that must be done to transform the
  /// type of LHS and RHS into the type of V is returned in CastOp.
  ///
  /// For example:
  ///   %1 = icmp slt i32 %a, i32 4
  ///   %2 = sext i32 %a to i64
  ///   %3 = select i1 %1, i64 %2, i64 4
  ///
  /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
  ///
  SelectPatternFlavor matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
                                         Instruction::CastOps *CastOp = nullptr);

} // end namespace llvm

#endif