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llvm-mirror/include/llvm/Analysis/ValueTracking.h
Zaara Syeda 39139cb634 [PPC] Inline expansion of memcmp 
This patch does an inline expansion of memcmp.
It changes the memcmp library call into an inline expansion when the size is
known at compile time and is under a target specified threshold.
This expansion is implemented in CodeGenPrepare and expands into straight line
code. The target specifies a maximum load size and the expansion works by using
this size to load the two sources, compare, and exit early if a difference is
found. It also has a special case when the memcmp result is used in a compare
to zero equality.

Differential Revision: https://reviews.llvm.org/D28637

llvm-svn: 304313
2017-05-31 17:12:38 +00:00

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//===- 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/IR/CallSite.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/DataTypes.h"
namespace llvm {
template <typename T> class ArrayRef;
class APInt;
class AddOperator;
class AssumptionCache;
class DataLayout;
class DominatorTree;
class GEPOperator;
class Instruction;
struct KnownBits;
class Loop;
class LoopInfo;
class OptimizationRemarkEmitter;
class MDNode;
class StringRef;
class TargetLibraryInfo;
class Value;
namespace Intrinsic {
enum ID : unsigned;
}
/// 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(const Value *V, KnownBits &Known,
const DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// Returns the known bits rather than passing by reference.
KnownBits computeKnownBits(const Value *V, const DataLayout &DL,
unsigned Depth = 0, AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// Compute known bits from the range metadata.
/// \p KnownZero the set of bits that are known to be zero
/// \p KnownOne the set of bits that are known to be one
void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
KnownBits &Known);
/// Return true if LHS and RHS have no common bits set.
bool haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// 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(const Value *V, const DataLayout &DL,
bool OrZero = false, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
bool isOnlyUsedInZeroEqualityComparison(const Instruction *CxtI);
/// 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. For pointers, if the context instruction and dominator tree are
/// specified, perform context-sensitive analysis and return true if the
/// pointer couldn't possibly be null at the specified instruction.
/// Supports values with integer or pointer type and vectors of integers.
bool isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the give value is known to be non-negative.
bool isKnownNonNegative(const Value *V, const DataLayout &DL,
unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the given value is known be positive (i.e. non-negative
/// and non-zero).
bool isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the given value is known be negative (i.e. non-positive
/// and non-zero).
bool isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Return true if the given values are known to be non-equal when defined.
/// Supports scalar integer types only.
bool isKnownNonEqual(const Value *V1, const Value *V2, const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// 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(const Value *V, const APInt &Mask,
const DataLayout &DL,
unsigned Depth = 0, AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// 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. For vectors, return the number of
/// sign bits for the vector element with the mininum number of known sign
/// bits.
unsigned ComputeNumSignBits(const Value *Op, const DataLayout &DL,
unsigned Depth = 0, AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// 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);
/// Map a call instruction to an intrinsic ID. Libcalls which have equivalent
/// intrinsics are treated as-if they were intrinsics.
Intrinsic::ID getIntrinsicForCallSite(ImmutableCallSite ICS,
const TargetLibraryInfo *TLI);
/// Return true if we can prove that the specified FP value is never equal to
/// -0.0.
bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI,
unsigned Depth = 0);
/// Return true if we can prove that the specified FP value is either NaN or
/// never less than -0.0.
///
/// NaN --> true
/// +0 --> true
/// -0 --> true
/// x > +0 --> true
/// x < -0 --> false
///
bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI);
/// Return true if we can prove that the specified FP value's sign bit is 0.
///
/// NaN --> true/false (depending on the NaN's sign bit)
/// +0 --> true
/// -0 --> false
/// x > +0 --> true
/// x < -0 --> false
///
bool SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI);
/// 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);
/// 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);
/// 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);
}
/// Returns true if the GEP is based on a pointer to a string (array of
// \p CharSize integers) and is indexing into this string.
bool isGEPBasedOnPointerToString(const GEPOperator *GEP,
unsigned CharSize = 8);
/// Represents offset+length into a ConstantDataArray.
struct ConstantDataArraySlice {
/// ConstantDataArray pointer. nullptr indicates a zeroinitializer (a valid
/// initializer, it just doesn't fit the ConstantDataArray interface).
const ConstantDataArray *Array;
/// Slice starts at this Offset.
uint64_t Offset;
/// Length of the slice.
uint64_t Length;
/// Moves the Offset and adjusts Length accordingly.
void move(uint64_t Delta) {
assert(Delta < Length);
Offset += Delta;
Length -= Delta;
}
/// Convenience accessor for elements in the slice.
uint64_t operator[](unsigned I) const {
return Array==nullptr ? 0 : Array->getElementAsInteger(I + Offset);
}
};
/// Returns true if the value \p V is a pointer into a ContantDataArray.
/// If successfull \p Index will point to a ConstantDataArray info object
/// with an apropriate offset.
bool getConstantDataArrayInfo(const Value *V, ConstantDataArraySlice &Slice,
unsigned ElementSize, uint64_t Offset = 0);
/// 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 null
/// character by default. If TrimAtNul is set to false, then this returns any
/// trailing null 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);
/// 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(const Value *V, unsigned CharSize = 8);
/// 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);
/// Return true if the only users of this pointer are lifetime markers.
bool onlyUsedByLifetimeMarkers(const Value *V);
/// 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);
/// Returns true if the result or effects of the given instructions \p I
/// depend on or influence global memory.
/// Memory dependence arises for example if the instruction reads from
/// memory or may produce effects or undefined behaviour. Memory dependent
/// instructions generally cannot be reorderd with respect to other memory
/// dependent instructions or moved into non-dominated basic blocks.
/// Instructions which just compute a value based on the values of their
/// operands are not memory dependent.
bool mayBeMemoryDependent(const Instruction &I);
/// 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);
/// Return true if this pointer couldn't possibly be null. If the context
/// instruction and dominator tree are 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);
/// 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(const Value *LHS,
const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT);
OverflowResult computeOverflowForUnsignedAdd(const Value *LHS,
const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT);
OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// This version also leverages the sign bit of Add if known.
OverflowResult computeOverflowForSignedAdd(const AddOperator *Add,
const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the arithmetic part of the \p II 's result is
/// used only along the paths control dependent on the computation
/// not overflowing, \p II being an <op>.with.overflow intrinsic.
bool isOverflowIntrinsicNoWrap(const IntrinsicInst *II,
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 programUndefinedIfFullPoison(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_FMINNUM, /// Floating point minnum
SPF_FMAXNUM, /// Floating point maxnum
SPF_ABS, /// Absolute value
SPF_NABS /// Negated absolute value
};
/// \brief Behavior when a floating point min/max is given one NaN and one
/// non-NaN as input.
enum SelectPatternNaNBehavior {
SPNB_NA = 0, /// NaN behavior not applicable.
SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN.
SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN.
SPNB_RETURNS_ANY /// Given one NaN input, can return either (or
/// it has been determined that no operands can
/// be NaN).
};
struct SelectPatternResult {
SelectPatternFlavor Flavor;
SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is
/// SPF_FMINNUM or SPF_FMAXNUM.
bool Ordered; /// When implementing this min/max pattern as
/// fcmp; select, does the fcmp have to be
/// ordered?
/// \brief Return true if \p SPF is a min or a max pattern.
static bool isMinOrMax(SelectPatternFlavor SPF) {
return !(SPF == SPF_UNKNOWN || SPF == SPF_ABS || SPF == SPF_NABS);
}
};
/// 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
///
SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
Instruction::CastOps *CastOp = nullptr);
static inline SelectPatternResult
matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS,
Instruction::CastOps *CastOp = nullptr) {
Value *L = const_cast<Value*>(LHS);
Value *R = const_cast<Value*>(RHS);
auto Result = matchSelectPattern(const_cast<Value*>(V), L, R);
LHS = L;
RHS = R;
return Result;
}
/// Return true if RHS is known to be implied true by LHS. Return false if
/// RHS is known to be implied false by LHS. Otherwise, return None if no
/// implication can be made.
/// A & B must be i1 (boolean) values or a vector of such values. Note that
/// the truth table for implication is the same as <=u on i1 values (but not
/// <=s!). The truth table for both is:
/// | T | F (B)
/// T | T | F
/// F | T | T
/// (A)
Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS,
const DataLayout &DL,
bool InvertAPred = false,
unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
} // end namespace llvm
#endif
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