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bea74e4271
llvm-svn: 247543
428 lines
21 KiB
C++
428 lines
21 KiB
C++
//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains routines that help analyze properties that chains of
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// computations have.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_VALUETRACKING_H
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#define LLVM_ANALYSIS_VALUETRACKING_H
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/Support/DataTypes.h"
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namespace llvm {
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class APInt;
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class AddOperator;
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class AssumptionCache;
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class DataLayout;
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class DominatorTree;
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class Instruction;
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class Loop;
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class LoopInfo;
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class MDNode;
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class StringRef;
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class TargetLibraryInfo;
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class Value;
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/// Determine which bits of V are known to be either zero or one and return
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/// them in the KnownZero/KnownOne bit sets.
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///
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/// This function is defined on values with integer type, values with pointer
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/// type, and vectors of integers. In the case
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/// where V is a vector, the known zero and known one values are the
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/// same width as the vector element, and the bit is set only if it is true
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/// for all of the elements in the vector.
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void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
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const DataLayout &DL, unsigned Depth = 0,
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AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// Compute known bits from the range metadata.
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/// \p KnownZero the set of bits that are known to be zero
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void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
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APInt &KnownZero);
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/// Return true if LHS and RHS have no common bits set.
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bool haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL,
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AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// ComputeSignBit - Determine whether the sign bit is known to be zero or
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/// one. Convenience wrapper around computeKnownBits.
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void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
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const DataLayout &DL, unsigned Depth = 0,
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AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// isKnownToBeAPowerOfTwo - Return true if the given value is known to have
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/// exactly one bit set when defined. For vectors return true if every
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/// element is known to be a power of two when defined. Supports values with
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/// integer or pointer type and vectors of integers. If 'OrZero' is set then
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/// return true if the given value is either a power of two or zero.
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bool isKnownToBeAPowerOfTwo(Value *V, const DataLayout &DL,
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bool OrZero = false, unsigned Depth = 0,
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AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// isKnownNonZero - Return true if the given value is known to be non-zero
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/// when defined. For vectors return true if every element is known to be
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/// non-zero when defined. Supports values with integer or pointer type and
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/// vectors of integers.
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bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth = 0,
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AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// Returns true if the give value is known to be non-negative.
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bool isKnownNonNegative(Value *V, const DataLayout &DL, unsigned Depth = 0,
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AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
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/// this predicate to simplify operations downstream. Mask is known to be
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/// zero for bits that V cannot have.
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///
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/// This function is defined on values with integer type, values with pointer
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/// type, and vectors of integers. In the case
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/// where V is a vector, the mask, known zero, and known one values are the
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/// same width as the vector element, and the bit is set only if it is true
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/// for all of the elements in the vector.
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bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
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unsigned Depth = 0, AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// ComputeNumSignBits - Return the number of times the sign bit of the
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/// register is replicated into the other bits. We know that at least 1 bit
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/// is always equal to the sign bit (itself), but other cases can give us
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/// information. For example, immediately after an "ashr X, 2", we know that
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/// the top 3 bits are all equal to each other, so we return 3.
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///
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/// 'Op' must have a scalar integer type.
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///
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unsigned ComputeNumSignBits(Value *Op, const DataLayout &DL,
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unsigned Depth = 0, AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// ComputeMultiple - This function computes the integer multiple of Base that
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/// equals V. If successful, it returns true and returns the multiple in
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/// Multiple. If unsuccessful, it returns false. Also, if V can be
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/// simplified to an integer, then the simplified V is returned in Val. Look
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/// through sext only if LookThroughSExt=true.
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bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
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bool LookThroughSExt = false,
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unsigned Depth = 0);
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/// CannotBeNegativeZero - Return true if we can prove that the specified FP
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/// value is never equal to -0.0.
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///
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bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
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/// CannotBeOrderedLessThanZero - Return true if we can prove that the
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/// specified FP value is either a NaN or never less than 0.0.
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///
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bool CannotBeOrderedLessThanZero(const Value *V, unsigned Depth = 0);
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/// isBytewiseValue - If the specified value can be set by repeating the same
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/// byte in memory, return the i8 value that it is represented with. This is
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/// true for all i8 values obviously, but is also true for i32 0, i32 -1,
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/// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
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/// byte store (e.g. i16 0x1234), return null.
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Value *isBytewiseValue(Value *V);
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/// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
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/// the scalar value indexed is already around as a register, for example if
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/// it were inserted directly into the aggregrate.
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///
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/// If InsertBefore is not null, this function will duplicate (modified)
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/// insertvalues when a part of a nested struct is extracted.
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Value *FindInsertedValue(Value *V,
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ArrayRef<unsigned> idx_range,
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Instruction *InsertBefore = nullptr);
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/// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
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/// it can be expressed as a base pointer plus a constant offset. Return the
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/// base and offset to the caller.
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Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
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const DataLayout &DL);
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static inline const Value *
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GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
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const DataLayout &DL) {
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return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset,
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DL);
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}
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/// getConstantStringInfo - This function computes the length of a
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/// null-terminated C string pointed to by V. If successful, it returns true
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/// and returns the string in Str. If unsuccessful, it returns false. This
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/// does not include the trailing nul character by default. If TrimAtNul is
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/// set to false, then this returns any trailing nul characters as well as any
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/// other characters that come after it.
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bool getConstantStringInfo(const Value *V, StringRef &Str,
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uint64_t Offset = 0, bool TrimAtNul = true);
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/// GetStringLength - If we can compute the length of the string pointed to by
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/// the specified pointer, return 'len+1'. If we can't, return 0.
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uint64_t GetStringLength(Value *V);
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/// GetUnderlyingObject - This method strips off any GEP address adjustments
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/// and pointer casts from the specified value, returning the original object
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/// being addressed. Note that the returned value has pointer type if the
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/// specified value does. If the MaxLookup value is non-zero, it limits the
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/// number of instructions to be stripped off.
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Value *GetUnderlyingObject(Value *V, const DataLayout &DL,
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unsigned MaxLookup = 6);
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static inline const Value *GetUnderlyingObject(const Value *V,
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const DataLayout &DL,
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unsigned MaxLookup = 6) {
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return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup);
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}
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/// \brief This method is similar to GetUnderlyingObject except that it can
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/// look through phi and select instructions and return multiple objects.
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///
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/// If LoopInfo is passed, loop phis are further analyzed. If a pointer
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/// accesses different objects in each iteration, we don't look through the
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/// phi node. E.g. consider this loop nest:
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///
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/// int **A;
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/// for (i)
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/// for (j) {
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/// A[i][j] = A[i-1][j] * B[j]
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/// }
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///
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/// This is transformed by Load-PRE to stash away A[i] for the next iteration
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/// of the outer loop:
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///
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/// Curr = A[0]; // Prev_0
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/// for (i: 1..N) {
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/// Prev = Curr; // Prev = PHI (Prev_0, Curr)
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/// Curr = A[i];
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/// for (j: 0..N) {
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/// Curr[j] = Prev[j] * B[j]
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/// }
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/// }
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///
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/// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects
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/// should not assume that Curr and Prev share the same underlying object thus
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/// it shouldn't look through the phi above.
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void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
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const DataLayout &DL, LoopInfo *LI = nullptr,
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unsigned MaxLookup = 6);
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/// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
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/// are lifetime markers.
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bool onlyUsedByLifetimeMarkers(const Value *V);
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/// isDereferenceablePointer - Return true if this is always a dereferenceable
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/// pointer. If the context instruction is specified perform context-sensitive
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/// analysis and return true if the pointer is dereferenceable at the
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/// specified instruction.
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bool isDereferenceablePointer(const Value *V, const DataLayout &DL,
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const Instruction *CtxI = nullptr,
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const DominatorTree *DT = nullptr,
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const TargetLibraryInfo *TLI = nullptr);
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/// Returns true if V is always a dereferenceable pointer with alignment
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/// greater or equal than requested. If the context instruction is specified
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/// performs context-sensitive analysis and returns true if the pointer is
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/// dereferenceable at the specified instruction.
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bool isDereferenceableAndAlignedPointer(const Value *V, unsigned Align,
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const DataLayout &DL,
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const Instruction *CtxI = nullptr,
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const DominatorTree *DT = nullptr,
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const TargetLibraryInfo *TLI = nullptr);
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/// isSafeToSpeculativelyExecute - Return true if the instruction does not
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/// have any effects besides calculating the result and does not have
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/// undefined behavior.
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///
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/// This method never returns true for an instruction that returns true for
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/// mayHaveSideEffects; however, this method also does some other checks in
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/// addition. It checks for undefined behavior, like dividing by zero or
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/// loading from an invalid pointer (but not for undefined results, like a
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/// shift with a shift amount larger than the width of the result). It checks
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/// for malloc and alloca because speculatively executing them might cause a
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/// memory leak. It also returns false for instructions related to control
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/// flow, specifically terminators and PHI nodes.
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///
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/// If the CtxI is specified this method performs context-sensitive analysis
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/// and returns true if it is safe to execute the instruction immediately
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/// before the CtxI.
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///
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/// If the CtxI is NOT specified this method only looks at the instruction
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/// itself and its operands, so if this method returns true, it is safe to
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/// move the instruction as long as the correct dominance relationships for
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/// the operands and users hold.
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///
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/// This method can return true for instructions that read memory;
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/// for such instructions, moving them may change the resulting value.
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bool isSafeToSpeculativelyExecute(const Value *V,
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const Instruction *CtxI = nullptr,
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const DominatorTree *DT = nullptr,
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const TargetLibraryInfo *TLI = nullptr);
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/// Returns true if the result or effects of the given instructions \p I
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/// depend on or influence global memory.
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/// Memory dependence arises for example if the the instruction reads from
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/// memory or may produce effects or undefined behaviour. Memory dependent
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/// instructions generally cannot be reorderd with respect to other memory
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/// dependent instructions or moved into non-dominated basic blocks.
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/// Instructions which just compute a value based on the values of their
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/// operands are not memory dependent.
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bool mayBeMemoryDependent(const Instruction &I);
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/// isKnownNonNull - Return true if this pointer couldn't possibly be null by
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/// its definition. This returns true for allocas, non-extern-weak globals
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/// and byval arguments.
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bool isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI = nullptr);
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/// isKnownNonNullAt - Return true if this pointer couldn't possibly be null.
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/// If the context instruction is specified perform context-sensitive analysis
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/// and return true if the pointer couldn't possibly be null at the specified
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/// instruction.
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bool isKnownNonNullAt(const Value *V,
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const Instruction *CtxI = nullptr,
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const DominatorTree *DT = nullptr,
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const TargetLibraryInfo *TLI = nullptr);
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/// Return true if it is valid to use the assumptions provided by an
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/// assume intrinsic, I, at the point in the control-flow identified by the
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/// context instruction, CxtI.
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bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
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const DominatorTree *DT = nullptr);
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enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
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OverflowResult computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
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const DataLayout &DL,
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AssumptionCache *AC,
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const Instruction *CxtI,
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const DominatorTree *DT);
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OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
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const DataLayout &DL,
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AssumptionCache *AC,
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const Instruction *CxtI,
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const DominatorTree *DT);
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OverflowResult computeOverflowForSignedAdd(Value *LHS, Value *RHS,
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const DataLayout &DL,
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AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// This version also leverages the sign bit of Add if known.
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OverflowResult computeOverflowForSignedAdd(AddOperator *Add,
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const DataLayout &DL,
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AssumptionCache *AC = nullptr,
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const Instruction *CxtI = nullptr,
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const DominatorTree *DT = nullptr);
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/// Return true if this function can prove that the instruction I will
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/// always transfer execution to one of its successors (including the next
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/// instruction that follows within a basic block). E.g. this is not
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/// guaranteed for function calls that could loop infinitely.
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///
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/// In other words, this function returns false for instructions that may
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/// transfer execution or fail to transfer execution in a way that is not
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/// captured in the CFG nor in the sequence of instructions within a basic
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/// block.
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///
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/// Undefined behavior is assumed not to happen, so e.g. division is
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/// guaranteed to transfer execution to the following instruction even
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/// though division by zero might cause undefined behavior.
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bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I);
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/// Return true if this function can prove that the instruction I
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/// is executed for every iteration of the loop L.
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///
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/// Note that this currently only considers the loop header.
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bool isGuaranteedToExecuteForEveryIteration(const Instruction *I,
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const Loop *L);
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/// Return true if this function can prove that I is guaranteed to yield
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/// full-poison (all bits poison) if at least one of its operands are
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/// full-poison (all bits poison).
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///
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/// The exact rules for how poison propagates through instructions have
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/// not been settled as of 2015-07-10, so this function is conservative
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/// and only considers poison to be propagated in uncontroversial
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/// cases. There is no attempt to track values that may be only partially
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/// poison.
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bool propagatesFullPoison(const Instruction *I);
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/// Return either nullptr or an operand of I such that I will trigger
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/// undefined behavior if I is executed and that operand has a full-poison
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/// value (all bits poison).
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const Value *getGuaranteedNonFullPoisonOp(const Instruction *I);
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/// Return true if this function can prove that if PoisonI is executed
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/// and yields a full-poison value (all bits poison), then that will
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/// trigger undefined behavior.
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///
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/// Note that this currently only considers the basic block that is
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/// the parent of I.
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bool isKnownNotFullPoison(const Instruction *PoisonI);
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/// \brief Specific patterns of select instructions we can match.
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enum SelectPatternFlavor {
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SPF_UNKNOWN = 0,
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SPF_SMIN, /// Signed minimum
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SPF_UMIN, /// Unsigned minimum
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SPF_SMAX, /// Signed maximum
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SPF_UMAX, /// Unsigned maximum
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SPF_FMINNUM, /// Floating point minnum
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SPF_FMAXNUM, /// Floating point maxnum
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SPF_ABS, /// Absolute value
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SPF_NABS /// Negated absolute value
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};
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/// \brief Behavior when a floating point min/max is given one NaN and one
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/// non-NaN as input.
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enum SelectPatternNaNBehavior {
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SPNB_NA = 0, /// NaN behavior not applicable.
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SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN.
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SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN.
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SPNB_RETURNS_ANY /// Given one NaN input, can return either (or
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/// it has been determined that no operands can
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/// be NaN).
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};
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struct SelectPatternResult {
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SelectPatternFlavor Flavor;
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SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is
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/// SPF_FMINNUM or SPF_FMAXNUM.
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bool Ordered; /// When implementing this min/max pattern as
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/// fcmp; select, does the fcmp have to be
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/// ordered?
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};
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/// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind
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/// and providing the out parameter results if we successfully match.
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///
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/// If CastOp is not nullptr, also match MIN/MAX idioms where the type does
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/// not match that of the original select. If this is the case, the cast
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/// operation (one of Trunc,SExt,Zext) that must be done to transform the
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/// type of LHS and RHS into the type of V is returned in CastOp.
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///
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/// For example:
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/// %1 = icmp slt i32 %a, i32 4
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/// %2 = sext i32 %a to i64
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/// %3 = select i1 %1, i64 %2, i64 4
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///
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/// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
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///
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SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
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Instruction::CastOps *CastOp = nullptr);
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} // end namespace llvm
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#endif
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