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6629210aaf
This is safe per C++11 18.6.1.1p3: [operator new returns] a non-null pointer to suitably aligned storage (3.7.4), or else throw a bad_alloc exception. This requirement is binding on a replacement version of this function. Brings us a tiny bit closer to eliminating more vector push_backs. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191310 91177308-0d34-0410-b5e6-96231b3b80d8
195 lines
9.5 KiB
C++
195 lines
9.5 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/Support/DataTypes.h"
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namespace llvm {
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class Value;
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class Instruction;
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class APInt;
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class DataLayout;
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class StringRef;
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class MDNode;
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class TargetLibraryInfo;
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/// ComputeMaskedBits - Determine which of the bits specified in Mask are
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/// known to be either zero or one and return them in the KnownZero/KnownOne
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/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
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/// processing.
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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 (but only if TD is non-null), 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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void ComputeMaskedBits(Value *V, APInt &KnownZero, APInt &KnownOne,
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const DataLayout *TD = 0, unsigned Depth = 0);
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void computeMaskedBitsLoad(const MDNode &Ranges, APInt &KnownZero);
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/// ComputeSignBit - Determine whether the sign bit is known to be zero or
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/// one. Convenience wrapper around ComputeMaskedBits.
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void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
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const DataLayout *TD = 0, unsigned Depth = 0);
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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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/// returns true if the given value is either a power of two or zero.
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bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero = false, unsigned Depth = 0);
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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 *TD = 0, unsigned Depth = 0);
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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 (but only if TD is non-null), 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,
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const DataLayout *TD = 0, unsigned Depth = 0);
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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 *TD = 0,
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unsigned Depth = 0);
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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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/// 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 = 0);
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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 *TD);
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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 *TD) {
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return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD);
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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 *TD = 0,
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unsigned MaxLookup = 6);
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static inline const Value *
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GetUnderlyingObject(const Value *V, const DataLayout *TD = 0,
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unsigned MaxLookup = 6) {
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return GetUnderlyingObject(const_cast<Value *>(V), TD, MaxLookup);
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}
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/// GetUnderlyingObjects - This method is similar to GetUnderlyingObject
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/// except that it can look through phi and select instructions and return
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/// multiple objects.
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void GetUnderlyingObjects(Value *V,
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SmallVectorImpl<Value *> &Objects,
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const DataLayout *TD = 0,
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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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/// 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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/// This method only looks at the instruction itself and its operands, so if
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/// this method returns true, it is safe to move the instruction as long as
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/// the correct dominance relationships for the operands and users hold.
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/// However, 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 DataLayout *TD = 0);
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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 = 0);
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} // end namespace llvm
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#endif
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