1 //===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains routines that help analyze properties that chains of
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_ANALYSIS_VALUETRACKING_H
16 #define LLVM_ANALYSIS_VALUETRACKING_H
18 #include "llvm/System/DataTypes.h"
22 template <typename T> class SmallVectorImpl;
29 /// ComputeMaskedBits - Determine which of the bits specified in Mask are
30 /// known to be either zero or one and return them in the KnownZero/KnownOne
31 /// bit sets. This code only analyzes bits in Mask, in order to short-circuit
34 /// This function is defined on values with integer type, values with pointer
35 /// type (but only if TD is non-null), and vectors of integers. In the case
36 /// where V is a vector, the mask, known zero, and known one values are the
37 /// same width as the vector element, and the bit is set only if it is true
38 /// for all of the elements in the vector.
39 void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
40 APInt &KnownOne, const TargetData *TD = 0,
43 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
44 /// this predicate to simplify operations downstream. Mask is known to be
45 /// zero for bits that V cannot have.
47 /// This function is defined on values with integer type, values with pointer
48 /// type (but only if TD is non-null), and vectors of integers. In the case
49 /// where V is a vector, the mask, known zero, and known one values are the
50 /// same width as the vector element, and the bit is set only if it is true
51 /// for all of the elements in the vector.
52 bool MaskedValueIsZero(Value *V, const APInt &Mask,
53 const TargetData *TD = 0, unsigned Depth = 0);
56 /// ComputeNumSignBits - Return the number of times the sign bit of the
57 /// register is replicated into the other bits. We know that at least 1 bit
58 /// is always equal to the sign bit (itself), but other cases can give us
59 /// information. For example, immediately after an "ashr X, 2", we know that
60 /// the top 3 bits are all equal to each other, so we return 3.
62 /// 'Op' must have a scalar integer type.
64 unsigned ComputeNumSignBits(Value *Op, const TargetData *TD = 0,
67 /// ComputeMultiple - This function computes the integer multiple of Base that
68 /// equals V. If successful, it returns true and returns the multiple in
69 /// Multiple. If unsuccessful, it returns false. Also, if V can be
70 /// simplified to an integer, then the simplified V is returned in Val. Look
71 /// through sext only if LookThroughSExt=true.
72 bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
73 bool LookThroughSExt = false,
76 /// CannotBeNegativeZero - Return true if we can prove that the specified FP
77 /// value is never equal to -0.0.
79 bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
81 /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose
82 /// it into a base pointer with a constant offset and a number of scaled
85 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale
86 /// in the VarIndices vector) are Value*'s that are known to be scaled by the
87 /// specified amount, but which may have other unrepresented high bits. As
88 /// such, the gep cannot necessarily be reconstructed from its decomposed
91 /// When TargetData is around, this function is capable of analyzing
92 /// everything that Value::getUnderlyingObject() can look through. When not,
93 /// it just looks through pointer casts.
95 const Value *DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
96 SmallVectorImpl<std::pair<const Value*, int64_t> > &VarIndices,
97 const TargetData *TD);
101 /// FindScalarValue - Given an aggregrate and an sequence of indices, see if
102 /// the scalar value indexed is already around as a register, for example if
103 /// it were inserted directly into the aggregrate.
105 /// If InsertBefore is not null, this function will duplicate (modified)
106 /// insertvalues when a part of a nested struct is extracted.
107 Value *FindInsertedValue(Value *V,
108 const unsigned *idx_begin,
109 const unsigned *idx_end,
110 Instruction *InsertBefore = 0);
112 /// This is a convenience wrapper for finding values indexed by a single index
114 inline Value *FindInsertedValue(Value *V, const unsigned Idx,
115 Instruction *InsertBefore = 0) {
116 const unsigned Idxs[1] = { Idx };
117 return FindInsertedValue(V, &Idxs[0], &Idxs[1], InsertBefore);
120 /// GetConstantStringInfo - This function computes the length of a
121 /// null-terminated C string pointed to by V. If successful, it returns true
122 /// and returns the string in Str. If unsuccessful, it returns false. If
123 /// StopAtNul is set to true (the default), the returned string is truncated
124 /// by a nul character in the global. If StopAtNul is false, the nul
125 /// character is included in the result string.
126 bool GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset = 0,
127 bool StopAtNul = true);
128 } // end namespace llvm