ValueTracking.h revision 8b67f774e9c38b7718b2b300b628388f966df4e0
1//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file contains routines that help analyze properties that chains of 11// computations have. 12// 13//===----------------------------------------------------------------------===// 14 15#ifndef LLVM_ANALYSIS_VALUETRACKING_H 16#define LLVM_ANALYSIS_VALUETRACKING_H 17 18#include "llvm/System/DataTypes.h" 19#include <string> 20 21namespace llvm { 22 class Value; 23 class Instruction; 24 class APInt; 25 class TargetData; 26 class LLVMContext; 27 28 /// ComputeMaskedBits - Determine which of the bits specified in Mask are 29 /// known to be either zero or one and return them in the KnownZero/KnownOne 30 /// bit sets. This code only analyzes bits in Mask, in order to short-circuit 31 /// processing. 32 /// 33 /// This function is defined on values with integer type, values with pointer 34 /// type (but only if TD is non-null), and vectors of integers. In the case 35 /// where V is a vector, the mask, known zero, and known one values are the 36 /// same width as the vector element, and the bit is set only if it is true 37 /// for all of the elements in the vector. 38 void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero, 39 APInt &KnownOne, const TargetData *TD = 0, 40 unsigned Depth = 0); 41 42 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use 43 /// this predicate to simplify operations downstream. Mask is known to be 44 /// zero for bits that V cannot have. 45 /// 46 /// This function is defined on values with integer type, values with pointer 47 /// type (but only if TD is non-null), and vectors of integers. In the case 48 /// where V is a vector, the mask, known zero, and known one values are the 49 /// same width as the vector element, and the bit is set only if it is true 50 /// for all of the elements in the vector. 51 bool MaskedValueIsZero(Value *V, const APInt &Mask, 52 const TargetData *TD = 0, unsigned Depth = 0); 53 54 55 /// ComputeNumSignBits - Return the number of times the sign bit of the 56 /// register is replicated into the other bits. We know that at least 1 bit 57 /// is always equal to the sign bit (itself), but other cases can give us 58 /// information. For example, immediately after an "ashr X, 2", we know that 59 /// the top 3 bits are all equal to each other, so we return 3. 60 /// 61 /// 'Op' must have a scalar integer type. 62 /// 63 unsigned ComputeNumSignBits(Value *Op, const TargetData *TD = 0, 64 unsigned Depth = 0); 65 66 /// CannotBeNegativeZero - Return true if we can prove that the specified FP 67 /// value is never equal to -0.0. 68 /// 69 bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0); 70 71 /// FindScalarValue - Given an aggregrate and an sequence of indices, see if 72 /// the scalar value indexed is already around as a register, for example if 73 /// it were inserted directly into the aggregrate. 74 /// 75 /// If InsertBefore is not null, this function will duplicate (modified) 76 /// insertvalues when a part of a nested struct is extracted. 77 Value *FindInsertedValue(Value *V, 78 const unsigned *idx_begin, 79 const unsigned *idx_end, 80 LLVMContext &Context, 81 Instruction *InsertBefore = 0); 82 83 /// This is a convenience wrapper for finding values indexed by a single index 84 /// only. 85 inline Value *FindInsertedValue(Value *V, const unsigned Idx, 86 LLVMContext &Context, 87 Instruction *InsertBefore = 0) { 88 const unsigned Idxs[1] = { Idx }; 89 return FindInsertedValue(V, &Idxs[0], &Idxs[1], Context, InsertBefore); 90 } 91 92 /// GetConstantStringInfo - This function computes the length of a 93 /// null-terminated C string pointed to by V. If successful, it returns true 94 /// and returns the string in Str. If unsuccessful, it returns false. If 95 /// StopAtNul is set to true (the default), the returned string is truncated 96 /// by a nul character in the global. If StopAtNul is false, the nul 97 /// character is included in the result string. 98 bool GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset = 0, 99 bool StopAtNul = true); 100} // end namespace llvm 101 102#endif 103