ValueTracking.h revision 48b2f3e4850cd27d54224cd42da8a160d6b95984
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/Support/DataTypes.h" 19#include <string> 20 21namespace llvm { 22 class Value; 23 class Instruction; 24 class APInt; 25 class TargetData; 26 struct 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 void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero, 33 APInt &KnownOne, TargetData *TD = 0, 34 unsigned Depth = 0); 35 36 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use 37 /// this predicate to simplify operations downstream. Mask is known to be 38 /// zero for bits that V cannot have. 39 bool MaskedValueIsZero(Value *V, const APInt &Mask, 40 TargetData *TD = 0, unsigned Depth = 0); 41 42 43 /// ComputeNumSignBits - Return the number of times the sign bit of the 44 /// register is replicated into the other bits. We know that at least 1 bit 45 /// is always equal to the sign bit (itself), but other cases can give us 46 /// information. For example, immediately after an "ashr X, 2", we know that 47 /// the top 3 bits are all equal to each other, so we return 3. 48 /// 49 /// 'Op' must have a scalar integer type. 50 /// 51 unsigned ComputeNumSignBits(Value *Op, TargetData *TD = 0, 52 unsigned Depth = 0); 53 54 /// CannotBeNegativeZero - Return true if we can prove that the specified FP 55 /// value is never equal to -0.0. 56 /// 57 bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0); 58 59 /// FindScalarValue - Given an aggregrate and an sequence of indices, see if 60 /// the scalar value indexed is already around as a register, for example if 61 /// it were inserted directly into the aggregrate. 62 /// 63 /// If InsertBefore is not null, this function will duplicate (modified) 64 /// insertvalues when a part of a nested struct is extracted. 65 Value *FindInsertedValue(Value *V, 66 const unsigned *idx_begin, 67 const unsigned *idx_end, 68 LLVMContext &Context, 69 Instruction *InsertBefore = 0); 70 71 /// This is a convenience wrapper for finding values indexed by a single index 72 /// only. 73 inline Value *FindInsertedValue(Value *V, const unsigned Idx, 74 LLVMContext &Context, 75 Instruction *InsertBefore = 0) { 76 const unsigned Idxs[1] = { Idx }; 77 return FindInsertedValue(V, &Idxs[0], &Idxs[1], Context, InsertBefore); 78 } 79 80 /// GetConstantStringInfo - This function computes the length of a 81 /// null-terminated C string pointed to by V. If successful, it returns true 82 /// and returns the string in Str. If unsuccessful, it returns false. If 83 /// StopAtNul is set to true (the default), the returned string is truncated 84 /// by a nul character in the global. If StopAtNul is false, the nul 85 /// character is included in the result string. 86 bool GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset = 0, 87 bool StopAtNul = true); 88} // end namespace llvm 89 90#endif 91