LLVM  9.0.0svn
Loads.h
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1 //===- Loads.h - Local load analysis --------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file declares simple local analyses for load instructions.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_ANALYSIS_LOADS_H
14 #define LLVM_ANALYSIS_LOADS_H
15 
17 #include "llvm/IR/BasicBlock.h"
19 
20 namespace llvm {
21 
22 class DataLayout;
23 class MDNode;
24 
25 /// Return true if this is always a dereferenceable pointer. If the context
26 /// instruction is specified perform context-sensitive analysis and return true
27 /// if the pointer is dereferenceable at the specified instruction.
28 bool isDereferenceablePointer(const Value *V, Type *Ty,
29  const DataLayout &DL,
30  const Instruction *CtxI = nullptr,
31  const DominatorTree *DT = nullptr);
32 
33 /// Returns true if V is always a dereferenceable pointer with alignment
34 /// greater or equal than requested. If the context instruction is specified
35 /// performs context-sensitive analysis and returns true if the pointer is
36 /// dereferenceable at the specified instruction.
38  unsigned Align, const DataLayout &DL,
39  const Instruction *CtxI = nullptr,
40  const DominatorTree *DT = nullptr);
41 
42 /// Returns true if V is always dereferenceable for Size byte with alignment
43 /// greater or equal than requested. If the context instruction is specified
44 /// performs context-sensitive analysis and returns true if the pointer is
45 /// dereferenceable at the specified instruction.
46 bool isDereferenceableAndAlignedPointer(const Value *V, unsigned Align,
47  const APInt &Size, const DataLayout &DL,
48  const Instruction *CtxI = nullptr,
49  const DominatorTree *DT = nullptr);
50 
51 /// Return true if we know that executing a load from this value cannot trap.
52 ///
53 /// If DT and ScanFrom are specified this method performs context-sensitive
54 /// analysis and returns true if it is safe to load immediately before ScanFrom.
55 ///
56 /// If it is not obviously safe to load from the specified pointer, we do a
57 /// quick local scan of the basic block containing ScanFrom, to determine if
58 /// the address is already accessed.
59 bool isSafeToLoadUnconditionally(Value *V, unsigned Align, APInt &Size,
60  const DataLayout &DL,
61  Instruction *ScanFrom = nullptr,
62  const DominatorTree *DT = nullptr);
63 
64 /// Return true if we know that executing a load from this value cannot trap.
65 ///
66 /// If DT and ScanFrom are specified this method performs context-sensitive
67 /// analysis and returns true if it is safe to load immediately before ScanFrom.
68 ///
69 /// If it is not obviously safe to load from the specified pointer, we do a
70 /// quick local scan of the basic block containing ScanFrom, to determine if
71 /// the address is already accessed.
72 bool isSafeToLoadUnconditionally(Value *V, Type *Ty, unsigned Align,
73  const DataLayout &DL,
74  Instruction *ScanFrom = nullptr,
75  const DominatorTree *DT = nullptr);
76 
77 /// The default number of maximum instructions to scan in the block, used by
78 /// FindAvailableLoadedValue().
79 extern cl::opt<unsigned> DefMaxInstsToScan;
80 
81 /// Scan backwards to see if we have the value of the given load available
82 /// locally within a small number of instructions.
83 ///
84 /// You can use this function to scan across multiple blocks: after you call
85 /// this function, if ScanFrom points at the beginning of the block, it's safe
86 /// to continue scanning the predecessors.
87 ///
88 /// Note that performing load CSE requires special care to make sure the
89 /// metadata is set appropriately. In particular, aliasing metadata needs
90 /// to be merged. (This doesn't matter for store-to-load forwarding because
91 /// the only relevant load gets deleted.)
92 ///
93 /// \param Load The load we want to replace.
94 /// \param ScanBB The basic block to scan.
95 /// \param [in,out] ScanFrom The location to start scanning from. When this
96 /// function returns, it points at the last instruction scanned.
97 /// \param MaxInstsToScan The maximum number of instructions to scan. If this
98 /// is zero, the whole block will be scanned.
99 /// \param AA Optional pointer to alias analysis, to make the scan more
100 /// precise.
101 /// \param [out] IsLoadCSE Whether the returned value is a load from the same
102 /// location in memory, as opposed to the value operand of a store.
103 ///
104 /// \returns The found value, or nullptr if no value is found.
106  BasicBlock *ScanBB,
107  BasicBlock::iterator &ScanFrom,
108  unsigned MaxInstsToScan = DefMaxInstsToScan,
109  AliasAnalysis *AA = nullptr,
110  bool *IsLoadCSE = nullptr,
111  unsigned *NumScanedInst = nullptr);
112 
113 /// Scan backwards to see if we have the value of the given pointer available
114 /// locally within a small number of instructions.
115 ///
116 /// You can use this function to scan across multiple blocks: after you call
117 /// this function, if ScanFrom points at the beginning of the block, it's safe
118 /// to continue scanning the predecessors.
119 ///
120 /// \param Ptr The pointer we want the load and store to originate from.
121 /// \param AccessTy The access type of the pointer.
122 /// \param AtLeastAtomic Are we looking for at-least an atomic load/store ? In
123 /// case it is false, we can return an atomic or non-atomic load or store. In
124 /// case it is true, we need to return an atomic load or store.
125 /// \param ScanBB The basic block to scan.
126 /// \param [in,out] ScanFrom The location to start scanning from. When this
127 /// function returns, it points at the last instruction scanned.
128 /// \param MaxInstsToScan The maximum number of instructions to scan. If this
129 /// is zero, the whole block will be scanned.
130 /// \param AA Optional pointer to alias analysis, to make the scan more
131 /// precise.
132 /// \param [out] IsLoad Whether the returned value is a load from the same
133 /// location in memory, as opposed to the value operand of a store.
134 ///
135 /// \returns The found value, or nullptr if no value is found.
136 Value *FindAvailablePtrLoadStore(Value *Ptr, Type *AccessTy, bool AtLeastAtomic,
137  BasicBlock *ScanBB,
138  BasicBlock::iterator &ScanFrom,
139  unsigned MaxInstsToScan, AliasAnalysis *AA,
140  bool *IsLoad, unsigned *NumScanedInst);
141 }
142 
143 #endif
constexpr char Align[]
Key for Kernel::Arg::Metadata::mAlign.
Type
MessagePack types as defined in the standard, with the exception of Integer being divided into a sign...
Definition: MsgPackReader.h:48
This class represents lattice values for constants.
Definition: AllocatorList.h:23
Various leaf nodes.
Definition: ISDOpcodes.h:59
cl::opt< unsigned > DefMaxInstsToScan
The default number of maximum instructions to scan in the block, used by FindAvailableLoadedValue().
bool isSafeToLoadUnconditionally(Value *V, unsigned Align, APInt &Size, const DataLayout &DL, Instruction *ScanFrom=nullptr, const DominatorTree *DT=nullptr)
Return true if we know that executing a load from this value cannot trap.
Definition: Loads.cpp:201
Value * FindAvailablePtrLoadStore(Value *Ptr, Type *AccessTy, bool AtLeastAtomic, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan, AliasAnalysis *AA, bool *IsLoad, unsigned *NumScanedInst)
Scan backwards to see if we have the value of the given pointer available locally within a small numb...
Definition: Loads.cpp:352
bool isDereferenceableAndAlignedPointer(const Value *V, Type *Ty, unsigned Align, const DataLayout &DL, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr)
Returns true if V is always a dereferenceable pointer with alignment greater or equal than requested...
Definition: Loads.cpp:128
Value * FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan=DefMaxInstsToScan, AliasAnalysis *AA=nullptr, bool *IsLoadCSE=nullptr, unsigned *NumScanedInst=nullptr)
Scan backwards to see if we have the value of the given load available locally within a small number ...
Definition: Loads.cpp:337
AAResults AliasAnalysis
Temporary typedef for legacy code that uses a generic AliasAnalysis pointer or reference.
bool isDereferenceablePointer(const Value *V, Type *Ty, const DataLayout &DL, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr)
Return true if this is always a dereferenceable pointer.
Definition: Loads.cpp:152
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:89
uint32_t Size
Definition: Profile.cpp:46