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, const DataLayout &DL,
29  const Instruction *CtxI = nullptr,
30  const DominatorTree *DT = nullptr);
31 
32 /// Returns true if V is always a dereferenceable pointer with alignment
33 /// greater or equal than requested. If the context instruction is specified
34 /// performs context-sensitive analysis and returns true if the pointer is
35 /// dereferenceable at the specified instruction.
36 bool isDereferenceableAndAlignedPointer(const Value *V, unsigned Align,
37  const DataLayout &DL,
38  const Instruction *CtxI = nullptr,
39  const DominatorTree *DT = nullptr);
40 
41 /// Returns true if V is always dereferenceable for Size byte with alignment
42 /// greater or equal than requested. If the context instruction is specified
43 /// performs context-sensitive analysis and returns true if the pointer is
44 /// dereferenceable at the specified instruction.
45 bool isDereferenceableAndAlignedPointer(const Value *V, unsigned Align,
46  const APInt &Size, const DataLayout &DL,
47  const Instruction *CtxI = nullptr,
48  const DominatorTree *DT = nullptr);
49 
50 /// Return true if we know that executing a load from this value cannot trap.
51 ///
52 /// If DT and ScanFrom are specified this method performs context-sensitive
53 /// analysis and returns true if it is safe to load immediately before ScanFrom.
54 ///
55 /// If it is not obviously safe to load from the specified pointer, we do a
56 /// quick local scan of the basic block containing ScanFrom, to determine if
57 /// the address is already accessed.
58 bool isSafeToLoadUnconditionally(Value *V, unsigned Align,
59  const DataLayout &DL,
60  Instruction *ScanFrom = nullptr,
61  const DominatorTree *DT = nullptr);
62 
63 /// The default number of maximum instructions to scan in the block, used by
64 /// FindAvailableLoadedValue().
65 extern cl::opt<unsigned> DefMaxInstsToScan;
66 
67 /// Scan backwards to see if we have the value of the given load available
68 /// locally within a small number of instructions.
69 ///
70 /// You can use this function to scan across multiple blocks: after you call
71 /// this function, if ScanFrom points at the beginning of the block, it's safe
72 /// to continue scanning the predecessors.
73 ///
74 /// Note that performing load CSE requires special care to make sure the
75 /// metadata is set appropriately. In particular, aliasing metadata needs
76 /// to be merged. (This doesn't matter for store-to-load forwarding because
77 /// the only relevant load gets deleted.)
78 ///
79 /// \param Load The load we want to replace.
80 /// \param ScanBB The basic block to scan.
81 /// \param [in,out] ScanFrom The location to start scanning from. When this
82 /// function returns, it points at the last instruction scanned.
83 /// \param MaxInstsToScan The maximum number of instructions to scan. If this
84 /// is zero, the whole block will be scanned.
85 /// \param AA Optional pointer to alias analysis, to make the scan more
86 /// precise.
87 /// \param [out] IsLoadCSE Whether the returned value is a load from the same
88 /// location in memory, as opposed to the value operand of a store.
89 ///
90 /// \returns The found value, or nullptr if no value is found.
91 Value *FindAvailableLoadedValue(LoadInst *Load,
92  BasicBlock *ScanBB,
93  BasicBlock::iterator &ScanFrom,
94  unsigned MaxInstsToScan = DefMaxInstsToScan,
95  AliasAnalysis *AA = nullptr,
96  bool *IsLoadCSE = nullptr,
97  unsigned *NumScanedInst = nullptr);
98 
99 /// Scan backwards to see if we have the value of the given pointer available
100 /// locally within a small number of instructions.
101 ///
102 /// You can use this function to scan across multiple blocks: after you call
103 /// this function, if ScanFrom points at the beginning of the block, it's safe
104 /// to continue scanning the predecessors.
105 ///
106 /// \param Ptr The pointer we want the load and store to originate from.
107 /// \param AccessTy The access type of the pointer.
108 /// \param AtLeastAtomic Are we looking for at-least an atomic load/store ? In
109 /// case it is false, we can return an atomic or non-atomic load or store. In
110 /// case it is true, we need to return an atomic load or store.
111 /// \param ScanBB The basic block to scan.
112 /// \param [in,out] ScanFrom The location to start scanning from. When this
113 /// function returns, it points at the last instruction scanned.
114 /// \param MaxInstsToScan The maximum number of instructions to scan. If this
115 /// is zero, the whole block will be scanned.
116 /// \param AA Optional pointer to alias analysis, to make the scan more
117 /// precise.
118 /// \param [out] IsLoad Whether the returned value is a load from the same
119 /// location in memory, as opposed to the value operand of a store.
120 ///
121 /// \returns The found value, or nullptr if no value is found.
122 Value *FindAvailablePtrLoadStore(Value *Ptr, Type *AccessTy, bool AtLeastAtomic,
123  BasicBlock *ScanBB,
124  BasicBlock::iterator &ScanFrom,
125  unsigned MaxInstsToScan, AliasAnalysis *AA,
126  bool *IsLoad, unsigned *NumScanedInst);
127 }
128 
129 #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().
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:343
bool isSafeToLoadUnconditionally(Value *V, unsigned Align, 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:200
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:328
AAResults AliasAnalysis
Temporary typedef for legacy code that uses a generic AliasAnalysis pointer or reference.
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:89
bool isDereferenceablePointer(const Value *V, const DataLayout &DL, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr)
Return true if this is always a dereferenceable pointer.
Definition: Loads.cpp:152
uint32_t Size
Definition: Profile.cpp:46
bool isDereferenceableAndAlignedPointer(const Value *V, 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