LLVM  15.0.0git
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 
16 #include "llvm/IR/BasicBlock.h"
18 
19 namespace llvm {
20 
21 class AAResults;
22 class DataLayout;
23 class DominatorTree;
24 class Instruction;
25 class LoadInst;
26 class Loop;
27 class MemoryLocation;
28 class ScalarEvolution;
29 class TargetLibraryInfo;
30 
31 /// Return true if this is always a dereferenceable pointer. If the context
32 /// instruction is specified perform context-sensitive analysis and return true
33 /// if the pointer is dereferenceable at the specified instruction.
34 bool isDereferenceablePointer(const Value *V, Type *Ty,
35  const DataLayout &DL,
36  const Instruction *CtxI = nullptr,
37  const DominatorTree *DT = nullptr,
38  const TargetLibraryInfo *TLI = nullptr);
39 
40 /// Returns true if V is always a dereferenceable pointer with alignment
41 /// greater or equal than requested. If the context instruction is specified
42 /// performs context-sensitive analysis and returns true if the pointer is
43 /// dereferenceable at the specified instruction.
45  Align Alignment, const DataLayout &DL,
46  const Instruction *CtxI = nullptr,
47  const DominatorTree *DT = nullptr,
48  const TargetLibraryInfo *TLI = nullptr);
49 
50 /// Returns true if V is always dereferenceable for Size byte with alignment
51 /// greater or equal than requested. If the context instruction is specified
52 /// performs context-sensitive analysis and returns true if the pointer is
53 /// dereferenceable at the specified instruction.
54 bool isDereferenceableAndAlignedPointer(const Value *V, Align Alignment,
55  const APInt &Size, const DataLayout &DL,
56  const Instruction *CtxI = nullptr,
57  const DominatorTree *DT = nullptr,
58  const TargetLibraryInfo *TLI = nullptr);
59 
60 /// Return true if we know that executing a load from this value cannot trap.
61 ///
62 /// If DT and ScanFrom are specified this method performs context-sensitive
63 /// analysis and returns true if it is safe to load immediately before ScanFrom.
64 ///
65 /// If it is not obviously safe to load from the specified pointer, we do a
66 /// quick local scan of the basic block containing ScanFrom, to determine if
67 /// the address is already accessed.
68 bool isSafeToLoadUnconditionally(Value *V, Align Alignment, APInt &Size,
69  const DataLayout &DL,
70  Instruction *ScanFrom = nullptr,
71  const DominatorTree *DT = nullptr,
72  const TargetLibraryInfo *TLI = nullptr);
73 
74 /// Return true if we can prove that the given load (which is assumed to be
75 /// within the specified loop) would access only dereferenceable memory, and
76 /// be properly aligned on every iteration of the specified loop regardless of
77 /// its placement within the loop. (i.e. does not require predication beyond
78 /// that required by the header itself and could be hoisted into the header
79 /// if desired.) This is more powerful than the variants above when the
80 /// address loaded from is analyzeable by SCEV.
81 bool isDereferenceableAndAlignedInLoop(LoadInst *LI, Loop *L,
82  ScalarEvolution &SE,
83  DominatorTree &DT);
84 
85 /// Return true if we know that executing a load from this value cannot trap.
86 ///
87 /// If DT and ScanFrom are specified this method performs context-sensitive
88 /// analysis and returns true if it is safe to load immediately before ScanFrom.
89 ///
90 /// If it is not obviously safe to load from the specified pointer, we do a
91 /// quick local scan of the basic block containing ScanFrom, to determine if
92 /// the address is already accessed.
93 bool isSafeToLoadUnconditionally(Value *V, Type *Ty, Align Alignment,
94  const DataLayout &DL,
95  Instruction *ScanFrom = nullptr,
96  const DominatorTree *DT = nullptr,
97  const TargetLibraryInfo *TLI = nullptr);
98 
99 /// The default number of maximum instructions to scan in the block, used by
100 /// FindAvailableLoadedValue().
101 extern cl::opt<unsigned> DefMaxInstsToScan;
102 
103 /// Scan backwards to see if we have the value of the given load available
104 /// locally within a small number of instructions.
105 ///
106 /// You can use this function to scan across multiple blocks: after you call
107 /// this function, if ScanFrom points at the beginning of the block, it's safe
108 /// to continue scanning the predecessors.
109 ///
110 /// Note that performing load CSE requires special care to make sure the
111 /// metadata is set appropriately. In particular, aliasing metadata needs
112 /// to be merged. (This doesn't matter for store-to-load forwarding because
113 /// the only relevant load gets deleted.)
114 ///
115 /// \param Load The load we want to replace.
116 /// \param ScanBB The basic block to scan.
117 /// \param [in,out] ScanFrom The location to start scanning from. When this
118 /// function returns, it points at the last instruction scanned.
119 /// \param MaxInstsToScan The maximum number of instructions to scan. If this
120 /// is zero, the whole block will be scanned.
121 /// \param AA Optional pointer to alias analysis, to make the scan more
122 /// precise.
123 /// \param [out] IsLoadCSE Whether the returned value is a load from the same
124 /// location in memory, as opposed to the value operand of a store.
125 ///
126 /// \returns The found value, or nullptr if no value is found.
128  BasicBlock *ScanBB,
129  BasicBlock::iterator &ScanFrom,
130  unsigned MaxInstsToScan = DefMaxInstsToScan,
131  AAResults *AA = nullptr,
132  bool *IsLoadCSE = nullptr,
133  unsigned *NumScanedInst = nullptr);
134 
135 /// This overload provides a more efficient implementation of
136 /// FindAvailableLoadedValue() for the case where we are not interested in
137 /// finding the closest clobbering instruction if no available load is found.
138 /// This overload cannot be used to scan across multiple blocks.
139 Value *FindAvailableLoadedValue(LoadInst *Load, AAResults &AA, bool *IsLoadCSE,
140  unsigned MaxInstsToScan = DefMaxInstsToScan);
141 
142 /// Scan backwards to see if we have the value of the given pointer available
143 /// locally within a small number of instructions.
144 ///
145 /// You can use this function to scan across multiple blocks: after you call
146 /// this function, if ScanFrom points at the beginning of the block, it's safe
147 /// to continue scanning the predecessors.
148 ///
149 /// \param Loc The location we want the load and store to originate from.
150 /// \param AccessTy The access type of the pointer.
151 /// \param AtLeastAtomic Are we looking for at-least an atomic load/store ? In
152 /// case it is false, we can return an atomic or non-atomic load or store. In
153 /// case it is true, we need to return an atomic load or store.
154 /// \param ScanBB The basic block to scan.
155 /// \param [in,out] ScanFrom The location to start scanning from. When this
156 /// function returns, it points at the last instruction scanned.
157 /// \param MaxInstsToScan The maximum number of instructions to scan. If this
158 /// is zero, the whole block will be scanned.
159 /// \param AA Optional pointer to alias analysis, to make the scan more
160 /// precise.
161 /// \param [out] IsLoadCSE Whether the returned value is a load from the same
162 /// location in memory, as opposed to the value operand of a store.
163 ///
164 /// \returns The found value, or nullptr if no value is found.
165 Value *findAvailablePtrLoadStore(const MemoryLocation &Loc, Type *AccessTy,
166  bool AtLeastAtomic, BasicBlock *ScanBB,
167  BasicBlock::iterator &ScanFrom,
168  unsigned MaxInstsToScan, AAResults *AA,
169  bool *IsLoadCSE, unsigned *NumScanedInst);
170 
171 /// Returns true if a pointer value \p A can be replace with another pointer
172 /// value \B if they are deemed equal through some means (e.g. information from
173 /// conditions).
174 /// NOTE: the current implementations is incomplete and unsound. It does not
175 /// reject all invalid cases yet, but will be made stricter in the future. In
176 /// particular this means returning true means unknown if replacement is safe.
177 bool canReplacePointersIfEqual(Value *A, Value *B, const DataLayout &DL,
178  Instruction *CtxI);
179 }
180 
181 #endif
llvm::Check::Size
@ Size
Definition: FileCheck.h:77
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:17
llvm::BasicBlock::iterator
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:87
llvm::canReplacePointersIfEqual
bool canReplacePointersIfEqual(Value *A, Value *B, const DataLayout &DL, Instruction *CtxI)
Returns true if a pointer value A can be replace with another pointer value \B if they are deemed equ...
Definition: Loads.cpp:646
CommandLine.h
llvm::SPII::Load
@ Load
Definition: SparcInstrInfo.h:32
B
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
llvm::isDereferenceablePointer
bool isDereferenceablePointer(const Value *V, Type *Ty, const DataLayout &DL, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr, const TargetLibraryInfo *TLI=nullptr)
Return true if this is always a dereferenceable pointer.
Definition: Loads.cpp:227
Align
uint64_t Align
Definition: ELFObjHandler.cpp:81
llvm::findAvailablePtrLoadStore
Value * findAvailablePtrLoadStore(const MemoryLocation &Loc, Type *AccessTy, bool AtLeastAtomic, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan, AAResults *AA, bool *IsLoadCSE, unsigned *NumScanedInst)
Scan backwards to see if we have the value of the given pointer available locally within a small numb...
Definition: Loads.cpp:517
BasicBlock.h
TemplateParamKind::Type
@ Type
llvm::ISD::BasicBlock
@ BasicBlock
Various leaf nodes.
Definition: ISDOpcodes.h:71
llvm::isDereferenceableAndAlignedInLoop
bool isDereferenceableAndAlignedInLoop(LoadInst *LI, Loop *L, ScalarEvolution &SE, DominatorTree &DT)
Return true if we can prove that the given load (which is assumed to be within the specified loop) wo...
Definition: Loads.cpp:266
A
* A
Definition: README_ALTIVEC.txt:89
DL
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
Definition: AArch64SLSHardening.cpp:76
llvm::FindAvailableLoadedValue
Value * FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan=DefMaxInstsToScan, AAResults *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:424
llvm::TargetStackID::Value
Value
Definition: TargetFrameLowering.h:27
AA
llvm::isSafeToLoadUnconditionally
bool isSafeToLoadUnconditionally(Value *V, Align Alignment, APInt &Size, const DataLayout &DL, Instruction *ScanFrom=nullptr, const DominatorTree *DT=nullptr, const TargetLibraryInfo *TLI=nullptr)
Return true if we know that executing a load from this value cannot trap.
Definition: Loads.cpp:328
llvm::DefMaxInstsToScan
cl::opt< unsigned > DefMaxInstsToScan
The default number of maximum instructions to scan in the block, used by FindAvailableLoadedValue().
llvm::isDereferenceableAndAlignedPointer
bool isDereferenceableAndAlignedPointer(const Value *V, Type *Ty, Align Alignment, const DataLayout &DL, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr, const TargetLibraryInfo *TLI=nullptr)
Returns true if V is always a dereferenceable pointer with alignment greater or equal than requested.
Definition: Loads.cpp:205