LLVM  12.0.0git
InstructionPrecedenceTracking.h
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1 //===-- InstructionPrecedenceTracking.h -------------------------*- C++ -*-===//
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 // Implements a class that is able to define some instructions as "special"
9 // (e.g. as having implicit control flow, or writing memory, or having another
10 // interesting property) and then efficiently answers queries of the types:
11 // 1. Are there any special instructions in the block of interest?
12 // 2. Return first of the special instructions in the given block;
13 // 3. Check if the given instruction is preceeded by the first special
14 // instruction in the same block.
15 // The class provides caching that allows to answer these queries quickly. The
16 // user must make sure that the cached data is invalidated properly whenever
17 // a content of some tracked block is changed.
18 //===----------------------------------------------------------------------===//
19 
20 #ifndef LLVM_ANALYSIS_INSTRUCTIONPRECEDENCETRACKING_H
21 #define LLVM_ANALYSIS_INSTRUCTIONPRECEDENCETRACKING_H
22 
23 #include "llvm/ADT/DenseMap.h"
24 
25 namespace llvm {
26 
27 class BasicBlock;
28 class Instruction;
29 
31  // Maps a block to the topmost special instruction in it. If the value is
32  // nullptr, it means that it is known that this block does not contain any
33  // special instructions.
35 
36  // Fills information about the given block's special instructions.
37  void fill(const BasicBlock *BB);
38 
39 #ifndef NDEBUG
40  /// Asserts that the cached info for \p BB is up-to-date. This helps to catch
41  /// the usage error of accessing a block without properly invalidating after a
42  /// previous transform.
43  void validate(const BasicBlock *BB) const;
44 
45  /// Asserts whether or not the contents of this tracking is up-to-date. This
46  /// helps to catch the usage error of accessing a block without properly
47  /// invalidating after a previous transform.
48  void validateAll() const;
49 #endif
50 
51 protected:
52  /// Returns the topmost special instruction from the block \p BB. Returns
53  /// nullptr if there is no special instructions in the block.
55 
56  /// Returns true iff at least one instruction from the basic block \p BB is
57  /// special.
58  bool hasSpecialInstructions(const BasicBlock *BB);
59 
60  /// Returns true iff the first special instruction of \p Insn's block exists
61  /// and dominates \p Insn.
63 
64  /// A predicate that defines whether or not the instruction \p Insn is
65  /// considered special and needs to be tracked. Implementing this method in
66  /// children classes allows to implement tracking of implicit control flow,
67  /// memory writing instructions or any other kinds of instructions we might
68  /// be interested in.
69  virtual bool isSpecialInstruction(const Instruction *Insn) const = 0;
70 
71  virtual ~InstructionPrecedenceTracking() = default;
72 
73 public:
74  /// Notifies this tracking that we are going to insert a new instruction \p
75  /// Inst to the basic block \p BB. It makes all necessary updates to internal
76  /// caches to keep them consistent.
77  void insertInstructionTo(const Instruction *Inst, const BasicBlock *BB);
78 
79  /// Notifies this tracking that we are going to remove the instruction \p Inst
80  /// It makes all necessary updates to internal caches to keep them consistent.
81  void removeInstruction(const Instruction *Inst);
82 
83  /// Invalidates all information from this tracking.
84  void clear();
85 };
86 
87 /// This class allows to keep track on instructions with implicit control flow.
88 /// These are instructions that may not pass execution to their successors. For
89 /// example, throwing calls and guards do not always do this. If we need to know
90 /// for sure that some instruction is guaranteed to execute if the given block
91 /// is reached, then we need to make sure that there is no implicit control flow
92 /// instruction (ICFI) preceding it. For example, this check is required if we
93 /// perform PRE moving non-speculable instruction to other place.
95 public:
96  /// Returns the topmost instruction with implicit control flow from the given
97  /// basic block. Returns nullptr if there is no such instructions in the block.
98  const Instruction *getFirstICFI(const BasicBlock *BB) {
99  return getFirstSpecialInstruction(BB);
100  }
101 
102  /// Returns true if at least one instruction from the given basic block has
103  /// implicit control flow.
104  bool hasICF(const BasicBlock *BB) {
105  return hasSpecialInstructions(BB);
106  }
107 
108  /// Returns true if the first ICFI of Insn's block exists and dominates Insn.
110  return isPreceededBySpecialInstruction(Insn);
111  }
112 
113  bool isSpecialInstruction(const Instruction *Insn) const override;
114 };
115 
117 public:
118  /// Returns the topmost instruction that may write memory from the given
119  /// basic block. Returns nullptr if there is no such instructions in the block.
121  return getFirstSpecialInstruction(BB);
122  }
123 
124  /// Returns true if at least one instruction from the given basic block may
125  /// write memory.
126  bool mayWriteToMemory(const BasicBlock *BB) {
127  return hasSpecialInstructions(BB);
128  }
129 
130  /// Returns true if the first memory writing instruction of Insn's block
131  /// exists and dominates Insn.
133  return isPreceededBySpecialInstruction(Insn);
134  }
135 
136  bool isSpecialInstruction(const Instruction *Insn) const override;
137 };
138 
139 } // llvm
140 
141 #endif // LLVM_ANALYSIS_INSTRUCTIONPRECEDENCETRACKING_H
This class represents lattice values for constants.
Definition: AllocatorList.h:23
Various leaf nodes.
Definition: ISDOpcodes.h:64
void clear()
Invalidates all information from this tracking.
bool hasSpecialInstructions(const BasicBlock *BB)
Returns true iff at least one instruction from the basic block BB is special.
LLVM Basic Block Representation.
Definition: BasicBlock.h:58
const Instruction * getFirstICFI(const BasicBlock *BB)
Returns the topmost instruction with implicit control flow from the given basic block.
bool hasICF(const BasicBlock *BB)
Returns true if at least one instruction from the given basic block has implicit control flow...
bool isDominatedByICFIFromSameBlock(const Instruction *Insn)
Returns true if the first ICFI of Insn's block exists and dominates Insn.
const Instruction * getFirstSpecialInstruction(const BasicBlock *BB)
Returns the topmost special instruction from the block BB.
void insertInstructionTo(const Instruction *Inst, const BasicBlock *BB)
Notifies this tracking that we are going to insert a new instruction Inst to the basic block BB...
void removeInstruction(const Instruction *Inst)
Notifies this tracking that we are going to remove the instruction Inst It makes all necessary update...
bool isPreceededBySpecialInstruction(const Instruction *Insn)
Returns true iff the first special instruction of Insn's block exists and dominates Insn...
This class allows to keep track on instructions with implicit control flow.
virtual bool isSpecialInstruction(const Instruction *Insn) const =0
A predicate that defines whether or not the instruction Insn is considered special and needs to be tr...
bool mayWriteToMemory(const BasicBlock *BB)
Returns true if at least one instruction from the given basic block may write memory.
virtual ~InstructionPrecedenceTracking()=default
const Instruction * getFirstMemoryWrite(const BasicBlock *BB)
Returns the topmost instruction that may write memory from the given basic block. ...
bool isDominatedByMemoryWriteFromSameBlock(const Instruction *Insn)
Returns true if the first memory writing instruction of Insn's block exists and dominates Insn...