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
25namespace llvm {
26
27class BasicBlock;
28class Instruction;
29
30class InstructionPrecedenceTracking {
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.
34  DenseMap<const BasicBlock *, const Instruction *> FirstSpecialInsts;
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
51protected:
52  /// Returns the topmost special instruction from the block \p BB. Returns
53  /// nullptr if there is no special instructions in the block.
54  const Instruction *getFirstSpecialInstruction(const BasicBlock *BB);
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.
62  bool isPreceededBySpecialInstruction(const Instruction *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
73public:
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  /// Notifies this tracking that we are going to replace all uses of \p Inst.
84  /// It makes all necessary updates to internal caches to keep them consistent.
85  /// Should typically be called before a RAUW.
86  void removeUsersOf(const Instruction *Inst);
87
88  /// Invalidates all information from this tracking.
89  void clear();
90};
91
92/// This class allows to keep track on instructions with implicit control flow.
93/// These are instructions that may not pass execution to their successors. For
94/// example, throwing calls and guards do not always do this. If we need to know
95/// for sure that some instruction is guaranteed to execute if the given block
96/// is reached, then we need to make sure that there is no implicit control flow
97/// instruction (ICFI) preceding it. For example, this check is required if we
98/// perform PRE moving non-speculable instruction to other place.
99class ImplicitControlFlowTracking : public InstructionPrecedenceTracking {
100public:
101  /// Returns the topmost instruction with implicit control flow from the given
102  /// basic block. Returns nullptr if there is no such instructions in the block.
103  const Instruction *getFirstICFI(const BasicBlock *BB) {
104    return getFirstSpecialInstruction(BB);
105  }
106
107  /// Returns true if at least one instruction from the given basic block has
108  /// implicit control flow.
109  bool hasICF(const BasicBlock *BB) {
110    return hasSpecialInstructions(BB);
111  }
112
113  /// Returns true if the first ICFI of Insn's block exists and dominates Insn.
114  bool isDominatedByICFIFromSameBlock(const Instruction *Insn) {
115    return isPreceededBySpecialInstruction(Insn);
116  }
117
118  bool isSpecialInstruction(const Instruction *Insn) const override;
119};
120
121class MemoryWriteTracking : public InstructionPrecedenceTracking {
122public:
123  /// Returns the topmost instruction that may write memory from the given
124  /// basic block. Returns nullptr if there is no such instructions in the block.
125  const Instruction *getFirstMemoryWrite(const BasicBlock *BB) {
126    return getFirstSpecialInstruction(BB);
127  }
128
129  /// Returns true if at least one instruction from the given basic block may
130  /// write memory.
131  bool mayWriteToMemory(const BasicBlock *BB) {
132    return hasSpecialInstructions(BB);
133  }
134
135  /// Returns true if the first memory writing instruction of Insn's block
136  /// exists and dominates Insn.
137  bool isDominatedByMemoryWriteFromSameBlock(const Instruction *Insn) {
138    return isPreceededBySpecialInstruction(Insn);
139  }
140
141  bool isSpecialInstruction(const Instruction *Insn) const override;
142};
143
144} // llvm
145
146#endif // LLVM_ANALYSIS_INSTRUCTIONPRECEDENCETRACKING_H
147