1 //===- CFGUpdate.h - Encode a CFG Edge Update. ------------------*- 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 //
9 // This file defines a CFG Edge Update: Insert or Delete, and two Nodes as the
10 // Edge ends.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #ifndef LLVM_SUPPORT_CFGUPDATE_H
15 #define LLVM_SUPPORT_CFGUPDATE_H
16
17 #include "llvm/ADT/APInt.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/PointerIntPair.h"
20 #include "llvm/Support/Compiler.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Support/raw_ostream.h"
23
24 namespace llvm {
25 namespace cfg {
26 enum class UpdateKind : unsigned char { Insert, Delete };
27
28 template <typename NodePtr> class Update {
29 using NodeKindPair = PointerIntPair<NodePtr, 1, UpdateKind>;
30 NodePtr From;
31 NodeKindPair ToAndKind;
32
33 public:
Update(UpdateKind Kind,NodePtr From,NodePtr To)34 Update(UpdateKind Kind, NodePtr From, NodePtr To)
35 : From(From), ToAndKind(To, Kind) {}
36
getKind()37 UpdateKind getKind() const { return ToAndKind.getInt(); }
getFrom()38 NodePtr getFrom() const { return From; }
getTo()39 NodePtr getTo() const { return ToAndKind.getPointer(); }
40 bool operator==(const Update &RHS) const {
41 return From == RHS.From && ToAndKind == RHS.ToAndKind;
42 }
43
print(raw_ostream & OS)44 void print(raw_ostream &OS) const {
45 OS << (getKind() == UpdateKind::Insert ? "Insert " : "Delete ");
46 getFrom()->printAsOperand(OS, false);
47 OS << " -> ";
48 getTo()->printAsOperand(OS, false);
49 }
50
51 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
dump()52 LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
53 #endif
54 };
55
56 // LegalizeUpdates function simplifies updates assuming a graph structure.
57 // This function serves double purpose:
58 // a) It removes redundant updates, which makes it easier to reverse-apply
59 // them when traversing CFG.
60 // b) It optimizes away updates that cancel each other out, as the end result
61 // is the same.
62 template <typename NodePtr>
LegalizeUpdates(ArrayRef<Update<NodePtr>> AllUpdates,SmallVectorImpl<Update<NodePtr>> & Result,bool InverseGraph)63 void LegalizeUpdates(ArrayRef<Update<NodePtr>> AllUpdates,
64 SmallVectorImpl<Update<NodePtr>> &Result,
65 bool InverseGraph) {
66 // Count the total number of inserions of each edge.
67 // Each insertion adds 1 and deletion subtracts 1. The end number should be
68 // one of {-1 (deletion), 0 (NOP), +1 (insertion)}. Otherwise, the sequence
69 // of updates contains multiple updates of the same kind and we assert for
70 // that case.
71 SmallDenseMap<std::pair<NodePtr, NodePtr>, int, 4> Operations;
72 Operations.reserve(AllUpdates.size());
73
74 for (const auto &U : AllUpdates) {
75 NodePtr From = U.getFrom();
76 NodePtr To = U.getTo();
77 if (InverseGraph)
78 std::swap(From, To); // Reverse edge for postdominators.
79
80 Operations[{From, To}] += (U.getKind() == UpdateKind::Insert ? 1 : -1);
81 }
82
83 Result.clear();
84 Result.reserve(Operations.size());
85 for (auto &Op : Operations) {
86 const int NumInsertions = Op.second;
87 assert(std::abs(NumInsertions) <= 1 && "Unbalanced operations!");
88 if (NumInsertions == 0)
89 continue;
90 const UpdateKind UK =
91 NumInsertions > 0 ? UpdateKind::Insert : UpdateKind::Delete;
92 Result.push_back({UK, Op.first.first, Op.first.second});
93 }
94
95 // Make the order consistent by not relying on pointer values within the
96 // set. Reuse the old Operations map.
97 // In the future, we should sort by something else to minimize the amount
98 // of work needed to perform the series of updates.
99 for (size_t i = 0, e = AllUpdates.size(); i != e; ++i) {
100 const auto &U = AllUpdates[i];
101 if (!InverseGraph)
102 Operations[{U.getFrom(), U.getTo()}] = int(i);
103 else
104 Operations[{U.getTo(), U.getFrom()}] = int(i);
105 }
106
107 llvm::sort(Result,
108 [&Operations](const Update<NodePtr> &A, const Update<NodePtr> &B) {
109 return Operations[{A.getFrom(), A.getTo()}] >
110 Operations[{B.getFrom(), B.getTo()}];
111 });
112 }
113
114 } // end namespace cfg
115 } // end namespace llvm
116
117 #endif // LLVM_SUPPORT_CFGUPDATE_H
118