1 //===-- CodeGen/MachineJumpTableInfo.h - Abstract Jump Tables  --*- 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 // The MachineJumpTableInfo class keeps track of jump tables referenced by
10 // lowered switch instructions in the MachineFunction.
11 //
12 // Instructions reference the address of these jump tables through the use of
13 // MO_JumpTableIndex values.  When emitting assembly or machine code, these
14 // virtual address references are converted to refer to the address of the
15 // function jump tables.
16 //
17 //===----------------------------------------------------------------------===//
18 
19 #ifndef LLVM_CODEGEN_MACHINEJUMPTABLEINFO_H
20 #define LLVM_CODEGEN_MACHINEJUMPTABLEINFO_H
21 
22 #include "llvm/Support/Printable.h"
23 #include <cassert>
24 #include <vector>
25 
26 namespace llvm {
27 
28 class MachineBasicBlock;
29 class DataLayout;
30 class raw_ostream;
31 
32 /// MachineJumpTableEntry - One jump table in the jump table info.
33 ///
34 struct MachineJumpTableEntry {
35   /// MBBs - The vector of basic blocks from which to create the jump table.
36   std::vector<MachineBasicBlock*> MBBs;
37 
MachineJumpTableEntryMachineJumpTableEntry38   explicit MachineJumpTableEntry(const std::vector<MachineBasicBlock*> &M)
39   : MBBs(M) {}
40 };
41 
42 class MachineJumpTableInfo {
43 public:
44   /// JTEntryKind - This enum indicates how each entry of the jump table is
45   /// represented and emitted.
46   enum JTEntryKind {
47     /// EK_BlockAddress - Each entry is a plain address of block, e.g.:
48     ///     .word LBB123
49     EK_BlockAddress,
50 
51     /// EK_GPRel64BlockAddress - Each entry is an address of block, encoded
52     /// with a relocation as gp-relative, e.g.:
53     ///     .gpdword LBB123
54     EK_GPRel64BlockAddress,
55 
56     /// EK_GPRel32BlockAddress - Each entry is an address of block, encoded
57     /// with a relocation as gp-relative, e.g.:
58     ///     .gprel32 LBB123
59     EK_GPRel32BlockAddress,
60 
61     /// EK_LabelDifference32 - Each entry is the address of the block minus
62     /// the address of the jump table.  This is used for PIC jump tables where
63     /// gprel32 is not supported.  e.g.:
64     ///      .word LBB123 - LJTI1_2
65     /// If the .set directive is supported, this is emitted as:
66     ///      .set L4_5_set_123, LBB123 - LJTI1_2
67     ///      .word L4_5_set_123
68     EK_LabelDifference32,
69 
70     /// EK_Inline - Jump table entries are emitted inline at their point of
71     /// use. It is the responsibility of the target to emit the entries.
72     EK_Inline,
73 
74     /// EK_Custom32 - Each entry is a 32-bit value that is custom lowered by the
75     /// TargetLowering::LowerCustomJumpTableEntry hook.
76     EK_Custom32
77   };
78 private:
79   JTEntryKind EntryKind;
80   std::vector<MachineJumpTableEntry> JumpTables;
81 public:
MachineJumpTableInfo(JTEntryKind Kind)82   explicit MachineJumpTableInfo(JTEntryKind Kind): EntryKind(Kind) {}
83 
getEntryKind()84   JTEntryKind getEntryKind() const { return EntryKind; }
85 
86   /// getEntrySize - Return the size of each entry in the jump table.
87   unsigned getEntrySize(const DataLayout &TD) const;
88   /// getEntryAlignment - Return the alignment of each entry in the jump table.
89   unsigned getEntryAlignment(const DataLayout &TD) const;
90 
91   /// createJumpTableIndex - Create a new jump table.
92   ///
93   unsigned createJumpTableIndex(const std::vector<MachineBasicBlock*> &DestBBs);
94 
95   /// isEmpty - Return true if there are no jump tables.
96   ///
isEmpty()97   bool isEmpty() const { return JumpTables.empty(); }
98 
getJumpTables()99   const std::vector<MachineJumpTableEntry> &getJumpTables() const {
100     return JumpTables;
101   }
102 
103   /// RemoveJumpTable - Mark the specific index as being dead.  This will
104   /// prevent it from being emitted.
RemoveJumpTable(unsigned Idx)105   void RemoveJumpTable(unsigned Idx) {
106     JumpTables[Idx].MBBs.clear();
107   }
108 
109   /// RemoveMBBFromJumpTables - If MBB is present in any jump tables, remove it.
110   bool RemoveMBBFromJumpTables(MachineBasicBlock *MBB);
111 
112   /// ReplaceMBBInJumpTables - If Old is the target of any jump tables, update
113   /// the jump tables to branch to New instead.
114   bool ReplaceMBBInJumpTables(MachineBasicBlock *Old, MachineBasicBlock *New);
115 
116   /// ReplaceMBBInJumpTable - If Old is a target of the jump tables, update
117   /// the jump table to branch to New instead.
118   bool ReplaceMBBInJumpTable(unsigned Idx, MachineBasicBlock *Old,
119                              MachineBasicBlock *New);
120 
121   /// print - Used by the MachineFunction printer to print information about
122   /// jump tables.  Implemented in MachineFunction.cpp
123   ///
124   void print(raw_ostream &OS) const;
125 
126   /// dump - Call to stderr.
127   ///
128   void dump() const;
129 };
130 
131 
132 /// Prints a jump table entry reference.
133 ///
134 /// The format is:
135 ///   %jump-table.5       - a jump table entry with index == 5.
136 ///
137 /// Usage: OS << printJumpTableEntryReference(Idx) << '\n';
138 Printable printJumpTableEntryReference(unsigned Idx);
139 
140 } // End llvm namespace
141 
142 #endif
143