1//===- EHStreamer.h - Exception Handling Directive Streamer -----*- 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 contains support for writing exception info into assembly files.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H
14#define LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H
15
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/CodeGen/AsmPrinterHandler.h"
18#include "llvm/Support/Compiler.h"
19
20namespace llvm {
21
22class AsmPrinter;
23struct LandingPadInfo;
24class MachineInstr;
25class MachineModuleInfo;
26class MCSymbol;
27template <typename T> class SmallVectorImpl;
28
29/// Emits exception handling directives.
30class LLVM_LIBRARY_VISIBILITY EHStreamer : public AsmPrinterHandler {
31protected:
32  /// Target of directive emission.
33  AsmPrinter *Asm;
34
35  /// Collected machine module information.
36  MachineModuleInfo *MMI;
37
38  /// How many leading type ids two landing pads have in common.
39  static unsigned sharedTypeIDs(const LandingPadInfo *L,
40                                const LandingPadInfo *R);
41
42  /// Structure holding a try-range and the associated landing pad.
43  struct PadRange {
44    // The index of the landing pad.
45    unsigned PadIndex;
46
47    // The index of the begin and end labels in the landing pad's label lists.
48    unsigned RangeIndex;
49  };
50
51  using RangeMapType = DenseMap<MCSymbol *, PadRange>;
52
53  /// Structure describing an entry in the actions table.
54  struct ActionEntry {
55    int ValueForTypeID; // The value to write - may not be equal to the type id.
56    int NextAction;
57    unsigned Previous;
58  };
59
60  /// Structure describing an entry in the call-site table.
61  struct CallSiteEntry {
62    // The 'try-range' is BeginLabel .. EndLabel.
63    MCSymbol *BeginLabel; // Null indicates the start of the function.
64    MCSymbol *EndLabel;   // Null indicates the end of the function.
65
66    // LPad contains the landing pad start labels.
67    const LandingPadInfo *LPad; // Null indicates that there is no landing pad.
68
69    unsigned Action;
70  };
71
72  /// Compute the actions table and gather the first action index for each
73  /// landing pad site.
74  void computeActionsTable(const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
75                           SmallVectorImpl<ActionEntry> &Actions,
76                           SmallVectorImpl<unsigned> &FirstActions);
77
78  void computePadMap(const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
79                     RangeMapType &PadMap);
80
81  /// Compute the call-site table.  The entry for an invoke has a try-range
82  /// containing the call, a non-zero landing pad and an appropriate action.
83  /// The entry for an ordinary call has a try-range containing the call and
84  /// zero for the landing pad and the action.  Calls marked 'nounwind' have
85  /// no entry and must not be contained in the try-range of any entry - they
86  /// form gaps in the table.  Entries must be ordered by try-range address.
87  virtual void computeCallSiteTable(
88      SmallVectorImpl<CallSiteEntry> &CallSites,
89      const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
90      const SmallVectorImpl<unsigned> &FirstActions);
91
92  /// Emit landing pads and actions.
93  ///
94  /// The general organization of the table is complex, but the basic concepts
95  /// are easy.  First there is a header which describes the location and
96  /// organization of the three components that follow.
97  ///  1. The landing pad site information describes the range of code covered
98  ///     by the try.  In our case it's an accumulation of the ranges covered
99  ///     by the invokes in the try.  There is also a reference to the landing
100  ///     pad that handles the exception once processed.  Finally an index into
101  ///     the actions table.
102  ///  2. The action table, in our case, is composed of pairs of type ids
103  ///     and next action offset.  Starting with the action index from the
104  ///     landing pad site, each type Id is checked for a match to the current
105  ///     exception.  If it matches then the exception and type id are passed
106  ///     on to the landing pad.  Otherwise the next action is looked up.  This
107  ///     chain is terminated with a next action of zero.  If no type id is
108  ///     found the frame is unwound and handling continues.
109  ///  3. Type id table contains references to all the C++ typeinfo for all
110  ///     catches in the function.  This tables is reversed indexed base 1.
111  ///
112  /// Returns the starting symbol of an exception table.
113  MCSymbol *emitExceptionTable();
114
115  virtual void emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel);
116
117  // Helpers for identifying what kind of clause an EH typeid or selector
118  // corresponds to. Negative selectors are for filter clauses, the zero
119  // selector is for cleanups, and positive selectors are for catch clauses.
120  static bool isFilterEHSelector(int Selector) { return Selector < 0; }
121  static bool isCleanupEHSelector(int Selector) { return Selector == 0; }
122  static bool isCatchEHSelector(int Selector) { return Selector > 0; }
123
124public:
125  EHStreamer(AsmPrinter *A);
126  ~EHStreamer() override;
127
128  // Unused.
129  void setSymbolSize(const MCSymbol *Sym, uint64_t Size) override {}
130  void beginInstruction(const MachineInstr *MI) override {}
131  void endInstruction() override {}
132
133  /// Return `true' if this is a call to a function marked `nounwind'. Return
134  /// `false' otherwise.
135  static bool callToNoUnwindFunction(const MachineInstr *MI);
136};
137
138} // end namespace llvm
139
140#endif // LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H
141