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 /// Structure describing a contiguous range of call-sites which reside
73 /// in the same procedure fragment. With -fbasic-block-sections, there will
74 /// be one call site range per basic block section. Otherwise, we will have
75 /// one call site range containing all the call sites in the function.
76 struct CallSiteRange {
77 // Symbol marking the beginning of the precedure fragment.
78 MCSymbol *FragmentBeginLabel = nullptr;
79 // Symbol marking the end of the procedure fragment.
80 MCSymbol *FragmentEndLabel = nullptr;
81 // LSDA symbol for this call-site range.
82 MCSymbol *ExceptionLabel = nullptr;
83 // Index of the first call-site entry in the call-site table which
84 // belongs to this range.
85 size_t CallSiteBeginIdx = 0;
86 // Index just after the last call-site entry in the call-site table which
87 // belongs to this range.
88 size_t CallSiteEndIdx = 0;
89 // Whether this is the call-site range containing all the landing pads.
90 bool IsLPRange = false;
91 };
92
93 /// Compute the actions table and gather the first action index for each
94 /// landing pad site.
95 void computeActionsTable(
96 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
97 SmallVectorImpl<ActionEntry> &Actions,
98 SmallVectorImpl<unsigned> &FirstActions);
99
100 void computePadMap(const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
101 RangeMapType &PadMap);
102
103 /// Compute the call-site table and the call-site ranges. The entry for an
104 /// invoke has a try-range containing the call, a non-zero landing pad and an
105 /// appropriate action. The entry for an ordinary call has a try-range
106 /// containing the call and zero for the landing pad and the action. Calls
107 /// marked 'nounwind' have no entry and must not be contained in the try-range
108 /// of any entry - they form gaps in the table. Entries must be ordered by
109 /// try-range address. CallSiteRanges vector is only populated for Itanium
110 /// exception handling.
111 virtual void computeCallSiteTable(
112 SmallVectorImpl<CallSiteEntry> &CallSites,
113 SmallVectorImpl<CallSiteRange> &CallSiteRanges,
114 const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
115 const SmallVectorImpl<unsigned> &FirstActions);
116
117 /// Emit landing pads and actions.
118 ///
119 /// The general organization of the table is complex, but the basic concepts
120 /// are easy. First there is a header which describes the location and
121 /// organization of the three components that follow.
122 /// 1. The landing pad site information describes the range of code covered
123 /// by the try. In our case it's an accumulation of the ranges covered
124 /// by the invokes in the try. There is also a reference to the landing
125 /// pad that handles the exception once processed. Finally an index into
126 /// the actions table.
127 /// 2. The action table, in our case, is composed of pairs of type ids
128 /// and next action offset. Starting with the action index from the
129 /// landing pad site, each type Id is checked for a match to the current
130 /// exception. If it matches then the exception and type id are passed
131 /// on to the landing pad. Otherwise the next action is looked up. This
132 /// chain is terminated with a next action of zero. If no type id is
133 /// found the frame is unwound and handling continues.
134 /// 3. Type id table contains references to all the C++ typeinfo for all
135 /// catches in the function. This tables is reversed indexed base 1.
136 ///
137 /// Returns the starting symbol of an exception table.
138 MCSymbol *emitExceptionTable();
139
140 virtual void emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel);
141
142 // Helpers for identifying what kind of clause an EH typeid or selector
143 // corresponds to. Negative selectors are for filter clauses, the zero
144 // selector is for cleanups, and positive selectors are for catch clauses.
145 static bool isFilterEHSelector(int Selector) { return Selector < 0; }
146 static bool isCleanupEHSelector(int Selector) { return Selector == 0; }
147 static bool isCatchEHSelector(int Selector) { return Selector > 0; }
148
149public:
150 EHStreamer(AsmPrinter *A);
151 ~EHStreamer() override;
152
153 /// Return `true' if this is a call to a function marked `nounwind'. Return
154 /// `false' otherwise.
155 static bool callToNoUnwindFunction(const MachineInstr *MI);
156};
157
158} // end namespace llvm
159
160#endif // LLVM_LIB_CODEGEN_ASMPRINTER_EHSTREAMER_H
161