1//===- SectionPriorities.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
9#ifndef LLD_MACHO_SECTION_PRIORITIES_H
10#define LLD_MACHO_SECTION_PRIORITIES_H
11
12#include "InputSection.h"
13#include "llvm/ADT/DenseMap.h"
14
15namespace lld::macho {
16
17using SectionPair = std::pair<const InputSection *, const InputSection *>;
18
19class PriorityBuilder {
20public:
21  // Reads every input section's call graph profile, and combines them into
22  // callGraphProfile. If an order file is present, any edges where one or both
23  // of the vertices are specified in the order file are discarded.
24  void extractCallGraphProfile();
25
26  // Reads the order file at `path` into config->priorities.
27  //
28  // An order file has one entry per line, in the following format:
29  //
30  //   <cpu>:<object file>:<symbol name>
31  //
32  // <cpu> and <object file> are optional. If not specified, then that entry
33  // matches any symbol of that name. Parsing this format is not quite
34  // straightforward because the symbol name itself can contain colons, so when
35  // encountering a colon, we consider the preceding characters to decide if it
36  // can be a valid CPU type or file path.
37  //
38  // If a symbol is matched by multiple entries, then it takes the
39  // lowest-ordered entry (the one nearest to the front of the list.)
40  //
41  // The file can also have line comments that start with '#'.
42  void parseOrderFile(StringRef path);
43
44  // Returns layout priorities for some or all input sections. Sections are laid
45  // out in decreasing order; that is, a higher priority section will be closer
46  // to the beginning of its output section.
47  //
48  // If either an order file or a call graph profile are present, this is used
49  // as the source of priorities. If both are present, the order file takes
50  // precedence, but the call graph profile is still used for symbols that don't
51  // appear in the order file. If neither is present, an empty map is returned.
52  //
53  // Each section gets assigned the priority of the highest-priority symbol it
54  // contains.
55  llvm::DenseMap<const InputSection *, size_t> buildInputSectionPriorities();
56
57private:
58  // The symbol with the highest priority should be ordered first in the output
59  // section (modulo input section contiguity constraints). Using priority
60  // (highest first) instead of order (lowest first) has the convenient property
61  // that the default-constructed zero priority -- for symbols/sections without
62  // a user-defined order -- naturally ends up putting them at the end of the
63  // output.
64  struct SymbolPriorityEntry {
65    // The priority given to a matching symbol, regardless of which object file
66    // it originated from.
67    size_t anyObjectFile = 0;
68    // The priority given to a matching symbol from a particular object file.
69    llvm::DenseMap<llvm::StringRef, size_t> objectFiles;
70  };
71
72  std::optional<size_t> getSymbolPriority(const Defined *sym);
73  llvm::DenseMap<llvm::StringRef, SymbolPriorityEntry> priorities;
74  llvm::MapVector<SectionPair, uint64_t> callGraphProfile;
75};
76
77extern PriorityBuilder priorityBuilder;
78} // namespace lld::macho
79
80#endif
81