xref: /freebsd/contrib/llvm-project/lld/MachO/SectionPriorities.h (revision a90b9d0159070121c221b966469c3e36d912bf82)
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 
15 namespace lld::macho {
16 
17 using SectionPair = std::pair<const InputSection *, const InputSection *>;
18 
19 class PriorityBuilder {
20 public:
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 
57 private:
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 
77 extern PriorityBuilder priorityBuilder;
78 } // namespace lld::macho
79 
80 #endif
81