40933fd410
Expand the `-order_file` also accept cstrings to order. The purpose is to order hot cstrings for performance (implemented in this diff), and then later on we can also order cold cstrings for compression size win. Due to the speciality of cstrings, there's no way to pass in symbol names in the order file as the existing -order_file, so we expect `<hash of cstring literal content>` to represent/identify each cstring. ``` // An order file has one entry per line, in the following format: // // <cpu>:<object file>:[<symbol name> | CStringEntryPrefix <cstring hash>] // // <cpu> and <object file> are optional. // If not specified, then that entry tries to match either, // // 1) any symbol of the <symbol name>; // Parsing this format is not quite straightforward because the symbol name // itself can contain colons, so when encountering a colon, we consider the // preceding characters to decide if it can be a valid CPU type or file path. // If a symbol is matched by multiple entries, then it takes the // lowest-ordered entry (the one nearest to the front of the list.) // // or 2) any cstring literal with the given hash, if the entry has the // CStringEntryPrefix prefix defined below in the file. <cstring hash> is the // hash of cstring literal content. // // Cstring literals are not symbolized, we can't identify them by name // However, cstrings are deduplicated, hence unique, so we use the hash of // the content of cstring literals to identify them and assign priority to it. // We use the same hash as used in StringPiece, i.e. 31 bit: // xxh3_64bits(string) & 0x7fffffff // ``` The ordering of cstring has to happen during/before the finalizing of the cstring section content in the `finalizeContents()` function, which happens before the writer is run --------- Co-authored-by: Sharon Xu <sharonxu@fb.com>
95 lines
4.0 KiB
C++
95 lines
4.0 KiB
C++
//===- SectionPriorities.h --------------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLD_MACHO_SECTION_PRIORITIES_H
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#define LLD_MACHO_SECTION_PRIORITIES_H
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#include "InputSection.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/MapVector.h"
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namespace lld::macho {
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using SectionPair = std::pair<const InputSection *, const InputSection *>;
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using StringPiecePair = std::pair<CStringInputSection *, size_t>;
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class PriorityBuilder {
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public:
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// Reads every input section's call graph profile, and combines them into
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// callGraphProfile. If an order file is present, any edges where one or both
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// of the vertices are specified in the order file are discarded.
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void extractCallGraphProfile();
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// Reads the order file at `path` into config->priorities.
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//
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// An order file has one entry per line, in the following format:
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//
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// <cpu>:<object file>:[<symbol name> | CStringEntryPrefix <cstring hash>]
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//
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// <cpu> and <object file> are optional.
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// If not specified, then that entry tries to match either,
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//
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// 1) any symbol of the <symbol name>;
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// Parsing this format is not quite straightforward because the symbol name
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// itself can contain colons, so when encountering a colon, we consider the
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// preceding characters to decide if it can be a valid CPU type or file path.
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// If a symbol is matched by multiple entries, then it takes the
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// lowest-ordered entry (the one nearest to the front of the list.)
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//
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// or 2) any cstring literal with the given hash, if the entry has the
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// CStringEntryPrefix prefix defined below in the file. <cstring hash> is the
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// hash of cstring literal content.
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//
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// Cstring literals are not symbolized, we can't identify them by name
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// However, cstrings are deduplicated, hence unique, so we use the hash of
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// the content of cstring literals to identify them and assign priority to it.
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// We use the same hash as used in StringPiece, i.e. 31 bit:
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// xxh3_64bits(string) & 0x7fffffff
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//
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// The file can also have line comments that start with '#'.
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void parseOrderFile(StringRef path);
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// Returns layout priorities for some or all input sections. Sections are laid
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// out in decreasing order; that is, a higher priority section will be closer
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// to the beginning of its output section.
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//
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// If either an order file or a call graph profile are present, this is used
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// as the source of priorities. If both are present, the order file takes
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// precedence, but the call graph profile is still used for symbols that don't
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// appear in the order file. If neither is present, an empty map is returned.
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//
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// Each section gets assigned the priority of the highest-priority symbol it
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// contains.
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llvm::DenseMap<const InputSection *, int> buildInputSectionPriorities();
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std::vector<StringPiecePair>
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buildCStringPriorities(ArrayRef<CStringInputSection *>);
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private:
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// The symbol with the smallest priority should be ordered first in the output
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// section (modulo input section contiguity constraints).
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struct SymbolPriorityEntry {
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// The priority given to a matching symbol, regardless of which object file
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// it originated from.
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int anyObjectFile = 0;
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// The priority given to a matching symbol from a particular object file.
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llvm::DenseMap<llvm::StringRef, int> objectFiles;
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};
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const llvm::StringRef CStringEntryPrefix = "CSTR;";
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std::optional<int> getSymbolPriority(const Defined *sym);
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std::optional<int> getSymbolOrCStringPriority(const StringRef key,
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InputFile *f);
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llvm::DenseMap<llvm::StringRef, SymbolPriorityEntry> priorities;
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llvm::MapVector<SectionPair, uint64_t> callGraphProfile;
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};
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extern PriorityBuilder priorityBuilder;
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} // namespace lld::macho
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#endif
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