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When looking for a Swift module on disk, we were scanning all module search paths if they contain the module we are searching for. In a setup where each module is contained in its own framework search path, this scaled quadratically with the number of modules being imported. E.g. a setup with 100 modules being imported form 100 module search paths could cause on the order of 10,000 checks of `FileSystem::exists`. While these checks are fairly fast (~10µs), they add up to ~100ms. To improve this, perform a first scan of all module search paths and list the files they contain. From this, create a lookup map that maps filenames to the search paths they can be found in. E.g. for ``` searchPath1/ Module1.framework searchPath2/ Module1.framework Module2.swiftmodule ``` we create the following lookup table ``` Module1.framework -> [searchPath1, searchPath2] Module2.swiftmodule -> [searchPath2] ```
80 lines
2.7 KiB
C++
80 lines
2.7 KiB
C++
//===--- PathRemapper.h - Transforms path prefixes --------------*- C++ -*-===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines a data structure that stores a string-to-string
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// mapping used to transform file paths based on a prefix mapping. It
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// is optimized for the common case, which is that there will be
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// extremely few mappings (i.e., one or two).
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//
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// Remappings are stored such that they are applied in the order they
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// are passed on the command line. This would only matter if one
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// source mapping was a prefix of another.
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_BASIC_PATHREMAPPER_H
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#define SWIFT_BASIC_PATHREMAPPER_H
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#include "swift/Basic/LLVM.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Twine.h"
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#include <string>
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#include <utility>
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namespace swift {
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class PathRemapper {
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SmallVector<std::pair<std::string, std::string>, 2> PathMappings;
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public:
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/// Adds a mapping such that any paths starting with `FromPrefix` have that
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/// portion replaced with `ToPrefix`.
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void addMapping(StringRef FromPrefix, StringRef ToPrefix) {
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PathMappings.emplace_back(FromPrefix.str(), ToPrefix.str());
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}
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/// Returns a remapped `Path` if it starts with a prefix in the map; otherwise
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/// the original path is returned.
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std::string remapPath(StringRef Path) const {
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// Clang's implementation of this feature also compares the path string
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// directly instead of treating path segments as indivisible units. The
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// latter would arguably be more accurate, but we choose to preserve
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// compatibility with Clang (especially because we propagate the flag to
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// ClangImporter as well).
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for (const auto &Mapping : PathMappings)
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if (Path.startswith(Mapping.first))
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return (Twine(Mapping.second) +
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Path.substr(Mapping.first.size())).str();
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return Path.str();
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}
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};
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class PathObfuscator {
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PathRemapper obfuscator, recoverer;
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public:
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void addMapping(StringRef FromPrefix, StringRef ToPrefix) {
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obfuscator.addMapping(FromPrefix, ToPrefix);
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recoverer.addMapping(ToPrefix, FromPrefix);
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}
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std::string obfuscate(StringRef Path) const {
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return obfuscator.remapPath(Path);
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}
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std::string recover(StringRef Path) const {
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return recoverer.remapPath(Path);
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}
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};
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} // end namespace swift
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#endif // SWIFT_BASIC_PATHREMAPPER_H
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