efcb07bf6e
The `Twine::str()` function currently always allocates heap memory via `std::string`. However, some instances of `Twine` don't need an intermediate buffer at all, and the rest can attempt to print into a stack buffer first. This is intentionally not making use of `Twine::isSingleStringLiteral()` from D157010 to skip saving the string in the bump-pointer allocator, since the `StringSaver` documentation suggests that MUST happen for every given string. Reviewed By: benlangmuir Differential Revision: https://reviews.llvm.org/D157015
60 lines
1.9 KiB
C++
60 lines
1.9 KiB
C++
//===- llvm/Support/StringSaver.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 LLVM_SUPPORT_STRINGSAVER_H
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#define LLVM_SUPPORT_STRINGSAVER_H
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#include "llvm/ADT/DenseSet.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/ADT/Twine.h"
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#include "llvm/Support/Allocator.h"
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namespace llvm {
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/// Saves strings in the provided stable storage and returns a
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/// StringRef with a stable character pointer.
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class StringSaver final {
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BumpPtrAllocator &Alloc;
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public:
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StringSaver(BumpPtrAllocator &Alloc) : Alloc(Alloc) {}
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BumpPtrAllocator &getAllocator() const { return Alloc; }
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// All returned strings are null-terminated: *save(S).end() == 0.
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StringRef save(const char *S) { return save(StringRef(S)); }
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StringRef save(StringRef S);
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StringRef save(const Twine &S);
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StringRef save(const std::string &S) { return save(StringRef(S)); }
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};
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/// Saves strings in the provided stable storage and returns a StringRef with a
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/// stable character pointer. Saving the same string yields the same StringRef.
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///
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/// Compared to StringSaver, it does more work but avoids saving the same string
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/// multiple times.
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///
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/// Compared to StringPool, it performs fewer allocations but doesn't support
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/// refcounting/deletion.
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class UniqueStringSaver final {
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StringSaver Strings;
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llvm::DenseSet<llvm::StringRef> Unique;
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public:
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UniqueStringSaver(BumpPtrAllocator &Alloc) : Strings(Alloc) {}
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// All returned strings are null-terminated: *save(S).end() == 0.
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StringRef save(const char *S) { return save(StringRef(S)); }
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StringRef save(StringRef S);
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StringRef save(const Twine &S);
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StringRef save(const std::string &S) { return save(StringRef(S)); }
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};
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} // namespace llvm
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#endif
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