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ELFObjectWriter: deduplicate suffices in strtab
We already do this for shstrtab, so might as well do it for strtab. This extracts the string table building code into a separate class. The idea is to use it for other object formats too. I mostly wanted to do this for the general principle, but it does save a little bit on object file size. I tried this on a clang bootstrap and saved 0.54% on the sum of object file sizes (1.14 MB out of 212 MB for a release build). Differential Revision: http://reviews.llvm.org/D3533 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207670 91177308-0d34-0410-b5e6-96231b3b80d8
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,59 @@ | ||
| //===-- StringTableBuilder.h - String table building utility ------*- C++ -*-=// | ||
| // | ||
| // The LLVM Compiler Infrastructure | ||
| // | ||
| // This file is distributed under the University of Illinois Open Source | ||
| // License. See LICENSE.TXT for details. | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #ifndef LLVM_OBJECT_STRINGTABLE_BUILDER_H | ||
| #define LLVM_OBJECT_STRINGTABLE_BUILDER_H | ||
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| #include "llvm/ADT/SmallString.h" | ||
| #include "llvm/ADT/StringMap.h" | ||
| #include <cassert> | ||
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| namespace llvm { | ||
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| /// \brief Utility for building string tables with deduplicated suffixes. | ||
| class StringTableBuilder { | ||
| SmallString<256> StringTable; | ||
| StringMap<size_t> StringIndexMap; | ||
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| public: | ||
| /// \brief Add a string to the builder. Returns a StringRef to the internal | ||
| /// copy of s. Can only be used before the table is finalized. | ||
| StringRef add(StringRef s) { | ||
| assert(!isFinalized()); | ||
| return StringIndexMap.GetOrCreateValue(s, 0).getKey(); | ||
| } | ||
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| /// \brief Analyze the strings and build the final table. No more strings can | ||
| /// be added after this point. | ||
| void finalize(); | ||
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| /// \brief Retrieve the string table data. Can only be used after the table | ||
| /// is finalized. | ||
| StringRef data() { | ||
| assert(isFinalized()); | ||
| return StringTable; | ||
| } | ||
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| /// \brief Get the offest of a string in the string table. Can only be used | ||
| /// after the table is finalized. | ||
| size_t getOffset(StringRef s) { | ||
| assert(isFinalized()); | ||
| assert(StringIndexMap.count(s) && "String is not in table!"); | ||
| return StringIndexMap[s]; | ||
| } | ||
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| private: | ||
| bool isFinalized() { | ||
| return !StringTable.empty(); | ||
| } | ||
| }; | ||
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| } // end llvm namespace | ||
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| #endif |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,51 @@ | ||
| //===-- StringTableBuilder.cpp - String table building utility ------------===// | ||
| // | ||
| // The LLVM Compiler Infrastructure | ||
| // | ||
| // This file is distributed under the University of Illinois Open Source | ||
| // License. See LICENSE.TXT for details. | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #include "llvm/ADT/SmallVector.h" | ||
| #include "llvm/Object/StringTableBuilder.h" | ||
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| using namespace llvm; | ||
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| static bool compareBySuffix(StringRef a, StringRef b) { | ||
| size_t sizeA = a.size(); | ||
| size_t sizeB = b.size(); | ||
| size_t len = std::min(sizeA, sizeB); | ||
| for (size_t i = 0; i < len; ++i) { | ||
| char ca = a[sizeA - i - 1]; | ||
| char cb = b[sizeB - i - 1]; | ||
| if (ca != cb) | ||
| return ca > cb; | ||
| } | ||
| return sizeA > sizeB; | ||
| } | ||
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| void StringTableBuilder::finalize() { | ||
| SmallVector<StringRef, 8> Strings; | ||
| for (auto i = StringIndexMap.begin(), e = StringIndexMap.end(); i != e; ++i) | ||
| Strings.push_back(i->getKey()); | ||
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| std::sort(Strings.begin(), Strings.end(), compareBySuffix); | ||
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| // FIXME: Starting with a null byte is ELF specific. Generalize this so we | ||
| // can use the class with other object formats. | ||
| StringTable += '\x00'; | ||
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| StringRef Previous; | ||
| for (StringRef s : Strings) { | ||
| if (Previous.endswith(s)) { | ||
| StringIndexMap[s] = StringTable.size() - 1 - s.size(); | ||
| continue; | ||
| } | ||
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| StringIndexMap[s] = StringTable.size(); | ||
| StringTable += s; | ||
| StringTable += '\x00'; | ||
| Previous = s; | ||
| } | ||
| } |
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