llvm/lib/MC/StringTableBuilder.cpp
Hans Wennborg 7fcd5f8c89 MachObjectWriter: optimize the string table for common suffices
This is a follow-up to r207670 (ELF) and r218636 (COFF).

Differential Revision: http://reviews.llvm.org/D5622

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219126 91177308-0d34-0410-b5e6-96231b3b80d8
2014-10-06 17:05:19 +00:00

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2.3 KiB
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//===-- 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.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/COFF.h"
#include "llvm/Support/Endian.h"
using namespace llvm;
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;
}
void StringTableBuilder::finalize(Kind kind) {
SmallVector<StringRef, 8> Strings;
Strings.reserve(StringIndexMap.size());
for (auto i = StringIndexMap.begin(), e = StringIndexMap.end(); i != e; ++i)
Strings.push_back(i->getKey());
std::sort(Strings.begin(), Strings.end(), compareBySuffix);
switch (kind) {
case ELF:
case MachO:
// Start the table with a NUL byte.
StringTable += '\x00';
break;
case WinCOFF:
// Make room to write the table size later.
StringTable.append(4, '\x00');
break;
}
StringRef Previous;
for (StringRef s : Strings) {
if (kind == WinCOFF)
assert(s.size() > COFF::NameSize && "Short string in COFF string table!");
if (Previous.endswith(s)) {
StringIndexMap[s] = StringTable.size() - 1 - s.size();
continue;
}
StringIndexMap[s] = StringTable.size();
StringTable += s;
StringTable += '\x00';
Previous = s;
}
switch (kind) {
case ELF:
break;
case MachO:
// Pad to multiple of 4.
while (StringTable.size() % 4)
StringTable += '\x00';
break;
case WinCOFF:
// Write the table size in the first word.
assert(StringTable.size() <= std::numeric_limits<uint32_t>::max());
uint32_t size = static_cast<uint32_t>(StringTable.size());
support::endian::write<uint32_t, support::little, support::unaligned>(
StringTable.data(), size);
break;
}
}
void StringTableBuilder::clear() {
StringTable.clear();
StringIndexMap.clear();
}