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Cache modulo values for the .gnu.hash section. 

This change actually makes the linker slightly faster. My observation
is that, with this patch, link time of clang without debug is about 1%
faster.

Differential Revision: https://reviews.llvm.org/D40697

llvm-svn: 319600
This commit is contained in:
Rui Ueyama 2017-12-02 00:37:13 +00:00
parent a6d5464cfe
commit 2278826c60
2 changed files with 13 additions and 11 deletions
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23
lld/ELF/SyntheticSections.cpp
View File

@ -1745,7 +1745,7 @@ void GnuHashTableSection::writeHashTable(uint8_t *Buf) {
// Group symbols by hash value.
std::vector<std::vector<Entry>> Syms(NBuckets);
for (const Entry &Ent : Symbols)
Syms[Ent.Hash % NBuckets].push_back(Ent);
Syms[Ent.BucketIdx].push_back(Ent);
// Write hash buckets. Hash buckets contain indices in the following
// hash value table.
@ -1792,21 +1792,22 @@ void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &V) {
if (Mid == V.end())
return;
for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
Symbol *B = Ent.Sym;
Symbols.push_back({B, Ent.StrTabOffset, hashGnu(B->getName())});
}
// We chose load factor 4 for the on-disk hash table. For each hash
// collision, the dynamic linker will compare a uint32_t hash value.
// Since the integer comparison is quite fast, we believe we can make
// the load factor even larger. 4 is just a conservative choice.
NBuckets = std::max<size_t>(Symbols.size() / 4, 1);
NBuckets = std::max<size_t>((V.end() - Mid) / 4, 1);
std::stable_sort(Symbols.begin(), Symbols.end(),
[&](const Entry &L, const Entry &R) {
return L.Hash % NBuckets < R.Hash % NBuckets;
});
for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
Symbol *B = Ent.Sym;
uint32_t Hash = hashGnu(B->getName());
uint32_t BucketIdx = Hash % NBuckets;
Symbols.push_back({B, Ent.StrTabOffset, Hash, BucketIdx});
}
std::stable_sort(
Symbols.begin(), Symbols.end(),
[](const Entry &L, const Entry &R) { return L.BucketIdx < R.BucketIdx; });
V.erase(Mid, V.end());
for (const Entry &Ent : Symbols)

1
lld/ELF/SyntheticSections.h
View File

@ -465,6 +465,7 @@ private:
Symbol *Sym;
size_t StrTabOffset;
uint32_t Hash;
uint32_t BucketIdx;
};
std::vector<Entry> Symbols;