[PATCH] D40697: Cache modulo values for the .gnu.hash section.
Rafael Avila de Espindola via llvm-commits
llvm-commits at lists.llvm.org
Fri Dec 1 13:41:10 PST 2017
Rui Ueyama via Phabricator <reviews at reviews.llvm.org> writes:
> ruiu updated this revision to Diff 125067.
> ruiu added a comment.
>
> - clang-format
>
> It seems this patch actually makes that test case 2% faster, which
> isn't a negligible improvement.
Please benchmark more than clang. There is a set of different benchmarks
in https://s3-us-west-2.amazonaws.com/linker-tests/lld-speed-test.tar.xz.
> // Write hash buckets. Hash buckets contain indices in the following
> // hash value table.
> @@ -1792,21 +1792,22 @@
> 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())});
> - }
> -
I would leave something like
auto HashedSyms = llvm::make_range(Mid, V.end();
> // 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);
And use it here.
> - 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())) {
And here.
> + Symbol *B = Ent.Sym;
> + uint32_t Hash = hashGnu(B->getName());
> + uint32_t BucketIdx = Hash % NBuckets;
> + Symbols.push_back({B, Ent.StrTabOffset, Hash, BucketIdx});
> + }
> +
Cheers,
Rafael
More information about the llvm-commits
mailing list