tree a96cf634fd788036d6a516eb2beccdd5d6ed92a4
parent 45524b4fb1827487968f8cdb754071fc4c1f75b8
author Rui Ueyama <ruiu@google.com> 1544037211 +0000
committer Rui Ueyama <ruiu@google.com> 1544037211 +0000

Do not use a hash table to uniquify mergeable strings.

Previously, we have a hash table containing strings and their offsets
to manage mergeable strings. Technically we can live without that, because
we can do binary search on a vector of mergeable strings to find a mergeable
strings.

We did have both the hash table and the binary search because we thought
that that is faster.

We recently observed that lld tend to consume more memory than gold when
building an output with debug info. A few percent of memory is consumed by
the hash table. So, we needed to reevaluate whether or not having the extra
hash table is a good CPU/memory tradeoff. I run a few benchmarks with and
without the hash table.

I got a mixed result for the benchmark. We observed a regression for some
programs by removing the hash table (that's what we expected), but we also
observed that performance imrpovements for some programs. This is perhaps
due to reduced memory usage.

Differential Revision: https://reviews.llvm.org/D55234

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@348401 91177308-0d34-0410-b5e6-96231b3b80d8