tree 43771d071ff4728930a594043fc78b4a7bf37e18
parent cae0227219c89c60a2ccda49d2106ee3a8896678
author Rui Ueyama <ruiu@google.com> 1539017939 +0000
committer Rui Ueyama <ruiu@google.com> 1539017939 +0000

Avoid unnecessary buffer allocation and memcpy for compressed sections.

Previously, we uncompress all compressed sections before doing anything.
That works, and that is conceptually simple, but that could results in
a waste of CPU time and memory if uncompressed sections are then
discarded or just copied to the output buffer.

In particular, if .debug_gnu_pub{names,types} are compressed and if no
-gdb-index option is given, we wasted CPU and memory because we
uncompress them into newly allocated bufers and then memcpy the buffers
to the output buffer. That temporary buffer was redundant.

This patch changes how to uncompress sections. Now, compressed sections
are uncompressed lazily. To do that, `Data` member of `InputSectionBase`
is now hidden from outside, and `data()` accessor automatically expands
an compressed buffer if necessary.

If no one calls `data()`, then `writeTo()` directly uncompresses
compressed data into the output buffer. That eliminates the redundant
memory allocation and redundant memcpy.

This patch significantly reduces memory consumption (20 GiB max RSS to
15 Gib) for an executable whose .debug_gnu_pub{names,types} are in total
5 GiB in an uncompressed form.

Differential Revision: https://reviews.llvm.org/D52917

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@343979 91177308-0d34-0410-b5e6-96231b3b80d8