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I've been testing the changes on net_parse_cookie_line_fuzzer,
which is a fuzz target of average size written in C++.

Improvements step by step:

0) Original configuration, Coverage + ASan:
158 MB  1,000 exec/s

1) Prohibit ASan (and other sanitizers), use only Coverage instrumentation:
132 MB  same speed

The following change hasn't been applied, but let's keep it in the description FTR:
- 2) Disable sanitizer coverage (which is different from clang source-based coverage):
- 90 MB   1,088 exec/s (speed +8-10%)

3) Avoid optimize_for_fuzzing config (i.e. use -O3 instead of -O1 for coverage build):
Same size  1,773 exec/s (speed +60-65% on top of the previous change)

4) Disable coverage for libFuzzer source code:
88 MB  3,988 exec/s (speed +125% on top of previous changes)

5) Disable coverage for libc++ and libc++abi sources
(https://chromium-review.googlesource.com/#/c/chromium/buildtools/+/693570):
86 MB  4,110 exec/s (speed +3% on top of previous changes)

In total, for that particular target:
- build size reduced by ~45%
- execution speed increased by ~310%

I've also tested the changes with zlib_uncompress_fuzzer (a tiny fuzz target for C-library):
- build size reduced by ~83%
- execution speed increased by ~120%

I haven't measured impact on the other fuzz targets, so it may vary a lot,
but the result seems to be quite significant anyway.


Bug: 759794
Change-Id: Icf61c979e38d0f7849ab7281bd9e24cf2b7a7d02
Reviewed-on: https://chromium-review.googlesource.com/693564Reviewed-by: Brett Wilson <brettw@chromium.org>
Reviewed-by: Oliver Chang <ochang@chromium.org>
Commit-Queue: Abhishek Arya <inferno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506454}