Clang-format(-fuzzer) is very slow on a tiny input.
May not be a big problem by itself (or may be it is),
but this hurts fuzzing very much. With all the fuzzer instrumentation
it takes ~1.5 second to format 60 bytes.
W.o. instrumentation it takes ~0.5 second.

cat << EOF | base64 --decode | clang-format
PDw8SAQEMigqLCioKjFoLGgKPDw8PDw8Cjw8PCxkKiQcPDw8KCosKKgiaCxoCigKCjw8PAo8PGQq
KKA6
EOF

Perf:
51.83% clang::format::(anonymous namespace)::AnnotatingParser::next()
13.12% clang::format::(anonymous namespace)::AnnotatingParser::parseParens(bool)
11.87% clang::format::(anonymous namespace)::AnnotatingParser::consumeToken()
8.32% clang::format::(anonymous namespace)::AnnotatingParser::parseAngle()
5.01% clang::getBinOpPrecedence(clang::tok::TokenKind, bool, bool)
4.90% clang::format::(anonymous namespace)::AnnotatingParser::updateParameterCount(clang::format::FormatToken*, clang::format::Format
2.27% clang::format::FormatToken::isSimpleTypeSpecifier() const

This one is worse: 31 seconds w/o instrumentation for 64 bytes, same profile.

cat << EOF | base64 --decode | clang-format
PDw8SAQEMigqLCioKDFoLGgKPDw8PDw8CjwKPDw8PEhoCjw8PBw8PDwoKiwoqCJoLGgKKAoKPDw8
Cjw8PDw8PA==
EOF

A chain of < seems to trigger superlinear runtime in the parser.

perl -e 'print "<" x 20'|clang-format

n | seconds
20 | 0.101
21 | 0.191
22 | 0.367
23 | 0.722
24 | 1.431
25 | 2.730
26 | 5.173
27 | 10.026
28 | 19.779
29 | 39.350

echo LypcAAov | base64 --decode | clang-format -

Assertion `TokenText.startswith("/") && TokenText.endswith("/")' failed.

echo PCo+Iis/J2FjIDpTDT46zvxcXAp1NzI49zxGPg== | base64 --decode | clang-format -

Assertion `EndColumn >= StartColumn' failed.

*** Bug #23294 has been marked as a duplicate of this bug. ***

the clang/clang-format fuzzer bot
lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fuzzer
has been extended to run both with and w/o assertions.
whenever a bug is found, the fuzzer will print the base64-encoded reproducer
so that one can copy-paste it from the buildbot logs:
E.g. from the bot logs:

SUMMARY: AddressSanitizer: ...
CRASHED; file written to crash-80193815206841682354717562770799349303
Base64: OiDgO3gKUyYhU0Z4KhFoEztFKGV1bZNTe5Hsk1MmKUMheCoTIWgTO0VTKMFldW2TUzs=

Just do this:
echo OiDgO3gKUyYhU0Z4KhFoEztFKGV1bZNTe5Hsk1MmKUMheCoTIWgTO0VTKMFldW2TUzs= | base64 -d | clang -x c++ -

Daniel, many thanks for the fixes.
The next biggest offender is

clang-format-fuzzer: /mnt/b/sanitizer-buildbot5/sanitizer-x86_64-linux-fuzzer/build/llvm/tools/clang/lib/Format/ContinuationIndenter.cpp:1066: unsigned int clang::format::ContinuationIndenter::breakProtrudingToken(const clang::format::FormatToken &, clang::format::LineState &, bool): Assertion `NewRemainingTokenColumns < RemainingTokenColumns' failed.

reproducer (base64-encoded):
SCQhJCwxLGNvbnN0ZQx4ciBjaHIzaDJ0IDMqMiAjJCgpABkMLTo9IGdldCxRKiJzdFwwXPSKpKQ6JFxcIg==

You may get more reproducers from the bot:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fuzzer

Fixed crasher in r242738.

The clang-format-fuzzer bot has been mostly green lately,
with only one periodic assert failure, bug 26032
I've changed the bot to treat clang-format-fuzzer failures as real ones,
not just warnings.