GCC-9.0.1-RC-20190426 excessive memory usage with -ggdb

[Arvind Sankar <niveditas98 at gmail dot com>]

While building clang-8.0.0 or firefox-66.0.3 on a gentoo system (x86_64)
gcc 9 release candidate runs out of memory with -O2 -ggdb. Gcc 8.3.0
succeeds without issues. For clang there are about 5-6 compilations
where the memory usage seems to grow without bound (I have 128Gb RAM +
128Gb swap and at least two of them were observed to reach 80+Gb each
before getting killed).

For 8.3.0 nothing seems to reach more than single-digit Gb. Without the
-ggdb switch gcc 9 also builds fine without excessive memory usage.

Files running out of memory:
lib/Parse/ParseDeclCXX.cpp
lib/Parse/ParseTentative.cpp
lib/StaticAnalyzer/Checkers/MallocSizeofChecker.cpp
lib/Format/FormatTokenLexer.cpp
lib/Format/TokenAnnotator.cpp

The assembler output for all but the MallocSizeChecker.cpp was still 0
bytes when the compiler crashed, and it wasn't growing for that one.

Experimenting with different -g and -gdwarf levels instead of passing in
-ggdb, -g2 -gdwarf-4 crashes, -g2 -gdwarf-3 crashes, -g1 -gdwarf-4
crashes.

Both gcc 8.3.0 and 9 were bootstrapped using profiledbootstrap + --with-build-config=bootstrap-lto at -O2.
In addition my gcc 9 is currently built with some additional
optimization options: ira-loop-pressure, live-range-shrinkage, tree-lrs.

I'll try bootstrapping 9 with regular -O2 without pgo/lto and see if
that is better.

I realize this is a rather low-quality report :) but have little
experience in trying to narrow this down esp with cmake being used in
clang build, and throwing this out there in case someone else can take a
quick look.

PS I am not on the list, please include me explicitly on replies.