[Bug default/29464] abidw performance regression on vmlinux

["gprocida at google dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29464

--- Comment #6 from gprocida at google dot com ---
It turns out that there is now a new infinite loop in the XML writer when
compiled with Clang. This is our old "friend" where containers have
inconsistent equality and hash functions.

In particular:

Commit 7ecef636 "Canonicalize DIEs w/o assuming ODR & handle typedefs
transparently" introduced new sets and a map in the XML writer to track
referencing, emission and type ids for "non canonicalized" types as a separate
category.

It added non_canonicalized_type_equal and non_canonicalized_type_hash function
objects. The former is a deep equality and the latter hashes the non-internal
name.

The net effect is that I see a typedef being repeatedly emitted in a tight
loop. It's recorded as emitted but not found when checked to see if it was
emitted.

The last time these issues occurred they were eventually resolved by using much
safer and more efficient bare pointers as the keys to the containers.

I don't understand why new sets and maps were added or why they need to have
bespoke equality and hash functions.

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