[Bug lto/78140] [7 Regression] libxul -flto uses 1GB more memory than gcc-6

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78140

--- Comment #30 from Martin Jambor <jamborm at gcc dot gnu.org> ---
With the above commit, we hae avoided the vast majority of memory use
increase.  I think that using the same approach to cache ipa_vr
structures (used to store results of IPA-VR) could bring further
savings (possibly a hundred of megabytes?) so I will try that.
In any event, this may no longer qualify as P1.