Hi Jakub,
It is worse than that, usually the LTO format changes e.g. any time any
option or parameter is added on a release branch (several times a year) and
at other times as well.
Hm, that makes LTO not very well suited for libraries...
Though, admittedly GCC is the single package that actually could get away
with LTO in lib*.a libraries, at least in some packagings (if the static
libraries are in gcc specific subdirectories rather than say /usr/lib{,64}
or similar and if the packaging of gcc updates both the compiler and
corresponding static libraries in a lock-step. Because in that case LTO
in there will be always used only by the same snapshot from the release
branch and so should be compatible with the LTO in it.
Maybe another approach: Instead of storing version-dependent LTO code in
the *.a files, we could just store preprocessed C code there, somewhat
shortened by removing whitespace, comments and unused declarations
(and/or store them in compressed format).
This would also allow the something like sanitizers to look into the
runtime libraries, and other instrumentation.
It would also be a much more extensive project, also involving
modifications to the linker. Not sure how realistic that would be.
Best regards
Thomas
