Hans-Peter Nilsson via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
>> Date: Tue, 29 Aug 2023 15:42:27 -0400 >> From: Marek Polacek via Gcc-patches <gcc-patches@gcc.gnu.org> > >> Surely, there must be no ABI impact, the option cannot cause >> severe performance issues, > >> Currently, -fhardened enables: > ... >> -ftrivial-auto-var-init=zero > >> Thoughts? > > Regarding -ftrivial-auto-var-init=zero, I was consulted when > colleagues investigating a performance regression > pint-pointed it as *causing severe performance issues*; > cf. https://github.com/systemd/systemd.git commit 1a4e392760 > (TL;DR: adds "-ftrivial-auto-var-init=zero" to the systemd > build). > > The situation was described as "we noticed that some test > suites takes 35% percent longer time to finish. After > further investigation it was noticed that running systemctl > unmask x takes around 5s more time on [version including > patch vs. before that patch]" (timing out some tests). > Reverting that patch fixed the drop in performance. Did some bug ever get filed for this to see if we can do a bit better here? Some slowdown doesn't mean it's of the expected magnitude. > > Just a data point, but I believe also exactly your intended > use. IMO including -ftrivial-auto-var-init is worth extra > consideration. > > Alternatively, strike the while "cannot cause severe > performance issues". > > brgds, H-P
