On 7/24/19 12:32 AM, Jeff Law wrote: > On 7/23/19 8:23 AM, Martin Liška wrote: >> On 7/23/19 3:57 PM, Jeff Law wrote: >>> On 7/23/19 7:50 AM, Michael Matz wrote: >>>> Hi, >>>> >>>> On Tue, 23 Jul 2019, Jeff Law wrote: >>>> >>>>>> great you found time to make this. It should become the default for >>>>>> -flto IMO. >>>>> I was going to hack it into the rpm configury bits since we have access >>>>> to the # cores there. But an auto-selector within GCC is even better. >>>>> >>>>> BTW, isn't this all going to wreck havoc with reproducible builds since >>>>> partitioning can affect code generation? That's one of our open >>>>> questions... >>>> >>>> See Richi for this, but the reason for -flto=auto (or just -flto, or >>>> whatever the endresult will be) is _also_ reproducible builds, because >>>> some packages like to encode the compile flags into their binaries and >>>> hence would change depending on build host just because of "-flto=32" vs. >>>> "-flto=64" even when the code remains exactly the same. >>> Makes sense. >>> >>> What did you end up doing with old autoconf scripts that aren't LTO >>> safe? Many of the older style tests to see if a function exists are >>> broken by LTO. I've seen more issues with this than anything in the LTO >>> space so far. >> >> Well, I've seen some of these failures, but only a few. > Many appear to be silent, possibly not really affecting anything (like > all the packages that test for doprnt, but really don't care about it in > the end). But there were enough real failures that I put in auditing > to detect any cases where we get different config.h files with LTO vs > non-LTO and that is tripping often enough to have my concerns about how > much work it's going to be to get everything fixed.
I see. > > > But still, overall we're moving forward. Next step is to get everything > classified into buckets and start iterating. Presumably you'd be open > to a google doc of some kind where we can coordinate any such efforts? Sure, I'm open. In the meantime, I've got a META issue that I use for tracking of LTO-related issues in openSUSE: https://bugzilla.opensuse.org/show_bug.cgi?id=1133084 Martin > > jeff > > ps. I'm on PTO July 25 to Aug 5, so not much is going to happen in the > next couple weeks :-) >
