On Thu, 14 Apr 2016, Ramana Radhakrishnan wrote: > > > > > What happens in practice? GCC doesn't put functions in random > > partitions. > > > > The data goes into a separate partition AFAIU - it means that all data > accesses are as though they are extern references which means there's > not necessarily any CSE'ing ability that's available with section > anchors.
No, they are added to partitions referencing them. Actually they end up in the first partition that references them. > >> If it's not desired by default could we gate it on an option ? > >> AFIAU, section anchors optimization is important for ARM and AArch64. > > > > For code size or for performance? I wonder why section anchors cannot > > be "implemented" using some special relocations and thus as linker > > optimization. > > For performance (and probably code size too) as you can end up CSE'ing > the anchor point. the difference in performance with -flto-partitions=1 > is visible on quite a few of the spec2k benchmarks. I don't remember > which ones immediately but yeah it makes a difference. Yeah, as said elsewhere for things like spec2k we should have been less aggressive with the goal to parallelize and build larger partitions for small programs. Thus increase lto-min-partition up to a point where all benchmarks end up in a single partition (small benchmarks, so spec2k6 doesn't count at all). After all our inlining limits only start with large-unit-insns as well, which is 10 times of lto-min-partition... Richard.
