On Fri, Sep 27, 2019 at 1:43 PM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > On Fri, Sep 27, 2019 at 5:49 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > Barring LTO the above works for perf because of inter-translation-unit > > function calls, which imply a compiler barrier. > > > > Now, when the compiler inlines, it looses that sync point (and thereby > > subtlely changes semantics from the non-inline variant). I suspect LTO > > does the same and can cause subtle breakage through this transformation. > > Do you have a bug report or godbolt link for the above? I trust that > you're familiar enough with the issue to be able to quickly reproduce > it? These descriptions of problems are difficult for me to picture in > code or generated code, and when I try to read through > memory-barriers.txt my eyes start to glaze over (then something else > catches fire and I have to go put that out). Having a concise test > case I think would better illustrate potential issues with LTO that > we'd then be able to focus on trying to fix/support. > Further, if we identified a case were the existing invariants were broken under LTO, such a case could be added to CONFIG_DEBUG_LOCKING_API_SELFTESTS (or whatever the most appropriate kself test is). -- Thanks, ~Nick Desaulniers
