[Bug tree-optimization/86573] Failure to optimise passing simple values to inlined function
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86573 --- Comment #8 from Niall Douglas --- Added revised bug to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86590
[Bug tree-optimization/86573] Failure to optimise passing simple values to inlined function
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86573 --- Comment #7 from Marc Glisse --- The real difference in -std=c++17 is _GLIBCXX_EXTERN_TEMPLATE. With -std=c++14, we have many extern templates which the compiler almost never inlines. This leaves existing inline functions small enough to be inlined in main (once it is renamed). With -std=c++17, extern templates are gone, everything is inlined, and the function that used to be small enough to be inlined is now too big (several smaller functions have been inlined into it first). Without inlining, the compiler cannot notice all the simplifications. (this is in large part guesswork, feel free to verify) If someone wants to improve it, I would look into the inliner heuristics, but that's probably going to be hard.
[Bug tree-optimization/86573] Failure to optimise passing simple values to inlined function
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86573 --- Comment #6 from Richard Biener --- (In reply to Niall Douglas from comment #5) > Thanks for the rapid feedback. Very very interesting that -std=c++17 causes > spew for the copy case https://godbolt.org/g/Xnrgg2, yet -std=c++14 or > -std=c++11 does not. > > Is the -std=c++17 case worth opening a new bug report for? I guess so (same for -std=c++2a btw)
[Bug tree-optimization/86573] Failure to optimise passing simple values to inlined function
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86573 --- Comment #5 from Niall Douglas --- Thanks for the rapid feedback. Very very interesting that -std=c++17 causes spew for the copy case https://godbolt.org/g/Xnrgg2, yet -std=c++14 or -std=c++11 does not. Is the -std=c++17 case worth opening a new bug report for?
[Bug tree-optimization/86573] Failure to optimise passing simple values to inlined function
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86573 --- Comment #4 from Richard Biener --- Note we only manage to optimize it with the C++11 std::string.
[Bug tree-optimization/86573] Failure to optimise passing simple values to inlined function
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86573 Andrew Pinski changed: What|Removed |Added Keywords||missed-optimization Status|UNCONFIRMED |RESOLVED Component|c++ |tree-optimization Version|tree-ssa|7.0 Resolution|--- |INVALID --- Comment #3 from Andrew Pinski --- Using f instead of main allows it be optimized so closing as invalid. NOTE GCC has a heuristic around main function being done as ever called once so it does less inlining into it.
