Hello Jakub, On Fri, 19 Apr 2019 11:34:33 +0200 Jakub Jelinek <ja...@redhat.com> wrote:
> On Fri, Apr 19, 2019 at 11:09:27AM +0200, Jens Gustedt wrote: > > > similarly, if one of the > > > pointers is &object or &object + sizeof (object). > > > > Here I don't follow. Why would one waste brain and ressources to > > optimize code that does such tricks? > > What tricks? &object + sizeof (object) > A normal pointer comparison either of two pointers > or a pointer and address of something is something that happens in > real-world code all the time, and in many cases it is essential > that optimizing compilers attempt to optimize such tests as much as > possible. Yes, but not if one of the addresses is a one-passed pointer, this is a marginal use case. > In the http://gcc.gnu.org/PR88775 (yes, it is C++, not C, but I don't > see significant differences there), Hm, probably my C++ is a bit rusty, but I see huge differences here. What understand is that you have difficulties for some C++ code that uses `operator=` overloading (instead of initialization) to optimize that assignment. I see a lot of difficulties here, of which some are common for C and C++ (the lack of proper treatement of string literals as constants, for example) to purely C++ difficulties, e.g not being able to model `restrict` pointer arguments, and to deal with possible (or impossible) aliasing between a just created object and a string literal. So, I see a whole chain of reasoning breaking down with that code, but nothing that convinces me that `operator==` for pointer types is the culprit. The wrong is probably already done when it comes to it. Jens -- :: INRIA Nancy Grand Est ::: Camus ::::::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt ::
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