https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94103
--- Comment #16 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 20 Mar 2020, ch3root at openwall dot com wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94103 > > --- Comment #15 from Alexander Cherepanov <ch3root at openwall dot com> --- > (In reply to rguent...@suse.de from comment #14) > > From a language Pov that's the same. > > But memcpy and friends work on any dynamic type so have to copy all bytes. > Sorry, I don't understand. Bug 61872, comment 1, and bug 92486, comment 9, > look > the same -- a memset followed by an assignment. But the former is with long > double while the latter is with a struct. > > You mean that assignments of structs are equivalent to memcpy while > assignments > of long doubles aren't? Why the difference? No, assignment of structs from a language POV are not equivalent to memcpy. For those the issue is that GCC thinks they are (and forever did that). Which means for the GCC middle-end (GIMPLE) assignment of structs are equivalent to memcpy. So are long double assigns btw - but the bugs that I think are important to fix are those where even the source language semantics dictate they are well-defined. I do think the long double issue eventually needs to be sorted out in the middle-end. So do I think SRA needs to be fixed to preserve memcpy behavior of aggregate copies.
