https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96945
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|c++ |tree-optimization
Last reconfirmed| |2023-07-13
Status|UNCONFIRMED |NEW
Summary|optimizations regression |unused std::vector is not
|when defaulting copy |always optimized away
|constructor |
Ever confirmed|0 |1
Severity|normal |enhancement
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
In the case of having a move constructor, there is a loop generated for the
constructor (and since this is an empty struct, the loop is empty).
In the case of not having a move constructo, we get:
MEM <unsigned char[3]> [(char * {ref-all})_30] = MEM <unsigned char[3]>
[(char * {ref-all})&D.26026];
In the end DSE does not remove that store even though it is dead right before
the operator delete.
_30 = operator new (3);
MEM <unsigned char[3]> [(char * {ref-all})_30] = MEM <unsigned char[3]>
[(char * {ref-all})&D.26026];
D.26026 ={v} {CLOBBER(eol)};
operator delete (_30, 3); [tail call]
Also if we add an field and initialize it to 0, we get a memcpy:
__builtin_memcpy (_40, &D.26033, 12);
Which is also not DSEd:
_40 = operator new (12);
__builtin_memcpy (_40, &D.26033, 12);
D.26033 ={v} {CLOBBER(eol)};
operator delete (_40, 12); [tail call]
Maybe the clobber is getting in the way here ....
