https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89458
Bug ID: 89458
Summary: adding aligned attribute to struct causes too much to
be copied
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
Assignee: unassigned at gcc dot gnu.org
Reporter: dnikitin at 3redpartners dot com
Target Milestone: ---
If I add __attribute__ ((aligned (256))) to a small struct, the whole 256 bytes
are copied by the default copy constructor. I don't think it's correct. This is
with -O3 optimization. Attached is a piece of code to demo:
struct Obj {
void clone(Obj& r);
void clone2(Obj& r);
int a;
int b;
int c; int c1; int c2; int c3; long c4; long c5; long c6;
}__attribute__ ((aligned (256)));
void Obj::clone(Obj& r) {
*this = r;
}
built like so:
g++ -O3 -std=c++14 -march=skylake
The compilation result is a giant "clone" function that copies 256 bytes of
memory
