https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110249
--- Comment #2 from David Brown <david at westcontrol dot com> ---
My apologies - it does not optimise the code to a single aligned load at -O1
(at least, not with the combinations I have now tried). The code was
originally C++, with a reference, which /does/ exhibit this behaviour of having
better code at -O1 than -O2. I had translated the reference to a pointer to
get more generic code that is valid as C and C++, but I don't see the same
effect with the pointer.
For a reference, the issue is as I first described:
#include <stdint.h>
#include <string.h>
uint64_t read64r(const uint64_t &x) {
if ((uint64_t) &x % 8 ) {
__builtin_unreachable();
}
uint64_t value;
memcpy( &value, &x, sizeof(uint64_t) );
return value;
}
I tested with 64-bit RISC-V and 32-bit ARM using trunk (gcc 13.1, I think) on
godbolt.org. The only relevant flag was the optimisation level.
<https://godbolt.org/z/TaqdqeGch>
