I'm seeing what appears to be a bug with the -O flag in dmd. Here is a reduced test case:

struct SomeStruct
{
    long value;
}
bool isNumberOne(int i)
{
	SomeStruct l;
	if(i == 1)
		l = SomeStruct(10);
	return (l == SomeStruct(10));
}
void main()
{
    if (!isNumberOne(1))
        assert(false);
}

See: https://run.dlang.io/is/zlrDvy

rdmd test.d    # Runs fine
rdmd -O test.d # Assert trips

The assert trips when run with "rdmd -O test.d" and it does not trip when run with "rdmd test.d". This bug is observed in all compiler versions from dmd-2.060 through to dmd-2.095.

Forum discussion: https://forum.dlang.org/post/dpwzsxjksoqjzjvrwehw@forum.dlang.org

Thanks,
Saurabh