On Sunday, 14 June 2015 at 11:03:00 UTC, Marc Schütz wrote:
On Saturday, 13 June 2015 at 22:07:26 UTC, deadalnix wrote:
On Saturday, 13 June 2015 at 11:32:20 UTC, rsw0x wrote:
http://dlang.org/garbage.html
Do not take advantage of alignment of pointers to store bit
flags in the low order bits:
p = cast(void*)(cast(int)p | 1); // error: undefined behavior
if this restriction is actually imposed - why does
std.bitmanip.tagged{ClassRef,Pointer} even exist?
That seems like an arbitrary limitation. This will create an
interior pointer, which the GC needs to recognize anyway.
The doc need to be updated.
I see David Nadlinger already said so in the PR, but that's how
I understand it:
AFAIU the purpose of this restriction is to allow the GC to
take advantage of alignment: a pointer with the lowest bit set
cannot point to a 4-byte aligned struct, for example. The GC
doc [1] mentions alignment several times, among them:
"Do not misalign pointers if those pointers may point into the
GC heap"
As for arbitrary pointer arithmetic being allowed, I guess
that's because the language doesn't distinguish between GC and
non-GC pointers. And note that it is un-@safe anyway.
[1] http://dlang.org/garbage.html
Wouldn't it make sense to do so?
Active Oberon, Modula-3 and .NET make such difference in their
pointer types.
I would imagine it could help in terms of what is possible for GC
improvements.
--
Paulo
