On 26-09-2012 13:45, Iain Buclaw wrote:
On Wednesday, 26 September 2012 at 08:12:16 UTC, Walter Bright wrote:
On 9/26/2012 12:36 AM, Iain Buclaw wrote:
On Tuesday, 25 September 2012 at 23:39:39 UTC, Walter Bright wrote:
On 9/25/2012 3:58 PM, Iain Buclaw wrote:
The problem here is that the array operation A[] = B[] + C[] gets
transformed
into an extern(C) call. And because there's no strict rules in
place over the
order of which it's parameters are evaluated, it could go either
way (LTR, or
RTL).
Serious note: This test is bogus as this and similar other failing
tests on
non-x86 platforms are not at all obvious to the users who get
issues. So what
are we to do about it?
D needs to move towards a defined order of evaluation. I understand
that
there's a problem when using parts of a C compiler that feels free
to reorder
within the C rules. It's something we have to deal with sooner or
later, by
either:
1. adjusting the C optimizer so it follows D rules for D code
2. assigning terms to temporaries that are executed in a specific
order by C
rules
Indeed, but where does that leave code that gets compiled down to a
extern(C) call?
C functions all seem to evaluate their args right-to-left, even though
the C Standard doesn't specify that. So we should be all right by
simply defining that D do it that way for C functions.
It doesn't actually matter what order D does things, we just have to
pick one. And so we might as well pick one that C compilers naturally
do anyway.
Speaking as a generalisation, no that is not true. C functions for
x86/x86_64 all seem to evaluate their args right-to-left. However - and
this may be different from compiler to compiler - GCC at least does
left-to-right evaluation for everything else (ARM, SPARC, etc) because
that is the order that arguments are pushed onto the stack for those
architecture backends.
If right-to-left should be the strict standard to follow for extern(C),
then document this behaviour as part of the specification, and I'll
implement it. :~)
Regards
Iain
There is a pull request that does this, but it has not yet been merged
because it's waiting on compilers to catch up... ;)
--
Alex Rønne Petersen
[email protected]
http://lycus.org
