[cfe-dev] Question about stripping address-space qualifier with C++

[mats petersson]

So, at least in our world, just removing the address-space qualifier
wouldn't work, you would need to also convert the pointer to an
"absolute" (non-address-space) pointer before you can do that.

If you have a model where addresses are always linear and address
spaces don't matter, then perhaps "removing them" would work (and no,
I don't know immediately how to do that - I'd probably write a small
function that takes a generic type with qualifier, and "rebuild" the
type without address spaces, and then call that on encountering a
valid place where it's needed).

--
Mats

On 13 January 2015 at 16:15, JinGu Kang <jingu at codeplay.com> wrote:
> Hi Mats,
>
> We are also working on OpenCL. We have implemented some of OpenCL functions
> using clang's builtin functions. For example,
>
> int atomic_or(volatile int local * p, int val) { return atomic_or(p, val); }
> ...
> int atomic_max(volatile int global * p, int val) { return atomic_max(p,
> val); }
> int atomic_max(volatile uint global * p, uint val) { return atomic_max(p,
> val); }
> ...
>
> template <typename P, typename T>
> T atomic_or(P p, const T t) {
>   return __sync_fetch_and_or(p, t);
> }
>
> template <typename P, typename T>
> int atomic_max(volatile int global *p, const int t) {
>   if (__is_signedof(T))
>     return __sync_fetch_and_max(reinterpret_cast<volatile T *>(p), t);
>   else
>     return __sync_fetch_and_umax(reinterpret_cast<volatile T *>(p), t);
> }
>
> '__sync_fetch_and_or' and '__sync_fetch_and_[u]max' function's prototypes
> are as follows:
> BUILTIN(__sync_fetch_and_or, "v.", "t")
> ...
> BUILTIN(__sync_fetch_and_min, "iiD*i", "n")
> BUILTIN(__sync_fetch_and_max, "iiD*i", "n")
> BUILTIN(__sync_fetch_and_umin, "UiUiD*Ui", "n")
> BUILTIN(__sync_fetch_and_umax, "UiUiD*Ui", "n")
>
> If builtin functions use custom type checking like '__sync_fetch_and_or', it
> is not problem. But we should match the function prototype in other cases
> like '__sync_fetch_and_max'. So we need to strip address space qualifier In
> order to call '__sync_fetch_and_max' function.
>
> I think it depends on just only our implementation so I wanted to check some
> ways to strip address space qualifier.
>
> Thanks,
> JinGu Kang
>
>
> On 01/13/2015 03:24 PM, mats petersson wrote:
>>
>> What is the overall problem you are trying to solve? In general,
>> adress space casts either generate no code (no problem) or will modify
>> the behaviour of the code (necessary for correct operation). I don't
>> see much point in fixing the former, and breaking things by "fixing"
>> the latter doesn't seem like a brilliant idea either...
>>
>> Can you give an example of C++ code that uses address space casts, and
>> that you want to remove them in?
>>
>> (Caveat, I work on OpenCL, and we do use address space casts quite a bit)
>>
>> --
>> Mats
>>
>> On 13 January 2015 at 11:48, JinGu Kang <jingu at codeplay.com> wrote:
>>>
>>> Hi all,
>>>
>>> I am looking for some ways to strip address-space qualifiers with C++
>>> from
>>> clang. I think we can use the 'addrspacecast' instruction to do it in IR
>>> level. Before doing it in an IR pass, I would like to try to do it with
>>> clang. But I can not find some ways to strip it with C++ source code from
>>> clang or generate 'addrspacecast' instructions with C++ from clang. Is
>>> there
>>> some C++ syntax to do it such as reinterpret_cast? If you have some
>>> ideas,
>>> please let me know.
>>>
>>> Thanks,
>>> JinGu Kang
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
>