Re: JIT patch: add gcc_jit_magic_int

[Andrew Pinski <pinskia at gmail dot com>]

On Tue, Jun 7, 2016 at 12:19 PM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Mon, May 23, 2016 at 5:26 AM, Basile Starynkevitch
> <basile@starynkevitch.net> wrote:
>> Hello All,
>>
>> As I explained in https://gcc.gnu.org/ml/jit/2016-q2/msg00042.html it is
>> difficult (or tricky without using dirty tricks involving the GCC plugin
>> headers) to use GCCJIT to emit code equivalent to the following C file:
>>
>>    extern int a;
>>    int get_atomic_a (void) {
>>      return __atomic_load_n (&a, __ATOMIC_SEQ_CST);
>>    }
>>
>> The issue is that __ATOMIC_SEQ_CST is a magic preprocessor (but
>> non-standard!) symbol which might not be available
>> (or might have a different value) in the C code for GCCJIT building such an
>> AST.
>
>>
>> So we need a function to retrieve some magic integral value from the GCCJIT
>> compiler.
>
> Huh?    Why can't you just use the enum:
> enum memmodel
> {
>   MEMMODEL_RELAXED = 0,
>   MEMMODEL_CONSUME = 1,
>   MEMMODEL_ACQUIRE = 2,
>   MEMMODEL_RELEASE = 3,
>   MEMMODEL_ACQ_REL = 4,
>   MEMMODEL_SEQ_CST = 5,
>   MEMMODEL_LAST = 6,
>   MEMMODEL_SYNC_ACQUIRE = MEMMODEL_ACQUIRE | MEMMODEL_SYNC,
>   MEMMODEL_SYNC_RELEASE = MEMMODEL_RELEASE | MEMMODEL_SYNC,
>   MEMMODEL_SYNC_SEQ_CST = MEMMODEL_SEQ_CST | MEMMODEL_SYNC
> };
>
>
> For the values?  I don't understand why you need to have a direct
> relationship to preprocessed macros to these values here.
> Have your own lookup table inside your own JIT rather than a generic
> way of doing it.
> Having a generic way seems more incorrect way of doing it and even
> says that the JIT is supposed to JITting C code but it is not JITing C
> code.


That is move enum memmodel to be included in the JIT API too.

>
> Thanks,
> Andrew Pinski
>
>>
>> The attached patch (relative to trunk svn 236583) is a first attempt to
>> solve that issue
>>  (and also give ability to query some other magic numbers).
>>
>> Proposed ChangeLog entry (in gcc/jit/)
>>
>> 2016-05-23  Basile Starynkevitch  <basile@starynkevitch.net>
>>         * libgccjit.h (LIBGCCJIT_HAVE_gcc_jit_magic_int): New macro.
>>         (gcc_jit_magic_int): New public function declaration.
>>
>>         * libgccjit.c: Include "cppbuiltin.h", "options.h", "flag-types.h"
>>         (gcc_jit_magic_int): New function.
>>
>>         * libgccjit.map: Add gcc_jit_magic_int to LIBGCCJIT_ABI_6.
>>
>> Comments (or an ok to commit) are welcome. (I am not sure that
>> __SANITIZE_ADDRESS__ is correctly handled,
>> because I would believe that optimization flags are not globals in GCCJIT)
>>
>> Regards.
>>
>> --
>> Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
>> email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
>> 8, rue de la Faiencerie, 92340 Bourg La Reine, France
>> *** opinions {are only mine, sont seulement les miennes} ***
>>