[Mesa-dev] [PATCH 06/40] glsl: add helper to convert pointers to uint64_t

[Davin McCall]

On 11/02/17 12:03, Timothy Arceri wrote:
>
>
> On 10/02/17 21:43, Nicolai Hähnle wrote:
>> On 07.02.2017 04:42, Timothy Arceri wrote:
>>> From: Timothy Arceri <timothy.arceri at collabora.com>
>>>
>>> This will be used to store all pointers in the cache as 64bit ints
>>> allowing us to avoid issues when a 32bit program reads a cached
>>> shader that was created by a 64bit application.
>>> ---
>>>  src/compiler/glsl/shader_cache.h | 10 ++++++++++
>>>  1 file changed, 10 insertions(+)
>>>
>>> diff --git a/src/compiler/glsl/shader_cache.h
>>> b/src/compiler/glsl/shader_cache.h
>>> index 8bd0a3c..1596c33 100644
>>> --- a/src/compiler/glsl/shader_cache.h
>>> +++ b/src/compiler/glsl/shader_cache.h
>>> @@ -27,6 +27,16 @@
>>>
>>>  #include "util/disk_cache.h"
>>>
>>> +static uint64_t inline
>>> +ptr_to_uint64_t(void *ptr)
>>> +{
>>> +   uint64_t ptr_int = (uint64_t) ptr;
>>> +#if __i386__
>>> +   ptr_int &= 0xFFFFFFFF;
>>> +#endif
>>
>> Is the bit-wise and here really necessary?
> Yes. See [1] for an example and the standard and gcc quotes.
>
> [1]
> http://stackoverflow.com/questions/25039796/cast-from-32-bit-address-to-64-bit-integer-yields-unexpected-results
>

I'm just an occasional reader so sorry if this is out-of-place, but
wouldn't it be better to check the size directly rather than tie to a
specific architecture; i.e. rather than:

    #if __i386__
       ptr_int &= 0xFFFFFFFF;
    #endif

It seems like what you really want is:

    if (sizeof(uint64_t) > sizeof(ptr)) {
        ptr_int &= 0xFFFFFFFF;
    }

On any arch where the conversion is not sign-extended, the compiler
should in theory be able to optimise away the unecessary bitwise-and.

Davin

>>
>> Nicolai
>>
>>> +   return ptr_int;
>>> +}
>>> +
>>>  void
>>>  shader_cache_write_program_metadata(struct gl_context *ctx,
>>>                                      struct gl_shader_program *prog);
>>>
>>
>
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