[cfe-dev] sizeof(long) in OpenCL C

[David Tweed]

Hi,

| Picking 'size_t' as example: on a 64bit target I would expect that 'size_t' will
| be mapped to an unsigned 64bit builtin integer type. If I declare LongWidth =
| LongLongWidth = 64 then both 'unsigned long' and 'unsigned long long' would be
| valid choice for 'size_t'. Expressing the relationship in a indirect way then
| the definition of implementation defined types is not affected by the potential
| changes that OpenCL language definition may impose respect to the choice done
| for the C compiler.

Ah, I see. I think I probably used an ambiguous term in "implementation defined" that caused confusion. All I basically mean was that we can't assume that there's only one implementation of OpenCL on a given platform (pocl on platforms with existing vendor OpenCL implementations illustrates that, and also illustrates that the term "vendor" that's commonly used can be misleading): as a trivial example, one could easily have a 64-bit platform that can run both 64- and 32-bit userspace APIs and then have one implementor's OpenCL implementation using 32-bit pointers and another implementor's implementation using 64-bit pointers. As such, the pointer size decided to be supported is not a property just of the platform, but also the OpenCL implementation.

Maintaining this flexibility is going to be particularly important if there's a push to encourage OpenCL implementors to use as much OSS clang infrastructure as possible.

Cheers,
Dave


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