[cfe-dev] OpenCL support

[Anton Lokhmotov]

We have updated the patch and added couple of test cases.  We trust it can
be accepted now?

Thanks,
Anton.


> -----Original Message-----
> From: Anton Lokhmotov [mailto:Anton.Lokhmotov at arm.com]
> Sent: 19 January 2011 16:02
> To: 'Chris Lattner'
> Cc: 'Peter Collingbourne'; cfe-dev at cs.uiuc.edu
> Subject: RE: [cfe-dev] OpenCL support
> 
> Hi Chris and Peter,
> 
> Many thanks for your comments.  We agree with everything (a revised
> patch attached) but this:
> 
> > Why define these as keywords in the language?  OpenCL requires an
> > implicit prefix header to be included (which has all the conversion
> > functions and a bunch of other stuff).  It seems cleaner to just put
> a
> > #define in this header that defines __kernel to expand to an
> attribute.
> 
> Initially, we indeed implemented "kernel" and "__kernel" in this way:
> 
>   #define __kernel __attribute__((opencl_kernel_function))
>   #define kernel __kernel
> 
> The OpenCL specification, however, requires them to be keywords in the
> language (section 6.1.9).  This means that the frontend must report if
> these are used in an invalid context.
> 
> 
> For example, if we define:
> 
> #define fakekernel __attribute__((opencl_kernel_function))
> 
> and the programmer uses it in a valid context:
> 
> fakekernel void fk() {}
> void fakekernel fk2() {}
> 
> the net result is the same as if the programmer writes:
> 
> kernel void k() {}
> void kernel k2() {}
> 
> 
> Here are couple of invalid examples and the compiler's response in each
> case:
> 
> 1) The kernel function qualifier is used between the function name and
> the function body.
> 
> - macro implementation
> fakekernel_2.cl:2:22: error: expected ';' after top level declarator
> void fk() fakekernel {}
>                      ^
> - keyword implementation
> kernel_2.cl:1:10: error: expected function body after function
> declarator
> void k() kernel {}
>          ^
> The keyword implementation results in a precise error message.
> 
> 
> 2) The kernel function qualifier is used instead of the function name.
> 
> - macro implementation
> fakekernel_3.cl:2:17: error: expected identifier or '('
> void fakekernel() {}
>                 ^
> - keyword implementation
> kernel_3.cl:1:13: error: expected identifier or '('
> void kernel() {}
>             ^
> The error messages are (confusingly) the same.
> 
> 
> 3) The kernel function qualifier is used as the name of a variable.
> 
> - macro implementation
> int_fakekernel.cl:2:1: warning: declaration does not declare anything
> int fakekernel;
> ^~~
> 
> - keyword implementation
> int_kernel.cl:1:1: warning: declaration does not declare anything
> int kernel;
> ^~~~~~~~~~
> 
> Again, the error messages are the same.  Syntax highlighting, however,
> differs.  The keyword implementation behaves similar to most other C99
> keywords, e.g. "register":
> 
> - register
> int_register.cl:1:1: warning: declaration does not declare anything
> int register;
> ^~~~~~~~~~~~
> 
> [
> Slightly confusingly, for some other keywords in this context the error
> messages differ, e.g. "while", "for", "return":
> 
> - while
> int_while.cl:1:5: error: expected identifier or '('
> int while = 0;
>     ^
> ]
> 
> 
> In summary, we believe that qualifiers that are defined in the
> specification as keywords must be implemented as Clang keywords, even
> if an alternative implementation is possible.  In that way, error
> messages can be improved and behaviour will be consistent with other
> keywords.
> 
> Cheers,
> Anton.
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