Question about OpenCL language standard option

jingu jingu at
Sat Nov 30 00:49:03 PST 2013

Hi Arthur, Joey,

I  appreciate your response. As Arthur mentioned, I assumed this is not 
VLA because there is 'const' qualifier and this example is included in 
one OpenCL test-suite and clang folded this with 'GNUMode' not VLA. I am 
sorry it was my mistake. Thank you for your response, again.

JinGu Kang

2013-11-30 오전 10:59, Arthur O'Dwyer 쓴 글:
> Joey, JinGu,
> I believe JinGu was expecting the array to be not-a-VLA, because its
> size is "const". In C++ JinGu would be correct; that array's size *is*
> a compile-time constant in C++, but in C (and therefore in OpenCL)
> it's not constant, because it depends on the value of a variable. (The
> variable's type happens to be const-qualified, but that doesn't matter
> in C.)
> If this test case came from an official OpenCL test suite, IMHO the
> right course of action is almost certainly to contact the maker of
> that test suite and get them to change their test, rather than add an
> extension to Clang just for this one special case.  (Alternatively, is
> there such a thing as OpenCL++? Should this test be compiled in that
> mode?)
> HTH,
> –Arthur
> On Fri, Nov 29, 2013 at 5:32 PM, Joey Gouly <Joey.Gouly at> wrote:
>> Hi JinGu,
>> I'm not sure I understand.. VLAs are *not* supported in OpenCL. See Restrictions 6.9.d.
>> Thanks,
>> Joey
>> ________________________________________
>> From: cfe-commits-bounces at [cfe-commits-bounces at] On Behalf Of JinGu Kang [jingu at]
>> Sent: 29 November 2013 17:32
>> To: cfe-dev at; cfe-commits at
>> Subject: Question about OpenCL language standard option
>> Hi all,
>> I got a error from a opencl test. The test code is as following:
>> source code:
>> __kernel void test_fn(__global uint *src, __global uint4 *results) {
>>     const size_t SIZE = 128;
>>     int tid = get_global_id(0);
>>     if (tid*4 >= SIZE)
>>       return;
>>     __private uint sPrivateStorage[SIZE];
>>     for (size_t i=0 ; i<SIZE ; i++)
>>       sPrivateStorage[i] = src[i];
>>     results[tid] = vload4(tid, sPrivateStorage);
>> }
>> and the error message is as following:
>> "error: variable length arrays are not supported in OpenCL
>>     __private uint sPrivateStorage[SIZE];"
>> The problem is that 'isArraySizeVLA' function calls
>> 'VerifyIntegerConstantExpression' with 'S.LangOpts.GNUMode'. The OpenCL
>> Language standard option does not have this option. It causes a error
>> because 'AllowFold' is not set to 1. In order to fix this error, I think
>> that we need to insert 'GNUMode' to  OpenCL LANGSTANDARD or modify
>> sligtly checking code. How do you feel about this? I can not guarantee
>> the side effect of 'GNUMode' with OpenCL. I have attached a simple patch
>> as reference. If there is something wrong, please let me know.
>> Thanks,
>> JinGu Kang
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