clang does not support extern for OpenCL

Clang Frontend
1

I was trying to compile a simple OpenCL source with clang:

extern int foo(int, int);

I got an error msg:

clang.exe : tmp.cl:1:1: error: OpenCL does not support the ‘extern’ storage class specifier

OpenCL spec 1.2 says:

The typedef, extern, and static storage-class specifiers are supported.

Is this a bug? Or did I miss anything? Thanks.

Sam

2

You need to set the cl-std value to 1.2. By default its 1.1.

-Tanya

3

It’d be useful to mention this in the diagnostic. How about

‘extern’ storage class specifier is an OpenCL 1.2 extension

… and downgrading this from an Error to an ExtWarn?

4

Thanks. I got it.

For those who are curious, the command line is like

clang -cc1 -cl-std=CL1.2 tmp.cl

Sam

5

It’d be useful to mention this in the diagnostic. How about

‘extern’ storage class specifier is an OpenCL 1.2 extension

Sure. I can change this.

… and downgrading this from an Error to an ExtWarn?

I wouldn’t mind this being a warning instead. Technically the CL spec says its not supported, but I don’t think it says it MUST be an error.

-Tanya

6

Thanks. I got it.

For those who are curious, the command line is like

clang -cc1 -cl-std=CL1.2 tmp.cl

Sam

7

Thanks. I got it.

8

It seems it isn’t, but why not -std? We already use this to refer to both the C and C++ standards.

Jordan

9

I totally agree with you, but I did not write the OpenCL Spec and I have no idea why they decided they needed another std option.

Its not a high priority to me to change it to be a driver level option, but someone else might complain (and they can fix it).

-Tanya

10

I’m not familiar with the OpenCL part of the compiler, but I’m pretty sure you’re not supposed to invoke -cc1 mode directly, just like the C compiler. The right way to do this is with the usual -std option:

clang -std=cl1.2 tmp.cl

This ensures that all the other driver-specified options get handled appropriately.

I agree that you shouldn’t use -cc1, but -cl-std= should be a driver level option. If not, then it should be fixed.

It seems it isn’t, but why not -std? We already use this to refer to both the C and C++ standards.

I totally agree with you, but I did not write the OpenCL Spec and I have no idea why they decided they needed another std option.

Ah, I didn’t realize the command-line interface was specified by the standard. My bad.

Its not a high priority to me to change it to be a driver level option, but someone else might complain (and they can fix it).

Since we are unlikely to have a separate openclc driver tool anytime soon, this does seem like the right way to go.

Thanks for the explanation,
Jordan