[cfe-dev] Fwd: intptr_t support in llvm

[ankur deshwal]

Hi Dave,

Thanks for the help.

I see my mistake. "*a+=*b" works great.

I was hoping there is a  portable way of handling intptr_t ( hoping clang's
some hidden feature for the same).

Thanks again for the reply,

Ankur



On Fri, Feb 1, 2013 at 6:22 PM, David Tweed <david.tweed at arm.com> wrote:

> Leaving aside any OpenCL specific issues (you can use pointers in a more
> restricted way than in general C), are you sure that the final line is
> doing what you want (I think that's what the warning is about). You're
> adding _the int* address held in b_ to the _int value stored at the address
> held in a_. C will let you do this primarily because it's got quite weak
> rules about which conversions you must do explicitly, so this will go
> through on a machine where the int width is the same as an int* width.****
>
> Does the error go away if you do *a+=*b ?****
>
> ** **
>
> I don't think either of your typedefs will reliably work (ie, in the
> interesting cases where sizeof(int*) != sizeof(int)), I think the only way
> to do it is via explicit pre-processor typedefs based on the pointer size
> of the machine you're compiling on.****
>
> ** **
>
> Regards,****
>
> Dave****
>
> ** **
>
> *From:* cfe-dev-bounces at cs.uiuc.edu [mailto:cfe-dev-bounces at cs.uiuc.edu] *On
> Behalf Of *ankur deshwal
> *Sent:* 01 February 2013 12:02
> *To:* cfe-dev at cs.uiuc.edu
> *Subject:* [cfe-dev] Fwd: intptr_t support in llvm****
>
> ** **
>
> Hi all,****
>
> ** **
>
> I tried compiling an opencl kernel with intptr_t datatype. However it
> gives error by default using LLVM/Clang 3.2 for nvptx . To allow usage, I
> tried following typedefs ( by looking at tests in llvm sources ).****
>
> ** **
>
> typedef int intptr_t;****
>
> and****
>
> typedef __typeof( (int*) 0) intptr_t;****
>
> ** **
>
> Both definitions compiles the code, however gives following warning. ****
>
> warning: incompatible pointer to integer conversion assigning to 'int'
> from 'int *'; dereference with *****
>
> ** **
>
> Is it safe to use the above typedefs ? The generated code seems correct
> for x86 machines (with llvm instruction ptrtoint). Or is there better way
> to make sure that the semantics of intprt_t are preserved in clang/llvm for
> all archs ? ****
>
> ** **
>
> The code I tried to compile is ****
>
> ** **
>
> __kernel void intptr_t_kernel(int *a, int *b)****
>
> {****
>
>   intptr_t c = (intptr_t)a;****
>
>   b = (int*) c;****
>
>   *a += b;****
>
> }****
>
> ** **
>
> and the code generated is ****
>
> ** **
>
> define ptx_kernel void @intptr_t_kernel(i32* %a, i32* nocapture %b)
> nounwind noinline {****
>
> entry:****
>
>   %0 = load i32* %a, align 4, !tbaa !1****
>
>   %add.ptr = getelementptr inbounds i32* %a, i32 %0****
>
>   %conv = ptrtoint i32* %add.ptr to i32****
>
>   store i32 %conv, i32* %a, align 4, !tbaa !1****
>
>   ret void****
>
> }****
>
> ** **
>
> Thanks a lot for help.****
>
> ** **
>
> Regards,****
>
> Ankur****
>
> ** **
>
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