[LLVMdev] c const

[Chris Lattner]

On Wed, 8 Aug 2007, Nikhil A. Patil wrote:
> I think I found a bug. I don't know if it's in upstream gcc or llvm-gcc4.

Looks like a bug, please file a bugzilla entry.

-Chris

> int func()
> {
>    const int *arr;
>    arr[0] = 1;
> }
>
> $ llvm-gcc main.c -c; echo $?
> 0
>
> $ gcc main.c -c
> main.c: In function 'func':
> main.c:4: error: assignment of read-only location
>
> The difference disappears when arr[0] is replaced by *arr.
>
> (I tried the above with gcc 4.1.2, 3.4.6, 4.0.3. (I don't have access
> to 4.0.1, off which llvm-gcc seems to be derived.)
>
> nikhil
>
> On 08/08/2007, Chris Lattner <sabre at nondot.org> wrote:
>> This property isn't preserved on the llvm ir, because const can always
>> be cast away.  If you want mod information, then I suggest using the
>> aliasanalysis interface to get mod ref info for a call.
>>
>> -Chris
>>
>> http://nondot.org/sabre
>> http://llvm.org
>>
>> On Aug 8, 2007, at 12:07 AM, "Ryan M. Lefever" <lefever at crhc.uiuc.edu>
>> wrote:
>>
>>> How is c's const keyword translated when compiling c into llvm
>>> bytecode.
>>>  I'm specifically interested in const pointer function arguments.
>>> Consider a function declared as follows in c:
>>>
>>> void f(const int* arg);
>>>
>>> When I examine f in llvm bytecode, how can I tell that arg is a
>>> pointer,
>>> whose contents can only be read, not written.
>>>
>>> Regards,
>>> Ryan
>>> _______________________________________________
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-Chris

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