[LLVMdev] c const

[Bill Wendling]

Constness is preserved by the front-end. It's the front-end's job to  
check that a "const" attribute for a language (and its meaning  
differs among them) is used correctly according to the semantics of  
that language. So, if you have a language that prevents you from  
assigning a value to a const variable, then there will never be an  
assignment to that variable in LLVM's IR.

-bw

On Aug 14, 2007, at 11:58 PM, Ryan M. Lefever wrote:

> I don't mean to be a pain, but I was thinking about this a bit more.
> Does gcc ignore the const keyword?  If not, why has LLVM chosen to
> deviate from gcc with respect to the const keyword?  If so, then  
> why do
> we bother using const in LLVM API code?  I'm just curious and  
> wanted to
> understand the thinking behind not preserving const.
>
> Thanks,
> Ryan
>
> Chris Lattner 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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>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
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>
> -- 
> Ryan M. Lefever  [http://www.crhc.uiuc.edu/~lefever/index.html]
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