[LLVMdev] Clang question

[Owen Anderson]

Does -fno-builtin[-memcpy] handle this?

--Owen

On Mar 5, 2012, at 12:35 PM, Eric Christopher wrote:

> You'll need to do the work then. I'd also question why? On most platforms a decent memcpy exists.
> 
> -eric
> 
> On Mar 5, 2012, at 12:28 PM, Ryan Taylor <ryta1203 at gmail.com> wrote:
> 
>> I would like it to always be lowered, I don't want it.
>> 
>> On Mon, Mar 5, 2012 at 12:27 PM, Eric Christopher <echristo at apple.com> wrote:
>> You don't have memcpy or want it to always lower it?
>> 
>> -eric
>> 
>> On Mar 5, 2012, at 11:56 AM, Ryan Taylor <ryta1203 at gmail.com> wrote:
>> 
>>> Christoph,
>>> 
>>> Yes, you are correct on the lifetime calls, they are just markers for liveness.
>>> 
>>> However, the backend is not optimizing these calls away. I could try to deal with them outside of llvm but I was hoping for a cleaner solution using llvm?
>>> 
>>> On Mon, Mar 5, 2012 at 11:51 AM, Christoph Erhardt <christoph at sicherha.de> wrote:
>>> Hi Ryan,
>>> 
>>> the compiler is free to insert implicit calls to memcpy(), for instance
>>> for assignments from one struct/class variable to another. The same goes
>>> for memset(), which may be inserted implicitly for the initialization of
>>> local structs or arrays.
>>> 
>>> The good news is that the backend normally optimizes these calls away
>>> where possible, replacing them with simple moves - at least as long as
>>> the number of bytes to copy does not exceed a certain threshold.
>>> 
>>> As for the llvm.lifetime intrinsics, take a look at the documentation:
>>> http://llvm.org/docs/LangRef.html#int_memorymarkers
>>> If I'm not mistaken, these calls seem to be used to mark the lifespan of
>>> a stack-allocated object.
>>> 
>>> Regards,
>>> Christoph
>>> 
>>> _______________________________________________
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>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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>> 
>> 
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