[LLVMdev] Clang question

[Eric Christopher]

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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