[LLVMdev] Clang question

[Eric Christopher]

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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