[LLVMdev] Memcpy / Memset for address spaces >= 256

[David Chisnall]

On 13 Mar 2014, at 05:34, Manuel Jacob <me at manueljacob.de> wrote:

> On 2014-03-12 09:48, David Chisnall wrote:
>> I have some patches that automatically expand all memcpy and similar
>> if the operands are not in AS 0.  I think this is probably not quite
>> the right approach though, and we should be asking the back end for
>> the function that does a memcpy / memset / whatever in a non-0 address
>> space, and expand automatically if it doesn't provide one.
> 
> Can you share these patches?  This would be a tentative solution for the reporter of the bug I linked in the original post.

They're quite ugly (hence not upstreaming yet - most of the stuff in this repo needs some tidying and may be the wrong approach).  Looking at the specific change, it's actually a one liner (and a really, really ugly hack):

https://github.com/CTSRD-CHERI/llvm/commit/a3e044242ab109a7dad2589f4cc1461b08cb513d

This basically sets the limit for the size of a memcpy to expand to infinite.  I'm not sure it works for variable-sized memcpys, but I don't think those are inserted by optimisations so we haven't hit them yet.

David