[llvm-dev] SROA and volatile memcpy/memset

[Krzysztof Parzyszek via llvm-dev]

Hi,

I have a customer testcase where SROA splits a volatile memcpy and we 
end up generating bad code[1].  While this looks like a bug, simply 
preventing SROA from splitting volatile memory intrinsics causes 
basictest.ll for SROA to fail.  Not only that, but it also seems like 
handling of volatile memory transfers was done with some intent.

What are the design decisions in SROA regarding handling of volatile 
memcpy/memset?


[1] In our applications, in most cases volatile objects are used to 
communicate with external devices.  Both, the address and the transfer 
size must match what the device is expecting, so breaking up volatile 
memcpy/memset in smaller pieces must be done very carefully, if at all. 
  Generally, target-independent transformations aren't expected to have 
that knowledge and so it would be preferable that they leave such memory 
traffic alone.

-Krzysztof


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