[LLVMdev] Address space extension

[Matt Arsenault]

On 08/07/2013 01:52 PM, Michele Scandale wrote:
>
> IMHO this information should be a plus that could be *safely* ignored 
> when not necessary and used where it can provide an improvement in 
> optimizations. This does not necessary mean the the middle-end (and 
> the back-ends) must be aware of the semantic of these logical address 
> spaces, it would be enough just to distinguish between two logically 
> different address spaces.
> The first application I see is alias analysis: for targets that do not 
> have different physical address spaces (e.g. X86), meaning that in the 
> IR the 'addrspace' modifier *should* not be present, the knowledge 
> that two pointers refers to different logical address spaces (e.g. 
> OpenCL address spaces) can be used to decide the aliasing.
>
>
There was this patch from a long time ago that never went in to use the 
address spaces for alias analysis:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20111010/129728.html

The decision seems to be that LLVM addrspaces aren't required to not 
alias. I was thinking of following the suggestion to make the datalayout 
contain which address spaces can / cannot alias. Alternatively, the tbaa 
metadata might be appropriate for this, but I haven't looked at how that 
works.
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