[LLVMdev] A question about pointer aliasing rules in LLVM

Krzysztof Parzyszek kparzysz at codeaurora.org
Thu Oct 25 17:32:47 PDT 2012

On 10/25/2012 5:36 PM, Dan Gohman wrote:
> First, yes, it is wrong for AliasAnalysis implementations to trust LLVM
> IR types, for the most part. There's nothing in LLVM IR which would
> prevent you from having two myStruct instances which overlap here,
> sharing 4 bytes. Because of that, next really could be equal to &prev.
> In theory, you could help this situation by using TBAA; you could give
> next and prev fields different TBAA tags to say that a store to a next
> field never stores to a prev field.

In practice this is impossible to guarantee.  The only safe way of 
disambiguating the two objects is to prove that the pointers are different.


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