[LLVMdev] tbaa

Dan Gohman gohman at apple.com
Tue Dec 6 09:26:59 PST 2011

On Dec 5, 2011, at 9:32 PM, Daniel Berlin wrote:

> On Mon, Dec 5, 2011 at 11:01 PM, Dan Gohman <gohman at apple.com> wrote:
>> On Dec 5, 2011, at 6:04 PM, Daniel Berlin wrote:
>>> Yet, aa-eval still says otherwise.
>> The problem is with aa-eval. It collects all the pointer values in a
>> function, and then just makes a bunch of raw pointer queries, rather than
>> considering dereferences. TBAA tags are only attached to dereferences.
>> So TBAA always has to say MayAlias for every aa-eval query.
> Makes sense.  In that case, it would give the expected answers if
> clang was enhanced to properly deal with similar/dissimilar pointer
> types, instead of giving all pointer types the "everything" tag :)

No, you've confused pointer types with pointee types.  That "any pointer"
tag is for describing when the in-memory objects themselves have pointer

The real issue here is that -aa-eval is just a limited debugging tool that
tends to get misinterpreted as a general-purpose AA benchmark due to
there being no easy alternatives.


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