[LLVMdev] PROPOSAL: struct-access-path aware TBAA

[Krzysztof Parzyszek]

On 3/12/2013 9:56 PM, Shuxin Yang wrote:
> Based on my understanding of her design, following is one obtuse
> motivating example:
>
> --------------------------
> class A;
> class B;
>
> int foo(A* p, B* q) {
>
>     p->a_int_field = 2;
>     q->another_int_field = 3;
>     return p->a_int_field; // !!!!!
> }
> ----------------------------------
>
> the *-statement can be optimized into "return 2" if optimizer can prove
> type-A does not include type-B,
> and type-B does not include type-A either.
>

And my example shows that they can alias regardless of that.  Granted, 
it's somewhat contrived and I'm not 100% sure if it's legal.  Once there 
are pointers, there is little that can be done without knowing at least 
something about what they point to.

-Krzysztof

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