[LLVMdev] Alias analysis interface

[Shuxin Yang]

Sorry the 1st example I gave it bit lame, it is changed to following:

    // a[] is local array, no addr taken. die right after the loop
    for (i = 0; i < N; i++) {
        a[i] = ... /* s1 */
        sum += a[i-1];
    }

  S1 could be easily deleted if alias analyizer say a[i] and a[i-1].


On 11/8/12 6:07 PM, Shuxin Yang wrote:
> Hi,
>
>     In today meeting, Dan gave a very impressive talk about alias 
> analysis.
> I had a question about the example in his slide, something like:
>
>   for (i = 0; i < N; i++) a[i] = a[i-1] + 1;
>
>  For the sake of convenience, let A1, A2 be a[i] and a[i-1] respectively.
> In Dan's design, Alias(A1, A2) would give "no alias", and in order to
> prevent A2 from being mistakenly moved out of loop, the optimizer
> needs to query dependence test as well.
>
>   The problems is how optimizer combine the results from alias analysis
> and dependence test?
>
>   If I change the code little bit, into following, then combining the
> querying dependence testing would prevent hosting *q.
>
>   // points-to(p) = { a, b }
>   // points-to(q) = { c, d }
>   for (i = 0; i < N; i++) *p += *q + 1;
>
> Thanks
> Shuxin
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