[LLVMdev] Alias analysis interface

[Dan Gohman]

Hello,

I'm afraid I don't understand your question. Could you restate your example
and your question, and say what specifically you would like alias analysis
to do?

Dan

On Fri, Nov 9, 2012 at 9:31 AM, Shuxin Yang <shuxin.llvm at gmail.com> wrote:

> 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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