[PATCH] D20665: Claim NoAlias if two GEPs index different fields of the same struct

[Daniel Berlin via llvm-commits]

and the obvious modification still gives right answers (ie using x->a):

  %5 = getelementptr inbounds %struct.A, %struct.A* %x, i32 0, i32 0
  %6 = getelementptr inbounds [10 x i8], [10 x i8]* %5, i32 0, i32 0
  %7 = getelementptr inbounds i8, i8* %6, i64 %4
  %8 = load i8, i8* %7, align 1
  %9 = zext i8 %8 to i32
  %10 = getelementptr inbounds %struct.A, %struct.A* %x, i32 0, i32 1


%5 and %10 do *not* alias.
The code says nothing about %10 and %6 or %7

On Wed, Jun 1, 2016 at 7:01 PM, Daniel Berlin <dberlin at dberlin.org> wrote:

> Errr, this is not two GEPS of a struct type base pointer with the same
> type, with a minimum of two operands, etc.
>
> It's
>   %6 = getelementptr inbounds i8, i8* %5, i64 %4
>    %9 = getelementptr inbounds %struct.A, %struct.A* %x, i32 0, i32 1
>
> This code will do nothing with this.
>
> Want to try again?
> :)
>
>
> On Wed, Jun 1, 2016 at 5:49 PM, Eli Friedman <eli.friedman at gmail.com>
> wrote:
>
>> eli.friedman added a comment.
>>
>> Example:
>>
>>   struct A {
>>     unsigned char a[10];
>>     unsigned char b;
>>   };
>>   void f(A* x) {
>>     for (unsigned i = 0; i < 11; ++i)
>>       x->b += ((unsigned char*)x)[i];
>>   }
>>
>>
>> Repository:
>>   rL LLVM
>>
>> http://reviews.llvm.org/D20665
>>
>>
>>
>>
>
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