[llvm-dev] RFC: Resolving TBAA issues

[Ivan A. Kosarev via llvm-dev]

Daniel,

 >> the type of (*x) is not compatible with the type of (*b) or,
 >> recursively, type of b->i. Similarly, the type of (*b) is not
 >> compatible with (*x) or, recursively, x->i.
...
 > I think these are interesting interpretations.  I'm not sure
 > i'd personally agree with them (and there are definitely
 > compilers out there that do not).

I wonder how you know that those compilers interpret it differently. If 
the correct answer for a specific case is "no alias", then reloading of 
values does not say anything about how authors interpret the cited clause.

It's only omission of reloading that does matter.

 > It gets more weird with unions.

Would you mind if we proceed with concrete examples from this point?

 >> Consider these two accesses:
 >>
 >>     struct A { int i; };
 >>     struct B { struct A a; } *b;
 >>
 >>     struct X { int i; } *x;
 >>
 >>     b->a
 >>     x->i
 >
 > Do you believe the answer changes if you had struct A *x
 > instead of struct X *x?
 > If so, why?

So then it reads:

   struct A { int i; } *x;
   struct B { struct A a; } *b;

   b->a
   x->i

These two accesses are allowed overlap as the type of b->a is compatible 
with the type of (*x).

I should admit I don't see what makes this case special. Can you 
elaborate please?

Thanks,

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