IMA vs tree-ssa

[Mark Mitchell]

Neil Booth wrote:

>Geoff Keating wrote:-
>
>  
>
>>In any case, it's still not transitive, because 'bar' in:
>>
>>struct foo;
>>struct bar { 
>>  struct foo *f;
>>};
>>
>>is compatible with
>>
>>struct foo { int a; };
>>struct bar { 
>>  struct foo *f;
>>};
>>
>>and
>>
>>struct foo { int b; };
>>struct bar { 
>>  struct foo *f;
>>};
>>
>>but they are not compatible with each other.
>>    
>>
Has anyone asked the C committee what they think about this?

I strongly expect that their intention was to create a requirement that 
compatibility be an equivalence relation.  Certainly, there's no reason 
to suspect that passing pointers to "struct foo" from the second to 
third translation unit above would work, at least if the two "struct 
foo" objects were not themselves so similar.  I would expect that this 
is a defect in the standard.

If so, IMA could just "break" this code in the same way that 
strict-aliasing "broke" lots of other "always-worked-for-me" code.

-- 
Mark Mitchell
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