Re: [PATCHES] fix for strict-alias warnings

Tom Lane wrote:

>"Andrew Dunstan" <andrew@dunslane.net> writes:
>  
>
>>I was inder the impression, perhaps incorrectly, the casting the pointers to
>>(void *) would inhibit the compiler from making any assumptions about what
>>it pointed to, and hence inhibit bad effects from those assumptions. The
>>only way to know would be to examine the assembler output, I suppose. The
>>alternative is that it would merely inhibit the compiler from issuing a
>>warning and mask a bad effect. That would be nasty
>>    
>>
>
>IIUC the issue is whether the compiler might incorrectly rearrange the
>order of operations based on the assumption that two pointers point
>to different storage (when in fact they point to the same storage).
>

*nod*

>I don't see what about introducing "(void *)" would be likely to keep
>the compiler from making such assumptions --- you'll still have the same
>two pointers and the exact same sequence of operations.  Accordingly,
>I think it's very likely that the so-far-proposed patches are indeed
>masking the symptom and not solving the real problem.
>
>  
>
My thinking was that it makes those assumptions based on the type of the 
pointer, and it doesn't know the type in the case of (void *).  
Otherwise it really ought to omit a warning even when you cast to (void 
*), IMNSHO.

You could well be right (as I implied above :-) ), and there are at 
least some clues that gcc isn't very smart about this.

So I still think adding -fno-strict-aliasing is the way to go for now.

(back to my day job)

cheers

andrew