[Bug target/21479] optimizer removes incorrectly variable comparision in if clause

[schlie at comcast dot net]

------- Additional Comments From schlie at comcast dot net  2005-05-10 08:31 -------
(In reply to comment #5)
> see comment #1 ...  
>   
> you already derefenced the pointer in ppv (in the line  
>  unsigned long lv = *lvp; 
> ) 
>  
> so the compiler assumes that anohter NULL ptr check is not needed. 

- yes, however as the loigical extention of:
   "a null reference is undefined" => "may trap" => "will trap"
   is simply wrong, and is not justifyable; such an optimization
   is target specific, as it depends on "will trap" target semantics.

   (not to mention that even if it is trapped for a particular target,
    that the target won't simply return some value, so pointer null
    comparsions can't be reliably optimized away unless the compiler
    can also enforce dereferenced null pointer trap semantics for that
    particualr target, which GCC does not appear to do.)



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21479