[LLVMdev] Reference Manual Clarifications 2

Jon Sargeant delta17 at cox.net
Sat Apr 19 15:27:56 PDT 2008

Thanks for your reply.

Chris Lattner wrote:

>> Regarding free, I also think your wording isn't clear enough: "If the
>> pointer is null, the result is undefined."  The free result is void.
>> Consider rewording as "If the pointer is null, the operation is valid
>> but does not free the pointer."
> It isn't though.  free(NULL) could segfault the app, for example.

See Nick's post.

>> Regarding malloc and alloca, I realized that the size is unsigned,  
>> so a
>> negative value for NumElements is impossible.  I suggest replacing "it
>> is the number of elements allocated" with "it is the UNSIGNED number  
>> of
>> elements allocated".
> I'm not sure why this is more clear.

The semantics of malloc and alloca depend on whether you interpret 
NumElements as a signed or unsigned 32-bit integer.  For example, if 
NumElements is 0xffffFFFF, should the instruction fail (because 
allocating a negative number of elements doesn't make sense), or should 
the instruction allocate 2^32-1 elements?  I don't see any mention of 
whether NumElements is signed or unsigned in the documentation.

>> I'm working on another set of changes now.  If it's not too much
>> trouble, it would be more convenient for me to post the changes (as  
>> I've
>> done in this e-mail) and let you integrate them into LangRef.html.
> It would definitely be easier to integrate in patch form.  Here is  
> what I committed:
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20080414/061277.html

Very well.  I'll submit future changes as patches.

Best Regards,

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