[LLVMdev] Reference Manual Clarifications 2

[Chris Lattner]

On Apr 19, 2008, at 3:27 PM, Jon Sargeant wrote:
>>> 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.

How could an element count be treated as negative?  It doesn't make  
sense to allocate negative elements.

-Chris