[LLVMdev] Can we assume const parameter and to-be-modified parameter do not alias?

[yi_jiang]

Hi, 

This question is raised from the following example:
 
int foo (const int a[], int b[])
{
     ...
     b[i] = …
     …
}

Basically a[] is defined as read-only while b[] will be explicitly modified in the function.  At the first glance, they can not be alias but  it seems that we can not figure out the alias info between them now which prevent us from doing some optimizations.   Here is the quote from:

c99 rationale, v5.10, p. 77

const is specified in such a way that an implementation is at liberty to put const objects in read-only storage, and is encouraged to diagnose obvious attempts to modify them, but is not required to track down all the subtle ways that such checking can be subverted.

Our understanding is that it is user’s responsibility to guarantee that const array will not be touched in any way and if not the behavior is undefined and in this case it is safe to assume that they are not alias?