> On 03/16/2012 02:46 PM, Richard Guenther wrote:
> > In the end what we want is a POINTER_PLUS_EXPR variant
> > that does not make alias-analysis assume the result still points
> > to within the objects the pointer pointed to before the increment/decrement.
> Hold on, is alias analysis really affected by this? Sure, we create
> temporary pointers that point outside their base object, but we don't
> dereference them. Anything value that ends up in a MEM_REF can only
> point into that object again.

it can be affected; by standard pointer arithmetics rules, you cannot
create a pointer that would be outside of an object (unless you convert
it from an integer).  Thus, alias analysis may deduce that if we have
something like

int a[100];
int *p = a + 10;
int *q = p - i;
*(q + 5) = 1;
a[1] = 2;

then q points inside a, and consequently q + 5 >= a + 5, hence the
assignments do not alias.  Ivopts may however produce this (in an equivalent
form with casts to unsigned) even if i > 10.


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