Hello, > 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. Zdenek
