Mill Computing, Inc. Forums The Mill Architecture array bound checking Reply To: array bound checking

Ivan Godard
Keymaster
Post count: 629

Yes and no.
We have to support C, and C has no arrays in expressions – any array name is promoted to a pointer. For explicit indexing where the type is known the compiler can insert explicit bounds checks, but often the underlying type is no longer known. For other languages, or under compiler option, checking using ordinary operations and the machine width does about as well as custom operations for bounds checking. The predicated fault op (for stores) and the one-legged NaR pick (for loads and LEA) are useful.

Valgrind and similar tools check for access outside of an allocated object, not just array indexing. To do that properly requires capabilities or fat pointers, which break data structures that assume skinny pointers. We have some NYF support for this usage.