On Tue, 2006-02-21 at 13:31 -0500, Richard Kenner wrote: > Err, no they don't. Clearly an object of the type can hold a value > outside TYPE_MIN_VALUE/TYPE_MAX_VALUE at runtime. That IMHO means > that TYPE_MIN_VALUE/TYPE_MAX_VALUE do not reflect reality. > > What does "can" mean here? If it means "is physically capable of", then > TYPE_MIN_VALUE and TYPE_MAX_VALUE have no meaning an any context. Can a conforming program set the object to a value outside of TYPE_MIN_VALUE/TYPE_MAX_VALUE. Clearly the answer for Ada today is yes, and that is horribly bad as it means TYPE_MIN_VALUE and TYPE_MAX_VALUE are effectively useless.
> I interpret "can" as meaning "is allowed to according to the semantics > of the language", meaning that if the value is outside that range, it's > an invalid (technicallly "erroneous" in Ada terminology). According to a previous message from you, it's not invalid. For example, you can get such a value from an unchecked conversion and you can use that value in an meaningful way (runtime bounds checking). > No, I don't think the Ada code in question is bogus. My understanding > of this thread is that somebody (either the Ada front end, gimplification, > or the optimizer) is breaking the type-correctness of the tree. Type conversions aren't being lost. The fundamental problem is with the setting of TYPE_MIN_VALUE/TYPE_MAX_VALUE. Please read the data in the PR. I've detailed pretty well what's happening and the fundamental problem is the bogus value for TYPE_MAX_VALUE. > No, because in the absence of a 'Value, the unchecked conversion must > *also* produce a value in the range to be non-erroneous. The *only* > case we need to worry about is an object that is *both* the target of > an unchecked conversion *and* the operand of a 'Valid. That applies > to an exceedingly tiny number of objects and they should not drive the > entire type system, as I said. Instead, what we need to do is define > some tree node (or flag) that tells VRP "don't deduce any value > through this node". That's enough to handle this rare case. I disagree strongly -- the Ada front-end is lying to the rest of the compiler about the range of types. That's a problem that needs to be fixed in the Ada front-end, not VRP. VRP shouldn't need to know about this kind of braindamange. > > No they are not. The ADa front-end says that an object of a particular > type as a set of values [x .. y]. However, at runtime the object is > allowed to have values outside that range. > > Not for the normal meaning of "allowed". With the single exception above, > a program is erroneous if, at run time, the values are otuside that range. But this exception is *VERY* important. THe exception fundamentally allows you to set the object to a value outside the range and the exception then allows the program to detect such an assignment at runtime. That effectively makes TYPE_MIN_VALUE/TYPE_MAX_VALUE useless. jeff
