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Re: [RFC] Isolate & simplify paths with undefined behaviour

On Fri, 18 Oct 2013, Jeff Law wrote:

On 10/18/13 14:31, Marc Glisse wrote:

But once you have that pointer defined by a PHI containing a zero, you
look at all its uses, trying to find one that proves the pointer is
What are you going to do with that information?

Uh? I must have been very unclear in my post, this sentence was supposed to describe what *your* patch is doing...

The only use I can see for this pass would be discovering more statements that, if a NULL value flows in, result in undefined behaviour.

Yes, precisely. All I was talking about was separating the predicate: "this statement results in UB if that SSA_NAME pointer is NULL" into its own function, and we happen to already have a function in VRP which does that.

The comment about the non-null attribute refers to cases where we've decorated an argument as "must be non-null". If we see a NULL flowing into such a call, then we've crossed the line into undefined behaviour. We'd want to treat the call just like *0 -- isolate the path with NULL flowing to that call and turn the call into a trap.

Yes, and I think you would get that for free if you called the VRP function instead of manually checking if the statement is an indirection.

Similarly if we find a NULL flowing to a return statement in a function decorated as never returning NULL.

Good idea.

Sorry for the misunderstandings...

Marc Glisse

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