xazax.hun added inline comments.
================
Comment at: clang/lib/Analysis/UnsafeBufferUsage.cpp:168-169
+ static Matcher matcher() {
+ // FIXME: What if the index is integer literal 0? Should this be
+ // a safe gadget in this case?
+ return stmt(
----------------
NoQ wrote:
> aaron.ballman wrote:
> > xazax.hun wrote:
> > > As per some of the discussions, in the future the compiler might be able
> > > to recognize certain safe patterns, e.g., when there is a simple for loop
> > > with known bounds, or when both the index and the array size is
> > > statically known.
> > >
> > > I think here we need to make a very important design decision: Do we want
> > > the gadgets to have the right "safety" category when it is created (e.g.,
> > > we have to be able to decide if a gadget is safe or not using matchers),
> > > or do we want some mechanisms to be able to promote an unsafe gadget to
> > > be a safe one? (E.g., do we want to be able to prove some unsafe gadgets
> > > safe using dataflow analysis in a later pass?)
> > (FWIW, this is a great question and I really appreciate you asking it!)
> My original design implies that safe gadgets are a separate hierarchy, so
> there will be a new gadget class for index zero, and this gadget will be
> changed to skip index zero. But I don't immediately see why such early
> separation is strictly necessary, other than for a bit of extra type safety
> (extra virtual methods of the `UnsafeGadget` class don't make sense on safe
> gadgets). We *do* have time to make this distinction later, before we get to
> emitting warnings.
>
> So maybe eventually we'll end up replacing `isSafe()` with a pure virtual
> method and deprecate `SafeGadget` and `UnsafeGadget` base classes, if we see
> it cause too much duplication or it turns out that the extra analysis
> necessary to establish safety can't be nicely implemented in ASTMatchers. In
> this case I'll admit that I over-engineered it a bit.
I'd strongly prefer `isSafe()` method over inheritance. While adding safe and
unsafe gadgets for zero indices is not too bad, if we plan to expand this to
more cases, like known array size + compile time constant index, it will get
harder and harder to keep all the gadgets in sync. We can end up missing cases
or detecting a code snippet both as safe and unsafe. The `isSafe` method would
basically get rid of a whole class of problems, where safe and unsafe versions
of the gadgets are overlapping. That being said, I am not insisting doing this
change in this PR, it is OK doing the change later in a follow-up.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D137379/new/
https://reviews.llvm.org/D137379
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