[PATCH] D74973: [analyzer] StdLibraryFunctionsChecker refactor w/ inheritance

[Kristóf Umann via Phabricator via cfe-commits]

Szelethus added a comment.

I have some high level questions, you have spent far more time with this code and I'm happy to be proven wrong! :)

In D74973#1889188 <https://reviews.llvm.org/D74973#1889188>, @martong wrote:

> > Is really more kind of constraint needed than range constraint?
>
> Yes, there are other constraints I am planning to implement:
>
> - Size requirements E.g.: asctime_s(char *buf, rsize_t bufsz, const struct tm *time_ptr); `buf` size must be at least `bufsz`.
> - Not-null
> - Not-uninitalized
> - Not-tainted


Are we really sure that we need to express that with constraints? Can't we just change the name of `ValueRange` (or encapsulate it in another class) and add more fields to it, such as taintedness or initializedness? Is there an incentive to keep `ValueRange` lean?

This doesn't look too bad:

  auto Getc = [&]() {
    return Summary(ArgTypes{Irrelevant}, RetType{IntTy}, NoEvalCall)
        .Case(
            {ReturnValueDescription(RangeConstraints(WithinRange, {{EOFv, EOFv}, {0, UCharMax}},
                                    Tainted, Non_Uninitialized});
  };



>> A non-null can be represented as range constraint too.
> 
> Actually, to implement that we should have a branch in all `ValueRange::apply*` functions that handles `Loc` SVals. Unfortunately, a pointer cannot be handled as `NonLoc`, and the current Range based implementation handles `NonLoc`s only.

So, why didn't we take that route instead? Marking a pointer non-null seems to be a less invasive change.

>> The compare constraint is used only for the return value for which a special `ReturnConstraint` can be used to handle the return value not like a normal argument (and then the `Ret` special value is not needed).
> 
> The Compare constraint is already forced into a Range "concept" whereas it has nothing to do with ranges. By handling compare constraints separately, we attach a single responsibility to each constraint class, instead of having a monolithic god constraint class. Take a look at this coerced data representation that we have today in ValueRange:
> 
>   BinaryOperator::Opcode getOpcode() const {
>     assert(Kind == ComparesToArgument);
>     assert(Args.size() == 1);
>     BinaryOperator::Opcode Op =
>         static_cast<BinaryOperator::Opcode>(Args[0].first);
>     assert(BinaryOperator::isComparisonOp(Op) &&
>            "Only comparison ops are supported for ComparesToArgument");
>     return Op;
>   }
>    
> 
> Subclasses are a good way to get rid of this not-so-intuitive structure and assertions.

Having more fields feels like another possible solution.



================
Comment at: clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp:151
+
+  using ValueConstraintPtr = std::shared_ptr<ValueConstraint>;
+  /// The complete list of constraints that defines a single branch.
----------------
gamesh411 wrote:
> martong wrote:
> > Note here, we need a copyable, polymorphic and default initializable type (vector needs that). A raw pointer were good, however, we cannot default initialize that. unique_ptr makes the Summary class non-copyable, therefore not an option.
> > Releasing the copyablitly requirement would render the initialization of the Summary map infeasible.
> > Perhaps we could come up with a [[ https://www.youtube.com/watch?v=bIhUE5uUFOA | type erasure technique without inheritance ]] once we consider the shared_ptr as restriction, but for now that seems to be overkill.
> std::variant (with std::monostate for the default constructibility) would also be an option  (if c++17 were supported). But this is not really an issue, i agree with that.
Ugh, we've historically been very hostile towards virtual functions. We don't mind them that much when they don't have to run a lot, like during bug report construction, but as a core part of the analysis, I'm not sure what the current stance is on it.

I'm not inherently (haha) against it, and I'm fine with leaving this as-is for the time being, though I'd prefer if you placed a `TODO` to revisit this issue.


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  https://reviews.llvm.org/D74973/new/

https://reviews.llvm.org/D74973