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

[Kristóf Umann via Phabricator via cfe-commits]

Szelethus added a comment.

Ah, okay I think I got why you chose this direction. Summaries are little more then a collection of constraints, and at select points in the execution we check and apply them one-by-one. If we want to preserve this architecture (and it seems great, why not?), inheritance is indeed the correct design decision.

The costliest code to run according to my limited knowledge about C++ development is indeed the one that is hard to understand and maintain, and this seems to have a good bit of thought behind it. I'll check your followup patches to gain some confidence before formally accepting, but the general idea seems great.



================
Comment at: clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp:88
   typedef uint32_t ArgNo;
-  static const ArgNo Ret = std::numeric_limits<ArgNo>::max();
+  static const ArgNo Ret;
+
----------------
Why did we remove the initialization here? Can we make this `constexpr`?


================
Comment at: clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp:90
+
+  class ValueConstraint {
+  public:
----------------
We should totally have a good bit of documentation here.


================
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.
----------------
martong wrote:
> martong wrote:
> > Szelethus wrote:
> > > 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.
> > > 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.
> > 
> > Variant would be useful if we knew the set of classes prior and we wanted to add operations gradually. Class hierarchies (or run-time concepts [Sean Parent]) are very useful if we know the set of operations prior and we want to add classes gradually, and we have this case here.
> > 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 did not find any evidence for this statement. Consider as a counter example the ExternalASTSource interface in Clang, which is filled with virtual functions and is part of the C/C++ lookup mechanism, which is quite on the hot path of C/C++ parsing I think. Did not find any prohibition in LLVM coding guidelines neither. I do believe virtual functions have their use cases exactly where (runtime) polimorphism is needed, such as in this patch.
> 
I consider myself proven wrong here then.


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