[analyzer] Fix in self assignment checker

[bruntib]

Summary

For self assignment checker it was necessary to force checking of assignment operators even if those are not called. The reason of this is to check whether "this" is equal to the address of the assignee object.

The buffer overlap checker checks if the intervals of the arguments of a memcpy() call are disjoint. If a class has an array member then the compiler generated assignment operator copies it with memcpy() function without checking self assignment at the beginning. Since the analyzer forces the check of assignment operators, the buffer overflow checker reported a false positive on classes with compiler generated assignment operator and array member.

This commit prevents the forced check of compiler generated assignment operators.

[xazax.hun]

LG!

Just wanted to make sure I get it right. You did not add a test since it is only reproducible with an internal (non-upstreamed) checker. Since the change is trivial, I think it is ok to commit this without a test.

[NoQ]

Sounds reasonable, but it also sounds like something that should be reproducible on the upstream clang. Do you have a code snippet that causes the problematic AST to appear? Even if we don't have the false positive up here in upstream, Is it something we can test via -analyzer-display-progress | FileCheck or with the help of the analysis order checker or something like that?

[Szelethus]

Yup, I agree.

[baloghadamsoftware]

I think you can create a unit test for this: create a pre-call checker that checks for the assignment operator and asserts that we are not in top level. Create a test code with a simple class without user provided copy operator and a function that uses the auto-generated copy operator. Run the checker on this sample code.

lib/StaticAnalyzer/Frontend/AnalysisConsumer.cpp

static bool shouldSkipFunction(const Decl *D,
   //   Count naming convention errors more aggressively.
   if (isa<ObjCMethodDecl>(D))
     return false;
   // We also want to reanalyze all C++ copy and move assignment operators to
   // separately check the two cases where 'this' aliases with the parameter and
   // where it may not. (cplusplus.SelfAssignmentChecker)
   if (const auto *MD = dyn_cast<CXXMethodDecl>(D)) {
     if (MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator())
-      return false;
+      return !MD->isUserProvided();
   }
 
   // Otherwise, if we visited the function before, do not reanalyze it.
   return Visited.count(D);
 }
 
 ExprEngine::InliningModes
 AnalysisConsumer::getInliningModeForFunction(const Decl *D,