[clang] [clang][dataflow] Ignore assignment where base class's operator is used (PR #66364)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang
            
<details>
<summary>Changes</summary>
In C++ it seems it is legit to use base class's operator (e.g. `using 
Base::operator=`) to perform copy if the base class is the common ancestor of 
the source and destination object. In such a case we shouldn't try to access 
fields beyond that of the base class, however such a case seems to be very rare 
(typical code would implement a copy constructor instead), and could add 
complexities, so in this patch we simply bail if the method operator's parent 
class is different from the type of the destination object that this framework 
recognizes.
--
Full diff: https://github.com/llvm/llvm-project/pull/66364.diff

2 Files Affected:

- (modified) clang/lib/Analysis/FlowSensitive/Transfer.cpp (+7) 
- (modified) clang/unittests/Analysis/FlowSensitive/TransferTest.cpp (+24) 


<pre>
diff --git a/clang/lib/Analysis/FlowSensitive/Transfer.cpp 
b/clang/lib/Analysis/FlowSensitive/Transfer.cpp
index b46c947c691b9b9..b510114a7a355eb 100644
--- a/clang/lib/Analysis/FlowSensitive/Transfer.cpp
+++ b/clang/lib/Analysis/FlowSensitive/Transfer.cpp
@@ -531,6 +531,13 @@ class TransferVisitor : public 
ConstStmtVisitor&amp;lt;TransferVisitor&amp;gt; {
       auto *LocDst =
           
cast_or_null&amp;lt;RecordStorageLocation&amp;gt;(Env.getStorageLocation(*Arg0));
 
+      // The assignment operators are different from the type of the 
destination
+      // in this model (i.e. in one of their base classes). This must be very 
rare
+      // and we just bail.
+      if 
(Method-&amp;gt;getThisObjectType().getCanonicalType().getUnqualifiedType() !=
+          LocDst-&amp;gt;getType().getCanonicalType().getUnqualifiedType())
+        return;
+
       if (LocSrc != nullptr &amp;amp;&amp;amp; LocDst != nullptr) {
         copyRecord(*LocSrc, *LocDst, Env);
         Env.setStorageLocation(*S, *LocDst);
diff --git a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp 
b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
index 0abd171f1d0b7cb..e0e3b71503d2176 100644
--- a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -2124,6 +2124,30 @@ TEST(TransferTest, AssignmentOperator) {
       });
 }
 
+TEST(TransferTest, AssignmentOperatorFromBase) {
+  // This is a crash repro. We don&amp;#x27;t model the copy this case, so no
+  // expectations on the copied field of the base class are checked.
+  std::string Code = R&amp;quot;(
+    struct Base {
+      int base;
+    };
+    struct Derived : public Base {
+      using Base::operator=;
+      int derived;
+    };
+    void target(Base B, Derived D) {
+      D.base = 1;
+      D.derived = 1;
+      D = B;
+      // [[p]]
+    }
+  )&amp;quot;;
+  runDataflow(
+      Code,
+      [](const 
llvm::StringMap&amp;lt;DataflowAnalysisState&amp;lt;NoopLattice&amp;gt;&amp;gt; 
&amp;amp;Results,
+         ASTContext &amp;amp;ASTCtx) {});
+}
+
 TEST(TransferTest, AssignmentOperatorFromCallResult) {
   std::string Code = R&amp;quot;(
     struct A {};
</pre>
</details>


https://github.com/llvm/llvm-project/pull/66364
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