[PATCH] D126405: [clang][dataflow] Relax assert on existence of `this` pointee storage

[Eric Li via Phabricator via cfe-commits]

li.zhe.hua created this revision.
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Support for unions is incomplete (per 99f7d55e <https://reviews.llvm.org/rG99f7d55eeeecd56566d23ee222e272729e05535c>) and the `this` pointee
storage location is not set for unions. The assert in
`VisitCXXThisExpr` is then guaranteed to trigger when analyzing member
functions of a union.

This commit changes the assert to an early-return. Any expression may
be undefined, and so having a value for the `CXXThisExpr` is not a
postcondition of the transfer function.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D126405

Files:
  clang/lib/Analysis/FlowSensitive/Transfer.cpp
  clang/unittests/Analysis/FlowSensitive/TransferTest.cpp


Index: clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
===================================================================
--- clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -42,10 +42,11 @@
   template <typename Matcher>
   void runDataflow(llvm::StringRef Code, Matcher Match,
                    LangStandard::Kind Std = LangStandard::lang_cxx17,
-                   bool ApplyBuiltinTransfer = true) {
+                   bool ApplyBuiltinTransfer = true,
+                   llvm::StringRef TargetFun = "target") {
     ASSERT_THAT_ERROR(
         test::checkDataflow<NoopAnalysis>(
-            Code, "target",
+            Code, TargetFun,
             [ApplyBuiltinTransfer](ASTContext &C, Environment &) {
               return NoopAnalysis(C, ApplyBuiltinTransfer);
             },
@@ -3175,4 +3176,27 @@
 });
 }
 
+TEST_F(TransferTest, DoesNotCrashOnUnionThisExpr) {
+  std::string Code = R"(
+    union Union {
+        int A;
+        float B;
+    };
+
+    void foo() {
+        Union A;
+        Union B;
+        A = B;
+    }
+  )";
+  // This is a crash regression test when calling the transfer function on a
+  // `CXXThisExpr` that refers to a union.
+  runDataflow(
+      Code,
+      [](llvm::ArrayRef<
+             std::pair<std::string, DataflowAnalysisState<NoopLattice>>>,
+         ASTContext &) {},
+      LangStandard::lang_cxx17, /*ApplyBuiltinTransfer=*/true, "operator=");
+}
+
 } // namespace
Index: clang/lib/Analysis/FlowSensitive/Transfer.cpp
===================================================================
--- clang/lib/Analysis/FlowSensitive/Transfer.cpp
+++ clang/lib/Analysis/FlowSensitive/Transfer.cpp
@@ -279,7 +279,8 @@
 
   void VisitCXXThisExpr(const CXXThisExpr *S) {
     auto *ThisPointeeLoc = Env.getThisPointeeStorageLocation();
-    assert(ThisPointeeLoc != nullptr);
+    if (ThisPointeeLoc == nullptr)
+      return;
 
     auto &Loc = Env.createStorageLocation(*S);
     Env.setStorageLocation(*S, Loc);


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