[clang][dataflow] Fix getResultObjectLocation() on CXXDefaultArgExpr.

[martinboehme]

This patch includes a test that causes an assertion failure without the other
changes in this patch.

[llvmbot]

@llvm/pr-subscribers-clang-analysis

@llvm/pr-subscribers-clang

Author: None (martinboehme)

Changes

I'm working on an upcoming change that will improve the semantics of
Environment::GetResultObjectLocation() (see the FIXME in the method comment),
and this patch improves the test coverage for this change.

---

Full diff: https://github.com/llvm/llvm-project/pull/85072.diff

1 Files Affected:

• (modified) clang/unittests/Analysis/FlowSensitive/TransferTest.cpp (+30)

diff --git a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
index a8c282f140b4cd..86c7f32f0104be 100644
--- a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -2924,6 +2924,36 @@ TEST(TransferTest, ResultObjectLocation) {
       });
 }
 
+TEST(TransferTest, ResultObjectLocationForDefaultArgExpr) {
+  std::string Code = R"(
+    struct S {};
+    void funcWithDefaultArg(S s = S());
+    void target() {
+      funcWithDefaultArg();
+      // [[p]]
+    }
+  )";
+
+  using ast_matchers::cxxDefaultArgExpr;
+  using ast_matchers::match;
+  using ast_matchers::selectFirst;
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+
+        auto *DefaultArg = selectFirst<CXXDefaultArgExpr>(
+            "default_arg",
+            match(cxxDefaultArgExpr().bind("default_arg"), ASTCtx));
+        ASSERT_NE(DefaultArg, nullptr);
+
+        // The values for default arguments aren't modeled; we merely verify
+        // that we can get a result object location for a default arg.
+        Env.getResultObjectLocation(*DefaultArg);
+      });
+}
+
 TEST(TransferTest, ResultObjectLocationForDefaultInitExpr) {
   std::string Code = R"(
     struct S {};

[martinboehme]

The newly added test is failing, but apparently only on Windows. Will need to take a closer look at why this is, and will update this PR when I have something new.

[martinboehme]

The new test now does actually also fail for me locally. Not sure why I didn't notice this before. Will add a fix.

[martinboehme]

New commit pushed with fix. I have changed the title and description of the PR accordingly.