[clang] [StaticAnalyzer] Make it a noop when initializing a field of empty record (PR #138594)

[Ziqing Luo via cfe-commits]

https://github.com/ziqingluo-90 updated https://github.com/llvm/llvm-project/pull/138594

>From 4e6f2ce82744322a35614532732281eacb2fe79a Mon Sep 17 00:00:00 2001
From: Ziqing Luo <ziqing at udel.edu>
Date: Mon, 5 May 2025 14:27:48 -0700
Subject: [PATCH 1/2] [StaticAnalyzer] Make it a noop when initializing a field
 of empty record.

Previously, Static Analyzer initializes empty type fields with zeroes.
This can cause problems when those fields have no unique addresses.
For example, https://github.com/llvm/llvm-project/issues/137252.

rdar://146753089
---
 .../lib/StaticAnalyzer/Core/ExprEngineCXX.cpp |  8 +++-
 clang/test/Analysis/issue-137252.cpp          | 45 +++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/Analysis/issue-137252.cpp

diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
index 92ce3fa2225c8..219d7b4d2278c 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/AST/ASTContext.h"
 #include "clang/AST/AttrIterator.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/ParentMap.h"
@@ -700,6 +701,7 @@ void ExprEngine::handleConstructor(const Expr *E,
   if (CE) {
     // FIXME: Is it possible and/or useful to do this before PreStmt?
     StmtNodeBuilder Bldr(DstPreVisit, PreInitialized, *currBldrCtx);
+    ASTContext &Ctx = LCtx->getAnalysisDeclContext()->getASTContext();
     for (ExplodedNode *N : DstPreVisit) {
       ProgramStateRef State = N->getState();
       if (CE->requiresZeroInitialization()) {
@@ -715,7 +717,11 @@ void ExprEngine::handleConstructor(const Expr *E,
         // actually make things worse. Placement new makes this tricky as well,
         // since it's then possible to be initializing one part of a multi-
         // dimensional array.
-        State = State->bindDefaultZero(Target, LCtx);
+        const CXXRecordDecl *TargetHeldRecord =
+            Target.getType(Ctx)->getPointeeCXXRecordDecl();
+
+        if (!TargetHeldRecord || !TargetHeldRecord->isEmpty())
+          State = State->bindDefaultZero(Target, LCtx);
       }
 
       Bldr.generateNode(CE, N, State, /*tag=*/nullptr,
diff --git a/clang/test/Analysis/issue-137252.cpp b/clang/test/Analysis/issue-137252.cpp
new file mode 100644
index 0000000000000..8064e3f54d9fd
--- /dev/null
+++ b/clang/test/Analysis/issue-137252.cpp
@@ -0,0 +1,45 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=cplusplus -verify %s
+// RUN: %clang_analyze_cc1 -analyzer-checker=cplusplus -verify %s -DEMPTY_CLASS
+
+// expected-no-diagnostics
+
+// This test reproduces the issue that previously the static analyzer
+// initialized an [[__no_unique_address__]] empty field to zero,
+// over-writing a non-empty field with the same offset.
+
+namespace std {
+#ifdef EMPTY_CLASS
+
+  template <typename T>
+  class default_delete {
+    T dump();
+    static T x;
+  };
+  template <class _Tp, class _Dp = default_delete<_Tp> >
+#else
+
+  struct default_delete {};
+  template <class _Tp, class _Dp = default_delete >
+#endif
+  class unique_ptr {
+    [[__no_unique_address__]]  _Tp * __ptr_;
+    [[__no_unique_address__]] _Dp __deleter_;
+
+  public:
+    explicit unique_ptr(_Tp* __p) noexcept
+      : __ptr_(__p),
+        __deleter_() {}
+
+    ~unique_ptr() {
+      delete __ptr_;
+    }
+  };
+}
+
+struct X {};
+
+int main()
+{
+    std::unique_ptr<X> a(new X());          // previously leak falsely reported
+    return 0;
+}

>From 148008d8e6058485821c784686ca0476faef6254 Mon Sep 17 00:00:00 2001
From: Ziqing Luo <ziqing at udel.edu>
Date: Tue, 6 May 2025 16:06:49 -0700
Subject: [PATCH 2/2] address comments

---
 .../lib/StaticAnalyzer/Core/ExprEngineCXX.cpp |  3 +--
 clang/test/Analysis/issue-137252.cpp          | 21 ++++++++++++-------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
index 219d7b4d2278c..184569336b9e8 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
@@ -701,7 +701,6 @@ void ExprEngine::handleConstructor(const Expr *E,
   if (CE) {
     // FIXME: Is it possible and/or useful to do this before PreStmt?
     StmtNodeBuilder Bldr(DstPreVisit, PreInitialized, *currBldrCtx);
-    ASTContext &Ctx = LCtx->getAnalysisDeclContext()->getASTContext();
     for (ExplodedNode *N : DstPreVisit) {
       ProgramStateRef State = N->getState();
       if (CE->requiresZeroInitialization()) {
@@ -718,7 +717,7 @@ void ExprEngine::handleConstructor(const Expr *E,
         // since it's then possible to be initializing one part of a multi-
         // dimensional array.
         const CXXRecordDecl *TargetHeldRecord =
-            Target.getType(Ctx)->getPointeeCXXRecordDecl();
+            dyn_cast_or_null<CXXRecordDecl>(CE->getType()->getAsRecordDecl());
 
         if (!TargetHeldRecord || !TargetHeldRecord->isEmpty())
           State = State->bindDefaultZero(Target, LCtx);
diff --git a/clang/test/Analysis/issue-137252.cpp b/clang/test/Analysis/issue-137252.cpp
index 8064e3f54d9fd..6cc0af21f1f85 100644
--- a/clang/test/Analysis/issue-137252.cpp
+++ b/clang/test/Analysis/issue-137252.cpp
@@ -10,20 +10,20 @@
 namespace std {
 #ifdef EMPTY_CLASS
 
+  struct default_delete {};
+  template <class _Tp, class _Dp = default_delete >
+#else
+  // Class with methods and static members is still empty:
   template <typename T>
   class default_delete {
     T dump();
     static T x;
   };
   template <class _Tp, class _Dp = default_delete<_Tp> >
-#else
-
-  struct default_delete {};
-  template <class _Tp, class _Dp = default_delete >
 #endif
   class unique_ptr {
-    [[__no_unique_address__]]  _Tp * __ptr_;
-    [[__no_unique_address__]] _Dp __deleter_;
+    [[no_unique_address]]  _Tp * __ptr_;
+    [[no_unique_address]] _Dp __deleter_;
 
   public:
     explicit unique_ptr(_Tp* __p) noexcept
@@ -40,6 +40,11 @@ struct X {};
 
 int main()
 {
-    std::unique_ptr<X> a(new X());          // previously leak falsely reported
-    return 0;
+  // Previously a leak falsely reported here.  It was because the
+  // Static Analyzer engine simulated the initialization of
+  // `__deleter__` incorrectly.  The engine assigned zero to
+  // `__deleter__`--an empty record sharing offset with `__ptr__`.
+  // The assignment over wrote `__ptr__`.
+  std::unique_ptr<X> a(new X()); 
+  return 0;
 }