[clang] [WebKit Checkers] Treat offsetof as a trivial expression. (PR #126996)

[Ryosuke Niwa via cfe-commits]

https://github.com/rniwa created 
https://github.com/llvm/llvm-project/pull/126996

None

>From f7eafbfd258fb0acf60a01d033958f859c426ff3 Mon Sep 17 00:00:00 2001
From: Ryosuke Niwa <rn...@webkit.org>
Date: Wed, 12 Feb 2025 17:52:45 -0800
Subject: [PATCH] [WebKit Checkers] Treat offsetof as a trivial expression.

---
 .../lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp | 5 +++++
 clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp    | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp 
b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
index d40b4b4dbb560..b823e048a4d10 100644
--- a/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/WebKit/PtrTypesSemantics.cpp
@@ -503,6 +503,11 @@ class TrivialFunctionAnalysisVisitor
     return true;
   }
 
+  bool VisitOffsetOfExpr(const OffsetOfExpr* OE) {
+      // offsetof(T) is considered trivial.
+      return true;
+  }
+
   bool VisitCXXMemberCallExpr(const CXXMemberCallExpr *MCE) {
     if (!checkArguments(MCE))
       return false;
diff --git a/clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp 
b/clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp
index ffeecbf87c451..cf403851b74fd 100644
--- a/clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp
+++ b/clang/test/Analysis/Checkers/WebKit/uncounted-obj-arg.cpp
@@ -77,6 +77,8 @@ T&& forward(T& arg);
 template<typename T>
 T&& move( T&& t );
 
+#define offsetof(t, d) __builtin_offsetof(t, d)
+
 } // namespace std
 
 bool isMainThread();
@@ -373,6 +375,7 @@ class RefCounted {
     double y;
   };
   void trivial68() { point pt = { 1.0 }; }
+  unsigned trivial69() { return offsetof(RefCounted, children); }
 
   static RefCounted& singleton() {
     static RefCounted s_RefCounted;
@@ -560,6 +563,7 @@ class UnrelatedClass {
     getFieldTrivial().trivial66()->trivial6(); // no-warning
     getFieldTrivial().trivial67()->trivial6(); // no-warning
     getFieldTrivial().trivial68(); // no-warning
+    getFieldTrivial().trivial69(); // no-warning
 
     RefCounted::singleton().trivial18(); // no-warning
     RefCounted::singleton().someFunction(); // no-warning

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