[clang][analyzer] Ignore unnamed bitfields in UninitializedObjectChecker (#132427)

Fixes #132001 

Co-authored-by: YLChenZ <chentongyongcz@gmail.com>

Author: kr-2003

clang/lib/StaticAnalyzer/Checkers/UninitializedObject/UninitializedObjectChecker.cpp

@@ -291,7 +291,9 @@ bool FindUninitializedFields::isNonUnionUninit(const TypedValueRegion *R,
 
   // Are all of this non-union's fields initialized?
   for (const FieldDecl *I : RD->fields()) {
-
+    if (I->isUnnamedBitField()) {
+      continue;
+    }
     const auto FieldVal =
         State->getLValue(I, loc::MemRegionVal(R)).castAs<loc::MemRegionVal>();
     const auto *FR = FieldVal.getRegionAs<FieldRegion>();

clang/test/Analysis/cxx-uninitialized-object.cpp

@@ -1182,3 +1182,24 @@ void fComplexTest() {
   // TODO: we should emit a warning for x2.x and x2.y.
   ComplexUninitTest x2;
 }
+
+struct PaddingBitfieldTest {
+  int a;
+  long long : 7; // padding, previously flagged as uninitialized
+  PaddingBitfieldTest(int a) : a(a) {}
+};
+
+void fPaddingBitfieldTest() {
+  PaddingBitfieldTest pb(42);
+  // no-warning: Unnamed bitfield is now ignored, fixing false positive
+}
+
+struct NamedBitfieldTest {
+  int b; 
+  long long named : 7; // expected-note{{uninitialized field 'this->named'}}
+  NamedBitfieldTest(int b) : b(b) {} // expected-warning{{1 uninitialized field at the end of the constructor call}}
+};
+
+void fNamedBitfieldTest() {
+  NamedBitfieldTest nb(42); 
+}