[clang] [Analyzer][CFG] Correctly handle rebuilt default arg and default init expression (PR #117437)

[via cfe-commits]

================
@@ -850,11 +854,17 @@ class alignas(void *) Stmt {
     LLVM_PREFERRED_TYPE(ExprBitfields)
     unsigned : NumExprBits;
 
-    /// Whether this CXXDefaultInitExprBitfields rewrote its argument and stores
-    /// a copy.
+    /// Whether this CXXDefaultInitExpr rewrote its argument and stores
+    /// a copy, unlike HasRebuiltInit, when this flag is true, the argument may
+    /// be partial rebuilt.
----------------
yronglin wrote:

For example:
```c++
struct A {};
struct B {
    A a = A{};
};

B c{}, d{};

```
```
|-CXXRecordDecl 0x13f1289d8 <line:2:1, line:4:1> line:2:8 referenced struct B definition
| |-DefinitionData pass_in_registers aggregate standard_layout trivially_copyable literal has_constexpr_non_copy_move_ctor can_const_default_init
| | |-DefaultConstructor exists non_trivial constexpr needs_implicit defaulted_is_constexpr
| | |-CopyConstructor simple trivial has_const_param needs_implicit implicit_has_const_param
| | |-MoveConstructor exists simple trivial needs_implicit
| | |-CopyAssignment simple trivial has_const_param needs_implicit implicit_has_const_param
| | |-MoveAssignment exists simple trivial needs_implicit
| | `-Destructor simple irrelevant trivial constexpr needs_implicit
| |-CXXRecordDecl 0x13f128b10 <col:1, col:8> col:8 implicit struct B
| `-FieldDecl 0x13f149808 <line:3:5, col:13> col:7 a 'A'
|   `-CXXFunctionalCastExpr 0x13f149aa0 <col:11, col:13> 'A' functional cast to A <NoOp>
|     `-InitListExpr 0x13f1498f0 <col:12, col:13> 'A'
|-VarDecl 0x13f149b18 <line:6:1, col:5> col:3 c 'B' listinit
| `-InitListExpr 0x13f149c10 <col:4, col:5> 'B'
|   `-CXXDefaultInitExpr 0x13f149c58 <col:5> 'A' has rewritten init
|     `-CXXFunctionalCastExpr 0x13f149aa0 <line:3:11, col:13> 'A' functional cast to A <NoOp>
|       `-InitListExpr 0x13f1498f0 <col:12, col:13> 'A'
`-VarDecl 0x13f149ea0 <line:6:1, col:10> col:8 d 'B' listinit
  `-InitListExpr 0x13f149f48 <col:9, col:10> 'B'
    `-CXXDefaultInitExpr 0x13f149f90 <col:10> 'A' has rewritten init
      `-CXXFunctionalCastExpr 0x13f149aa0 <line:3:11, col:13> 'A' functional cast to A <NoOp>
        `-InitListExpr 0x13f1498f0 <col:12, col:13> 'A'
```
The sub-expr in `CXXDefaultInitExpr` will appears multiple times in the AST. We can't add the default argument if it's not rewritten because we could end up with the same expression appearing multiple times.

https://github.com/llvm/llvm-project/pull/117437