[clang] [clang][ExprConst] Support virtual bases in C++26 (PR #204289)

[Yihan Wang via cfe-commits]

================
@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 -triple x86_64-linux -std=c++26 -fexperimental-new-constant-interpreter %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-linux -std=c++26                                         %s -emit-llvm -o - | FileCheck %s
+
+struct A { int a; };
+struct B : virtual A {
+  constexpr B() : A(127) {}
+};
+
+
+// CHECK: @b1 =  global { ptr, i32 } { {{.*}} i32 127 }
+B b1{};
+
+struct C : B {
+  constexpr C(int) : B(), A(128) {}
+};
+
+// CHECK: @c1 =  global { ptr, i32 } { {{.*}} i32 128 }
+C c1 = C(12);
+
+// CHECK: @a1 = global ptr getelementptr (i8, {{.*}}, i64 8)
+A* a1 = (A*)&c1;
+
+struct X {
+  char x[4] = {};
+};
+struct Y {
+  char y[4] = {};
+};
+struct Z : virtual X, virtual Y {
+  char z[4] = {};
+};
+
+struct W : Z {};
+
+
+// CHECK @w = global {{.*}}
----------------
yronglin wrote:

```suggestion
// CHECK: @w = global {{.*}}
```

https://github.com/llvm/llvm-project/pull/204289