[clang][bytecode] Register decomposition holding vars (#123515)

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -4984,6 +4984,15 @@ bool Compiler<Emitter>::visitDeclStmt(const DeclStmt *DS) {
       return false;
     if (!this->visitVarDecl(VD))
       return false;
+
+    // Register decomposition decl holding vars.
+    if (const auto *DD = dyn_cast<DecompositionDecl>(VD)) {
+      for (auto *BD : DD->bindings())
+        if (auto *KD = BD->getHoldingVar()) {
+          if (!this->visitVarDecl(KD))
+            return false;
+        }
+    }
   }
 
   return true;

clang/test/AST/ByteCode/cxx17.cpp

@@ -105,3 +105,23 @@ constexpr S s = getS(); // both-error {{must be initialized by a constant expres
                         // both-note {{declared here}}
 static_assert(s.a == 12, ""); // both-error {{not an integral constant expression}} \
                               // both-note {{initializer of 's' is not a constant expression}}
+
+using size_t = decltype(sizeof(0));
+namespace std { template<typename T> struct tuple_size; }
+namespace std { template<size_t, typename> struct tuple_element; }
+
+namespace constant {
+  struct Q {};
+  template<int N> constexpr int get(Q &&) { return N * N; }
+}
+template<> struct std::tuple_size<constant::Q> { static const int value = 3; };
+template<int N> struct std::tuple_element<N, constant::Q> { typedef int type; };
+
+namespace constant {
+  Q q;
+  constexpr bool f() {
+    auto [a, b, c] = q;
+    return a == 0 && b == 1 && c == 4;
+  }
+  static_assert(f());
+}