Fix miscompile when performing template instantiation of non-dependent

doubly-nested implicit CXXConstructExprs.

Ensure that we transform the parameter initializer using
TransformInitializer rather than TransformExpr so that we properly strip
down and rebuild the initialization, including any necessary
CXXBindTemporaryExprs. Otherwise we can end up forgetting to destroy
temporary objects used to construct a constructor parameter.

clang/lib/Sema/TreeTransform.h

@@ -12241,7 +12241,8 @@ TreeTransform<Derived>::TransformCXXConstructExpr(CXXConstructExpr *E) {
         (E->getNumArgs() > 1 && getDerived().DropCallArgument(E->getArg(1)))) &&
        (!getDerived().DropCallArgument(E->getArg(0))) &&
        !E->isListInitialization()))
-    return getDerived().TransformExpr(E->getArg(0));
+    return getDerived().TransformInitializer(E->getArg(0),
+                                             /*DirectInit*/ false);
 
   TemporaryBase Rebase(*this, /*FIXME*/ E->getBeginLoc(), DeclarationName());
 

clang/test/CodeGenCXX/instantiate-init.cpp

@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -std=c++14 %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -std=c++17 %s -emit-llvm -o - | FileCheck %s
+
+namespace std {
+  template<typename T> class initializer_list {
+    const T *data;
+    __SIZE_TYPE__ size;
+
+  public:
+    initializer_list();
+  };
+}
+
+namespace ParenBraceInitList {
+  struct Vector {
+    Vector(std::initializer_list<int>);
+    ~Vector();
+  };
+
+  struct Base { Base(Vector) {} };
+
+  // CHECK: define {{.*}}18ParenBraceInitList1fILi0EE
+  template<int> void f() {
+    // CHECK: call {{.*}}18ParenBraceInitList6VectorC1
+    // CHECK: call {{.*}}18ParenBraceInitList6VectorD1
+    Base({0});
+  }
+  template void f<0>();
+}