From cde8d2fddbff55cae520d90f47f6faf124d3f953 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard@metafoo.co.uk>
Date: Wed, 3 Feb 2021 23:31:51 -0800
Subject: [PATCH] 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             |  3 ++-
 clang/test/CodeGenCXX/instantiate-init.cpp | 29 ++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CodeGenCXX/instantiate-init.cpp

diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 1bff267cffc8..1da28a3bb94c 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/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());
 
diff --git a/clang/test/CodeGenCXX/instantiate-init.cpp b/clang/test/CodeGenCXX/instantiate-init.cpp
new file mode 100644
index 000000000000..dd8a1a13bdf0
--- /dev/null
+++ b/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>();
+}