From 8aa561ba328d84dd0bdb4bb64688fc24e4f3f428 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Thu, 17 Jul 2014 23:12:06 +0000
Subject: [PATCH] PR20346: fix aggregate initialization / template
 instantiation bug:

If, during the initial parse of a template, we perform aggregate initialization
and form an implicit value initialization for an array type, then when we come
to instantiate the template and redo the initialization step, we would try to
match the implicit value initialization up against an array *element*, not to
the complete array.

Remarkably, we've had this bug since ~the dawn of time, but only noticed it
recently.

llvm-svn: 213332
---
 clang/lib/Sema/SemaInit.cpp                       |  9 +++++++++
 clang/test/SemaTemplate/instantiate-decl-init.cpp | 20 ++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 4b75606..3ed1d7f 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -914,6 +914,15 @@ void InitListChecker::CheckSubElementType(const InitializedEntity &Entity,
     assert(SemaRef.getLangOpts().CPlusPlus &&
            "non-aggregate records are only possible in C++");
     // C++ initialization is handled later.
+  } else if (auto *VIE = dyn_cast<ImplicitValueInitExpr>(expr)) {
+    // This happens during template instantiation when we see an InitListExpr
+    // that we've already checked once.
+    assert(SemaRef.Context.hasSameType(VIE->getType(), ElemType) &&
+           "found implicit initialization for the wrong type");
+    if (!VerifyOnly)
+      UpdateStructuredListElement(StructuredList, StructuredIndex, expr);
+    ++Index;
+    return;
   }
 
   // FIXME: Need to handle atomic aggregate types with implicit init lists.
diff --git a/clang/test/SemaTemplate/instantiate-decl-init.cpp b/clang/test/SemaTemplate/instantiate-decl-init.cpp
index 9658fc1..f5daa79 100644
--- a/clang/test/SemaTemplate/instantiate-decl-init.cpp
+++ b/clang/test/SemaTemplate/instantiate-decl-init.cpp
@@ -45,3 +45,23 @@ template<int N> void f1() {
   NonTrivial array[N];
 }
 template<> void f1<2>();
+
+namespace PR20346 {
+  struct S { short inner_s; };
+
+  struct outer_struct {
+    wchar_t arr[32];
+    S outer_s;
+  };
+
+  template <class T>
+  void OpenFileSession() {
+    // Ensure that we don't think the ImplicitValueInitExpr generated here
+    // during the initial parse only initializes the first array element!
+    outer_struct asdfasdf = {};
+  };
+
+  void foo() {
+    OpenFileSession<int>();
+  }
+}
-- 
2.7.4