From 9ac40524fe1216e5d8e475e0cd24a2bd2f55cedd Mon Sep 17 00:00:00 2001
From: Hans Wennborg <hans@hanshq.net>
Date: Fri, 4 Aug 2017 16:48:43 +0000
Subject: Merging r309975: (except the docs/ part)
 ------------------------------------------------------------------------
 r309975 | rsmith | 2017-08-03 12:24:27 -0700 (Thu, 03 Aug 2017) | 4 lines

Don't emit undefined-internal warnings for CXXDeductionGuideDecls.

Patch by ~paul (cynecx on phabricator)! Some test massaging by me.

------------------------------------------------------------------------


git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_50@310067 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/Sema.cpp                                  |  3 +++
 .../cxx1z-class-template-argument-deduction.cpp    | 25 +++++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/lib/Sema/Sema.cpp b/lib/Sema/Sema.cpp
index 6f0db6ce1c..a18f71422f 100644
--- a/lib/Sema/Sema.cpp
+++ b/lib/Sema/Sema.cpp
@@ -542,6 +542,9 @@ void Sema::getUndefinedButUsed(
     // __attribute__((weakref)) is basically a definition.
     if (ND->hasAttr<WeakRefAttr>()) continue;
 
+    if (isa<CXXDeductionGuideDecl>(ND))
+      continue;
+
     if (FunctionDecl *FD = dyn_cast<FunctionDecl>(ND)) {
       if (FD->isDefined())
         continue;
diff --git a/test/SemaCXX/cxx1z-class-template-argument-deduction.cpp b/test/SemaCXX/cxx1z-class-template-argument-deduction.cpp
index 159b7072e6..668c242802 100644
--- a/test/SemaCXX/cxx1z-class-template-argument-deduction.cpp
+++ b/test/SemaCXX/cxx1z-class-template-argument-deduction.cpp
@@ -1,4 +1,9 @@
-// RUN: %clang_cc1 -std=c++1z -verify %s
+// RUN: %clang_cc1 -std=c++1z -verify %s -DERRORS
+// RUN: %clang_cc1 -std=c++1z -verify %s -UERRORS
+
+// This test is split into two because we only produce "undefined internal"
+// warnings if we didn't produce any errors.
+#if ERRORS
 
 namespace std {
   using size_t = decltype(sizeof(0));
@@ -280,3 +285,21 @@ namespace tuple_tests {
     scoped_lock l = {};
   }
 }
+
+#else
+
+// expected-no-diagnostics
+namespace undefined_warnings {
+  // Make sure we don't get an "undefined but used internal symbol" warning for the deduction guide here.
+  namespace {
+    template <typename T>
+    struct TemplDObj {
+      explicit TemplDObj(T func) noexcept {}
+    };
+    auto test1 = TemplDObj(0);
+
+    TemplDObj(float) -> TemplDObj<double>;
+    auto test2 = TemplDObj(.0f);
+  }
+}
+#endif
-- 
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