From 9ce9d444a389e0e0179dda133269d6ca4f28a35f Mon Sep 17 00:00:00 2001
From: Reid Kleckner <reid@kleckner.net>
Date: Sat, 11 Apr 2015 01:25:36 +0000
Subject: [PATCH] Only notify consumers about static data members of class
 templates once

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@234675 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaTemplateInstantiateDecl.cpp      | 21 ++++++++-----
 .../static-data-member-single-emission.cpp    | 30 +++++++++++++++++++
 2 files changed, 44 insertions(+), 7 deletions(-)
 create mode 100644 test/CodeGenCXX/static-data-member-single-emission.cpp

diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 6936539f1c..014400822c 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3865,6 +3865,17 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
   if (TSK == TSK_ExplicitInstantiationDeclaration)
     return;
 
+  // We may be explicitly instantiating something we've already implicitly
+  // instantiated.
+  VarDecl *InstantiatedDef = Var->getDefinition();
+  if (InstantiatedDef)
+    InstantiatedDef->setTemplateSpecializationKind(TSK, PointOfInstantiation);
+
+  // If we've already instantiated the definition and we're not
+  // re-instantiating it explicitly, we don't need to do anything.
+  if (InstantiatedDef && TSK != TSK_ExplicitInstantiationDefinition)
+    return;
+
   // Make sure to pass the instantiated variable to the consumer at the end.
   struct PassToConsumerRAII {
     ASTConsumer &Consumer;
@@ -3878,14 +3889,10 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
     }
   } PassToConsumerRAII(Consumer, Var);
 
-  // If we already have a definition, we're done.
-  if (VarDecl *Def = Var->getDefinition()) {
-    // We may be explicitly instantiating something we've already implicitly
-    // instantiated.
-    Def->setTemplateSpecializationKind(Var->getTemplateSpecializationKind(),
-                                       PointOfInstantiation);
+  // If we already implicitly instantiated this, just let the consumer know that
+  // it needs to handle an explicit instantiation now.
+  if (InstantiatedDef && TSK == TSK_ExplicitInstantiationDefinition)
     return;
-  }
 
   InstantiatingTemplate Inst(*this, PointOfInstantiation, Var);
   if (Inst.isInvalid())
diff --git a/test/CodeGenCXX/static-data-member-single-emission.cpp b/test/CodeGenCXX/static-data-member-single-emission.cpp
new file mode 100644
index 0000000000..2b821a90b2
--- /dev/null
+++ b/test/CodeGenCXX/static-data-member-single-emission.cpp
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s
+
+template <typename T>
+struct HasStaticInit {
+static const int index;
+};
+int the_count = 0;
+template <typename T>
+const int HasStaticInit<T>::index = the_count++;
+
+template <typename T> int func_tmpl1() { return HasStaticInit<T>::index; }
+template <typename T> int func_tmpl2() { return HasStaticInit<T>::index; }
+template <typename T> int func_tmpl3() { return HasStaticInit<T>::index; }
+void useit() {
+  func_tmpl1<int>();
+  func_tmpl2<int>();
+  func_tmpl3<int>();
+}
+
+// Throw in a final explicit instantiation to see that it doesn't screw things
+// up.
+template struct HasStaticInit<int>;
+
+// There should only be one entry, not 3.
+// CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }]
+
+// There should only be one update to @the_count.
+// CHECK-NOT: store i32 %{{.*}}, i32* @the_count
+// CHECK: store i32 %{{.*}}, i32* @the_count
+// CHECK-NOT: store i32 %{{.*}}, i32* @the_count
-- 
2.40.0