Recommit "Support attribute used in member funcs of class templates"

This diff previously exposed a bug in LLVM's IRLinker, breaking
buildbots that tried to self-host LLVM with monolithic LTO.
The bug is now in LLVM by D59552

Original commit message:
As PR17480 describes, clang does not support the used attribute
for member functions of class templates. This means that if the member
function is not used, its definition is never instantiated. This patch
changes clang to emit the definition if it has the used attribute.

Test Plan: Added a testcase

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D56928

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@356598 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index c71fa7ac57b755e56e8eb2345ad9dad20e81660b..4615fbc974933afcdb600b5d7146a372227fc9b1 100644 (file)
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -2232,6 +2232,20 @@ TemplateDeclInstantiator::VisitCXXMethodDecl(CXXMethodDecl *D,
     Owner->addDecl(Method);
   }
 
+  // PR17480: Honor the used attribute to instantiate member function
+  // definitions
+  if (Method->hasAttr<UsedAttr>()) {
+    if (const auto *A = dyn_cast<CXXRecordDecl>(Owner)) {
+      SourceLocation Loc;
+      if (const MemberSpecializationInfo *MSInfo =
+              A->getMemberSpecializationInfo())
+        Loc = MSInfo->getPointOfInstantiation();
+      else if (const auto *Spec = dyn_cast<ClassTemplateSpecializationDecl>(A))
+        Loc = Spec->getPointOfInstantiation();
+      SemaRef.MarkFunctionReferenced(Loc, Method);
+    }
+  }
+
   return Method;
 }
 

diff --git a/test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp b/test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp
new file mode 100644 (file)
index 0000000..7d2062f
--- /dev/null
+++ b/test/CodeGenCXX/attr-used-member-function-implicit-instantiation.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+
+// Check that PR17480 is fixed: __attribute__((used)) ignored in templated
+// classes
+namespace InstantiateUsedMemberDefinition {
+template <typename T>
+struct S {
+  int __attribute__((used)) f() {
+    return 0;
+  }
+};
+
+void test() {
+  // Check that InstantiateUsedMemberDefinition::S<int>::f() is defined
+  // as a result of the S class template implicit instantiation
+  // CHECK: define linkonce_odr i32 @_ZN31InstantiateUsedMemberDefinition1SIiE1fEv
+  S<int> inst;
+}
+} // namespace InstantiateUsedMemberDefinition