r344157 - [Sema] Fix a multiple definition bug with friends and templates

[Erik Pilkington via cfe-commits]

Author: epilk
Date: Wed Oct 10 10:17:51 2018
New Revision: 344157

URL: http://llvm.org/viewvc/llvm-project?rev=344157&view=rev
Log:
[Sema] Fix a multiple definition bug with friends and templates

The problem was that MergeFunctionDecl sometimes needs the injected template
arguments of a FunctionTemplateDecl, but is called before adding the new
template to the redecl chain. This leads to multiple common pointers in the same
redecl chain, each with their own identical instantiation. Fix this by merging
the the common state before inserting the new template into the redecl chain.

rdar://44810129

Differential revision: https://reviews.llvm.org/D53046

Added:
    cfe/trunk/test/SemaCXX/friend-template-redecl.cpp
Modified:
    cfe/trunk/include/clang/AST/DeclTemplate.h
    cfe/trunk/lib/AST/DeclTemplate.cpp
    cfe/trunk/lib/Sema/SemaDecl.cpp

Modified: cfe/trunk/include/clang/AST/DeclTemplate.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/DeclTemplate.h?rev=344157&r1=344156&r2=344157&view=diff
==============================================================================
--- cfe/trunk/include/clang/AST/DeclTemplate.h (original)
+++ cfe/trunk/include/clang/AST/DeclTemplate.h Wed Oct 10 10:17:51 2018
@@ -1093,6 +1093,9 @@ public:
   /// template.
   ArrayRef<TemplateArgument> getInjectedTemplateArgs();
 
+  /// Merge our RedeclarableTemplateDecl::Common with \param Prev.
+  void mergePrevDecl(FunctionTemplateDecl *Prev);
+
   /// Create a function template node.
   static FunctionTemplateDecl *Create(ASTContext &C, DeclContext *DC,
                                       SourceLocation L,

Modified: cfe/trunk/lib/AST/DeclTemplate.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/DeclTemplate.cpp?rev=344157&r1=344156&r2=344157&view=diff
==============================================================================
--- cfe/trunk/lib/AST/DeclTemplate.cpp (original)
+++ cfe/trunk/lib/AST/DeclTemplate.cpp Wed Oct 10 10:17:51 2018
@@ -300,6 +300,42 @@ ArrayRef<TemplateArgument> FunctionTempl
   return llvm::makeArrayRef(CommonPtr->InjectedArgs, Params->size());
 }
 
+void FunctionTemplateDecl::mergePrevDecl(FunctionTemplateDecl *Prev) {
+  using Base = RedeclarableTemplateDecl;
+
+  // If we haven't created a common pointer yet, then it can just be created
+  // with the usual method.
+  if (!Base::Common)
+    return;
+
+  Common *ThisCommon = static_cast<Common *>(Base::Common);
+  Common *PrevCommon = nullptr;
+  SmallVector<FunctionTemplateDecl *, 8> PreviousDecls;
+  for (; Prev; Prev = Prev->getPreviousDecl()) {
+    if (Prev->Base::Common) {
+      PrevCommon = static_cast<Common *>(Prev->Base::Common);
+      break;
+    }
+    PreviousDecls.push_back(Prev);
+  }
+
+  // If the previous redecl chain hasn't created a common pointer yet, then just
+  // use this common pointer.
+  if (!PrevCommon) {
+    for (auto *D : PreviousDecls)
+      D->Base::Common = ThisCommon;
+    return;
+  }
+
+  // Ensure we don't leak any important state.
+  assert(ThisCommon->Specializations.size() == 0 &&
+         !ThisCommon->InstantiatedFromMember.getPointer() &&
+         !ThisCommon->InstantiatedFromMember.getInt() &&
+         "Can't merge incompatible declarations!");
+
+  Base::Common = PrevCommon;
+}
+
 //===----------------------------------------------------------------------===//
 // ClassTemplateDecl Implementation
 //===----------------------------------------------------------------------===//

Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=344157&r1=344156&r2=344157&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDecl.cpp Wed Oct 10 10:17:51 2018
@@ -10022,11 +10022,17 @@ bool Sema::CheckFunctionDeclaration(Scop
     if (FunctionTemplateDecl *OldTemplateDecl =
             dyn_cast<FunctionTemplateDecl>(OldDecl)) {
       auto *OldFD = OldTemplateDecl->getTemplatedDecl();
-      NewFD->setPreviousDeclaration(OldFD);
-      adjustDeclContextForDeclaratorDecl(NewFD, OldFD);
       FunctionTemplateDecl *NewTemplateDecl
         = NewFD->getDescribedFunctionTemplate();
       assert(NewTemplateDecl && "Template/non-template mismatch");
+
+      // The call to MergeFunctionDecl above may have created some state in
+      // NewTemplateDecl that needs to be merged with OldTemplateDecl before we
+      // can add it as a redeclaration.
+      NewTemplateDecl->mergePrevDecl(OldTemplateDecl);
+
+      NewFD->setPreviousDeclaration(OldFD);
+      adjustDeclContextForDeclaratorDecl(NewFD, OldFD);
       if (NewFD->isCXXClassMember()) {
         NewFD->setAccess(OldTemplateDecl->getAccess());
         NewTemplateDecl->setAccess(OldTemplateDecl->getAccess());

Added: cfe/trunk/test/SemaCXX/friend-template-redecl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/friend-template-redecl.cpp?rev=344157&view=auto
==============================================================================
--- cfe/trunk/test/SemaCXX/friend-template-redecl.cpp (added)
+++ cfe/trunk/test/SemaCXX/friend-template-redecl.cpp Wed Oct 10 10:17:51 2018
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -std=c++17 -verify -emit-llvm-only %s
+
+// expected-no-diagnostics
+
+template <class T> void bar(const T &t) { foo(t); }
+
+template <class>
+struct HasFriend {
+  template <class T>
+  friend void foo(const HasFriend<T> &m) noexcept(false);
+};
+
+template <class T>
+void foo(const HasFriend<T> &m) noexcept(false) {}
+
+void f() {
+  HasFriend<int> x;
+  foo(x);
+  bar(x);
+}