PR28394: For compatibility with c++11 and c++14, if a static constexpr data

member is redundantly redeclared outside the class definition in code built in
c++17 mode, ensure we emit a non-discardable definition of the data member for
c++11 and c++14 compilations to use.

llvm-svn: 274416

1 files changed, 13 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index fb1763551a3..c6e20a5f9c7 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1447,6 +1447,12 @@ bool CodeGenModule::MayBeEmittedEagerly(const ValueDecl *Global) {
       // Implicit template instantiations may change linkage if they are later
       // explicitly instantiated, so they should not be emitted eagerly.
       return false;
+  if (const auto *VD = dyn_cast<VarDecl>(Global))
+    if (Context.getInlineVariableDefinitionKind(VD) ==
+        ASTContext::InlineVariableDefinitionKind::WeakUnknown)
+      // A definition of an inline constexpr static data member may change
+      // linkage later if it's redeclared outside the class.
+      return false;
   // If OpenMP is enabled and threadprivates must be generated like TLS, delay
   // codegen for global variables, because they may be marked as threadprivate.
   if (LangOpts.OpenMP && LangOpts.OpenMPUseTLS &&
@@ -1595,8 +1601,14 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
                             VD->hasAttr<CUDADeviceAttr>());
     if (!MustEmitForCuda &&
         VD->isThisDeclarationADefinition() != VarDecl::Definition &&
-        !Context.isMSStaticDataMemberInlineDefinition(VD))
+        !Context.isMSStaticDataMemberInlineDefinition(VD)) {
+      // If this declaration may have caused an inline variable definition to
+      // change linkage, make sure that it's emitted.
+      if (Context.getInlineVariableDefinitionKind(VD) ==
+          ASTContext::InlineVariableDefinitionKind::Strong)
+        GetAddrOfGlobalVar(VD);
       return;
+    }
   }
 
   // Defer code generation to first use when possible, e.g. if this is an inline