1 files changed, 19 insertions, 4 deletions
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index fff49b7..7589701 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -6977,11 +6977,26 @@ void Sema::AddOverloadCandidate(
     /// have linkage. So that all entities of the same should share one
     /// linkage. But in clang, different entities of the same could have
     /// different linkage.
-    NamedDecl *ND = Function;
-    if (auto *SpecInfo = Function->getTemplateSpecializationInfo())
+    const NamedDecl *ND = Function;
+    bool IsImplicitlyInstantiated = false;
+    if (auto *SpecInfo = Function->getTemplateSpecializationInfo()) {
       ND = SpecInfo->getTemplate();
-
-    if (ND->getFormalLinkage() == Linkage::Internal) {
+      IsImplicitlyInstantiated = SpecInfo->getTemplateSpecializationKind() ==
+                                 TSK_ImplicitInstantiation;
+    }
+
+    /// Don't remove inline functions with internal linkage from the overload
+    /// set if they are declared in a GMF, in violation of C++ [basic.link]p17.
+    /// However:
+    /// - Inline functions with internal linkage are a common pattern in
+    ///   headers to avoid ODR issues.
+    /// - The global module is meant to be a transition mechanism for C and C++
+    ///   headers, and the current rules as written work against that goal.
+    const bool IsInlineFunctionInGMF =
+        Function->isFromGlobalModule() &&
+        (IsImplicitlyInstantiated || Function->isInlined());
+
+    if (ND->getFormalLinkage() == Linkage::Internal && !IsInlineFunctionInGMF) {
       Candidate.Viable = false;
       Candidate.FailureKind = ovl_fail_module_mismatched;
       return;