2 files changed, 57 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index db741bc6e30..0c3c4399f6e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2398,6 +2398,24 @@ void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
     }
   }
 
+  // Re-declaration cannot add abi_tag's.
+  if (const auto *NewAbiTagAttr = New->getAttr<AbiTagAttr>()) {
+    if (const auto *OldAbiTagAttr = Old->getAttr<AbiTagAttr>()) {
+      for (const auto &NewTag : NewAbiTagAttr->tags()) {
+        if (std::find(OldAbiTagAttr->tags_begin(), OldAbiTagAttr->tags_end(),
+                      NewTag) == OldAbiTagAttr->tags_end()) {
+          Diag(NewAbiTagAttr->getLocation(),
+               diag::err_new_abi_tag_on_redeclaration)
+              << NewTag;
+          Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
+        }
+      }
+    } else {
+      Diag(NewAbiTagAttr->getLocation(), diag::err_abi_tag_on_redeclaration);
+      Diag(Old->getLocation(), diag::note_previous_declaration);
+    }
+  }
+
   if (!Old->hasAttrs())
     return;
 
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 1fca27f8b95..f8cec752041 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4615,6 +4615,42 @@ static void handleDeclspecThreadAttr(Sema &S, Decl *D,
       Attr.getRange(), S.Context, Attr.getAttributeSpellingListIndex()));
 }
 
+static void handleAbiTagAttr(Sema &S, Decl *D, const AttributeList &Attr) {
+  SmallVector<StringRef, 4> Tags;
+  for (unsigned I = 0, E = Attr.getNumArgs(); I != E; ++I) {
+    StringRef Tag;
+    if (!S.checkStringLiteralArgumentAttr(Attr, I, Tag))
+      return;
+    Tags.push_back(Tag);
+  }
+
+  if (const auto *NS = dyn_cast<NamespaceDecl>(D)) {
+    if (!NS->isInline()) {
+      S.Diag(Attr.getLoc(), diag::warn_attr_abi_tag_namespace) << 0;
+      return;
+    }
+    if (NS->isAnonymousNamespace()) {
+      S.Diag(Attr.getLoc(), diag::warn_attr_abi_tag_namespace) << 1;
+      return;
+    }
+    if (Attr.getNumArgs() == 0)
+      Tags.push_back(NS->getName());
+  } else if (!checkAttributeAtLeastNumArgs(S, Attr, 1))
+    return;
+
+  // Store tags sorted and without duplicates.
+  std::sort(Tags.begin(), Tags.end());
+  Tags.erase(std::unique(Tags.begin(), Tags.end()), Tags.end());
+
+  D->addAttr(::new (S.Context)
+             AbiTagAttr(Attr.getRange(), S.Context, Tags.data(), Tags.size(),
+                        Attr.getAttributeSpellingListIndex()));
+
+  // FIXME: remove this warning as soon as mangled part is ready.
+  S.Diag(Attr.getRange().getBegin(), diag::warn_attribute_ignored)
+        << Attr.getName();
+}
+
 static void handleARMInterruptAttr(Sema &S, Decl *D,
                                    const AttributeList &Attr) {
   // Check the attribute arguments.
@@ -5637,6 +5673,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_Thread:
     handleDeclspecThreadAttr(S, D, Attr);
     break;
+  case AttributeList::AT_AbiTag:
+    handleAbiTagAttr(S, D, Attr);
+    break;
 
   // Thread safety attributes:
   case AttributeList::AT_AssertExclusiveLock: