Index: src/cxa_demangle.cpp
===================================================================
--- src/cxa_demangle.cpp
+++ src/cxa_demangle.cpp
@@ -7,6 +7,12 @@
 //
 //===----------------------------------------------------------------------===//
 
+// FIXME: (possibly) incomplete list of features that clang mangles that this
+// file does not yet support:
+//   - enable_if attribute
+//   - decomposition declarations
+//   - C++ modules TS
+
 #define _LIBCPP_NO_EXCEPTIONS
 
 #include "__cxxabi_config.h"
@@ -178,6 +184,7 @@
     KConversionOperatorType,
     KPostfixQualifiedType,
     KNameType,
+    KAbiTagAttr,
     KObjCProtoName,
     KPointerType,
     KLValueReferenceType,
@@ -384,6 +391,21 @@
   void printLeft(OutputStream &s) const override { s += Name; }
 };
 
+class AbiTagAttr final : public Node {
+  const Node* Base;
+  StringView Tag;
+public:
+  AbiTagAttr(const Node* Base_, StringView Tag_)
+      : Node(KAbiTagAttr), Base(Base_), Tag(Tag_) {}
+
+  void printLeft(OutputStream &S) const override {
+    Base->printLeft(S);
+    S += "[abi:";
+    S += Tag;
+    S += "]";
+  }
+};
+
 class ObjCProtoName : public Node {
   Node *Ty;
   Node *Protocol;
@@ -1795,10 +1817,10 @@
     return first;
 }
 
-// <source-name> ::= <positive length number> <identifier>
+// <positive length number> ::= [0-9]*
 
 const char*
-parse_source_name(const char* first, const char* last, Db& db)
+parse_positive_integer(const char* first, const char* last, size_t* out)
 {
     if (first != last)
     {
@@ -1813,15 +1835,55 @@
                 if (++t == last)
                     return first;
             }
-            if (static_cast<size_t>(last - t) >= n)
-            {
-                StringView r(t, t + n);
-                if (r.substr(0, 10) == "_GLOBAL__N")
-                    db.Names.push_back(db.make<NameType>("(anonymous namespace)"));
-                else
-                    db.Names.push_back(db.make<NameType>(r));
-                first = t + n;
-            }
+            *out = n;
+            first = t;
+        }
+    }
+    return first;
+}
+
+// extension
+// <abi-tag-seq> ::= <abi-tag>*
+// <abi-tag>     ::= B <positive length number> <identifier>
+
+const char*
+parse_abi_tag_seq(const char* first, const char* last, Db& db)
+{
+    while (first != last && *first == 'B' && first+1 != last)
+    {
+        size_t length;
+        const char* t = parse_positive_integer(first+1, last, &length);
+        if (t == first+1)
+            return first;
+        if (static_cast<size_t>(last - t) < length || db.Names.empty())
+            return first;
+        db.Names.back() = db.make<AbiTagAttr>(
+            db.Names.back(), StringView(t, t + length));
+        first = t + length;
+    }
+    return first;
+}
+
+// <source-name> ::= <positive length number> <identifier>
+
+const char*
+parse_source_name(const char* first, const char* last, Db& db)
+{
+    if (first != last)
+    {
+        size_t length;
+        const char* t = parse_positive_integer(first, last, &length);
+        if (t == first)
+            return first;
+        if (static_cast<size_t>(last - t) >= length)
+        {
+            StringView r(t, t + length);
+            if (r.substr(0, 10) == "_GLOBAL__N")
+                db.Names.push_back(db.make<NameType>("(anonymous namespace)"));
+            else
+                db.Names.push_back(db.make<NameType>(r));
+            first = t + length;
+            first = parse_abi_tag_seq(first, last, db);
         }
     }
     return first;
@@ -4315,6 +4377,7 @@
                 db.Names.push_back(
                     db.make<CtorDtorName>(db.Names.back(), false));
                 first += 2;
+                first = parse_abi_tag_seq(first, last, db);
                 db.ParsedCtorDtorCV = true;
                 break;
             }
@@ -4331,6 +4394,7 @@
                 db.Names.push_back(
                     db.make<CtorDtorName>(db.Names.back(), true));
                 first += 2;
+                first = parse_abi_tag_seq(first, last, db);
                 db.ParsedCtorDtorCV = true;
                 break;
             }
@@ -4373,6 +4437,7 @@
                 return first;
             db.Names.push_back(db.make<UnnamedTypeName>(count));
             first = t0 + 1;
+            first = parse_abi_tag_seq(first, last, db);
           }
             break;
         case 'l':
@@ -4462,7 +4527,7 @@
         default:
             t = parse_operator_name(first, last, db);
             if (t != first)
-                first = t;
+                first = parse_abi_tag_seq(t, last, db);
             break;
         };
     }
Index: test/test_demangle.pass.cpp
===================================================================
--- test/test_demangle.pass.cpp
+++ test/test_demangle.pass.cpp
@@ -29605,6 +29605,12 @@
     {"_ZTW1x", "thread-local wrapper routine for x"},
     {"_ZTHN3fooE", "thread-local initialization routine for foo"},
     {"_Z4algoIJiiiEEvZ1gEUlT_E_", "void algo<int, int, int>(g::'lambda'(int, int, int))"},
+
+    {"_Z1fB3foov", "f[abi:foo]()"},
+    {"_Z1fB3fooB3barv", "f[abi:foo][abi:bar]()"},
+    {"_ZN1SB5outer1fB5innerEv", "S[abi:outer]::f[abi:inner]()"},
+    {"_ZN1SC2B8ctor_tagEv", "S::S[abi:ctor_tag]()"},
+    {"_ZplB4MERP1SS_", "operator+[abi:MERP](S, S)"},
 };
 
 const unsigned N = sizeof(cases) / sizeof(cases[0]);