Index: lib/MC/MCParser/AsmParser.cpp
===================================================================
--- lib/MC/MCParser/AsmParser.cpp
+++ lib/MC/MCParser/AsmParser.cpp
@@ -67,6 +67,7 @@
   StringRef Name;
   StringRef Body;
   MCAsmMacroParameters Parameters;
+  unsigned AtPseudoVariableValue;
 
 public:
   MCAsmMacro(StringRef N, StringRef B, MCAsmMacroParameters P)
@@ -138,6 +139,9 @@
   /// \brief Map of currently defined macros.
   StringMap<MCAsmMacro> MacroMap;
 
+  /// \brief Keeps track of how many .macro's have been defined.
+  unsigned NumOfMacroDefs;
+
   /// \brief Stack of active macro instantiations.
   std::vector<MacroInstantiation*> ActiveMacros;
 
@@ -251,8 +255,8 @@
                         ArrayRef<MCAsmMacroParameter> Parameters);
   bool expandMacro(raw_svector_ostream &OS, StringRef Body,
                    ArrayRef<MCAsmMacroParameter> Parameters,
-                   ArrayRef<MCAsmMacroArgument> A,
-                   const SMLoc &L);
+                   ArrayRef<MCAsmMacroArgument> A, bool EnableAtPseudoVariable,
+                   unsigned AtPseudoVariableValue, const SMLoc &L);
 
   /// \brief Are macros enabled in the parser?
   bool areMacrosEnabled() {return MacrosEnabledFlag;}
@@ -503,6 +507,8 @@
   SrcMgr.setDiagHandler(DiagHandler, this);
   Lexer.setBuffer(SrcMgr.getMemoryBuffer(CurBuffer)->getBuffer());
 
+  NumOfMacroDefs = 0;
+
   // Initialize the platform / file format parser.
   switch (Ctx.getObjectFileInfo()->getObjectFileType()) {
   case MCObjectFileInfo::IsCOFF:
@@ -1764,7 +1770,9 @@
 
 bool AsmParser::expandMacro(raw_svector_ostream &OS, StringRef Body,
                             ArrayRef<MCAsmMacroParameter> Parameters,
-                            ArrayRef<MCAsmMacroArgument> A, const SMLoc &L) {
+                            ArrayRef<MCAsmMacroArgument> A,
+                            bool EnableAtPseudoVariable,
+                            unsigned AtPseudoVariableValue, const SMLoc &L) {
   unsigned NParameters = Parameters.size();
   bool HasVararg = NParameters ? Parameters.back().Vararg : false;
   if ((!IsDarwin || NParameters != 0) && NParameters != A.size())
@@ -1830,36 +1838,47 @@
       Pos += 2;
     } else {
       unsigned I = Pos + 1;
-      while (isIdentifierChar(Body[I]) && I + 1 != End)
+
+      // Check for the \@ pseudo-variable.
+      if (EnableAtPseudoVariable && Body[I] == '@' && I + 1 != End)
         ++I;
+      else
+        while (isIdentifierChar(Body[I]) && I + 1 != End)
+          ++I;
 
       const char *Begin = Body.data() + Pos + 1;
       StringRef Argument(Begin, I - (Pos + 1));
       unsigned Index = 0;
-      for (; Index < NParameters; ++Index)
-        if (Parameters[Index].Name == Argument)
-          break;
 
-      if (Index == NParameters) {
-        if (Body[Pos + 1] == '(' && Body[Pos + 2] == ')')
-          Pos += 3;
-        else {
-          OS << '\\' << Argument;
-          Pos = I;
-        }
+      if (EnableAtPseudoVariable && Argument == "@") {
+        OS << AtPseudoVariableValue;
+        Pos += 2;
       } else {
-        bool VarargParameter = HasVararg && Index == (NParameters - 1);
-        for (MCAsmMacroArgument::const_iterator it = A[Index].begin(),
-                                                ie = A[Index].end();
-             it != ie; ++it)
-          // We expect no quotes around the string's contents when
-          // parsing for varargs.
-          if (it->getKind() != AsmToken::String || VarargParameter)
-            OS << it->getString();
-          else
-            OS << it->getStringContents();
-
-        Pos += 1 + Argument.size();
+        for (; Index < NParameters; ++Index)
+          if (Parameters[Index].Name == Argument)
+            break;
+
+        if (Index == NParameters) {
+          if (Body[Pos + 1] == '(' && Body[Pos + 2] == ')')
+            Pos += 3;
+          else {
+            OS << '\\' << Argument;
+            Pos = I;
+          }
+        } else {
+          bool VarargParameter = HasVararg && Index == (NParameters - 1);
+          for (MCAsmMacroArgument::const_iterator it = A[Index].begin(),
+                                                  ie = A[Index].end();
+               it != ie; ++it)
+            // We expect no quotes around the string's contents when
+            // parsing for varargs.
+            if (it->getKind() != AsmToken::String || VarargParameter)
+              OS << it->getString();
+            else
+              OS << it->getStringContents();
+
+          Pos += 1 + Argument.size();
+        }
       }
     }
     // Update the scan point.
@@ -2096,10 +2115,18 @@
 }
 
 void AsmParser::defineMacro(StringRef Name, MCAsmMacro Macro) {
+  Macro.AtPseudoVariableValue = NumOfMacroDefs;
+  ++NumOfMacroDefs;
+
   MacroMap.insert(std::make_pair(Name, std::move(Macro)));
 }
 
-void AsmParser::undefineMacro(StringRef Name) { MacroMap.erase(Name); }
+void AsmParser::undefineMacro(StringRef Name) {
+  MacroMap.erase(Name);
+
+  assert(NumOfMacroDefs > 0 && "There are no .macros to undefine!");
+  --NumOfMacroDefs;
+}
 
 bool AsmParser::handleMacroEntry(const MCAsmMacro *M, SMLoc NameLoc) {
   // Arbitrarily limit macro nesting depth, to match 'as'. We can eliminate
@@ -2117,7 +2144,8 @@
   StringRef Body = M->Body;
   raw_svector_ostream OS(Buf);
 
-  if (expandMacro(OS, Body, M->Parameters, A, getTok().getLoc()))
+  if (expandMacro(OS, Body, M->Parameters, A, true, M->AtPseudoVariableValue,
+                  getTok().getLoc()))
     return true;
 
   // We include the .endmacro in the buffer as our cue to exit the macro
@@ -4378,7 +4406,7 @@
   SmallString<256> Buf;
   raw_svector_ostream OS(Buf);
   while (Count--) {
-    if (expandMacro(OS, M->Body, None, None, getTok().getLoc()))
+    if (expandMacro(OS, M->Body, None, None, false, 0, getTok().getLoc()))
       return true;
   }
   instantiateMacroLikeBody(M, DirectiveLoc, OS);
@@ -4417,7 +4445,7 @@
   raw_svector_ostream OS(Buf);
 
   for (MCAsmMacroArguments::iterator i = A.begin(), e = A.end(); i != e; ++i) {
-    if (expandMacro(OS, M->Body, Parameter, *i, getTok().getLoc()))
+    if (expandMacro(OS, M->Body, Parameter, *i, false, 0, getTok().getLoc()))
       return true;
   }
 
@@ -4464,7 +4492,7 @@
     MCAsmMacroArgument Arg;
     Arg.push_back(AsmToken(AsmToken::Identifier, Values.slice(I, I + 1)));
 
-    if (expandMacro(OS, M->Body, Parameter, Arg, getTok().getLoc()))
+    if (expandMacro(OS, M->Body, Parameter, Arg, false, 0,  getTok().getLoc()))
       return true;
   }
 
Index: test/MC/AsmParser/at-pseudo-variable-bad.s
===================================================================
--- /dev/null
+++ test/MC/AsmParser/at-pseudo-variable-bad.s
@@ -0,0 +1,9 @@
+# RUN: not llvm-mc -triple i386-unknown-unknown < %s 2>&1 | FileCheck %s
+
+add  $1\@, %eax
+# CHECK: :[[@LINE-1]]:8: error: unexpected token in argument list
+
+.macro A @
+  mov  %eax, %eax
+.endm
+# CHECK: :[[@LINE-3]]:11: error: expected identifier in '.macro' directive
Index: test/MC/AsmParser/at-pseudo-variable.s
===================================================================
--- /dev/null
+++ test/MC/AsmParser/at-pseudo-variable.s
@@ -0,0 +1,20 @@
+# RUN: llvm-mc -triple i386-unknown-unknown %s | FileCheck %s
+
+.macro A
+  mov  $1\@, %eax
+.endm
+
+.macro B
+  add  $1\@, %eax
+.endm
+
+.macro C
+  sub  $1\@, %eax
+.endm
+
+  A
+# CHECK: movl  $10, %eax
+  B
+# CHECK: addl  $11, %eax
+  C
+# CHECK: subl  $12, %eax