Index: MC/AsmParser/AltMacroEnable.s
===================================================================
--- /dev/null
+++ MC/AsmParser/AltMacroEnable.s
@@ -0,0 +1,6 @@
+# RUN: llvm-mc %s -o -| FileCheck %s
+
+#CHECK-NOT: error
+
+.altmacro
+.noaltmacro
Index: MC/MCParser/AsmParser.cpp
===================================================================
--- MC/MCParser/AsmParser.cpp
+++ MC/MCParser/AsmParser.cpp
@@ -412,7 +412,7 @@
     DK_CFI_REMEMBER_STATE, DK_CFI_RESTORE_STATE, DK_CFI_SAME_VALUE,
     DK_CFI_RESTORE, DK_CFI_ESCAPE, DK_CFI_SIGNAL_FRAME, DK_CFI_UNDEFINED,
     DK_CFI_REGISTER, DK_CFI_WINDOW_SAVE,
-    DK_MACROS_ON, DK_MACROS_OFF,
+    DK_MACROS_ON, DK_MACROS_OFF, DK_ALTMACRO, DK_NOALTMACRO,
     DK_MACRO, DK_EXITM, DK_ENDM, DK_ENDMACRO, DK_PURGEM,
     DK_SLEB128, DK_ULEB128,
     DK_ERR, DK_ERROR, DK_WARNING,
@@ -484,7 +484,8 @@
   bool parseDirectiveEndMacro(StringRef Directive);
   bool parseDirectiveMacro(SMLoc DirectiveLoc);
   bool parseDirectiveMacrosOnOff(StringRef Directive);
-
+  // AltMacros
+  bool parseDirectiveAltmacro(StringRef Directive);
   // ".bundle_align_mode"
   bool parseDirectiveBundleAlignMode();
   // ".bundle_lock"
@@ -1921,6 +1922,9 @@
       return parseDirectiveMacrosOnOff(IDVal);
     case DK_MACRO:
       return parseDirectiveMacro(IDLoc);
+    case DK_ALTMACRO:
+    case DK_NOALTMACRO:
+      return parseDirectiveAltmacro(IDVal);
     case DK_EXITM:
       return parseDirectiveExitMacro(IDVal);
     case DK_ENDM:
@@ -3840,6 +3844,15 @@
   return false;
 }
 
+/// parseDirectiveAltmacro
+/// ::= .altmacro
+/// ::= .noaltmacro
+bool AsmParser::parseDirectiveAltmacro(StringRef Directive) {
+  if (getLexer().isNot(AsmToken::EndOfStatement))
+    return TokError("unexpected token in '" + Directive + "' directive");
+  return false;
+}
+
 /// parseDirectiveMacrosOnOff
 /// ::= .macros_on
 /// ::= .macros_off
@@ -4937,6 +4950,8 @@
   DirectiveKindMap[".err"] = DK_ERR;
   DirectiveKindMap[".error"] = DK_ERROR;
   DirectiveKindMap[".warning"] = DK_WARNING;
+  DirectiveKindMap[".altmacro"] = DK_ALTMACRO;
+  DirectiveKindMap[".noaltmacro"] = DK_NOALTMACRO;
   DirectiveKindMap[".reloc"] = DK_RELOC;
   DirectiveKindMap[".dc"] = DK_DC;
   DirectiveKindMap[".dc.a"] = DK_DC_A;