Index: llvm/trunk/include/llvm/MC/MCAsmMacro.h
===================================================================
--- llvm/trunk/include/llvm/MC/MCAsmMacro.h
+++ llvm/trunk/include/llvm/MC/MCAsmMacro.h
@@ -11,6 +11,7 @@
 #define LLVM_MC_MCASMMACRO_H
 
 #include "llvm/MC/MCParser/MCAsmLexer.h"
+#include "llvm/Support/Debug.h"
 
 namespace llvm {
 
@@ -21,6 +22,9 @@
   bool Vararg = false;
 
   MCAsmMacroParameter() = default;
+
+  void dump() const { dump(dbgs()); }
+  void dump(raw_ostream &OS) const;
 };
 
 typedef std::vector<MCAsmMacroParameter> MCAsmMacroParameters;
@@ -32,6 +36,9 @@
 public:
   MCAsmMacro(StringRef N, StringRef B, MCAsmMacroParameters P)
       : Name(N), Body(B), Parameters(std::move(P)) {}
+
+  void dump() const { dump(dbgs()); }
+  void dump(raw_ostream &OS) const;
 };
 } // namespace llvm
 
Index: llvm/trunk/include/llvm/MC/MCContext.h
===================================================================
--- llvm/trunk/include/llvm/MC/MCContext.h
+++ llvm/trunk/include/llvm/MC/MCContext.h
@@ -634,10 +634,17 @@
     }
 
     void defineMacro(StringRef Name, MCAsmMacro Macro) {
+      DEBUG_WITH_TYPE("asm-macros", dbgs() << "Defining new macro:\n";
+                      Macro.dump());
       MacroMap.insert(std::make_pair(Name, std::move(Macro)));
     }
 
-    void undefineMacro(StringRef Name) { MacroMap.erase(Name); }
+    void undefineMacro(StringRef Name) {
+      if (MacroMap.erase(Name)) {
+        DEBUG_WITH_TYPE("asm-macros",
+                        dbgs() << "Un-defining macro: " << Name << "\n");
+      }
+    }
   };
 
 } // end namespace llvm
Index: llvm/trunk/lib/MC/CMakeLists.txt
===================================================================
--- llvm/trunk/lib/MC/CMakeLists.txt
+++ llvm/trunk/lib/MC/CMakeLists.txt
@@ -7,6 +7,7 @@
   MCAsmInfoDarwin.cpp
   MCAsmInfoELF.cpp
   MCAsmInfoWasm.cpp
+  MCAsmMacro.cpp
   MCAsmStreamer.cpp
   MCAssembler.cpp
   MCCodeEmitter.cpp
Index: llvm/trunk/lib/MC/MCAsmMacro.cpp
===================================================================
--- llvm/trunk/lib/MC/MCAsmMacro.cpp
+++ llvm/trunk/lib/MC/MCAsmMacro.cpp
@@ -0,0 +1,42 @@
+//===- MCAsmMacro.h - Assembly Macros ---------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCAsmMacro.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+void MCAsmMacroParameter::dump(raw_ostream &OS) const {
+  OS << "\"" << Name << "\"";
+  if (Required)
+    OS << ":req";
+  if (Vararg)
+    OS << ":vararg";
+  if (!Value.empty()) {
+    OS << " = ";
+    bool first = true;
+    for (const AsmToken &T : Value) {
+      if (!first)
+        OS << ", ";
+      first = false;
+      T.dump();
+    }
+  }
+  OS << "\n";
+}
+
+void MCAsmMacro::dump(raw_ostream &OS) const {
+  OS << "Macro " << Name << ":\n";
+  OS << "  Parameters:\n";
+  for (const MCAsmMacroParameter &P : Parameters) {
+    OS << "    ";
+    P.dump();
+  }
+  OS << "  (BEGIN BODY)" << Body << "(END BODY)\n";
+}