Index: include/llvm/TableGen/StringMatcher.h
===================================================================
--- include/llvm/TableGen/StringMatcher.h
+++ include/llvm/TableGen/StringMatcher.h
@@ -43,11 +43,12 @@
                 const std::vector<StringPair> &matches, raw_ostream &os)
     : StrVariableName(strVariableName), Matches(matches), OS(os) {}
 
-  void Emit(unsigned Indent = 0) const;
+  void Emit(unsigned Indent = 0, bool IgnoreDuplicates = false) const;
 
 private:
-  bool EmitStringMatcherForChar(const std::vector<const StringPair*> &Matches,
-                                unsigned CharNo, unsigned IndentCount) const;
+  bool EmitStringMatcherForChar(const std::vector<const StringPair *> &Matches,
+                                unsigned CharNo, unsigned IndentCount,
+                                bool IgnoreDuplicates) const;
 };
 
 } // end namespace llvm
Index: include/llvm/Target/Target.td
===================================================================
--- include/llvm/Target/Target.td
+++ include/llvm/Target/Target.td
@@ -1160,6 +1160,12 @@
   // several registers share the same alias (i.e. not a 1:1 mapping).
   bit ShouldEmitMatchRegisterAltName = 0;
 
+  // Set to true if MatchRegisterName and MatchRegisterAltName functions
+  // should be generated even if there are duplicate register names. The
+  // target is responsible for coercing aliased registers as necessary
+  // (e.g. in validateTargetOperandClass).
+  bit AllowDuplicateRegisterNames = 0;
+
   // HasMnemonicFirst - Set to false if target instructions don't always
   // start with a mnemonic as the first token.
   bit HasMnemonicFirst = 1;
Index: lib/TableGen/StringMatcher.cpp
===================================================================
--- lib/TableGen/StringMatcher.cpp
+++ lib/TableGen/StringMatcher.cpp
@@ -46,17 +46,18 @@
 /// code to verify that CharNo and later are the same.
 ///
 /// \return - True if control can leave the emitted code fragment.
-bool StringMatcher::
-EmitStringMatcherForChar(const std::vector<const StringPair*> &Matches,
-                         unsigned CharNo, unsigned IndentCount) const {
+bool StringMatcher::EmitStringMatcherForChar(
+    const std::vector<const StringPair *> &Matches, unsigned CharNo,
+    unsigned IndentCount, bool IgnoreDuplicates) const {
   assert(!Matches.empty() && "Must have at least one string to match!");
   std::string Indent(IndentCount*2+4, ' ');
   
   // If we have verified that the entire string matches, we're done: output the
   // matching code.
   if (CharNo == Matches[0]->first.size()) {
-    assert(Matches.size() == 1 && "Had duplicate keys to match on");
-    
+    if (Matches.size() > 1 && !IgnoreDuplicates)
+      report_fatal_error("Had duplicate keys to match on");
+
     // If the to-execute code has \n's in it, indent each subsequent line.
     StringRef Code = Matches[0]->second;
     
@@ -100,8 +101,9 @@
          << NumChars << ") != 0)\n";
       OS << Indent << "  break;\n";
     }
-    
-    return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount);
+
+    return EmitStringMatcherForChar(Matches, FirstNonCommonLetter, IndentCount,
+                                    IgnoreDuplicates);
   }
   
   // Otherwise, we have multiple possible things, emit a switch on the
@@ -116,7 +118,8 @@
        << LI->second.size() << " string";
     if (LI->second.size() != 1) OS << 's';
     OS << " to match.\n";
-    if (EmitStringMatcherForChar(LI->second, CharNo+1, IndentCount+1))
+    if (EmitStringMatcherForChar(LI->second, CharNo + 1, IndentCount + 1,
+                                 IgnoreDuplicates))
       OS << Indent << "  break;\n";
   }
   
@@ -126,7 +129,7 @@
 
 /// Emit - Top level entry point.
 ///
-void StringMatcher::Emit(unsigned Indent) const {
+void StringMatcher::Emit(unsigned Indent, bool IgnoreDuplicates) const {
   // If nothing to match, just fall through.
   if (Matches.empty()) return;
   
@@ -146,7 +149,7 @@
     OS.indent(Indent*2+2) << "case " << LI->first << ":\t // "
        << LI->second.size()
        << " string" << (LI->second.size() == 1 ? "" : "s") << " to match.\n";
-    if (EmitStringMatcherForChar(LI->second, 0, Indent))
+    if (EmitStringMatcherForChar(LI->second, 0, Indent, IgnoreDuplicates))
       OS.indent(Indent*2+4) << "break;\n";
   }
   
Index: utils/TableGen/AsmMatcherEmitter.cpp
===================================================================
--- utils/TableGen/AsmMatcherEmitter.cpp
+++ utils/TableGen/AsmMatcherEmitter.cpp
@@ -2438,7 +2438,9 @@
 
   OS << "static unsigned MatchRegisterName(StringRef Name) {\n";
 
-  StringMatcher("Name", Matches, OS).Emit();
+  bool IgnoreDuplicates =
+      AsmParser->getValueAsBit("AllowDuplicateRegisterNames");
+  StringMatcher("Name", Matches, OS).Emit(0, IgnoreDuplicates);
 
   OS << "  return 0;\n";
   OS << "}\n\n";
@@ -2469,7 +2471,9 @@
 
   OS << "static unsigned MatchRegisterAltName(StringRef Name) {\n";
 
-  StringMatcher("Name", Matches, OS).Emit();
+  bool IgnoreDuplicates =
+      AsmParser->getValueAsBit("AllowDuplicateRegisterNames");
+  StringMatcher("Name", Matches, OS).Emit(0, IgnoreDuplicates);
 
   OS << "  return 0;\n";
   OS << "}\n\n";