diff --git a/utils/TableGen/AsmMatcherEmitter.cpp b/utils/TableGen/AsmMatcherEmitter.cpp
index b7f98a0..338a0b2 100644
--- a/utils/TableGen/AsmMatcherEmitter.cpp
+++ b/utils/TableGen/AsmMatcherEmitter.cpp
@@ -2681,11 +2681,21 @@
   emitComputeAvailableFeatures(Info, OS);
 
 
+  StringToOffsetTable StringTable;
+
   size_t MaxNumOperands = 0;
+  unsigned MaxMnemonicIndex = 0;
   for (std::vector<MatchableInfo*>::const_iterator it =
          Info.Matchables.begin(), ie = Info.Matchables.end();
-       it != ie; ++it)
-    MaxNumOperands = std::max(MaxNumOperands, (*it)->AsmOperands.size());
+       it != ie; ++it) {
+    MatchableInfo &II = **it;
+    MaxNumOperands = std::max(MaxNumOperands, II.AsmOperands.size());
+
+    // Store a pascal-style length byte in the mnemonic.
+    std::string LenMnemonic = char(II.Mnemonic.size()) + II.Mnemonic.str();
+    MaxMnemonicIndex = std::max(MaxMnemonicIndex,
+                        StringTable.GetOrAddStringOffset(LenMnemonic, false));
+  }
 
   // Emit the static match table; unused classes get initalized to 0 which is
   // guaranteed to be InvalidMatchClass.
@@ -2700,7 +2710,8 @@
   OS << "namespace {\n";
   OS << "  struct MatchEntry {\n";
   OS << "    static const char *const MnemonicTable;\n";
-  OS << "    uint32_t Mnemonic;\n";
+  OS << "    " << getMinimalTypeForRange(MaxMnemonicIndex)
+               << " Mnemonic;\n";
   OS << "    uint16_t Opcode;\n";
   OS << "    " << getMinimalTypeForRange(Info.Matchables.size())
                << " ConvertFn;\n";
@@ -2730,8 +2741,6 @@
 
   OS << "} // end anonymous namespace.\n\n";
 
-  StringToOffsetTable StringTable;
-
   OS << "static const MatchEntry MatchTable["
      << Info.Matchables.size() << "] = {\n";