Index: RegisterInfoEmitter.cpp
===================================================================
--- RegisterInfoEmitter.cpp	(revision 292532)
+++ RegisterInfoEmitter.cpp	(working copy)
@@ -1060,6 +1060,67 @@
   }
   OS << "};\n";       // End of HW encoding table
 
+  // Emit Reg decoding tables
+  OS << "\n#ifdef GET_REGINFO_REGISTER_DECODER\n";
+  OS << "#undef GET_REGINFO_REGISTER_DECODER\n\n";
+  for (const auto &RC : RegisterClasses) {
+    ArrayRef<Record*> Order = RC.getOrder();
+    unsigned HWEncodingWidth;
+    int e = Order.size();
+    for (HWEncodingWidth = 1;
+	 (1L<<HWEncodingWidth) < e;
+	 ++HWEncodingWidth) ;
+    uint64_t mask = (1 << HWEncodingWidth) - 1;
+    const std::string &Name = RC.getName();
+    OS << "extern const uint16_t " << TargetName;
+    OS << "RegDecodingTable_" << Name << "[] = {\n";
+    uint64_t max = 0;
+    for (int i = 0, e = Order.size(); i != e; ++i) {
+      auto Reg = Order[i];
+      BitsInit *BI = Reg->getValueAsBitsInit("HWEncoding");
+      uint64_t Value = 0;
+      for (unsigned b = 0, be = BI->getNumBits(); b != be; ++b) {
+	if (BitInit *B = dyn_cast<BitInit>(BI->getBit(b)))
+	  Value |= (uint64_t)B->getValue() << b;
+      }
+      Value &= mask;
+      if (Value >= max)
+	max = Value;
+    }
+    for (uint64_t HWE = 0; HWE <= max; ++HWE)
+      {
+	bool found = false;
+	for (unsigned i = 0, e = Order.size(); i != e; ++i) {
+	  auto Reg = Order[i];
+	  BitsInit *BI = Reg->getValueAsBitsInit("HWEncoding");
+	  uint64_t Value = 0;
+	  for (unsigned b = 0, be = BI->getNumBits(); b != be; ++b) {
+	    if (BitInit *B = dyn_cast<BitInit>(BI->getBit(b)))
+	      Value |= (uint64_t)B->getValue() << b;
+	  }
+	  Value &= mask;
+	  if (HWE == Value) {
+	    // First of any aliases wins.
+	    OS << "  /* [" << Value << "] = */ " << getQualifiedName(Reg) <<",\n";
+	    found = true;
+	    break;
+	  }
+	}
+	if (not found)
+	  OS << "  0,\n";
+      }
+    OS << "};\n";       // End of HW decoding tables
+  }
+  // Emit the main register decoding table
+  OS << "const uint16_t *" << TargetName;
+  OS << "RegDecodingTable[] = {\n";
+  for (const auto &RC : RegisterClasses) {
+    const std::string &Name = RC.getName();
+    OS << "  " << TargetName << "RegDecodingTable_" << Name << ",\n";
+  }
+  OS << "};\n";       // End of the main register decoding table
+  OS << "\n#endif // GET_REGINFO_REGISTER_DECODER\n\n";
+
   // MCRegisterInfo initialization routine.
   OS << "static inline void Init" << TargetName
      << "MCRegisterInfo(MCRegisterInfo *RI, unsigned RA, "