Index: tools/llvm-exegesis/lib/BenchmarkResult.cpp
===================================================================
--- tools/llvm-exegesis/lib/BenchmarkResult.cpp
+++ tools/llvm-exegesis/lib/BenchmarkResult.cpp
@@ -31,7 +31,8 @@
 struct YamlContext {
   YamlContext(const exegesis::LLVMState &State)
       : State(&State), ErrorStream(LastError),
-        OpcodeNameToOpcodeIdx(generateOpcodeNameToOpcodeIdxMapping()) {}
+        OpcodeNameToOpcodeIdx(generateOpcodeNameToOpcodeIdxMapping()),
+        RegNameToRegNo(generateRegNameToRegNoMapping()) {}
 
   llvm::StringMap<unsigned> generateOpcodeNameToOpcodeIdxMapping() {
     const llvm::MCInstrInfo &InstrInfo = State->getInstrInfo();
@@ -42,6 +43,15 @@
     return Map;
   };
 
+  llvm::StringMap<unsigned> generateRegNameToRegNoMapping() {
+    const llvm::MCRegisterInfo &RegInfo = State->getRegInfo();
+    llvm::StringMap<unsigned> Map(RegInfo.getNumRegs());
+    for (unsigned I = 0, E = RegInfo.getNumRegs(); I < E; ++I)
+      Map.insert(std::make_pair(RegInfo.getName(I), I));
+    assert(Map.size() == RegInfo.getNumRegs() && "Size prediction failed");
+    return Map;
+  };
+
   void serializeMCInst(const llvm::MCInst &MCInst, llvm::raw_ostream &OS) {
     OS << getInstrName(MCInst.getOpcode());
     for (const auto &Op : MCInst) {
@@ -79,10 +89,9 @@
   }
 
   unsigned getRegNo(llvm::StringRef RegName) {
-    const llvm::MCRegisterInfo &RegInfo = State->getRegInfo();
-    for (unsigned E = RegInfo.getNumRegs(), I = 0; I < E; ++I)
-      if (RegInfo.getName(I) == RegName)
-        return I;
+    auto Iter = RegNameToRegNo.find(RegName);
+    if (Iter != RegNameToRegNo.end())
+      return Iter->second;
     ErrorStream << "No register with name " << RegName;
     return 0;
   }
@@ -158,6 +167,7 @@
   std::string LastError;
   llvm::raw_string_ostream ErrorStream;
   const llvm::StringMap<unsigned> OpcodeNameToOpcodeIdx;
+  const llvm::StringMap<unsigned> RegNameToRegNo;
 };
 } // namespace