diff --git a/llvm/lib/Target/RISCV/RISCV.td b/llvm/lib/Target/RISCV/RISCV.td
--- a/llvm/lib/Target/RISCV/RISCV.td
+++ b/llvm/lib/Target/RISCV/RISCV.td
@@ -576,8 +576,8 @@
 class RISCVProcessorModel<string n,
                           SchedMachineModel m,
                           list<SubtargetFeature> f,
-                          string default_march = "",
-                          list<SubtargetFeature> tunef = []>
+                          list<SubtargetFeature> tunef = [],
+                          string default_march = "">
       :  ProcessorModel<n, m, f, tunef> {
   string DefaultMarch = default_march;
 }
@@ -615,16 +615,14 @@
                                      RocketModel,
                                      [Feature32Bit,
                                       FeatureStdExtM,
-                                      FeatureStdExtC],
-                                     "rv32imc">;
+                                      FeatureStdExtC]>;
 
 def SIFIVE_E21 : RISCVProcessorModel<"sifive-e21",
                                      RocketModel,
                                      [Feature32Bit,
                                       FeatureStdExtM,
                                       FeatureStdExtA,
-                                      FeatureStdExtC],
-                                     "rv32imac">;
+                                      FeatureStdExtC]>;
 
 def SIFIVE_E24 : RISCVProcessorModel<"sifive-e24",
                                      RocketModel,
@@ -632,16 +630,14 @@
                                       FeatureStdExtM,
                                       FeatureStdExtA,
                                       FeatureStdExtF,
-                                      FeatureStdExtC],
-                                     "rv32imafc">;
+                                      FeatureStdExtC]>;
 
 def SIFIVE_E31 : RISCVProcessorModel<"sifive-e31",
                                      RocketModel,
                                      [Feature32Bit,
                                       FeatureStdExtM,
                                       FeatureStdExtA,
-                                      FeatureStdExtC],
-                                     "rv32imac">;
+                                      FeatureStdExtC]>;
 
 def SIFIVE_E34 : RISCVProcessorModel<"sifive-e34",
                                      RocketModel,
@@ -649,8 +645,7 @@
                                       FeatureStdExtM,
                                       FeatureStdExtA,
                                       FeatureStdExtF,
-                                      FeatureStdExtC],
-                                     "rv32imafc">;
+                                      FeatureStdExtC]>;
 
 def SIFIVE_E76 : RISCVProcessorModel<"sifive-e76",
                                      SiFive7Model,
@@ -659,7 +654,6 @@
                                       FeatureStdExtA,
                                       FeatureStdExtF,
                                       FeatureStdExtC],
-                                     "rv32imafc",
                                      [TuneSiFive7]>;
 
 def SIFIVE_S21 : RISCVProcessorModel<"sifive-s21",
@@ -667,16 +661,14 @@
                                      [Feature64Bit,
                                       FeatureStdExtM,
                                       FeatureStdExtA,
-                                      FeatureStdExtC],
-                                     "rv64imac">;
+                                      FeatureStdExtC]>;
 
 def SIFIVE_S51 : RISCVProcessorModel<"sifive-s51",
                                      RocketModel,
                                      [Feature64Bit,
                                       FeatureStdExtM,
                                       FeatureStdExtA,
-                                      FeatureStdExtC],
-                                     "rv64imac">;
+                                      FeatureStdExtC]>;
 
 def SIFIVE_S54 : RISCVProcessorModel<"sifive-s54",
                                       RocketModel,
@@ -685,8 +677,7 @@
                                        FeatureStdExtA,
                                        FeatureStdExtF,
                                        FeatureStdExtD,
-                                       FeatureStdExtC],
-                                      "rv64gc">;
+                                       FeatureStdExtC]>;
 
 def SIFIVE_S76 : RISCVProcessorModel<"sifive-s76",
                                      SiFive7Model,
@@ -696,7 +687,6 @@
                                       FeatureStdExtF,
                                       FeatureStdExtD,
                                       FeatureStdExtC],
-                                     "rv64gc",
                                      [TuneSiFive7]>;
 
 def SIFIVE_U54 : RISCVProcessorModel<"sifive-u54",
@@ -706,8 +696,7 @@
                                       FeatureStdExtA,
                                       FeatureStdExtF,
                                       FeatureStdExtD,
-                                      FeatureStdExtC],
-                                     "rv64gc">;
+                                      FeatureStdExtC]>;
 
 def SIFIVE_U74 : RISCVProcessorModel<"sifive-u74",
                                      SiFive7Model,
@@ -717,14 +706,12 @@
                                       FeatureStdExtF,
                                       FeatureStdExtD,
                                       FeatureStdExtC],
-                                     "rv64gc",
                                      [TuneSiFive7] >;
 
 def SYNTACORE_SCR1_BASE : RISCVProcessorModel<"syntacore-scr1-base",
                                               SyntacoreSCR1Model,
                                               [Feature32Bit,
                                                FeatureStdExtC],
-                                              "rv32ic",
                                               [TuneNoDefaultUnroll]>;
 
 def SYNTACORE_SCR1_MAX : RISCVProcessorModel<"syntacore-scr1-max",
@@ -732,7 +719,6 @@
                                              [Feature32Bit,
                                               FeatureStdExtM,
                                               FeatureStdExtC],
-                                             "rv32imc",
                                              [TuneNoDefaultUnroll]>;
 
 //===----------------------------------------------------------------------===//
diff --git a/llvm/utils/TableGen/RISCVTargetDefEmitter.cpp b/llvm/utils/TableGen/RISCVTargetDefEmitter.cpp
--- a/llvm/utils/TableGen/RISCVTargetDefEmitter.cpp
+++ b/llvm/utils/TableGen/RISCVTargetDefEmitter.cpp
@@ -12,18 +12,45 @@
 //===----------------------------------------------------------------------===//
 
 #include "TableGenBackends.h"
+#include "llvm/Support/RISCVISAInfo.h"
 #include "llvm/TableGen/Record.h"
 
 using namespace llvm;
 
-static std::string getEnumFeatures(const Record &Rec) {
+static int getXLen(const Record &Rec) {
   std::vector<Record *> Features = Rec.getValueAsListOfDefs("Features");
   if (find_if(Features, [](const Record *R) {
         return R->getName() == "Feature64Bit";
       }) != Features.end())
-    return "FK_64BIT";
+    return 64;
 
-  return "FK_NONE";
+  return 32;
+}
+
+static std::string getMArch(int XLen, const Record &Rec) {
+  std::vector<std::string> FeatureVector;
+
+  // Convert features to FeatureVector. This is almost the same as
+  // RISCVFeatures::parseFeatureBits, except that we get feature name from
+  // feature records instead of feature bits.
+  for (auto *Feature : Rec.getValueAsListOfDefs("Features")) {
+    StringRef FeatureName = Feature->getValueAsString("Name");
+    if (llvm::RISCVISAInfo::isSupportedExtensionFeature(FeatureName))
+      FeatureVector.push_back(std::string("+") + FeatureName.str());
+  }
+
+  llvm::Expected<std::unique_ptr<RISCVISAInfo>> ISAInfo =
+      llvm::RISCVISAInfo::parseFeatures(XLen, FeatureVector);
+  if (!ISAInfo)
+    report_fatal_error("Invalid features");
+
+  // RISCVISAInfo::toString will generate a march string with all the extensions
+  // we have added to it.
+  return (*ISAInfo)->toString();
+}
+
+static std::string getEnumFeatures(int XLen) {
+  return XLen == 64 ? "FK_64BIT" : "FK_NONE";
 }
 
 void llvm::EmitRISCVTargetDef(const RecordKeeper &RK, raw_ostream &OS) {
@@ -39,11 +66,18 @@
   // Iterate on all definition records.
   for (const MapTy &Def : Map) {
     const Record &Rec = *(Def.second);
-    if (Rec.isSubClassOf("RISCVProcessorModel"))
+    if (Rec.isSubClassOf("RISCVProcessorModel")) {
+      int XLen = getXLen(Rec);
+      StringRef MArch = Rec.getValueAsString("DefaultMarch");
+
+      // Compute MArch from features if we don't specify it.
+      if (MArch.empty())
+        MArch = StringRef(getMArch(XLen, Rec));
       OS << "PROC(" << Rec.getName() << ", "
          << "{\"" << Rec.getValueAsString("Name") << "\"},"
-         << getEnumFeatures(Rec) << ", "
-         << "{\"" << Rec.getValueAsString("DefaultMarch") << "\"})\n";
+         << getEnumFeatures(XLen) << ", "
+         << "{\"" << MArch << "\"})\n";
+    }
   }
   OS << "\n#undef PROC\n";
   OS << "\n";