Index: lib/Driver/ToolChains/Arch/RISCV.cpp
===================================================================
--- lib/Driver/ToolChains/Arch/RISCV.cpp
+++ lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -23,16 +23,59 @@
 void riscv::getRISCVTargetFeatures(const Driver &D, const ArgList &Args,
                                    std::vector<StringRef> &Features) {
   if (const Arg *A = Args.getLastArg(options::OPT_march_EQ)) {
-    StringRef MArch = A->getValue();
-    // TODO: handle rv64
-    std::pair<StringRef, StringRef> MArchSplit = StringRef(MArch).split("rv32");
-    if (!MArchSplit.second.size())
+    StringRef March = A->getValue();
+    if (!(March.startswith("rv32") || March.startswith("rv64")) ||
+        (March.size() < 5)) {
+      // ISA string must begin with rv32 or rv64.
+      D.Diag(diag::err_drv_invalid_arch_name) << March;
       return;
+    }
+
+    // The canonical order specified in ISA manual.
+    StringRef StdExts = "mafdc";
+
+    bool hasF = false, hasD = false;
+    char baseline = March[4];
+
+    // TODO: Handle 'e' once backend supported.
+    switch (baseline) {
+    default:
+      // First letter should be 'e', 'i' or 'g'.
+      D.Diag(diag::err_drv_invalid_arch_name) << March;
+      return;
+    case 'i':
+      break;
+    case 'g':
+      // g = imafd
+      StdExts = StdExts.drop_front(4);
+      Features.push_back("+m");
+      Features.push_back("+a");
+      Features.push_back("+f");
+      Features.push_back("+d");
+      hasF = true;
+      hasD = true;
+      break;
+    }
 
-    for (char c : MArchSplit.second) {
+    auto StdExtsItr = StdExts.begin();
+    // Skip rvxxx
+    StringRef Exts = March.substr(5);
+
+    for (char c : Exts) {
+      // Check march is satisfied the canonical order.
+      while (StdExtsItr != StdExts.end() && *StdExtsItr != c)
+         ++StdExtsItr;
+
+      if (StdExtsItr == StdExts.end()) {
+        D.Diag(diag::err_drv_invalid_arch_name) << March;
+        return;
+      }
+
+      // The order is OK, then push it into features.
       switch (c) {
-      case 'i':
-        break;
+      default:
+        D.Diag(diag::err_drv_invalid_arch_name) << March;
+        return;
       case 'm':
         Features.push_back("+m");
         break;
@@ -41,15 +84,21 @@
         break;
       case 'f':
         Features.push_back("+f");
+        hasF = true;
         break;
       case 'd':
         Features.push_back("+d");
+        hasD = true;
         break;
       case 'c':
         Features.push_back("+c");
         break;
       }
     }
+
+    // Dependency check
+    if (hasD && !hasF)
+      D.Diag(diag::err_drv_invalid_arch_name) << March;
   }
 }
 
Index: test/Driver/riscv-arch.c
===================================================================
--- /dev/null
+++ test/Driver/riscv-arch.c
@@ -0,0 +1,29 @@
+// RUN: %clang -target riscv32-unknown-elf -march=rv32 -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32 %s
+// RV32: error: invalid arch name 'rv32'
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32m -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32M %s
+// RV32M: error: invalid arch name 'rv32m'
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32id -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32ID %s
+// RV32ID: error: invalid arch name 'rv32id'
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32l -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32L %s
+// RV32L: error: invalid arch name 'rv32l'
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32imadf -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32IMADF %s
+// RV32IMADF: error: invalid arch name 'rv32imadf'
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64 -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64 %s
+// RV64: error: invalid arch name 'rv64'
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64m -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64M %s
+// RV64M: error: invalid arch name 'rv64m'
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64id -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64ID %s
+// RV64ID: error: invalid arch name 'rv64id'
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64l -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64L %s
+// RV64L: error: invalid arch name 'rv64l'
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64imadf -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64IMADF %s
+// RV64IMADF: error: invalid arch name 'rv64imadf'