Index: lib/Driver/ToolChains/Arch/RISCV.cpp
===================================================================
--- lib/Driver/ToolChains/Arch/RISCV.cpp
+++ lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -24,15 +24,66 @@
                                    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())
+    if (!(MArch.startswith("rv32") || MArch.startswith("rv64")) ||
+        (MArch.size() < 5)) {
+      // ISA string must begin with rv32 or rv64.
+      // TODO: Improve diagnostic message.
+      D.Diag(diag::err_drv_invalid_arch_name) << MArch;
       return;
+    }
 
-    for (char c : MArchSplit.second) {
+    // The canonical order specified in ISA manual.
+    // Ref: Table 22.1 in RISC-V User-Level ISA V2.2
+    StringRef StdExts = "mafdc";
+
+    bool HasF = false, HasD = false;
+    char Baseline = MArch[4];
+
+    // TODO: Add 'e' once backend supported.
+    switch (Baseline) {
+    default:
+      // First letter should be 'e', 'i' or 'g'.
+      // TODO: Improve diagnostic message.
+      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;
+    }
+
+    auto StdExtsItr = StdExts.begin();
+    // Skip rvxxx
+    StringRef Exts = MArch.substr(5);
+
+    for (char c : Exts) {
+      // Check ISA extensions are specified in the canonical order.
+      while (StdExtsItr != StdExts.end() && *StdExtsItr != c)
+        ++StdExtsItr;
+
+      if (StdExtsItr == StdExts.end()) {
+        // TODO: Improve diagnostic message.
+        D.Diag(diag::err_drv_invalid_arch_name) << MArch;
+        return;
+      }
+
+      // Move to next char to prevent repeated letter.
+      ++StdExtsItr;
+
+      // The order is OK, then push it into features.
       switch (c) {
-      case 'i':
-        break;
+      default:
+        // TODO: Improve diagnostic message.
+        D.Diag(diag::err_drv_invalid_arch_name) << MArch;
+        return;
       case 'm':
         Features.push_back("+m");
         break;
@@ -41,15 +92,25 @@
         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
+    // It's illegal to specify the 'd' (double-precision floating point)
+    // extension without also specifying the 'f' (single precision
+    // floating-point) extension.
+    // TODO: Improve diagnostic message.
+    if (HasD && !HasF)
+      D.Diag(diag::err_drv_invalid_arch_name) << MArch;
   }
 }
 
Index: test/Driver/riscv-arch.c
===================================================================
--- test/Driver/riscv-arch.c
+++ test/Driver/riscv-arch.c
@@ -0,0 +1,89 @@
+// RUN: %clang -target riscv32-unknown-elf -march=rv32i -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32im -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32ima -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32imaf -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32imafd -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32ic -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32imc -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32imac -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32imafc -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32imafdc -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32ia -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32iaf -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32iafd -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32iac -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32iafc -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32iafdc -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv32-unknown-elf -march=rv32g -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv32-unknown-elf -march=rv32gc -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64i -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64im -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64ima -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64imaf -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64imafd -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64ic -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64imc -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64imac -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64imafc -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64imafdc -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64ia -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64iaf -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64iafd -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64iac -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64iafc -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64iafdc -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64g -### %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang -target riscv64-unknown-elf -march=rv64gc -### %s -fsyntax-only 2>&1 | FileCheck %s
+
+// CHECK-NOT: error: invalid arch name '
+
+// 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 riscv32-unknown-elf -march=rv32imm -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32IMM %s
+// RV32IMM: error: invalid arch name 'rv32imm'
+
+// RUN: %clang -target riscv32-unknown-elf -march=RV32I -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV32I-UPPER %s
+// RV32I-UPPER: error: invalid arch name 'RV32I'
+
+// 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'
+
+// RUN: %clang -target riscv64-unknown-elf -march=rv64imm -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64IMM %s
+// RV64IMM: error: invalid arch name 'rv64imm'
+
+// RUN: %clang -target riscv64-unknown-elf -march=RV64I -### %s -fsyntax-only 2>&1 | FileCheck -check-prefix=RV64I-UPPER %s
+// RV64I-UPPER: error: invalid arch name 'RV64I'