Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -151,6 +151,8 @@
                             Group<m_Group>, DocName<"WebAssembly">;
 def m_x86_Features_Group : OptionGroup<"<x86 features group>">,
                            Group<m_Group>, Flags<[CoreOption]>, DocName<"X86">;
+def m_riscv_Features_Group : OptionGroup<"<riscv features group>">,
+                             Group<m_Group>, DocName<"RISCV">;
 
 def m_libc_Group : OptionGroup<"<m libc group>">, Group<m_mips_Features_Group>,
                    Flags<[HelpHidden]>;
@@ -1950,6 +1952,11 @@
 def mno_soft_float : Flag<["-"], "mno-soft-float">, Group<m_Group>;
 def mno_stackrealign : Flag<["-"], "mno-stackrealign">, Group<m_Group>;
 
+def mrelax : Flag<["-"], "mrelax">, Group<m_riscv_Features_Group>,
+  HelpText<"Enable linker relaxation">;
+def mno_relax : Flag<["-"], "mno-relax">, Group<m_riscv_Features_Group>,
+  HelpText<"Disable linker relaxation">;
+
 def munaligned_access : Flag<["-"], "munaligned-access">, Group<m_arm_Features_Group>,
   HelpText<"Allow memory accesses to be unaligned (AArch32/AArch64 only)">;
 def mno_unaligned_access : Flag<["-"], "mno-unaligned-access">, Group<m_arm_Features_Group>,
Index: lib/Driver/ToolChains/Arch/RISCV.cpp
===================================================================
--- lib/Driver/ToolChains/Arch/RISCV.cpp
+++ lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/TargetParser.h"
 #include "llvm/Support/raw_ostream.h"
+#include "ToolChains/CommonArgs.h"
 
 using namespace clang::driver;
 using namespace clang::driver::tools;
@@ -363,6 +364,21 @@
     // Handle all other types of extensions.
     getExtensionFeatures(D, Args, Features, MArch, OtherExts);
   }
+
+  // -mrelax is default, unless -mno-relax is specified.
+  bool Relax = true;
+  if (auto *A = Args.getLastArg(options::OPT_mrelax, options::OPT_mno_relax))
+    if (A->getOption().matches(options::OPT_mno_relax)) {
+      Relax = false;
+      Features.push_back("-relax");
+    }
+
+  if (Relax)
+    Features.push_back("+relax");
+
+  // Now add any that the user explicitly requested on the command line,
+  // which may override the defaults.
+  handleTargetFeaturesGroup(Args, Features, options::OPT_m_riscv_Features_Group);
 }
 
 StringRef riscv::getRISCVABI(const ArgList &Args, const llvm::Triple &Triple) {
Index: test/Driver/riscv-features.c
===================================================================
--- test/Driver/riscv-features.c
+++ test/Driver/riscv-features.c
@@ -2,3 +2,9 @@
 // RUN: %clang -target riscv64-unknown-elf -### %s -fsyntax-only 2>&1 | FileCheck %s
 
 // CHECK: fno-signed-char
+
+// RUN: %clang -target riscv32-unknown-elf -### %s -mrelax 2>&1 | FileCheck %s -check-prefix=RELAX
+// RUN: %clang -target riscv32-unknown-elf -### %s -mno-relax 2>&1 | FileCheck %s -check-prefix=NO-RELAX
+
+// RELAX: "-target-feature" "+relax"
+// NO-RELAX: "-target-feature" "-relax"