Index: lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
===================================================================
--- lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
+++ lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
@@ -1055,9 +1055,33 @@
     return false;
   }
 
+  if (Option == "relax") {
+    getTargetStreamer().emitDirectiveOptionRelax();
+
+    Parser.Lex();
+    if (Parser.getTok().isNot(AsmToken::EndOfStatement))
+      return Error(Parser.getTok().getLoc(),
+                   "unexpected token, expected end of statement");
+
+    setFeatureBits(RISCV::FeatureRelax, "relax");
+    return false;
+  }
+
+  if (Option == "norelax") {
+    getTargetStreamer().emitDirectiveOptionNoRelax();
+
+    Parser.Lex();
+    if (Parser.getTok().isNot(AsmToken::EndOfStatement))
+      return Error(Parser.getTok().getLoc(),
+                   "unexpected token, expected end of statement");
+
+    clearFeatureBits(RISCV::FeatureRelax, "relax");
+    return false;
+  }
+
   // Unknown option.
   Warning(Parser.getTok().getLoc(),
-          "unknown option, expected 'rvc' or 'norvc'");
+          "unknown option, expected 'rvc', 'norvc', 'relax' or 'norelax'");
   Parser.eatToEndOfStatement();
   return false;
 }
Index: lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.h
===================================================================
--- lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.h
+++ lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.h
@@ -22,6 +22,8 @@
 
   virtual void emitDirectiveOptionRVC();
   virtual void emitDirectiveOptionNoRVC();
+  virtual void emitDirectiveOptionRelax();
+  virtual void emitDirectiveOptionNoRelax();
 };
 }
 #endif
Index: lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
===================================================================
--- lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
+++ lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
@@ -40,3 +40,5 @@
 
 void RISCVTargetELFStreamer::emitDirectiveOptionRVC() {}
 void RISCVTargetELFStreamer::emitDirectiveOptionNoRVC() {}
+void RISCVTargetELFStreamer::emitDirectiveOptionRelax() {}
+void RISCVTargetELFStreamer::emitDirectiveOptionNoRelax() {}
Index: lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.h
===================================================================
--- lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.h
+++ lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.h
@@ -20,6 +20,8 @@
 
   virtual void emitDirectiveOptionRVC() = 0;
   virtual void emitDirectiveOptionNoRVC() = 0;
+  virtual void emitDirectiveOptionRelax() = 0;
+  virtual void emitDirectiveOptionNoRelax() = 0;
 };
 
 // This part is for ascii assembly output
@@ -31,6 +33,8 @@
 
   void emitDirectiveOptionRVC() override;
   void emitDirectiveOptionNoRVC() override;
+  void emitDirectiveOptionRelax() override;
+  void emitDirectiveOptionNoRelax() override;
 };
 
 }
Index: lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
===================================================================
--- lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
+++ lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
@@ -30,3 +30,11 @@
 void RISCVTargetAsmStreamer::emitDirectiveOptionNoRVC() {
   OS << "\t.option\tnorvc\n";
 }
+
+void RISCVTargetAsmStreamer::emitDirectiveOptionRelax() {
+  OS << "\t.option\trelax\n";
+}
+
+void RISCVTargetAsmStreamer::emitDirectiveOptionNoRelax() {
+  OS << "\t.option\tnorelax\n";
+}
Index: test/MC/RISCV/option-invalid.s
===================================================================
--- test/MC/RISCV/option-invalid.s
+++ test/MC/RISCV/option-invalid.s
@@ -13,5 +13,5 @@
 # CHECK: error: unexpected token, expected end of statement
 .option rvc foo
 
-# CHECK: warning: unknown option, expected 'rvc' or 'norvc'
+# CHECK: warning: unknown option, expected 'rvc', 'norvc', 'relax' or 'norelax'
 .option bar
Index: test/MC/RISCV/option-relax.s
===================================================================
--- /dev/null
+++ test/MC/RISCV/option-relax.s
@@ -0,0 +1,27 @@
+# RUN: llvm-mc -triple riscv32 < %s \
+# RUN:     | FileCheck -check-prefix=CHECK-INST %s
+# RUN: llvm-mc -filetype=obj -triple riscv32 < %s \
+# RUN:     | llvm-readobj -r | FileCheck -check-prefix=CHECK-RELOC %s
+
+# RUN: llvm-mc -triple riscv64 < %s \
+# RUN:     | FileCheck -check-prefix=CHECK-INST %s
+# RUN: llvm-mc -filetype=obj -triple riscv64 < %s \
+# RUN:     | llvm-readobj -r | FileCheck -check-prefix=CHECK-RELOC %s
+
+# CHECK-INST: call foo
+# CHECK-RELOC: R_RISCV_CALL foo 0x0
+call foo
+
+.option relax
+# CHECK-INST: .option relax
+# CHECK-INST: call bar
+# CHECK-RELOC-NEXT: R_RISCV_CALL bar 0x0
+# CHECK-RELOC-NEXT: R_RISCV_RELAX bar 0x0
+call bar
+
+.option norelax
+# CHECK-INST: .option norelax
+# CHECK-INST: call baz
+# CHECK-RELOC: R_RISCV_CALL baz 0x0
+# CHECK-RELOC-NOT: R_RISCV_RELAX baz 0x0
+call baz