Index: llvm/trunk/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.h
===================================================================
--- llvm/trunk/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.h
+++ llvm/trunk/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.h
@@ -30,16 +30,21 @@
                  const MCSubtargetInfo &STI) override;
   void printRegName(raw_ostream &O, unsigned RegNo) const override;
 
-  void printOperand(const MCInst *MI, unsigned OpNo, raw_ostream &O,
-                    const char *Modifier = nullptr);
-  void printFenceArg(const MCInst *MI, unsigned OpNo, raw_ostream &O);
-  void printFRMArg(const MCInst *MI, unsigned OpNo, raw_ostream &O);
+  void printOperand(const MCInst *MI, unsigned OpNo, const MCSubtargetInfo &STI,
+                    raw_ostream &O, const char *Modifier = nullptr);
+  void printFenceArg(const MCInst *MI, unsigned OpNo,
+                     const MCSubtargetInfo &STI, raw_ostream &O);
+  void printFRMArg(const MCInst *MI, unsigned OpNo, const MCSubtargetInfo &STI,
+                   raw_ostream &O);
 
   // Autogenerated by tblgen.
-  void printInstruction(const MCInst *MI, raw_ostream &O);
-  bool printAliasInstr(const MCInst *MI, raw_ostream &O);
+  void printInstruction(const MCInst *MI, const MCSubtargetInfo &STI,
+                        raw_ostream &O);
+  bool printAliasInstr(const MCInst *MI, const MCSubtargetInfo &STI,
+                       raw_ostream &O);
   void printCustomAliasOperand(const MCInst *MI, unsigned OpIdx,
-                               unsigned PrintMethodIdx, raw_ostream &O);
+                               unsigned PrintMethodIdx,
+                               const MCSubtargetInfo &STI, raw_ostream &O);
   static const char *getRegisterName(unsigned RegNo,
                                      unsigned AltIdx = RISCV::ABIRegAltName);
 };
Index: llvm/trunk/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.cpp
===================================================================
--- llvm/trunk/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.cpp
+++ llvm/trunk/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.cpp
@@ -17,6 +17,7 @@
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -37,8 +38,8 @@
 
 void RISCVInstPrinter::printInst(const MCInst *MI, raw_ostream &O,
                                  StringRef Annot, const MCSubtargetInfo &STI) {
-  if (NoAliases || !printAliasInstr(MI, O))
-    printInstruction(MI, O);
+  if (NoAliases || !printAliasInstr(MI, STI, O))
+    printInstruction(MI, STI, O);
   printAnnotation(O, Annot);
 }
 
@@ -47,6 +48,7 @@
 }
 
 void RISCVInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
+                                    const MCSubtargetInfo &STI,
                                     raw_ostream &O, const char *Modifier) {
   assert((Modifier == 0 || Modifier[0] == 0) && "No modifiers supported");
   const MCOperand &MO = MI->getOperand(OpNo);
@@ -66,6 +68,7 @@
 }
 
 void RISCVInstPrinter::printFenceArg(const MCInst *MI, unsigned OpNo,
+                                     const MCSubtargetInfo &STI,
                                      raw_ostream &O) {
   unsigned FenceArg = MI->getOperand(OpNo).getImm();
   if ((FenceArg & RISCVFenceField::I) != 0)
@@ -79,6 +82,7 @@
 }
 
 void RISCVInstPrinter::printFRMArg(const MCInst *MI, unsigned OpNo,
+                                   const MCSubtargetInfo &STI,
                                    raw_ostream &O) {
   auto FRMArg =
       static_cast<RISCVFPRndMode::RoundingMode>(MI->getOperand(OpNo).getImm());
Index: llvm/trunk/lib/Target/RISCV/RISCV.td
===================================================================
--- llvm/trunk/lib/Target/RISCV/RISCV.td
+++ llvm/trunk/lib/Target/RISCV/RISCV.td
@@ -84,7 +84,12 @@
   let AllowDuplicateRegisterNames = 1;
 }
 
+def RISCVAsmWriter : AsmWriter {
+  int PassSubtarget = 1;
+}
+
 def RISCV : Target {
   let InstructionSet = RISCVInstrInfo;
   let AssemblyParsers = [RISCVAsmParser];
+  let AssemblyWriters = [RISCVAsmWriter];
 }
Index: llvm/trunk/test/MC/RISCV/csr-aliases.s
===================================================================
--- llvm/trunk/test/MC/RISCV/csr-aliases.s
+++ llvm/trunk/test/MC/RISCV/csr-aliases.s
@@ -0,0 +1,117 @@
+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+f < %s \
+# RUN:     | llvm-objdump -d -mattr=+f -riscv-no-aliases - \
+# RUN:     | FileCheck -check-prefix=CHECK-INST %s
+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+f < %s \
+# RUN:     | llvm-objdump -d -mattr=+f - \
+# RUN:     | FileCheck -check-prefix=CHECK-ALIAS %s
+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+f < %s \
+# RUN:     | llvm-objdump -d -mattr=+f - \
+# RUN:     | FileCheck -check-prefix=CHECK-EXT-F %s
+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=-f < %s \
+# RUN:     | llvm-objdump -d -mattr=+f - \
+# RUN:     | FileCheck -check-prefix=CHECK-EXT-F %s
+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=-f < %s \
+# RUN:     | llvm-objdump -d -mattr=-f - \
+# RUN:     | FileCheck -check-prefix=CHECK-EXT-F-OFF %s
+# RUN: llvm-mc -filetype=obj -triple riscv32 -mattr=+f < %s \
+# RUN:     | llvm-objdump -d -mattr=-f - \
+# RUN:     | FileCheck -check-prefix=CHECK-EXT-F-OFF %s
+
+# RUN: llvm-mc -filetype=obj -triple riscv64 -mattr=+f < %s \
+# RUN:     | llvm-objdump -d -mattr=+f -riscv-no-aliases - \
+# RUN:     | FileCheck -check-prefix=CHECK-INST %s
+# RUN: llvm-mc -filetype=obj -triple riscv64 -mattr=+f < %s \
+# RUN:     | llvm-objdump -d -mattr=+f - \
+# RUN:     | FileCheck -check-prefix=CHECK-ALIAS %s
+# RUN: llvm-mc -filetype=obj -triple riscv64 -mattr=+f < %s \
+# RUN:     | llvm-objdump -d -mattr=+f - \
+# RUN:     | FileCheck -check-prefix=CHECK-EXT-F %s
+# RUN: llvm-mc -filetype=obj -triple riscv64 -mattr=-f < %s \
+# RUN:     | llvm-objdump -d -mattr=+f - \
+# RUN:     | FileCheck -check-prefix=CHECK-EXT-F %s
+# RUN: llvm-mc -filetype=obj -triple riscv64 -mattr=-f < %s \
+# RUN:     | llvm-objdump -d -mattr=-f - \
+# RUN:     | FileCheck -check-prefix=CHECK-EXT-F-OFF %s
+# RUN: llvm-mc -filetype=obj -triple riscv64 -mattr=+f < %s \
+# RUN:     | llvm-objdump -d -mattr=-f - \
+# RUN:     | FileCheck -check-prefix=CHECK-EXT-F-OFF %s
+
+
+# CHECK-INST: csrrs t0, 3, zero
+# CHECK-ALIAS: frcsr t0
+# CHECK-EXT-F:  frcsr t0
+# CHECK-EXT-F-OFF: csrr t0, 3
+csrrs t0, 3, zero
+
+# CHECK-INST: csrrw t1, 3, t2
+# CHECK-ALIAS: fscsr t1, t2
+# CHECK-EXT-F-ON: fscsr t1, t2
+# CHECK-EXT-F-OFF: csrrw t1, 3, t2
+csrrw t1, 3, t2
+
+# CHECK-INST: csrrw zero, 3, t2
+# CHECK-ALIAS: fscsr t2
+# CHECK-EXT-F-ON: fscsr t2
+# CHECK-EXT-F-OFF: csrw 3, t2
+csrrw zero, 3, t2
+
+# CHECK-INST: csrrw zero, 3, t2
+# CHECK-ALIAS: fscsr t2
+# CHECK-EXT-F-ON: fscsr t2
+# CHECK-EXT-F-OFF: csrw 3, t2
+csrrw zero, 3, t2
+
+# CHECK-INST: csrrw t0, 2, zero
+# CHECK-ALIAS: fsrm  t0, zero
+# CHECK-EXT-F-ON: fsrm t0, zero
+# CHECK-EXT-F-OFF: csrrw t0, 2, zero
+csrrw t0, 2, zero
+
+# CHECK-INST: csrrw t0, 2, t1
+# CHECK-ALIAS: fsrm t0, t1
+# CHECK-EXT-F-ON: fsrm t0, t1
+# CHECK-EXT-F-OFF: csrrw t0, 2, t1
+csrrw t0, 2, t1
+
+# CHECK-INST: csrrwi t0, 2, 31
+# CHECK-ALIAS: fsrmi t0, 31
+# CHECK-EXT-F-ON: fsrmi t0, 31
+# CHECK-EXT-F-OFF: csrrwi t0, 2, 31
+csrrwi t0, 2, 31
+
+# CHECK-INST: csrrwi zero, 2, 31
+# CHECK-ALIAS: fsrmi 31
+# CHECK-EXT-F-ON: fsrmi 31
+# CHECK-EXT-F-OFF:  csrwi 2, 31
+csrrwi zero, 2, 31
+
+# CHECK-INST: csrrs t0, 1, zero
+# CHECK-ALIAS: frflags t0
+# CHECK-EXT-F-ON: frflags t0
+# CHECK-EXT-F-OFF: csrr t0, 1
+csrrs t0, 1, zero
+
+# CHECK-INST: csrrw t0, 1, t2
+# CHECK-ALIAS: fsflags t0, t2
+# CHECK-EXT-F-ON: fsflags t0, t2
+# CHECK-EXT-F-OFF: csrrw t0, 1, t2
+csrrw t0, 1, t2
+
+# CHECK-INST: csrrw zero, 1, t2
+# CHECK-ALIAS: fsflags t2
+# CHECK-EXT-F-ON: fsflags t2
+# CHECK-EXT-F-OFF: csrw 1, t2
+csrrw zero, 1, t2
+
+# CHECK-INST: csrrwi t0, 1, 31
+# CHECK-ALIAS: fsflagsi t0, 31
+# CHECK-EXT-F: fsflagsi t0, 31
+# CHECK-EXT-F-OFF: csrrwi t0, 1, 31
+csrrwi t0, 1, 31
+
+# CHECK-INST: csrrwi zero, 1, 31
+# CHECK-ALIAS: fsflagsi 31
+# CHECK-EXT-F: fsflagsi 31
+# CHECK-EXT-F-OFF: csrwi 1, 31
+csrrwi zero, 1, 31
+