Index: llvm/trunk/lib/Target/RISCV/RISCVInstrInfoF.td
===================================================================
--- llvm/trunk/lib/Target/RISCV/RISCVInstrInfoF.td
+++ llvm/trunk/lib/Target/RISCV/RISCVInstrInfoF.td
@@ -227,6 +227,12 @@
 def : InstAlias<"fscsr $rd, $rs", (CSRRW GPR:$rd, FCSR.Encoding, GPR:$rs)>;
 def : InstAlias<"fscsr $rs",      (CSRRW      X0, FCSR.Encoding, GPR:$rs), 2>;
 
+// frsr, fssr are obsolete aliases replaced by frcsr, fscsr, so give them
+// zero weight.
+def : InstAlias<"frsr $rd",       (CSRRS GPR:$rd, FCSR.Encoding, X0), 0>;
+def : InstAlias<"fssr $rd, $rs",  (CSRRW GPR:$rd, FCSR.Encoding, GPR:$rs), 0>;
+def : InstAlias<"fssr $rs",       (CSRRW      X0, FCSR.Encoding, GPR:$rs), 0>;
+
 def : InstAlias<"frrm $rd",        (CSRRS  GPR:$rd, FRM.Encoding, X0), 2>;
 def : InstAlias<"fsrm $rd, $rs",   (CSRRW  GPR:$rd, FRM.Encoding, GPR:$rs)>;
 def : InstAlias<"fsrm $rs",        (CSRRW       X0, FRM.Encoding, GPR:$rs), 2>;
Index: llvm/trunk/test/MC/RISCV/rvf-aliases-valid.s
===================================================================
--- llvm/trunk/test/MC/RISCV/rvf-aliases-valid.s
+++ llvm/trunk/test/MC/RISCV/rvf-aliases-valid.s
@@ -55,6 +55,18 @@
 # CHECK-ALIAS: fscsr t3
 fscsr x28
 
+# These are obsolete aliases of frcsr/fscsr. They are accepted by the assembler
+# but the disassembler should always print them as the equivalent, new aliases.
+# CHECK-INST: csrrs t4, fcsr, zero
+# CHECK-ALIAS: frcsr t4
+frsr x29
+# CHECK-INST: csrrw t5, fcsr, t6
+# CHECK-ALIAS: fscsr t5, t6
+fssr x30, x31
+# CHECK-INST: csrrw zero, fcsr, s0
+# CHECK-ALIAS: fscsr s0
+fssr x8
+
 # CHECK-INST: csrrs t4, frm, zero
 # CHECK-ALIAS: frrm t4
 frrm x29