diff --git a/lib/Target/AArch64/AArch64InstrInfo.td b/lib/Target/AArch64/AArch64InstrInfo.td
index 78c4ad16d76..319ec97cfcd 100644
--- a/lib/Target/AArch64/AArch64InstrInfo.td
+++ b/lib/Target/AArch64/AArch64InstrInfo.td
@@ -1945,43 +1945,41 @@ def fpz32 : Operand<f32>,
             ComplexPattern<f32, 1, "SelectFPZeroOperand", [fpimm]> {
   let ParserMatchClass = fpzero_asmoperand;
   let PrintMethod = "printFPZeroOperand";
+  let DecoderMethod = "DecodeFPZeroOperand";
 }
 
 def fpz64 : Operand<f64>,
             ComplexPattern<f64, 1, "SelectFPZeroOperand", [fpimm]> {
   let ParserMatchClass = fpzero_asmoperand;
   let PrintMethod = "printFPZeroOperand";
+  let DecoderMethod = "DecodeFPZeroOperand";
 }
 
-multiclass A64I_fpcmpSignal<bits<2> type, bit imm, dag ins, string asmop2,
-                            dag pattern> {
+multiclass A64I_fpcmpSignal<bits<2> type, bit imm, dag ins, dag pattern> {
   def _quiet : A64I_fpcmp<0b0, 0b0, type, 0b00, {0b0, imm, 0b0, 0b0, 0b0},
-                          (outs), ins, !strconcat("fcmp\t$Rn, ", asmop2),
-                          [pattern], NoItinerary> {
+                          (outs), ins, "fcmp\t$Rn, $Rm", [pattern],
+                          NoItinerary> {
     let Defs = [NZCV];
   }
 
   def _sig : A64I_fpcmp<0b0, 0b0, type, 0b00, {0b1, imm, 0b0, 0b0, 0b0},
-                        (outs), ins, !strconcat("fcmpe\t$Rn, ", asmop2),
-                        [], NoItinerary> {
+                        (outs), ins, "fcmpe\t$Rn, $Rm", [], NoItinerary> {
     let Defs = [NZCV];
   }
 }
 
-defm FCMPss : A64I_fpcmpSignal<0b00, 0b0, (ins FPR32:$Rn, FPR32:$Rm), "$Rm",
+defm FCMPss : A64I_fpcmpSignal<0b00, 0b0, (ins FPR32:$Rn, FPR32:$Rm),
                                (set NZCV, (A64cmp (f32 FPR32:$Rn), FPR32:$Rm))>;
-defm FCMPdd : A64I_fpcmpSignal<0b01, 0b0, (ins FPR64:$Rn, FPR64:$Rm), "$Rm",
+defm FCMPdd : A64I_fpcmpSignal<0b01, 0b0, (ins FPR64:$Rn, FPR64:$Rm),
                                (set NZCV, (A64cmp (f64 FPR64:$Rn), FPR64:$Rm))>;
 
-// What would be Rm should be written as 0, but anything is valid for
-// disassembly so we can't set the bits
-let PostEncoderMethod = "fixFCMPImm" in {
-  defm FCMPsi : A64I_fpcmpSignal<0b00, 0b1, (ins FPR32:$Rn, fpz32:$Imm), "$Imm",
-                              (set NZCV, (A64cmp (f32 FPR32:$Rn), fpz32:$Imm))>;
+// What would be Rm should be written as 0; note that even though it's called
+// "$Rm" here to fit in with the InstrFormats, it's actually an immediate.
+defm FCMPsi : A64I_fpcmpSignal<0b00, 0b1, (ins FPR32:$Rn, fpz32:$Rm),
+                               (set NZCV, (A64cmp (f32 FPR32:$Rn), fpz32:$Rm))>;
 
-  defm FCMPdi : A64I_fpcmpSignal<0b01, 0b1, (ins FPR64:$Rn, fpz64:$Imm), "$Imm",
-                              (set NZCV, (A64cmp (f64 FPR64:$Rn), fpz64:$Imm))>;
-}
+defm FCMPdi : A64I_fpcmpSignal<0b01, 0b1, (ins FPR64:$Rn, fpz64:$Rm),
+                               (set NZCV, (A64cmp (f64 FPR64:$Rn), fpz64:$Rm))>;
 
 
 //===----------------------------------------------------------------------===//
diff --git a/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp b/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
index eba76667e2b..12c1b8f4c81 100644
--- a/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
+++ b/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
@@ -106,6 +106,11 @@ static DecodeStatus DecodeCVT32FixedPosOperand(llvm::MCInst &Inst,
                                                uint64_t Address,
                                                const void *Decoder);
 
+static DecodeStatus DecodeFPZeroOperand(llvm::MCInst &Inst,
+                                        unsigned RmBits,
+                                        uint64_t Address,
+                                        const void *Decoder);
+
 template<int RegWidth>
 static DecodeStatus DecodeMoveWideImmOperand(llvm::MCInst &Inst,
                                              unsigned FullImm,
@@ -381,6 +386,17 @@ static DecodeStatus DecodeCVT32FixedPosOperand(llvm::MCInst &Inst,
   return MCDisassembler::Success;
 }
 
+static DecodeStatus DecodeFPZeroOperand(llvm::MCInst &Inst,
+                                        unsigned RmBits,
+                                        uint64_t Address,
+                                        const void *Decoder) {
+  // Any bits are valid in the instruction (they're architecturally ignored),
+  // but a code generator should insert 0.
+  Inst.addOperand(MCOperand::CreateImm(0));
+  return MCDisassembler::Success;
+}
+
+
 
 template<int RegWidth>
 static DecodeStatus DecodeMoveWideImmOperand(llvm::MCInst &Inst,
diff --git a/lib/Target/AArch64/MCTargetDesc/AArch64MCCodeEmitter.cpp b/lib/Target/AArch64/MCTargetDesc/AArch64MCCodeEmitter.cpp
index 756e037e93b..a5c591eee80 100644
--- a/lib/Target/AArch64/MCTargetDesc/AArch64MCCodeEmitter.cpp
+++ b/lib/Target/AArch64/MCTargetDesc/AArch64MCCodeEmitter.cpp
@@ -106,8 +106,6 @@ public:
   void EncodeInstruction(const MCInst &MI, raw_ostream &OS,
                          SmallVectorImpl<MCFixup> &Fixups) const;
 
-  unsigned fixFCMPImm(const MCInst &MI, unsigned EncodedValue) const;
-
   template<int hasRs, int hasRt2> unsigned
   fixLoadStoreExclusive(const MCInst &MI, unsigned EncodedValue) const;
 
@@ -423,15 +421,6 @@ AArch64MCCodeEmitter::getMoveWideImmOpValue(const MCInst &MI, unsigned OpIdx,
   return Result | getAddressWithFixup(UImm16MO, requestedFixup, Fixups);
 }
 
-unsigned AArch64MCCodeEmitter::fixFCMPImm(const MCInst &MI,
-                                          unsigned EncodedValue) const {
-    // For FCMP[E] Rn, #0.0, the Rm field has a canonical representation
-    // with 0s, but is architecturally ignored
-    EncodedValue &= ~0x1f0000u;
-
-    return EncodedValue;
-}
-
 template<int hasRs, int hasRt2> unsigned
 AArch64MCCodeEmitter::fixLoadStoreExclusive(const MCInst &MI,
                                             unsigned EncodedValue) const {
diff --git a/test/MC/Disassembler/AArch64/a64-ignored-fields.txt b/test/MC/Disassembler/AArch64/a64-ignored-fields.txt
new file mode 100644
index 00000000000..966530d36a3
--- /dev/null
+++ b/test/MC/Disassembler/AArch64/a64-ignored-fields.txt
@@ -0,0 +1,8 @@
+# RUN: llvm-mc -triple=aarch64 -disassemble -show-encoding < %s | FileCheck %s
+
+# The "Rm" bits are ignored, but the canonical representation has them filled
+# with 0s. This is what we should produce even if the input bit-pattern had
+# something else there.
+
+# CHECK: fcmp    s31, #0.0               // encoding: [0xe8,0x23,0x20,0x1e]
+0xe8 0x23 0x33 0x1e