Index: llvm/trunk/lib/Target/AArch64/AArch64.td
===================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64.td
+++ llvm/trunk/lib/Target/AArch64/AArch64.td
@@ -204,6 +204,9 @@
                    "true",
                    "Enable Aggressive FMA for floating-point.">;
 
+def FeatureAltFPCmp : SubtargetFeature<"altnzcv", "HasAlternativeNZCV", "true",
+  "Enable alternative NZCV format for floating point comparisons">;
+
 //===----------------------------------------------------------------------===//
 // Architectures.
 //
@@ -221,7 +224,7 @@
   "Support ARM v8.4a instructions", [HasV8_3aOps, FeatureDotProd]>;
 
 def HasV8_5aOps : SubtargetFeature<"v8.5a", "HasV8_5aOps", "true",
-  "Support ARM v8.5a instructions", [HasV8_4aOps]>;
+  "Support ARM v8.5a instructions", [HasV8_4aOps, FeatureAltFPCmp]>;
 
 //===----------------------------------------------------------------------===//
 // Register File Description
Index: llvm/trunk/lib/Target/AArch64/AArch64InstrInfo.td
===================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64InstrInfo.td
+++ llvm/trunk/lib/Target/AArch64/AArch64InstrInfo.td
@@ -62,7 +62,8 @@
                                  AssemblerPredicate<"FeatureSVE", "sve">;
 def HasRCPC          : Predicate<"Subtarget->hasRCPC()">,
                                  AssemblerPredicate<"FeatureRCPC", "rcpc">;
-
+def HasAltNZCV       : Predicate<"Subtarget->hasAlternativeNZCV()">,
+                       AssemblerPredicate<"FeatureAltFPCmp", "altnzcv">;
 def IsLE             : Predicate<"Subtarget->isLittleEndian()">;
 def IsBE             : Predicate<"!Subtarget->isLittleEndian()">;
 def UseAlternateSExtLoadCVTF32
@@ -608,6 +609,25 @@
                         "{\t$Rn, $imm, $mask}">;
 } // HasV8_4a
 
+// v8.5 flag manipulation instructions
+let Predicates = [HasAltNZCV], Uses = [NZCV], Defs = [NZCV] in {
+
+def XAFLAG : PstateWriteSimple<(ins), "xaflag", "">, Sched<[WriteSys]> {
+  let Inst{18-16} = 0b000;
+  let Inst{11-8} = 0b0000;
+  let Unpredictable{11-8} = 0b1111;
+  let Inst{7-5} = 0b001;
+}
+
+def AXFLAG : PstateWriteSimple<(ins), "axflag", "">, Sched<[WriteSys]> {
+  let Inst{18-16} = 0b000;
+  let Inst{11-8} = 0b0000;
+  let Unpredictable{11-8} = 0b1111;
+  let Inst{7-5} = 0b010;
+}
+
+} // HasAltNZCV
+
 def : InstAlias<"clrex", (CLREX 0xf)>;
 def : InstAlias<"isb", (ISB 0xf)>;
 
Index: llvm/trunk/lib/Target/AArch64/AArch64Subtarget.h
===================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64Subtarget.h
+++ llvm/trunk/lib/Target/AArch64/AArch64Subtarget.h
@@ -94,6 +94,9 @@
   bool HasRCPC = false;
   bool HasAggressiveFMA = false;
 
+  // Armv8.5-A Extensions
+  bool HasAlternativeNZCV = false;
+
   // HasZeroCycleRegMove - Has zero-cycle register mov instructions.
   bool HasZeroCycleRegMove = false;
 
@@ -306,6 +309,7 @@
   bool hasSVE() const { return HasSVE; }
   bool hasRCPC() const { return HasRCPC; }
   bool hasAggressiveFMA() const { return HasAggressiveFMA; }
+  bool hasAlternativeNZCV() const { return HasAlternativeNZCV; }
 
   bool isLittleEndian() const { return IsLittle; }
 
Index: llvm/trunk/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
===================================================================
--- llvm/trunk/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
+++ llvm/trunk/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
@@ -1712,9 +1712,14 @@
   uint64_t op1 = fieldFromInstruction(insn, 16, 3);
   uint64_t op2 = fieldFromInstruction(insn, 5, 3);
   uint64_t crm = fieldFromInstruction(insn, 8, 4);
-
   uint64_t pstate_field = (op1 << 3) | op2;
 
+  switch (pstate_field) {
+  case 0x01: // XAFlag
+  case 0x02: // AXFlag
+    return Fail;
+  }
+
   if ((pstate_field == AArch64PState::PAN  ||
        pstate_field == AArch64PState::UAO) && crm > 1)
     return Fail;
Index: llvm/trunk/test/MC/AArch64/armv8.5a-altnzcv.s
===================================================================
--- llvm/trunk/test/MC/AArch64/armv8.5a-altnzcv.s
+++ llvm/trunk/test/MC/AArch64/armv8.5a-altnzcv.s
@@ -0,0 +1,16 @@
+// RUN: llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+v8.5a < %s | FileCheck %s
+// RUN: llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+v8.4a,+altnzcv < %s | FileCheck %s
+// RUN: not llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+v8.4a,-v8.5a < %s 2>&1 | FileCheck %s --check-prefix=NOALTFP
+// RUN: not llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=-v8.5a < %s 2>&1 | FileCheck %s --check-prefix=NOALTFP
+
+// Flag manipulation
+xaflag
+axflag
+
+// CHECK: xaflag                          // encoding: [0x3f,0x40,0x00,0xd5]
+// CHECK: axflag                          // encoding: [0x5f,0x40,0x00,0xd5]
+
+// NOALTFP: instruction requires: altnzcv
+// NOALTFP-NEXT: xaflag
+// NOALTFP: instruction requires: altnzcv
+// NOALTFP-NEXT: axflag
Index: llvm/trunk/test/MC/AArch64/armv8.5a-xaflag-error.s
===================================================================
--- llvm/trunk/test/MC/AArch64/armv8.5a-xaflag-error.s
+++ llvm/trunk/test/MC/AArch64/armv8.5a-xaflag-error.s
@@ -0,0 +1,10 @@
+// RUN: not llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+v8.5a < %s 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR
+
+// Check that XAFlag/AXFlag don't accept operands like MSR does
+xaflag S0_0_C4_C0_1, xzr
+axflag S0_0_C4_C0_1, xzr
+
+// CHECK-ERROR: invalid operand for instruction
+// CHECK-ERROR-NEXT: xaflag S0_0_C4_C0_1, xzr
+// CHECK-ERROR: invalid operand for instruction
+// CHECK-ERROR-NEXT: axflag S0_0_C4_C0_1, xzr
Index: llvm/trunk/test/MC/Disassembler/AArch64/armv8.5a-dataproc.txt
===================================================================
--- llvm/trunk/test/MC/Disassembler/AArch64/armv8.5a-dataproc.txt
+++ llvm/trunk/test/MC/Disassembler/AArch64/armv8.5a-dataproc.txt
@@ -0,0 +1,12 @@
+# RUN: llvm-mc -triple aarch64-none-linux-gnu -mattr=+v8.5a --disassemble < %s | FileCheck %s
+# RUN: llvm-mc -triple aarch64-none-linux-gnu -mattr=-v8.5a --disassemble < %s 2>&1 | FileCheck %s --check-prefix=CHECK-NOV85
+
+# Flag manipulation
+[0x3f,0x40,0x00,0xd5]
+[0x5f,0x40,0x00,0xd5]
+
+#CHECK: xaflag
+#CHECK: axflag
+
+#CHECK-NOV85: msr S0_0_C4_C0_1, xzr
+#CHECK-NOV85: msr S0_0_C4_C0_2, xzr