Index: lib/Target/AArch64/Utils/AArch64BaseInfo.h
===================================================================
--- lib/Target/AArch64/Utils/AArch64BaseInfo.h
+++ lib/Target/AArch64/Utils/AArch64BaseInfo.h
@@ -603,6 +603,7 @@
     ISR_EL1           = 0xc608, // 11  000  1100  0001  000
     CNTPCT_EL0        = 0xdf01, // 11  011  1110  0000  001
     CNTVCT_EL0        = 0xdf02,  // 11  011  1110  0000  010
+    ID_MMFR4_EL1      = 0xc016,  // 11  000  0000  0010  110
 
     // Trace registers
     TRCSTATR          = 0x8818, // 10  001  0000  0011  000
Index: lib/Target/AArch64/Utils/AArch64BaseInfo.cpp
===================================================================
--- lib/Target/AArch64/Utils/AArch64BaseInfo.cpp
+++ lib/Target/AArch64/Utils/AArch64BaseInfo.cpp
@@ -175,6 +175,7 @@
   {"id_mmfr1_el1", ID_MMFR1_EL1, {}},
   {"id_mmfr2_el1", ID_MMFR2_EL1, {}},
   {"id_mmfr3_el1", ID_MMFR3_EL1, {}},
+  {"id_mmfr4_el1", ID_MMFR4_EL1, {}},
   {"id_isar0_el1", ID_ISAR0_EL1, {}},
   {"id_isar1_el1", ID_ISAR1_EL1, {}},
   {"id_isar2_el1", ID_ISAR2_EL1, {}},
Index: test/MC/AArch64/basic-a64-diagnostics.s
===================================================================
--- test/MC/AArch64/basic-a64-diagnostics.s
+++ test/MC/AArch64/basic-a64-diagnostics.s
@@ -3494,6 +3494,7 @@
         msr ID_MMFR1_EL1, x12
         msr ID_MMFR2_EL1, x12
         msr ID_MMFR3_EL1, x12
+        msr ID_MMFR4_EL1, x12
         msr ID_ISAR0_EL1, x12
         msr ID_ISAR1_EL1, x12
         msr ID_ISAR2_EL1, x12
@@ -3587,6 +3588,9 @@
 // CHECK-ERROR-NEXT:         msr ID_MMFR3_EL1, x12
 // CHECK-ERROR-NEXT:             ^
 // CHECK-ERROR-NEXT: error: expected writable system register or pstate
+// CHECK-ERROR-NEXT:         msr ID_MMFR4_EL1, x12
+// CHECK-ERROR-NEXT:             ^
+// CHECK-ERROR-NEXT: error: expected writable system register or pstate
 // CHECK-ERROR-NEXT:         msr ID_ISAR0_EL1, x12
 // CHECK-ERROR-NEXT:             ^
 // CHECK-ERROR-NEXT: error: expected writable system register or pstate
Index: test/MC/AArch64/basic-a64-instructions.s
===================================================================
--- test/MC/AArch64/basic-a64-instructions.s
+++ test/MC/AArch64/basic-a64-instructions.s
@@ -4306,6 +4306,7 @@
 	mrs x9, ID_MMFR1_EL1
 	mrs x9, ID_MMFR2_EL1
 	mrs x9, ID_MMFR3_EL1
+	mrs x9, ID_MMFR4_EL1
 	mrs x9, ID_ISAR0_EL1
 	mrs x9, ID_ISAR1_EL1
 	mrs x9, ID_ISAR2_EL1
@@ -4606,6 +4607,7 @@
 // CHECK: mrs      x9, {{id_mmfr1_el1|ID_MMFR1_EL1}}           // encoding: [0xa9,0x01,0x38,0xd5]
 // CHECK: mrs      x9, {{id_mmfr2_el1|ID_MMFR2_EL1}}           // encoding: [0xc9,0x01,0x38,0xd5]
 // CHECK: mrs      x9, {{id_mmfr3_el1|ID_MMFR3_EL1}}           // encoding: [0xe9,0x01,0x38,0xd5]
+// CHECK: mrs      x9, {{id_mmfr4_el1|ID_MMFR4_EL1}}           // encoding: [0xc9,0x02,0x38,0xd5]
 // CHECK: mrs      x9, {{id_isar0_el1|ID_ISAR0_EL1}}           // encoding: [0x09,0x02,0x38,0xd5]
 // CHECK: mrs      x9, {{id_isar1_el1|ID_ISAR1_EL1}}           // encoding: [0x29,0x02,0x38,0xd5]
 // CHECK: mrs      x9, {{id_isar2_el1|ID_ISAR2_EL1}}           // encoding: [0x49,0x02,0x38,0xd5]
Index: test/MC/Disassembler/AArch64/basic-a64-instructions.txt
===================================================================
--- test/MC/Disassembler/AArch64/basic-a64-instructions.txt
+++ test/MC/Disassembler/AArch64/basic-a64-instructions.txt
@@ -3414,6 +3414,7 @@
 # CHECK: mrs      x9, {{id_mmfr1_el1|ID_MMFR1_EL1}}
 # CHECK: mrs      x9, {{id_mmfr2_el1|ID_MMFR2_EL1}}
 # CHECK: mrs      x9, {{id_mmfr3_el1|ID_MMFR3_EL1}}
+# CHECK: mrs      x9, {{id_mmfr4_el1|ID_MMFR4_EL1}}
 # CHECK: mrs      x9, {{id_isar0_el1|ID_ISAR0_EL1}}
 # CHECK: mrs      x9, {{id_isar1_el1|ID_ISAR1_EL1}}
 # CHECK: mrs      x9, {{id_isar2_el1|ID_ISAR2_EL1}}
@@ -3968,6 +3969,7 @@
 0xa9 0x1 0x38 0xd5
 0xc9 0x1 0x38 0xd5
 0xe9 0x1 0x38 0xd5
+0xc9 0x2 0x38 0xd5
 0x9 0x2 0x38 0xd5
 0x29 0x2 0x38 0xd5
 0x49 0x2 0x38 0xd5