diff --git a/llvm/lib/Target/AArch64/AArch64.td b/llvm/lib/Target/AArch64/AArch64.td
--- a/llvm/lib/Target/AArch64/AArch64.td
+++ b/llvm/lib/Target/AArch64/AArch64.td
@@ -285,6 +285,10 @@
     "sel2", "HasSEL2", "true",
     "Enable v8.4-A Secure Exception Level 2 extension">;
 
+def FeaturePMU : SubtargetFeature<
+    "pmu", "HasPMU", "true",
+    "Enable v8.4-A PMU extension">;
+
 def FeatureTLB_RMI : SubtargetFeature<
     "tlb-rmi", "HasTLB_RMI", "true",
     "Enable v8.4-A TLB Range and Maintenance Instructions">;
@@ -380,7 +384,7 @@
 def HasV8_4aOps : SubtargetFeature<"v8.4a", "HasV8_4aOps", "true",
   "Support ARM v8.4a instructions", [HasV8_3aOps, FeatureDotProd,
   FeatureNV, FeatureRASv8_4, FeatureMPAM, FeatureDIT,
-  FeatureTRACEV8_4, FeatureAM, FeatureSEL2, FeatureTLB_RMI,
+  FeatureTRACEV8_4, FeatureAM, FeatureSEL2, FeaturePMU, FeatureTLB_RMI,
   FeatureFMI, FeatureRCPC_IMMO]>;
 
 def HasV8_5aOps : SubtargetFeature<
diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.td b/llvm/lib/Target/AArch64/AArch64InstrInfo.td
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.td
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.td
@@ -62,6 +62,9 @@
 def HasSEL2          : Predicate<"Subtarget->hasSEL2()">,
                        AssemblerPredicate<"FeatureSEL2", "sel2">;
 
+def HasPMU           : Predicate<"Subtarget->hasPMU()">,
+                       AssemblerPredicate<"FeaturePMU", "pmu">;
+
 def HasTLB_RMI          : Predicate<"Subtarget->hasTLB_RMI()">,
                        AssemblerPredicate<"FeatureTLB_RMI", "tlb-rmi">;
 
diff --git a/llvm/lib/Target/AArch64/AArch64Subtarget.h b/llvm/lib/Target/AArch64/AArch64Subtarget.h
--- a/llvm/lib/Target/AArch64/AArch64Subtarget.h
+++ b/llvm/lib/Target/AArch64/AArch64Subtarget.h
@@ -116,6 +116,7 @@
   bool HasTRACEV8_4 = false;
   bool HasAM = false;
   bool HasSEL2 = false;
+  bool HasPMU = false;
   bool HasTLB_RMI = false;
   bool HasFMI = false;
   bool HasRCPC_IMMO = false;
@@ -435,6 +436,7 @@
   bool hasTRACEV8_4() const { return HasTRACEV8_4; }
   bool hasAM() const { return HasAM; }
   bool hasSEL2() const { return HasSEL2; }
+  bool hasPMU() const { return HasPMU; }
   bool hasTLB_RMI() const { return HasTLB_RMI; }
   bool hasFMI() const { return HasFMI; }
   bool hasRCPC_IMMO() const { return HasRCPC_IMMO; }
diff --git a/llvm/lib/Target/AArch64/AArch64SystemOperands.td b/llvm/lib/Target/AArch64/AArch64SystemOperands.td
--- a/llvm/lib/Target/AArch64/AArch64SystemOperands.td
+++ b/llvm/lib/Target/AArch64/AArch64SystemOperands.td
@@ -1322,6 +1322,12 @@
 def : RWSysReg<"SDER32_EL2", 0b11, 0b100, 0b0001, 0b0011, 0b001>;
 } // FeatureSEL2
 
+// v8.4a PMU registers
+//                          Op0   Op1    CRn     CRm     Op2
+let Requires = [{ {AArch64::FeaturePMU} }] in {
+def : RWSysReg<"PMMIR_EL1", 0b11, 0b000, 0b1001, 0b1110, 0b110>;
+} // FeaturePMU
+
 // v8.4a RAS registers
 //                              Op0   Op1    CRn     CRm     Op2
 let Requires = [{ {AArch64::FeatureRASv8_4} }] in {
diff --git a/llvm/test/MC/AArch64/armv8.4a-pmu.s b/llvm/test/MC/AArch64/armv8.4a-pmu.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/AArch64/armv8.4a-pmu.s
@@ -0,0 +1,19 @@
+// RUN: llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+v8.4a < %s \
+// RUN: | FileCheck %s --check-prefix=CHECK
+
+// RUN: not llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=-v8.4a < %s 2>&1 \
+// RUN: | FileCheck %s --check-prefix=CHECK-ERROR
+
+//------------------------------------------------------------------------------
+// ARMV8.4-A PMU
+//------------------------------------------------------------------------------
+
+// Read/Write registers:
+
+msr PMMIR_EL1, x0
+mrs x0, PMMIR_EL1
+
+//CHECK: msr     PMMIR_EL1, x0           // encoding: [0xc0,0x9e,0x18,0xd5]
+//CHECK: mrs     x0, PMMIR_EL1           // encoding: [0xc0,0x9e,0x38,0xd5]
+//CHECK-ERROR: error: expected writable system register or pstate
+//CHECK-ERROR: error: expected readable system register
diff --git a/llvm/test/MC/Disassembler/AArch64/armv8.4a-pmu.txt b/llvm/test/MC/Disassembler/AArch64/armv8.4a-pmu.txt
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/Disassembler/AArch64/armv8.4a-pmu.txt
@@ -0,0 +1,10 @@
+#RUN: llvm-mc -triple aarch64-none-linux-gnu -mattr=+v8.4a --disassemble < %s | FileCheck %s
+#RUN: llvm-mc -triple aarch64-none-linux-gnu -mattr=-v8.4a --disassemble < %s | FileCheck %s --check-prefix=CHECK-NOV84
+
+[0xc0,0x9e,0x18,0xd5]
+[0xc0,0x9e,0x38,0xd5]
+
+#CHECK:  msr PMMIR_EL1, x0
+#CHECK:  mrs x0, PMMIR_EL1
+#CHECK-NOV84:  msr S3_0_C9_C14_6, x0
+#CHECK-NOV84:  mrs x0, S3_0_C9_C14_6