Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -1837,6 +1837,27 @@
   }
 
   AddAAPCSVolatileBitfieldArgs(Args, CmdArgs);
+
+  if (const Arg *A = Args.getLastArg(clang::driver::options::OPT_mtune_EQ)) {
+    StringRef Name = A->getValue();
+
+    std::string TuneCPU;
+    if (Name == "native") {
+      Name = llvm::sys::getHostCPUName();
+      if (!Name.empty())
+        TuneCPU = std::string(Name);
+      else
+        TuneCPU = "generic";
+    } else
+      TuneCPU = std::string(Name);
+
+    CmdArgs.push_back("-tune-cpu");
+    CmdArgs.push_back(Args.MakeArgString(TuneCPU));
+  }
+  else if (!Args.getLastArg(clang::driver::options::OPT_mcpu_EQ)) {
+    CmdArgs.push_back("-tune-cpu");
+    CmdArgs.push_back("generic");
+  }
 }
 
 void Clang::AddMIPSTargetArgs(const ArgList &Args,
Index: clang/test/Driver/aarch64-mtune.c
===================================================================
--- /dev/null
+++ clang/test/Driver/aarch64-mtune.c
@@ -0,0 +1,42 @@
+// Ensure we support the -mtune flag.
+
+// Default mtune should be generic.
+// RUN: %clang -target aarch64-unknown-unknown -c -### %s 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=notune
+// notune: "-tune-cpu" "generic"
+
+// RUN: %clang -target aarch64-unknown-unknown -c -### %s -mtune=generic 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=generic
+// generic: "-tune-cpu" "generic"
+
+// RUN: %clang -target aarch64-unknown-unknown -c -### %s -mtune=neoverse-n1 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=neoverse-n1
+// neoverse-n1: "-tune-cpu" "neoverse-n1"
+
+// RUN: %clang -target aarch64-unknown-unknown -c -### %s -mtune=thunderx2t99 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=thunderx2t99
+// thunderx2t99: "-tune-cpu" "thunderx2t99"
+
+// Check interaction between march and mtune.
+
+// RUN: %clang -target aarch64-unknown-unknown -c -### %s -march=armv8-a 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=marcharmv8a
+// marcharmv8a: "-target-cpu" "generic"
+// marcharmv8a: "-tune-cpu" "generic"
+
+// RUN: %clang -target aarch64-unknown-unknown -c -### %s -march=armv8-a -mtune=cortex-a75 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=marcharmv8a-a75
+// marcharmv8a-a75: "-target-cpu" "generic"
+// marcharmv8a-a75: "-tune-cpu" "cortex-a75"
+
+// Check interaction between mcpu and mtune.
+
+// RUN: %clang -target aarch64-unknown-unknown -c -### %s -mcpu=thunderx 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=mcputhunderx
+// mcputhunderx: "-target-cpu" "thunderx"
+// mcputhunderx-NOT: "-tune-cpu"
+
+// RUN: %clang -target aarch64-unknown-unknown -c -### %s -mcpu=cortex-a75 -mtune=cortex-a57 2>&1 \
+// RUN:   | FileCheck %s -check-prefix=mcpua75-mtunea57
+// mcpua75-mtunea57: "-target-cpu" "cortex-a75"
+// mcpua75-mtunea57: "-tune-cpu" "cortex-a57"