Index: clang/lib/Driver/ToolChains/Arch/AArch64.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Arch/AArch64.cpp
+++ clang/lib/Driver/ToolChains/Arch/AArch64.cpp
@@ -43,6 +43,12 @@
   else if (CPU.size())
     return CPU;
 
+  if (Triple.isTargetMachineMac() &&
+      Triple.getArch() == llvm::Triple::aarch64) {
+    // Apple Silicon macs default to A12 CPUs.
+    return "apple-a12";
+  }
+
   // Make sure we pick the appropriate Apple CPU if -arch is used or when
   // targetting a Darwin OS.
   if (Args.getLastArg(options::OPT_arch) || Triple.isOSDarwin())
Index: clang/test/Driver/aarch64-mac-cpus.c
===================================================================
--- /dev/null
+++ clang/test/Driver/aarch64-mac-cpus.c
@@ -0,0 +1,20 @@
+// arm64 Mac-based targets default to Apple A12.
+
+// RUN: %clang -target arm64-apple-macos             -### -c %s 2>&1 | FileCheck %s
+// RUN: %clang -target arm64-apple-ios-macabi        -### -c %s 2>&1 | FileCheck %s
+// RUN: %clang -target arm64-apple-ios-simulator     -### -c %s 2>&1 | FileCheck %s
+// RUN: %clang -target arm64-apple-watchos-simulator -### -c %s 2>&1 | FileCheck %s
+// RUN: %clang -target arm64-apple-tvos-simulator    -### -c %s 2>&1 | FileCheck %s
+
+// RUN: %clang -target arm64-apple-macos -arch arm64 -### -c %s 2>&1 | FileCheck %s
+
+// RUN: %clang -target arm64-apple-macos -mcpu=apple-a11 -### -c %s 2>&1 | FileCheck --check-prefix=EXPLICIT-A11 %s
+// RUN: %clang -target arm64-apple-macos -mcpu=apple-a7  -### -c %s 2>&1 | FileCheck --check-prefix=EXPLICIT-A7 %s
+// RUN: %clang -target arm64-apple-macos -mcpu=apple-a13 -### -c %s 2>&1 | FileCheck --check-prefix=EXPLICIT-A13 %s
+
+// CHECK: "-cc1"{{.*}} "-triple" "arm64{{.*}}" "-target-cpu" "apple-a12"
+// CHECK-SAME: "-target-feature" "+v8.3a"
+
+// EXPLICIT-A11: "-cc1"{{.*}} "-triple" "arm64{{.*}}" "-target-cpu" "apple-a11"
+// EXPLICIT-A7: "-cc1"{{.*}} "-triple" "arm64{{.*}}" "-target-cpu" "apple-a7"
+// EXPLICIT-A13: "-cc1"{{.*}} "-triple" "arm64{{.*}}" "-target-cpu" "apple-a13"
Index: llvm/include/llvm/ADT/Triple.h
===================================================================
--- llvm/include/llvm/ADT/Triple.h
+++ llvm/include/llvm/ADT/Triple.h
@@ -486,6 +486,12 @@
     return getEnvironment() == Triple::MacABI;
   }
 
+  /// Returns true for targets that run on a macOS machine.
+  bool isTargetMachineMac() const {
+    return isMacOSX() || (isOSDarwin() && (isSimulatorEnvironment() ||
+                                           isMacCatalystEnvironment()));
+  }
+
   bool isOSNetBSD() const {
     return getOS() == Triple::NetBSD;
   }