[Apple Silicon] [Platform] Default arm64 macOS and arm64 simulators to "vortex" CPU.

Author: shahmishal

lib/ClangImporter/ClangImporter.cpp

@@ -722,11 +722,20 @@ addCommonInvocationArguments(std::vector<std::string> &invocationArgStrs,
     invocationArgStrs.push_back("-mcpu=" + importerOpts.TargetCPU);
 
   } else if (triple.isOSDarwin()) {
-    // Special case: arm64 defaults to the "cyclone" CPU for Darwin,
-    // and arm64e defaults to the "vortex" CPU for Darwin,
-    // but Clang only detects this if we use -arch.
+    // Special case CPU based on known deployments:
+    //   - arm64 deploys to cyclone
+    //   - arm64 on macOS
+    //   - arm64 for iOS/tvOS/watchOS simulators
+    //   - arm64e deploys to vortex
+    // and arm64e (everywhere) and arm64e macOS defaults to the "vortex" CPU
+    // for Darwin, but Clang only detects this if we use -arch.
     if (triple.getArchName() == "arm64e")
       invocationArgStrs.push_back("-mcpu=vortex");
+    else if (triple.isAArch64() && triple.isMacOSX())
+      invocationArgStrs.push_back("-mcpu=vortex");
+    else if (triple.isAArch64() && triple.isSimulatorEnvironment() &&
+             (triple.isiOS() || triple.isWatchOS()))
+      invocationArgStrs.push_back("-mcpu=vortex");
     else if (triple.getArch() == llvm::Triple::aarch64 ||
              triple.getArch() == llvm::Triple::aarch64_be) {
       invocationArgStrs.push_back("-mcpu=cyclone");