Target Ivy bridge on macOS Mojave and later

[davezarzycki]

Summary

Ivy Bridge is required by macOS 10.14 (Mojave) and later.

[davezarzycki]

Hi @bob.wilson – Am I missing something here?

[davezarzycki]

@bob.wilson – Ping. While Ivy Bridge (or really, Sandy Bridge) has AVX1, which enables faster memcpy, memset, and even memcmp (for common scenarios). If there is something I'm missing? If you can't explain why, that's okay. :-)

[arphaman]

@bob.wilson no longer works on llvm-project. I added Gerolf and Duncan.

[dexonsmith]

Hi Dave, thanks for checking in on this, but unfortunately we're not ready for this yet.

[davezarzycki]

Okay. I'm going to abandon this patch on the assumption that Apple has an internal bug tracking this.

clang/lib/Driver/ToolChains/Arch/X86.cpp

if (Triple.getArch() != llvm::Triple::x86_64 &&
     return nullptr; // This routine is only handling x86 targets.
 
   bool Is64Bit = Triple.getArch() == llvm::Triple::x86_64;
 
   // FIXME: Need target hooks.
   if (Triple.isOSDarwin()) {
     if (Triple.getArchName() == "x86_64h")
       return "core-avx2";
-    // macosx10.12 drops support for all pre-Penryn Macs.
-    // Simulators can still run on 10.11 though, like Xcode.
-    if (Triple.isMacOSX() && !Triple.isOSVersionLT(10, 12))
-      return "penryn";
     // The oldest x86_64 Macs have core2/Merom; the oldest x86 Macs have Yonah.
+    // The simulators (i.e. Darwin but not macOS) can still run on older Macs.
+    // macosx10.12 requires Penryn.
+    if (!Triple.isMacOSX() || Triple.isOSVersionLT(10, 12))
       return Is64Bit ? "core2" : "yonah";
+    // macosx10.14 requires Ivy Bridge.
+    if (Triple.isOSVersionLT(10, 14))
+      return "penryn";
+    return "ivybridge";
   }
 
   // Set up default CPU name for PS4 compilers.
   if (Triple.isPS4CPU())
     return "btver2";
 
   // On Android use targets compatible with gcc
   if (Triple.isAndroid())