[LLVM][Support] Add macOS 12 to Triple.cpp

[gAlfonso-bit]

Summary

Since macOS 12 Monterey is around the corner, it might be good to prepare.

Also, since we are here, remove llvm-unreachable that is already taken care of by the default statements as well as comment typos.

[jrtc27]

llvm/lib/Support/Triple.cpp

1143

You're not touching these functions, leave them alone

1767

Don't include unrelated changes

1775

This function isn't used by LLVM, it's only used by Swift, and I don't know if they need to support 10.17 meaning 12 or whether 10.16 meaning 11 was just a one-off due to having a bunch of code already written that was using 10.16 in @available etc annotations. IMO this should be left alone until someone from Apple decides they do in fact need this; their fork of LLVM doesn't currently have this function changed, for example, though that could just be because they haven't made Monterey changes public yet (but if it's needed they'll have already discovered that long ago).

[dexonsmith]

I believe this code change isn't needed, but @arphaman can confirm. Adding him as a blocking reviewer since he's been upstreaming other related code.

@gAlfonso-bit, FYI, if you're eager to help out, many of Apple's downstream changes have been officially contributed to the LLVM project at https://github.com/llvm/llvm-project-staging (see, e.g., the staging/apple branch), but are waiting to be separated, likely cleaned up a bit, and then reviewed (here, at http://reviews.llvm.org). Reach out to me over email if you're interested in tackling something. I can help choose what to break off and/or help find a reviewer.

llvm/lib/Support/Triple.cpp

1143

BTW, I'd be happy to review a standalone, NFC patch that fixes these comments (IOS vs iOS). (I agree with @jrtc27 that it's better not to include unrelated changes in this patch.)

1637

I think the comment is referring to the vendor part of the triple, which is apple, so lowercase is better. Maybe could be in quotes though, something like "If vendor is 'apple'", but I'm not sure this is worth changing.

1683

The + seems redundant, since "starting from" should cover it.

1767

Why remove this?

1775

FWIW, this function is also used by clang downstream (e.g., see https://github.com/apple/llvm-project/blob/next/clang/lib/Sema/SemaDeclAttr.cpp#L2473).

[jrtc27]

llvm/lib/Support/Triple.cpp

1767

I assume because a sufficiently-smart compiler can notice it's dead code since the above switch is exhaustive and always returns. But a sufficiently-dumb compiler wouldn't notice that and need something to avoid a warning about the opposite...

1775

Ah, didn't think to look at your Clang, but in hindsight should probably have realised that the (Obj)C(++) equivalent attributes would likely have the same issue...

llvm/lib/Support/Triple.cpp

if (Major == 0) {
       Minor = 4;
     } else if (Major < 10)
       return false;
     break;
   case IOS:
   case TvOS:
   case WatchOS:
     // Ignore the version from the triple.  This is only handled because the
-    // the clang driver combines OS X and IOS support into a common Darwin
+    // the clang driver combines OS X and iOS support into a common Darwin
     // toolchain that wants to know the OS X version number even when targeting
-    // IOS.
+    // iOS.
     Major = 10;
     Minor = 4;
     Micro = 0;
     break;
   }
   return true;
 }
 
 void Triple::getiOSVersion(unsigned &Major, unsigned &Minor,
                            unsigned &Micro) const {
   switch (getOS()) {
   default: llvm_unreachable("unexpected OS for Darwin triple");
   case Darwin:
   case MacOSX:
     // Ignore the version from the triple.  This is only handled because the
-    // the clang driver combines OS X and IOS support into a common Darwin
+    // the clang driver combines OS X and iOS support into a common Darwin
     // toolchain that wants to know the iOS version number even when targeting
     // OS X.
     Major = 5;
     Minor = 0;
     Micro = 0;
     break;
   case IOS:
   case TvOS:
if (getVendor() == Triple::Apple)
              getVendor() == Other.getVendor() && getOS() == Other.getOS();
     else
       return getSubArch() == Other.getSubArch() &&
              getVendor() == Other.getVendor() && getOS() == Other.getOS() &&
              getEnvironment() == Other.getEnvironment() &&
              getObjectFormat() == Other.getObjectFormat();
   }
 
-  // If vendor is apple, ignore the version number.
+  // If vendor is Apple, ignore the version number.
   if (getVendor() == Triple::Apple)
     return getArch() == Other.getArch() && getSubArch() == Other.getSubArch() &&
            getVendor() == Other.getVendor() && getOS() == Other.getOS();
 
   return *this == Other;
 }
 
 std::string Triple::merge(const Triple &Other) const {
-  // If vendor is apple, pick the triple with the larger version number.
+  // If vendor is Apple, pick the triple with the larger version number.
   if (getVendor() == Triple::Apple)
     if (Other.isOSVersionLT(*this))
       return str();
 
   return Other.str();
 }
 
 bool Triple::isMacOSXVersionLT(unsigned Major, unsigned Minor,
VersionTuple Triple::getMinimumSupportedOSVersion() const {
   case Triple::MacOSX:
     // ARM64 slice is supported starting from macOS 11.0+.
     return VersionTuple(11, 0, 0);
   case Triple::IOS:
     // ARM64 slice is supported starting from Mac Catalyst 14 (macOS 11).
     // ARM64 simulators are supported for iOS 14+.
     if (isMacCatalystEnvironment() || isSimulatorEnvironment())
       return VersionTuple(14, 0, 0);
-    // ARM64e slice is supported starting from iOS 14.
+    // ARM64e slice is supported starting from iOS 14+.
     if (isArm64e())
       return VersionTuple(14, 0, 0);
     break;
   case Triple::TvOS:
     // ARM64 simulators are supported for tvOS 14+.
     if (isSimulatorEnvironment())
       return VersionTuple(14, 0, 0);
     break;
default:
     case llvm::Triple::EABIHF:
     case llvm::Triple::GNUEABIHF:
     case llvm::Triple::MuslEABIHF:
       return "arm1176jzf-s";
     default:
       return "arm7tdmi";
     }
   }
-
-  llvm_unreachable("invalid arch name");
 }
 
 VersionTuple Triple::getCanonicalVersionForOS(OSType OSKind,
                                               const VersionTuple &Version) {
   switch (OSKind) {
   case MacOSX:
     // macOS 10.16 is canonicalized to macOS 11.
     if (Version == VersionTuple(10, 16))
       return VersionTuple(11, 0);
+    // macOS 10.17 is canonicalized to macOS 12.
+    // TODO: Find a better way to do this going forward rather than hardcoding a
+    // new if statement every year
+    if (Version == VersionTuple(10, 17))
+      return VersionTuple(12, 0);
     LLVM_FALLTHROUGH;
   default:
     return Version;
   }
 }