Drop size of hello world to 745 kB (#118718)

(With `StackTraceSupport=false`, `OptimizationPreference=Size`, `UseSystemResourceKeys=true`)

The thing that makes the difference is that we are no longer boxing enums and we can get rid of the super expensive enum stringification logic.

Not boxing enums also means that #118640 can fully kick in because enums are the last remaining place that looks at custom attributes (looking for `FlagsAttribute`).

Co-authored-by: Jan Kotas <[email protected]>

Author: MichalStrehovsky

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/MethodTable.Runtime.cs

@@ -37,7 +37,7 @@ internal bool IsEnum
 
                 // Generic type definitions that return true for IsPrimitive are type definitions of generic enums.
                 // Otherwise check the base type.
-                return IsPrimitive && (IsGenericTypeDefinition || NonArrayBaseType == MethodTable.Of<Enum>());
+                return IsPrimitive && (IsGenericTypeDefinition || NonArrayBaseType != MethodTable.Of<ValueType>());
             }
         }
 

src/coreclr/nativeaot/System.Private.CoreLib/src/System/GC.NativeAot.cs

@@ -764,7 +764,7 @@ public static long GetTotalAllocatedBytes(bool precise = false)
 
         /// <summary>Gets garbage collection memory information.</summary>
         /// <returns>An object that contains information about the garbage collector's memory usage.</returns>
-        public static GCMemoryInfo GetGCMemoryInfo() => GetGCMemoryInfo(GCKind.Any);
+        public static GCMemoryInfo GetGCMemoryInfo() => GetGCMemoryInfoUnchecked(GCKind.Any);
 
         /// <summary>Gets garbage collection memory information.</summary>
         /// <param name="kind">The kind of collection for which to retrieve memory information.</param>
@@ -780,6 +780,11 @@ public static GCMemoryInfo GetGCMemoryInfo(GCKind kind)
                                           GCKind.Background));
             }
 
+            return GetGCMemoryInfoUnchecked(kind);
+        }
+
+        private static GCMemoryInfo GetGCMemoryInfoUnchecked(GCKind kind)
+        {
             var data = new GCMemoryInfoData();
             RuntimeImports.RhGetMemoryInfo(ref data.GetRawData(), kind);
             return new GCMemoryInfo(data);

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Threading/Thread.NativeAot.Windows.cs

@@ -289,7 +289,14 @@ private bool SetApartmentStateUnchecked(ApartmentState state, bool throwOnError)
             {
                 if (throwOnError)
                 {
-                    string msg = SR.Format(SR.Thread_ApartmentState_ChangeFailed, retState);
+                    // NOTE: We do the enum stringification manually to avoid introducing a dependency
+                    // on enum stringification in small apps. We set apartment state in the startup path.
+                    string msg = SR.Format(SR.Thread_ApartmentState_ChangeFailed, retState switch
+                    {
+                        ApartmentState.MTA => "MTA",
+                        ApartmentState.STA => "STA",
+                        _ => "Unknown"
+                    });
                     throw new InvalidOperationException(msg);
                 }
 

src/libraries/System.Private.CoreLib/src/System/Globalization/CultureData.cs

@@ -625,15 +625,11 @@ private static CultureData CreateCultureWithInvariantData()
             invariant._iFirstDayOfWeek = 0;                      // first day of week
             invariant._iFirstWeekOfYear = 0;                      // first week of year
 
-            // all available calendar type(s).  The first one is the default calendar
-            invariant._waCalendars = [CalendarId.GREGORIAN];
-
-            if (!GlobalizationMode.InvariantNoLoad)
-            {
-                // Store for specific data about each calendar
-                invariant._calendars = new CalendarData[CalendarData.MAX_CALENDARS];
-                invariant._calendars[0] = CalendarData.Invariant;
-            }
+            // Calendar information is expensive size-wise, especially for AOT.
+            // CalendarData.Invariant is special cased in _waCalendars and _calendars
+            // accessors and gets initialized lazily.
+            // invariant._waCalendars
+            // invariant._calendars
 
             // Text information
             invariant._iReadingLayout = 0;
@@ -1647,61 +1643,68 @@ internal CalendarId[] CalendarIds
         {
             get
             {
-                if (_waCalendars == null && !GlobalizationMode.Invariant)
+                if (_waCalendars == null)
                 {
-                    // We pass in an array of ints, and native side fills it up with count calendars.
-                    // We then have to copy that list to a new array of the right size.
-                    // Default calendar should be first
-                    CalendarId[] calendars = new CalendarId[23];
-                    Debug.Assert(_sWindowsName != null, "[CultureData.CalendarIds] Expected _sWindowsName to be populated by already");
-
-                    int count = CalendarData.GetCalendarsCore(_sWindowsName, _bUseOverrides, calendars);
-
-                    // See if we had a calendar to add.
-                    if (count == 0)
+                    if (GlobalizationMode.Invariant || IsInvariantCulture)
                     {
-                        // Failed for some reason, just grab Gregorian from Invariant
-                        _waCalendars = Invariant._waCalendars!;
+                        // We do this lazily as opposed in CreateCultureWithInvariantData to avoid introducing
+                        // enum arrays into apps that otherwise wouldn't have them. This helps with size in AOT.
+                        _waCalendars = [CalendarId.GREGORIAN];
                     }
                     else
                     {
-                        // The OS may not return calendar 4 for zh-TW, but we've always allowed it.
-                        // TODO: Is this hack necessary long-term?
-                        if (_sWindowsName == "zh-TW")
-                        {
-                            bool found = false;
+                        // We pass in an array of ints, and native side fills it up with count calendars.
+                        // We then have to copy that list to a new array of the right size.
+                        // Default calendar should be first
+                        CalendarId[] calendars = new CalendarId[23];
+                        Debug.Assert(_sWindowsName != null, "[CultureData.CalendarIds] Expected _sWindowsName to be populated by already");
+
+                        int count = CalendarData.GetCalendarsCore(_sWindowsName, _bUseOverrides, calendars);
 
-                            // Do we need to insert calendar 4?
-                            for (int i = 0; i < count; i++)
+                        // See if we had a calendar to add.
+                        if (count == 0)
+                        {
+                            // Failed for some reason, just use Gregorian
+                            _waCalendars = Invariant.CalendarIds;
+                        }
+                        else
+                        {
+                            // The OS may not return calendar 4 for zh-TW, but we've always allowed it.
+                            // TODO: Is this hack necessary long-term?
+                            if (_sWindowsName == "zh-TW")
                             {
-                                // Stop if we found calendar four
-                                if (calendars[i] == CalendarId.TAIWAN)
+                                bool found = false;
+
+                                // Do we need to insert calendar 4?
+                                for (int i = 0; i < count; i++)
                                 {
-                                    found = true;
-                                    break;
+                                    // Stop if we found calendar four
+                                    if (calendars[i] == CalendarId.TAIWAN)
+                                    {
+                                        found = true;
+                                        break;
+                                    }
                                 }
-                            }
 
-                            // If not found then insert it
-                            if (!found)
-                            {
-                                // Insert it as the 2nd calendar
-                                count++;
-                                // Copy them from the 2nd position to the end, -1 for skipping 1st, -1 for one being added.
-                                Array.Copy(calendars, 1, calendars, 2, 23 - 1 - 1);
-                                calendars[1] = CalendarId.TAIWAN;
+                                // If not found then insert it
+                                if (!found)
+                                {
+                                    // Insert it as the 2nd calendar
+                                    count++;
+                                    // Copy them from the 2nd position to the end, -1 for skipping 1st, -1 for one being added.
+                                    Array.Copy(calendars, 1, calendars, 2, 23 - 1 - 1);
+                                    calendars[1] = CalendarId.TAIWAN;
+                                }
                             }
-                        }
-
-                        // It worked, remember the list
-                        CalendarId[] temp = new CalendarId[count];
-                        Array.Copy(calendars, temp, count);
 
-                        _waCalendars = temp;
+                            // It worked, remember the list
+                            CalendarId[] temp = new CalendarId[count];
+                            Array.Copy(calendars, temp, count);
+                            _waCalendars = temp;
+                        }
                     }
                 }
-
-                return _waCalendars!;
+                return _waCalendars;
             }
         }
 
@@ -1737,8 +1740,17 @@ internal CalendarData GetCalendar(CalendarId calendarId)
             // Make sure that calendar has data
             if (calendarData == null)
             {
-                Debug.Assert(_sWindowsName != null, "[CultureData.GetCalendar] Expected _sWindowsName to be populated by already");
-                calendarData = new CalendarData(_sWindowsName, calendarId, _bUseOverrides);
+                if (calendarIndex == 0 && IsInvariantCulture)
+                {
+                    // We do this lazily as opposed in CreateCultureWithInvariantData to avoid introducing
+                    // invariant calendar data into apps that don't even need calendar.
+                    calendarData = CalendarData.Invariant;
+                }
+                else
+                {
+                    Debug.Assert(_sWindowsName != null, "[CultureData.GetCalendar] Expected _sWindowsName to be populated by already");
+                    calendarData = new CalendarData(_sWindowsName, calendarId, _bUseOverrides);
+                }
                 _calendars[calendarIndex] = calendarData;
             }