Merge pull request #3889 from dotnet-bot/from-tfs

Merge changes from TFS

2 files changed, 57 insertions, 0 deletions

diff --git a/src/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/EETypeCreator.cs b/src/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/EETypeCreator.cs
index e7b4b31dc..4942325c6 100644
--- a/src/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/EETypeCreator.cs
+++ b/src/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/EETypeCreator.cs
@@ -338,6 +338,24 @@ namespace Internal.Runtime.TypeLoader
                     else
                         rareFlags &= ~(uint)EETypeRareFlags.IsByRefLikeFlag;
 
+                    if (isNullable)
+                    {
+                        rareFlags |= (uint)EETypeRareFlags.IsNullableFlag;
+                        uint nullableValueOffset = state.NullableValueOffset;
+
+                        // The stored offset is never zero (Nullable has a boolean there indicating whether the value is valid). 
+                        // If the real offset is one, then the field isn't set. Otherwise the offset is encoded - 1 to save space.
+                        if (nullableValueOffset == 1)
+                            optionalFields.ClearField(EETypeOptionalFieldTag.NullableValueOffset);
+                        else
+                            optionalFields.SetFieldValue(EETypeOptionalFieldTag.NullableValueOffset, checked(nullableValueOffset - 1));
+                    }
+                    else
+                    {
+                        rareFlags &= ~(uint)EETypeRareFlags.IsNullableFlag;
+                        optionalFields.ClearField(EETypeOptionalFieldTag.NullableValueOffset);
+                    }
+
                     rareFlags |= (uint)EETypeRareFlags.HasDynamicModuleFlag;
 
                     optionalFields.SetFieldValue(EETypeOptionalFieldTag.RareFlags, rareFlags);
diff --git a/src/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilderState.cs b/src/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilderState.cs
index cd0142b0f..234de598b 100644
--- a/src/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilderState.cs
+++ b/src/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeBuilderState.cs
@@ -1010,6 +1010,45 @@ namespace Internal.Runtime.TypeLoader
             }
         }
 
+        public uint NullableValueOffset
+        {
+            get
+            {
+                if (!TypeBeingBuilt.IsNullable)
+                    return 0;
+
+                if (TypeBeingBuilt.IsTemplateCanonical())
+                {
+                    // Pull the GC Desc from the canonical instantiation
+                    TypeDesc templateType = TypeBeingBuilt.ComputeTemplate();
+                    bool success = templateType.RetrieveRuntimeTypeHandleIfPossible();
+                    Debug.Assert(success);
+                    unsafe
+                    {
+                        return templateType.RuntimeTypeHandle.ToEETypePtr()->NullableValueOffset;
+                    }
+                }
+                else
+                {
+                    int fieldCount = 0;
+                    uint nullableValueOffset = 0;
+
+                    foreach (FieldDesc f in GetFieldsForGCLayout())
+                    {
+                        if (fieldCount == 1)
+                        {
+                            nullableValueOffset = checked((uint)f.Offset.AsInt);
+                        }
+                        fieldCount++;
+                    }
+
+                    // Nullable<T> only has two fields. HasValue and Value
+                    Debug.Assert(fieldCount == 2);
+                    return nullableValueOffset;
+                }
+            }
+        }
+
         public bool IsHFA
         {
             get