[JIT] X64/ARM64 - Fold 'x & 255' and 'x & 65535' to a cast

src/coreclr/jit/gentree.cpp

@@ -13745,6 +13745,24 @@ GenTree* Compiler::gtFoldExprSpecial(GenTree* tree)
                     goto DONE_FOLD;
                 }
             }
+            else if ((val == 0xFF) && !varTypeIsLong(tree))
+            {
+                op = gtNewCastNode(tree->TypeGet(), op, false, TYP_UBYTE);
+                if (fgGlobalMorph)
+                {
+                    fgMorphTreeDone(op);
+                }
+                goto DONE_FOLD;
+            }
+            else if ((val == 0xFFFF) && !varTypeIsLong(tree))
+            {
+                op = gtNewCastNode(tree->TypeGet(), op, false, TYP_USHORT);
+                if (fgGlobalMorph)
+                {
+                    fgMorphTreeDone(op);
+                }
+                goto DONE_FOLD;
+            }
             else
             {
                 /* The GTF_BOOLEAN flag is set for nodes that are part

src/tests/JIT/opt/Remainder/IntRemainder.cs

@@ -1,6 +1,3 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
 using System;
 using System.Runtime.CompilerServices;
 
@@ -9,6 +6,7 @@ namespace CodeGenTests
     static class IntRemainder
     {
         static int _fieldValue = 123;
+        static uint _fieldValueUnsigned = 123;
 
         [MethodImpl(MethodImplOptions.NoInlining)]
         static int Int32_RemainderByOne()
@@ -32,6 +30,56 @@ static int Int32_RemainderByOneWithValue(int value)
             return value % 1;
         }
 
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        static byte Byte_RemainderByMaxValuePlusOne(uint value)
+        {
+            // X64-NOT: and {{[a-z]+}}
+
+            // X64: movzx {{[a-z]+}}, {{[a-z]+}}
+
+            return (byte)(value % (Byte.MaxValue + 1));
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        static ushort UInt16_RemainderByMaxValuePlusOne(uint value)
+        {
+            // X64-NOT: and {{[a-z]+}}
+
+            // X64: movzx {{[a-z]+}}, {{[a-z]+}}
+
+            return (ushort)(value % (UInt16.MaxValue + 1));
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        static uint Byte_RemainderByMaxValuePlusOne_Return_UInt32(uint value)
+        {
+            // X64-NOT: and {{[a-z]+}}
+
+            // X64: movzx {{[a-z]+}}, {{[a-z]+}}
+
+            return (value % (Byte.MaxValue + 1));
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        static uint UInt16_RemainderByMaxValuePlusOne_Return_UInt32(uint value)
+        {
+            // X64-NOT: and {{[a-z]+}}
+
+            // X64: movzx {{[a-z]+}}, {{[a-z]+}}
+
+            return (value % (UInt16.MaxValue + 1));
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        static byte Byte_RemainderByMaxValuePlusOne_WithField()
+        {
+            // X64-NOT: and {{[a-z]+}}
+
+            // X64: movzx {{[a-z]+}}, {{[a-z]+}}
+
+            return (byte)(_fieldValueUnsigned % (Byte.MaxValue + 1));
+        }
+
         static int Main()
         {
             if (Int32_RemainderByOne() != 0)
@@ -40,6 +88,21 @@ static int Main()
             if (Int32_RemainderByOneWithValue(-123) != 0)
                 return 0;
 
+            if (Byte_RemainderByMaxValuePlusOne(68000) != 160)
+                return 0;
+
+            if (UInt16_RemainderByMaxValuePlusOne(68000) != 2464)
+                return 0;
+
+            if (Byte_RemainderByMaxValuePlusOne_Return_UInt32(68000) != 160)
+                return 0;
+
+            if (UInt16_RemainderByMaxValuePlusOne_Return_UInt32(68000) != 2464)
+                return 0;
+
+            if (Byte_RemainderByMaxValuePlusOne_WithField() != 123)
+                return 0;
+
             return 100;
         }
     }