JIT: Fold "shift-by-zero" in lower (#61222)

src/coreclr/jit/lower.cpp

@@ -5773,7 +5773,7 @@ void Lowering::LowerShift(GenTreeOp* shift)
             assert(!cast->CastOp()->isContained());
 
             // It has to be an upcast and CNS must be in [1..srcBits) range
-            if ((srcBits < dstBits) && ((UINT32)cns->IconValue() < srcBits))
+            if ((srcBits < dstBits) && (cns->IconValue() > 0) && (cns->IconValue() < srcBits))
             {
                 JITDUMP("Recognized ubfix/sbfix pattern in LSH(CAST, CNS). Changing op to GT_BFIZ");
                 shift->ChangeOper(GT_BFIZ);

src/tests/JIT/Regression/JitBlue/Runtime_61045/Runtime_61045.cs

@@ -0,0 +1,38 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Generated by Fuzzlyn v1.5 on 2021-11-04 18:29:11
+// Run on Arm64 Linux
+// Seed: 1922924939431163374
+// Reduced from 261.1 KiB to 0.2 KiB in 00:05:39
+// Hits JIT assert in Release:
+// Assertion failed 'isValidImmShift(lsb, size)' in 'Program:M4():int' during 'Generate code' (IL size 26)
+//
+// File: /__w/1/s/src/coreclr/jit/emitarm64.cpp Line: 7052
+//
+
+using System;
+using System.Runtime.CompilerServices;
+
+public class Runtime_61045
+{
+    public static byte[] s_1;
+    public static int Main()
+    {
+        try
+        {
+            Test();
+        }
+        catch (NullReferenceException)
+        {
+            return 100;
+        }
+        return 101;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static uint Test()
+    {
+        return (uint)((ushort)~s_1[0] << (0 >> s_1[0]));
+    }
+}

src/tests/JIT/Regression/JitBlue/Runtime_61045/Runtime_61045.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>