Fix Issue 1104 (dotnet#1734)

* Fix the incorrect change where 'alreadyPresent' was incorrectly initialized.
The PR that introduced this issue: dotnet/coreclr#23109

* Add test case

Author: briansull

src/coreclr/src/jit/rangecheck.cpp

@@ -362,7 +362,7 @@ bool RangeCheck::IsMonotonicallyIncreasing(GenTree* expr, bool rejectNegativeCon
     JITDUMP("[RangeCheck::IsMonotonicallyIncreasing] [%06d]\n", Compiler::dspTreeID(expr));
 
     // Add hashtable entry for expr.
-    bool alreadyPresent = !m_pSearchPath->Set(expr, nullptr, SearchPath::Overwrite);
+    bool alreadyPresent = m_pSearchPath->Set(expr, nullptr, SearchPath::Overwrite);
     if (alreadyPresent)
     {
         return true;

src/coreclr/tests/src/JIT/Regression/JitBlue/Runtime_1104/Runtime_1104.cs

@@ -0,0 +1,62 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+
+class Runtime_1104
+{
+    static int TestOutOfBoundProxy(Func<int> actualTest)
+    {
+        try
+        {
+            actualTest();
+        }
+        catch (IndexOutOfRangeException)
+        {
+            Console.WriteLine("caught IndexOutOfRangeException");
+            return 100;
+        }
+        Debug.Fail("unreached");
+        return 101;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static int TestOutOfBoundLowerDecreasing()
+    {
+        int[] arr = new int[10];
+        int i = 9;
+        int j = 15;
+        int sum = 0;
+
+        // our range check optimizer is very naive, so if you don't have
+        // i < 10, then it thinks `i` can overflow and doesn't bother 
+        // calling `Widen` at all.
+        //
+        while (j >= 0 && i < 10)
+        {
+            --j;
+            --i;
+            sum += arr[i];  // range check will use 9 as lower bound.
+
+            Console.WriteLine("i = " + i + ", j = " + j);
+        }
+        return sum;
+    }
+
+    public static int Main()
+    {
+        try
+        {
+            TestOutOfBoundProxy(TestOutOfBoundLowerDecreasing);
+        }
+        catch (Exception)
+        {
+            return 101;
+        }
+
+        return 100;
+    }
+}

src/coreclr/tests/src/JIT/Regression/JitBlue/Runtime_1104/Runtime_1104.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <DebugType>None</DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>