JIT: port fix to defer removing statements during opt CSE to release/2.0.0 (#15360)

Port of #15323.
Related issue #15319.

Author: AndyAyersMS

src/jit/morph.cpp

@@ -15667,7 +15667,13 @@ bool Compiler::fgMorphBlockStmt(BasicBlock* block, GenTreeStmt* stmt DEBUGARG(co
     }
 
     // Can the entire tree be removed?
-    bool removedStmt = fgCheckRemoveStmt(block, stmt);
+    bool removedStmt = false;
+
+    // Defer removing statements during CSE so we don't inadvertently remove any CSE defs.
+    if (!optValnumCSE_phase)
+    {
+        removedStmt = fgCheckRemoveStmt(block, stmt);
+    }
 
     // Or this is the last statement of a conditional branch that was just folded?
     if (!removedStmt && (stmt->getNextStmt() == nullptr) && !fgRemoveRestOfBlock)

tests/src/JIT/Regression/JitBlue/GitHub_15319/GitHub_15319.cs

@@ -0,0 +1,44 @@
+// 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.Linq;
+
+// Bug where interacting CSEs of N - Old.Length and Old.Length
+// were not handled properly in optCSE
+
+class P
+{
+    private static int Main(string[] args)
+    {
+        var ar = new double[]
+        {
+            100
+        };
+        
+        FillTo1(ref ar, 5);
+        Console.WriteLine(string.Join(",", ar.Select(a => a.ToString()).ToArray()));
+        return (int)ar[4];
+    }
+    
+    public static void FillTo1(ref double[] dd, int N)
+    {
+        if (dd.Length >= N)
+        return;
+        
+        double[] Old = dd;
+        double d = double.NaN;
+        if (Old.Length > 0)
+        d = Old[0];
+        
+        dd = new double[N];
+        
+        for (int i = 0; i < Old.Length; i++)
+        {
+            dd[N - Old.Length + i] = Old[i];
+        }
+        for (int i = 0; i < N - Old.Length; i++)
+        dd[i] = d;
+    }
+}

tests/src/JIT/Regression/JitBlue/GitHub_15319/GitHub_15319.csproj

@@ -0,0 +1,38 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.props))\dir.props" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <AssemblyName>$(MSBuildProjectName)</AssemblyName>
+    <SchemaVersion>2.0</SchemaVersion>
+    <ProjectGuid>{95DFC527-4DC1-495E-97D7-E94EE1F7140D}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <AppDesignerFolder>Properties</AppDesignerFolder>
+    <FileAlignment>512</FileAlignment>
+    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
+    <ReferencePath>$(ProgramFiles)\Common Files\microsoft shared\VSTT\11.0\UITestExtensionPackages</ReferencePath>
+    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
+    <NuGetPackageImportStamp>7a9bfb7d</NuGetPackageImportStamp>
+  </PropertyGroup>
+  <!-- Default configurations to help VS understand the configurations -->
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' "></PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' "></PropertyGroup>
+  <ItemGroup>
+    <CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <PropertyGroup>
+    <DebugType></DebugType>
+    <Optimize>True</Optimize>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="GitHub_15319.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' "></PropertyGroup>
+</Project>