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erozenfeldRussKeldorph
erozenfeld
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Fix for a bug in tail recursion elimination.
Tail recursion elimination transforms a tail call into a loop. If compInitMem is set, we may need to zero-initialize some locals. Normally it's done in the prolog but the loop we are creating can't include the prolog. The fix is to insert zero-initialization for all non-parameter non-temp locals in the loop. Liveness phase will remove unnecessary initializations. We never hit this case with normal C# code since C# definite assignment rules ensure that there are no uninitialized locals in the generated msil. In the repro the method with tail recursion is a dynamic method and it has an uninitialized local.
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‎src/jit/morph.cpp‎

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@@ -7529,6 +7529,39 @@ void Compiler::fgMorphRecursiveFastTailCallIntoLoop(BasicBlock* block, GenTreeCa
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fgInsertStmtBefore(block, paramAssignmentInsertionPoint, arg0AssignmentStmt);
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}
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// If compInitMem is set, we may need to zero-initialize some locals. Normally it's done in the prolog
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// but this loop can't include the prolog. Since we don't have liveness information, we insert zero-initialization
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// for all non-parameter non-temp locals. Liveness phase will remove unnecessary initializations.
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if (info.compInitMem)
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{
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unsigned varNum;
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LclVarDsc* varDsc;
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for (varNum = 0, varDsc = lvaTable; varNum < info.compLocalsCount; varNum++, varDsc++)
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{
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if (!varDsc->lvIsParam)
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{
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assert(!varDsc->lvIsTemp);
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var_types lclType = varDsc->TypeGet();
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GenTreePtr lcl = gtNewLclvNode(varNum, lclType);
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GenTreePtr init = nullptr;
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if (lclType == TYP_STRUCT)
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{
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const bool isVolatile = false;
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const bool isCopyBlock = false;
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init = gtNewBlkOpNode(lcl, gtNewIconNode(0), varDsc->lvSize(), isVolatile, isCopyBlock);
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init = fgMorphInitBlock(init);
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}
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else
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{
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GenTreePtr zero = gtNewZeroConNode(genActualType(lclType));
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init = gtNewAssignNode(lcl, zero);
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}
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GenTreePtr initStmt = gtNewStmt(init, callILOffset);
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fgInsertStmtBefore(block, last, initStmt);
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}
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}
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}
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// Remove the call
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fgRemoveStmt(block, last);
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‎tests/src/JIT/Regression/JitBlue/DevDiv_461649/DevDiv_461649.cs‎

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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// See the LICENSE file in the project root for more information.
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using System;
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using System.IO;
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using System.Xml;
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using System.Xml.XPath;
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using System.Xml.Xsl;
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namespace XSLTest
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{
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class Program
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{
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// In this test a dynamic method with tail-prefixed call is created.
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// One of the locals is not explicitly initialized but a flag to init locals is set.
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// (That never happens in normal C# methods due to C# definite assignment rules.)
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// The jit performs an optimization transforming the tail call into a loop.
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// The bug was that the local was only zero-initialized for the first iteration of the loop.
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static int Main(string[] args)
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{
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string inputXml = "Input.xml";
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string inputXsl = "Transform.xsl";
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return DotNetXslCompiledTransform(inputXml, inputXsl);
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}
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private static int DotNetXslCompiledTransform(string inputXml, string inputXsl)
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{
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XslCompiledTransform transform = new XslCompiledTransform();
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transform.Load(inputXsl);
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StringWriter stringWriter = new StringWriter();
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XmlWriter writer = new XmlTextWriter(stringWriter);
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transform.Transform(inputXml, null, writer);
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string transformResult = stringWriter.ToString();
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if (transformResult == "<!--20.0 20.0 20.0 20.0 20.0--> 40 40 40 40 40")
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{
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Console.WriteLine("SUCCESS");
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return 100;
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}
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else
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{
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Console.WriteLine("FAILURE");
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return 0;
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}
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}
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}
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}
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‎tests/src/JIT/Regression/JitBlue/DevDiv_461649/DevDiv_461649.csproj‎

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<?xml version="1.0" encoding="utf-8"?>
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<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
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<Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.props))\dir.props" />
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<PropertyGroup>
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<Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
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<Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
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<AssemblyName>$(MSBuildProjectName)</AssemblyName>
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<SchemaVersion>2.0</SchemaVersion>
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<ProjectGuid>{95DFC527-4DC1-495E-97D7-E94EE1F7140D}</ProjectGuid>
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<OutputType>Exe</OutputType>
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<ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
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<SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
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</PropertyGroup>
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<!-- Default configurations to help VS understand the configurations -->
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<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
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</PropertyGroup>
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<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
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</PropertyGroup>
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<ItemGroup>
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<CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
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<Visible>False</Visible>
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</CodeAnalysisDependentAssemblyPaths>
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</ItemGroup>
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<PropertyGroup>
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<DebugType></DebugType>
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<Optimize>True</Optimize>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="$(MSBuildProjectName).cs" />
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<Reference Include="System.Private.Xml" />
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<Content Include="Input.xml">
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<CopyToOutputDirectory>Always</CopyToOutputDirectory>
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</Content>
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<Content Include="Transform.xsl">
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<CopyToOutputDirectory>Always</CopyToOutputDirectory>
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</Content>
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</ItemGroup>
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<ItemGroup>
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<Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
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</ItemGroup>
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<Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
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<PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' ">
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</PropertyGroup>
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</Project>

‎tests/src/JIT/Regression/JitBlue/DevDiv_461649/Input.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<root>
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<bla test="20.0 20.0 20.0 20.0 20.0"/>
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</root>

‎tests/src/JIT/Regression/JitBlue/DevDiv_461649/Transform.xsl‎

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<?xml version="1.0" encoding="utf-8"?>
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<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:l="http://www.schema.de/XSL/ST4DocuManagerlang" version="1.0">
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<xsl:template match="/">
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<xsl:for-each select="/root/bla">
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<xsl:comment>
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<xsl:value-of select="@test"/>
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</xsl:comment>
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<xsl:call-template name="duplicate">
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<xsl:with-param name="value" select="@test" />
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</xsl:call-template>
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</xsl:for-each>
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</xsl:template>
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<xsl:template name="duplicate">
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<xsl:param name="value" />
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<xsl:param name="result" />
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<xsl:choose>
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<xsl:when test="contains($value, ' ')">
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<xsl:call-template name="duplicate">
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<xsl:with-param name="value" select="substring-after($value, ' ')" />
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<xsl:with-param name="result" select="concat($result,' ', substring-before($value, ' ') * 2)" />
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</xsl:call-template>
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</xsl:when>
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<xsl:otherwise>
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<xsl:value-of select="concat($result,' ', $value * 2)" />
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</xsl:otherwise>
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</xsl:choose>
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</xsl:template>
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</xsl:stylesheet>

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