Merge pull request dotnet/coreclr#8461 from sivarv/shiftFix

Compare opt against zero involving a shift oper.

Commit migrated from dotnet/coreclr@1c8d3d9

src/coreclr/src/jit/lowerxarch.cpp

@@ -1175,13 +1175,17 @@ void Lowering::TreeNodeInfoInitShiftRotate(GenTree* tree)
  else
  {
  MakeSrcContained(tree, shiftBy);
- }
 
- // Codegen of shift oper sets ZF and SF flags.
- // Note that Rotate Left/Right instructions don't set ZF and SF flags.
- if (tree->OperIsShift())
- {
- tree->gtFlags |= GTF_ZSF_SET;
+ // Note that Rotate Left/Right instructions don't set ZF and SF flags.
+ //
+ // If the operand being shifted is 32-bits then upper three bits are masked
+ // by hardware to get actual shift count. Similarly for 64-bit operands
+ // shift count is narrowed to [0..63]. If the resulting shift count is zero,
+ // then shift operation won't modify flags.
+ //
+ // TODO-CQ-XARCH: We can optimize generating 'test' instruction for GT_EQ/NE(shift, 0)
+ // if the shift count is known to be non-zero and in the range depending on the
+ // operand size.
  }
 }
 

src/coreclr/tests/src/JIT/Regression/JitBlue/GitHub_8460/GitHub_8460.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.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+namespace bug
+{
+ class Program
+ {
+ static int Pass = 100;
+ static int Fail = -1;
+
+ // This test is meant to check that in case of
+ // GT_EQ/NE(shift, 0), JIT doesn't optimize out
+ // 'test' instruction incorrectly, because shift
+ // operations on xarch don't modify flags if the
+ // shift count is zero.
+ static int Main(string[] args)
+ {
+ // Absolute bits
+ int bitCount = 0;
+ while ((0 != (100 >> bitCount)) && (31 > bitCount))
+ {
+ bitCount++;
+ }
+ // Sign bit
+ bitCount++;
+
+ if (bitCount != 8)
+ {
+ return Fail;
+ }
+
+ return Pass;
+ }
+ }
+}

src/coreclr/tests/src/JIT/Regression/JitBlue/GitHub_8460/GitHub_8460.csproj

@@ -0,0 +1,46 @@
+<?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="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+ <Visible>False</Visible>
+ </CodeAnalysisDependentAssemblyPaths>
+ </ItemGroup>
+ <PropertyGroup>
+ <DebugType></DebugType>
+ <Optimize>True</Optimize>
+ </PropertyGroup>
+ <ItemGroup>
+ <Compile Include="$(MSBuildProjectName).cs" />
+ </ItemGroup>
+ <ItemGroup>
+ <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+ </ItemGroup>
+ <PropertyGroup>
+ <ProjectJson>$(JitPackagesConfigFileDirectory)minimal\project.json</ProjectJson>
+ <ProjectLockJson>$(JitPackagesConfigFileDirectory)minimal\project.lock.json</ProjectLockJson>
+ </PropertyGroup>
+ <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+ <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' ">
+ </PropertyGroup> 
+</Project>