[Question] <Optimize> default for pdbonly/Release configuration builds?

Is <Optimize> enabled by default when building with Release configuration or is it even coupled to pdbonly?

In a quick experiment a couple of weeks ago I compared hashes of an assembly with an without <Optimize> set to true and they were identical.

[jmarolf]

I assume this is identical for class libraries targeting full .NET Framework?

Nope in .NET Framework you need to fully specify most everything and nothing is implicit. Given the following project file:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <ProjectGuid>0635cbaa-d0b1-4314-bce0-f9c618139632</ProjectGuid>
    <OutputType>Library</OutputType>
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <RootNamespace>ClassLibrary8</RootNamespace>
    <AssemblyName>ClassLibrary8</AssemblyName>
    <TargetFrameworkVersion>v4.7.2</TargetFrameworkVersion>
    <FileAlignment>512</FileAlignment>
    <Deterministic>true</Deterministic>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
    <DebugSymbols>true</DebugSymbols>
    <DebugType>full</DebugType>
    <Optimize>false</Optimize>
    <OutputPath>bin\Debug\</OutputPath>
    <DefineConstants>DEBUG;TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
    <DebugType>pdbonly</DebugType>
    <Optimize>true</Optimize>
    <OutputPath>bin\Release\</OutputPath>
    <DefineConstants>TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
  </PropertyGroup>
  <ItemGroup>
    <Reference Include="System"/>
    <Reference Include="System.Core"/>
    <Reference Include="System.Xml.Linq"/>
    <Reference Include="System.Data.DataSetExtensions"/>
    <Reference Include="Microsoft.CSharp"/>
    <Reference Include="System.Data"/>
    <Reference Include="System.Net.Http"/>
    <Reference Include="System.Xml"/>
  </ItemGroup>
  <ItemGroup>
    <Compile Include="Class1.cs" />
    <Compile Include="Properties\AssemblyInfo.cs" />
  </ItemGroup>
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
 </Project>

This is what gets passed to the commandline on debug

 /noconfig
 /nowarn:1701,1702
 /nostdlib+
 /errorreport:prompt
 /warn:4
 /define:DEBUG;TRACE
 /highentropyva+
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\Microsoft.CSharp.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\mscorlib.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Core.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Data.DataSetExtensions.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Data.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Net.Http.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Xml.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Xml.Linq.dll"
 /debug+
 /debug:full
 /filealign:512
 /optimize-
 /out:obj\Debug\ClassLibrary8.dll
 /ruleset:"C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\Team Tools\Static Analysis Tools\\Rule Sets\MinimumRecommendedRules.ruleset"
 /subsystemversion:6.00
 /target:library
 /utf8output
 /deterministic+ 

This is what gets passed to the commandline on release

 /noconfig
 /nowarn:1701,1702
 /nostdlib+
 /errorreport:prompt
 /warn:4
 /define:TRACE
 /highentropyva+
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\Microsoft.CSharp.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\mscorlib.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Core.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Data.DataSetExtensions.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Data.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Net.Http.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Xml.dll"
 /reference:"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.2\System.Xml.Linq.dll"
 /debug:pdbonly
 /filealign:512
 /optimize+
 /out:obj\release\ClassLibrary8.dll
 /subsystemversion:6.00
 /target:library
 /utf8output
 /deterministic+ 

[jmarolf]

Can you give an example of your project file? /optimize+ is passed to the compiler on release builds by default.

In a new .NET Core project these are the relevant options that are passed to csc.exe for debug and release:

default debug build on .NET Core

/debug+ 
/optimize- 
/debug:portable 
/deterministic+ 

default release build on .NET Core

/debug- 
/optimize+ 
/debug:portable 
/deterministic+