Chapter 36: JIT compiler
JIT compilation, or just-in-time compilation, is an alternative approach to interpretation of code or ahead-of-time compilation. JIT compilation is used in the .NET framework. The CLR code (C#, F#, Visual Basic, etc.) is first compiled into something called Interpreted Language, or IL. This is lower level code that is closer to machine code, but is not platform specific. Rather, at runtime, this code is compiled into machine code for the relevant system.
Section 36.1: IL compilation sample
Simple Hello World Application:
using System;
namespace HelloWorld
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World");
}
}
}
Equivalent IL Code (which will be JIT compiled)
//Microsoft (R) .NET Framework IL Disassembler. Version 4.6.1055.0
//Copyright (c) Microsoft Corporation. All rights reserved.
//Metadata version: v4.0.30319
.assembly extern mscorlib |
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{ |
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.publickeytoken = (B7 7A 5C 56 19 34 E0 89 ) |
// .z\V.4.. |
.ver 4:0:0:0 |
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} |
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.assembly HelloWorld |
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{
.custom instance void [mscorlib]System.Runtime.CompilerServices.CompilationRelaxationsAttribute::.ctor(int32) = ( 01 00 08 00 00 00 00 00 )
.custom instance void [mscorlib]System.Runtime.CompilerServices.RuntimeCompatibilityAttribute::.ctor() = ( 01 00 01 00
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// ceptionThrows. |
//--- The following custom attribute is added automatically, do not uncomment -------
//.custom instance void [mscorlib]System.Diagnostics.DebuggableAttribute::.ctor(valuetype [mscorlib]System.Diagnostics.DebuggableAttribute/DebuggingModes) = ( 01 00 07 01 00 00 00 00 )
.custom |
instance |
void [mscorlib]System.Reflection.AssemblyTitleAttribute::.ctor(string) = ( 01 00 |
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48 65 6C |
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6F 57 6F 72 6C 64 00 00 ) |
// ...HelloWorld.. |
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void [mscorlib]System.Reflection.AssemblyDescriptionAttribute::.ctor(string) = ( |
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void [mscorlib]System.Reflection.AssemblyCompanyAttribute::.ctor(string) = ( 01 |
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GoalKicker.com – .NET Framework Notes for Professionals |
118 |
.custom instance void [mscorlib]System.Reflection.AssemblyProductAttribute::.ctor(string) = ( 01 00 0A 48 65 6C 6C 6F 57 6F 72 6C 64 00 00 ) // ...HelloWorld..
.custom instance void [mscorlib]System.Reflection.AssemblyCopyrightAttribute::.ctor(string) = ( 01
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72 69 67 68 74 20 C2 A9 20 |
// ...Copyright .. |
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// 2017.. |
.custom instance void [mscorlib]System.Reflection.AssemblyTrademarkAttribute::.ctor(string) = ( 01 00 00 00 00 )
.custom instance void [mscorlib]System.Runtime.InteropServices.ComVisibleAttribute::.ctor(bool) = ( 01 00 00 00 00 )
.custom instance void [mscorlib]System.Runtime.InteropServices.GuidAttribute::.ctor(string) = ( 01
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// |
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.custom instance void [mscorlib]System.Reflection.AssemblyFileVersionAttribute::.ctor(string) = ( 01 00 07 31 2E 30 2E 30 2E 30 00 00 ) // ...1.0.0.0..
.custom instance void [mscorlib]System.Runtime.Versioning.TargetFrameworkAttribute::.ctor(string)
= ( 01 00 1C 2E 4E 45 54 46 72 61 6D 65 77 6F 72 6B |
// ....NETFramework |
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// amework 4.5.2 |
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.hash algorithm 0x00008004 |
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.ver 1:0:0:0 |
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.module HelloWorld.exe |
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// MVID: {2A7E1D59-1272-4B47-85F6-D7E1ED057831} |
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.imagebase 0x00400000 |
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.file alignment 0x00000200 |
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.stackreserve 0x00100000 |
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.subsystem 0x0003 |
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// |
WINDOWS_CUI |
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.corflags 0x00020003 |
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// |
ILONLY 32BITPREFERRED |
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//Image base: 0x0000021C70230000
//=============== CLASS MEMBERS DECLARATION ===================
.class private auto ansi beforefieldinit HelloWorld.Program extends [mscorlib]System.Object
{
.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint |
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// Code size |
13 (0xd) |
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.maxstack |
8 |
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IL_0000: |
nop |
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IL_0001: |
ldstr |
"Hello World" |
IL_0006: |
call |
void [mscorlib]System.Console::WriteLine(string) |
IL_000b: |
nop |
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IL_000c: |
ret |
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} // end |
of method Program::Main |
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.method public |
hidebysig specialname rtspecialname |
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instance |
void |
.ctor() cil managed |
{ |
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// Code size |
8 (0x8) |
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.maxstack |
8 |
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IL_0000: |
ldarg.0 |
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IL_0001: |
call |
instance void [mscorlib]System.Object::.ctor() |
IL_0006: |
nop |
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IL_0007: |
ret |
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}// end of method Program::.ctor
}// end of class HelloWorld.Program
GoalKicker.com – .NET Framework Notes for Professionals |
119 |
Generated with MS ILDASM tool (IL disassembler)
GoalKicker.com – .NET Framework Notes for Professionals |
120 |