Comparing .NET Compiled CIL of Simple if vs switch Statements

Comparison Details:

Compiler and Framework Details

Operating System: Windows 10
Compiler: Rosyln Compiler
Framework Version: .NET Core 3.1.1
Source Code Editor: LinqPad 6

Review Description

This content reviews the .NET CIL (a.k.a. Common Intermediate Language) code compiled from the 3 C# code equivalents listed below.

See the code comments section for more background on why this code was created.

Code snippets for executing simple conditional logic.

Code Snippet 1 of 3: Basic if Statements
Code Snippet 2 of 3: Basic switch Statement
Code Snippet 3 of 3: Nested Ternary

Code Snippet 1 of 3: Basic if Statements

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C# Code

Simple variable assignments within traditional if / else blocks using conditional expressions.

var input = 9;
var result = 0;

if (input == 0) {
  result = input+10;
} else if (input == 10) {
  result = input + 100;        
}

.NET Intermediate Language

CIL generated from traditional if statements appears to be similar to the CIL for the switch statement in the next test.

IL_0000:  nop         
IL_0001:  ldc.i4.s    09 
IL_0003:  stloc.0     
IL_0004:  ldc.i4.0    
IL_0005:  stloc.1     
IL_0006:  ldloc.0     
IL_0007:  ldc.i4.0    
IL_0008:  ceq         
IL_000A:  stloc.2     
IL_000B:  ldloc.2     
IL_000C:  brfalse.s   IL_0017
IL_000E:  nop         
IL_000F:  ldloc.0     
IL_0010:  ldc.i4.s    0A 
IL_0012:  add         
IL_0013:  stloc.1     
IL_0014:  nop         
IL_0015:  br.s        IL_0027
IL_0017:  ldloc.0     
IL_0018:  ldc.i4.s    0A 
IL_001A:  ceq         
IL_001C:  stloc.3     
IL_001D:  ldloc.3     
IL_001E:  brfalse.s   IL_0027
IL_0020:  nop         
IL_0021:  ldloc.0     
IL_0022:  ldc.i4.s    64 
IL_0024:  add         
IL_0025:  stloc.1     
IL_0026:  nop         
IL_0027:  ret

Code Snippet 2 of 3: Basic switch Statement

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C# Code

Equivalent variable assignment using traditional switch statements.

var input = 9;
var result = 0;

switch (input) {
  case 0:
    result = input+10;
    break;
  case 10:
    result = input + 100;
    break;
}

.NET Common Intermediate Language

The CIL for this switch statement appears to be slightly more efficient or compact than CIL generated from the traditional if statement in the previous test.

IL_0000:  nop         
IL_0001:  ldc.i4.s    09 
IL_0003:  stloc.0     
IL_0004:  ldc.i4.0    
IL_0005:  stloc.1     
IL_0006:  ldloc.0     
IL_0007:  stloc.3     
IL_0008:  ldloc.3     
IL_0009:  stloc.2     
IL_000A:  ldloc.2     
IL_000B:  brfalse.s   IL_0016
IL_000D:  br.s        IL_000F
IL_000F:  ldloc.2     
IL_0010:  ldc.i4.s    0A 
IL_0012:  beq.s       IL_001D
IL_0014:  br.s        IL_0024
IL_0016:  ldloc.0     
IL_0017:  ldc.i4.s    0A 
IL_0019:  add         
IL_001A:  stloc.1     
IL_001B:  br.s        IL_0024
IL_001D:  ldloc.0     
IL_001E:  ldc.i4.s    64 
IL_0020:  add         
IL_0021:  stloc.1     
IL_0022:  br.s        IL_0024
IL_0024:  ret

Code Snippet 3 of 3: Nested Ternary

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C# Code

Equivalent variable assignment using the new switch expressions introduced in C #8.

var input = 9;
var result = (input == 0) 
    ? input + 10
    : input == 10
      ? input + 100
      : 0;

.NET Intermediate Language

The CIL for the new switch expression suprisingly appears to be more efficient or compact than the CIL generated for the equivalent variants in the above tests using if and switch statements.

IL_0000:  nop         
IL_0001:  ldc.i4.s    09 
IL_0003:  stloc.0     
IL_0004:  ldloc.0     
IL_0005:  brfalse.s   IL_0015
IL_0007:  ldloc.0     
IL_0008:  ldc.i4.s    0A 
IL_000A:  beq.s       IL_000F
IL_000C:  ldc.i4.0    
IL_000D:  br.s        IL_0013
IL_000F:  ldloc.0     
IL_0010:  ldc.i4.s    64 
IL_0012:  add         
IL_0013:  br.s        IL_0019
IL_0015:  ldloc.0     
IL_0016:  ldc.i4.s    0A 
IL_0018:  add         
IL_0019:  stloc.1     
IL_001A:  ret

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Comparing .NET Compiled CIL of Simple if vs switch Statements

Comparison Details:

Compiler and Framework Details

Review Description

Code Snippet 1 of 3: Basic if Statements

C# Code

.NET Intermediate Language

Code Snippet 2 of 3: Basic switch Statement

C# Code

.NET Common Intermediate Language

Code Snippet 3 of 3: Nested Ternary

C# Code

.NET Intermediate Language

Related Codes

SoloLearn CodeBits: C# to .NET CIL Review

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Compiler Explorer on godbolt.org

Simple if vs switch Statements in .NET CIL