CODEWITHSUNDEEP
c#unsafe
aybe
aybe

Reputation: 16672

Does the nesting of an 'unsafe' scope affects performance?

I would like to ask if the first example is somehow slower than the second example.

Example 1: for, unsafe, unsafe, unsafe, etc

for (var i = 0; i < ...; i++)
{
    unsafe
    {
        // ...
    }
}

Example 2: unsafe, for

unsafe
{
    for (var i = 0; i < ...; i++)
    {
        // ...
    }
}

Nowhere in the documentation this aspect is being covered.

Question:

Can someone assume than the location of an unsafe code block does not affect performance ?

Upvotes: 3

Views: 80

Answers (1)

Eamonn McEvoy
Eamonn McEvoy

Reputation: 8986

They produce the exact same IL code so no performance difference

nested: See on SharpLab

c#

using System;
public class C {
    public void M() {
        var x = 0;
        for (var i = 0; i < 100; i++)
        {            
            unsafe { x+=i; }
        }
    }
}

IL

.class private auto ansi '<Module>'
{
} // end of class <Module>

.class public auto ansi beforefieldinit C
    extends [System.Private.CoreLib]System.Object
{
    // Methods
    .method public hidebysig 
        instance void M () cil managed 
    {
        // Method begins at RVA 0x2050
        // Code size 20 (0x14)
        .maxstack 2
        .locals init (
            [0] int32,
            [1] int32
        )

        IL_0000: ldc.i4.0
        IL_0001: stloc.0
        IL_0002: ldc.i4.0
        IL_0003: stloc.1
        // sequence point: hidden
        IL_0004: br.s IL_000e
        // loop start (head: IL_000e)
            IL_0006: ldloc.0
            IL_0007: ldloc.1
            IL_0008: add
            IL_0009: stloc.0
            IL_000a: ldloc.1
            IL_000b: ldc.i4.1
            IL_000c: add
            IL_000d: stloc.1

            IL_000e: ldloc.1
            IL_000f: ldc.i4.s 100
            IL_0011: blt.s IL_0006
        // end loop

        IL_0013: ret
    } // end of method C::M

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        // Method begins at RVA 0x2070
        // Code size 7 (0x7)
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [System.Private.CoreLib]System.Object::.ctor()
        IL_0006: ret
    } // end of method C::.ctor

} // end of class C

surrounding: See on SharpLab

c#

using System;
public class C {
    public void M() {
        var x = 0;
        unsafe {
            for (var i = 0; i < 100; i++)
            {            
                x+=i;
            }
        }
    }
}

IL

.class private auto ansi '<Module>'
{
} // end of class <Module>

.class public auto ansi beforefieldinit C
    extends [System.Private.CoreLib]System.Object
{
    // Methods
    .method public hidebysig 
        instance void M () cil managed 
    {
        // Method begins at RVA 0x2050
        // Code size 20 (0x14)
        .maxstack 2
        .locals init (
            [0] int32,
            [1] int32
        )

        IL_0000: ldc.i4.0
        IL_0001: stloc.0
        IL_0002: ldc.i4.0
        IL_0003: stloc.1
        // sequence point: hidden
        IL_0004: br.s IL_000e
        // loop start (head: IL_000e)
            IL_0006: ldloc.0
            IL_0007: ldloc.1
            IL_0008: add
            IL_0009: stloc.0
            IL_000a: ldloc.1
            IL_000b: ldc.i4.1
            IL_000c: add
            IL_000d: stloc.1

            IL_000e: ldloc.1
            IL_000f: ldc.i4.s 100
            IL_0011: blt.s IL_0006
        // end loop

        IL_0013: ret
    } // end of method C::M

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        // Method begins at RVA 0x2070
        // Code size 7 (0x7)
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [System.Private.CoreLib]System.Object::.ctor()
        IL_0006: ret
    } // end of method C::.ctor

} // end of class C

Upvotes: 5

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