AlainD AlainD - 1 month ago 9
C# Question

Disable compiler optimisation for a specific function or block of code (C#)

The compiler does a great job of optimising for RELEASE builds, but occasionally it can be useful to ensure that optimisation is turned off for a local function (but not the entire project by unticking

Project Options > Optimize code
).

In C++ this is achieved using the following (with the
#pragma
normally commented out):

#pragma optimize( "", off )
// Some code such as a function (but not the whole project)
#pragma optimize( "", on )


Is there an equivalent in C#?

UPDATE



Several excellent answers suggest decorating the method with
MethodImplOptions.NoOptimization
. This was implemented in .NET 3.5, though not in the Compact Framework (CF) version. A related follow-on question is whether an equivalent for:

* projects targeting .NET 3.0 or earlier?
* projects deployed to a device such as Windows CE 6.0 using the .NET 3.5 CF?

Answer

You can decorate a specific method (or a property getter/setter) with [MethodImpl(MethodImplOptions.NoOptimization)] and [MethodImpl(MethodImplOptions.NoInlining)], this will prevent the JITter from optimizing and inlining the method:

[MethodImpl(MethodImplOptions.NoOptimization | MethodImplOptions.NoInlining)]
private void MethodWhichShouldNotBeOptimized()
{ }

However, there isn't a way to apply this attribute to a block of code. Also NoOptimization attribute was added in .NET 3.5, which might be important for legacy code or Compact Framework.

One hack might be to enclose your block in a try/finally clause, which seems to disable some IL optimizations as mentioned here, and then compare release IL and JITted disassembly for your specific case.