I am not expecting a definite yes or no. Any knowledge you might have I will consider as an answer.
private String CalculateCharge(Nullable<Decimal> bill, Nullable<Decimal> rate)
{
return ((bill ?? 0.0m) * (rate ?? 0.0m)).ToString("C");
}
Inlining is an implementation detail of the JIT, not of the C# compiler. From Eric Gunnerson's blog:
The JIT uses a number of heuristics to
decide whether a method should be
in-lined.
The following is a list of
the more significant of those (note
that this is not exhaustive):
Methods that are greater than 32 bytes of IL will not be inlined.
Virtual functions are not inlined.
Methods that have complex flow control will not be in-lined. Complex
flow control is any flow control other
than if/then/else; in this case,
switch or while.
Methods that contain exception-handling blocks are not
inlined, though methods that throw
exceptions are still candidates for
inlining.
If any of the method's formal arguments are structs, the method will
not be inlined.
Although your method is quite short and not very complex so it might match the heuristics, Nullable<T> is a struct so I'd guess your method is not inlined.
As a rule of thumb, if inlining this method improves performance, the JIT will inline this method; otherwise it will not. But this is really an implementation detail of the JIT and nothing you should code for:
I would carefully consider explicitly coding for these heuristics because they might change in future versions of the JIT. Don't compromise the correctness of the method to attempt to guarantee that it will be inlined.
EDIT: Apparently the bit about structs not being inlined is out-of-date; updated information can be found at Vance Morrison's blog.
Related
Do simple lambda expressions get inlined?
I have a tendency (thanks to F# and other functional forays) to encapsulate repeated code present within a single function into a lambda, and call it instead. I'm curious if I'm incurring a run-time overhead as a result:
var foo = a + b;
var bar = a + b;
vs
Func<T1, T2> op = () => a + b;
var foo = op();
var bar = op();
Which one costs more to run?
To answer the performance question: run it a billion times both ways. Measure the cost of each. Then you'll know. We have no idea what hardware you're using, what "noise" is present in your relevant scenarios, or what you consider to be an important performance metric. You're the only person who knows those things, so you're the only person who can answer the question.
To answer your codegen question: Jared is correct but the answer could be expanded upon.
First off, the C# compiler never does inlining of any code. The jit compiler does do inlining of code, but the fact that the C# compiler generates lambdas as delegate instances means that it is unlikely that the jitter can reasonably inline this code. (It is of course possible for the jitter to do this sophisticated analysis to determine that the same code is always in the delegate, but I do not believe that in practice those algorithms have been implemented.)
If you want the code to be inlined then you should write it in line. If you don't want to write it in line but you still want it inlined then you should write it as a static method and hope the jitter inlines it.
But regardless, this sounds like premature optimization. Write the code the way you want to write the code, and then analyze its performance, and then rewrite the slow stuff.
No. Lambda functions are not inlined but instead are stored as delegates under the hood and incur the same cost of execution as other delegates.
How do you do "inline functions" in C#? I don't think I understand the concept. Are they like anonymous methods? Like lambda functions?
Note: The answers almost entirely deal with the ability to inline functions, i.e. "a manual or compiler optimization that replaces a function call site with the body of the callee." If you are interested in anonymous (a.k.a. lambda) functions, see #jalf's answer or What is this 'Lambda' everyone keeps speaking of?.
Finally in .NET 4.5, the CLR allows one to hint/suggest1 method inlining using MethodImplOptions.AggressiveInlining value. It is also available in the Mono's trunk (committed today).
// The full attribute usage is in mscorlib.dll,
// so should not need to include extra references
using System.Runtime.CompilerServices;
...
[MethodImpl(MethodImplOptions.AggressiveInlining)]
void MyMethod(...)
1. Previously "force" was used here. I'll try to clarify the term. As in the comments and the documentation, The method should be inlined if possible. Especially considering Mono (which is open), there are some mono-specific technical limitations considering inlining or more general one (like virtual functions). Overall, yes, this is a hint to compiler, but I guess that is what was asked for.
Inline methods are simply a compiler optimization where the code of a function is rolled into the caller.
There's no mechanism by which to do this in C#, and they're to be used sparingly in languages where they are supported -- if you don't know why they should be used somewhere, they shouldn't be.
Edit: To clarify, there are two major reasons they need to be used sparingly:
It's easy to make massive binaries by using inline in cases where it's not necessary
The compiler tends to know better than you do when something should, from a performance standpoint, be inlined
It's best to leave things alone and let the compiler do its work, then profile and figure out if inline is the best solution for you. Of course, some things just make sense to be inlined (mathematical operators particularly), but letting the compiler handle it is typically the best practice.
Update: Per konrad.kruczynski's answer, the following is true for versions of .NET up to and including 4.0.
You can use the MethodImplAttribute class to prevent a method from being inlined...
[MethodImpl(MethodImplOptions.NoInlining)]
void SomeMethod()
{
// ...
}
...but there is no way to do the opposite and force it to be inlined.
You're mixing up two separate concepts. Function inlining is a compiler optimization which has no impact on the semantics. A function behaves the same whether it's inlined or not.
On the other hand, lambda functions are purely a semantic concept. There is no requirement on how they should be implemented or executed, as long as they follow the behavior set out in the language spec. They can be inlined if the JIT compiler feels like it, or not if it doesn't.
There is no inline keyword in C#, because it's an optimization that can usually be left to the compiler, especially in JIT'ed languages. The JIT compiler has access to runtime statistics which enables it to decide what to inline much more efficiently than you can when writing the code. A function will be inlined if the compiler decides to, and there's nothing you can do about it either way. :)
Cody has it right, but I want to provide an example of what an inline function is.
Let's say you have this code:
private void OutputItem(string x)
{
Console.WriteLine(x);
//maybe encapsulate additional logic to decide
// whether to also write the message to Trace or a log file
}
public IList<string> BuildListAndOutput(IEnumerable<string> x)
{ // let's pretend IEnumerable<T>.ToList() doesn't exist for the moment
IList<string> result = new List<string>();
foreach(string y in x)
{
result.Add(y);
OutputItem(y);
}
return result;
}
The compilerJust-In-Time optimizer could choose to alter the code to avoid repeatedly placing a call to OutputItem() on the stack, so that it would be as if you had written the code like this instead:
public IList<string> BuildListAndOutput(IEnumerable<string> x)
{
IList<string> result = new List<string>();
foreach(string y in x)
{
result.Add(y);
// full OutputItem() implementation is placed here
Console.WriteLine(y);
}
return result;
}
In this case, we would say the OutputItem() function was inlined. Note that it might do this even if the OutputItem() is called from other places as well.
Edited to show a scenario more-likely to be inlined.
Do you mean inline functions in the C++ sense? In which the contents of a normal function are automatically copied inline into the callsite? The end effect being that no function call actually happens when calling a function.
Example:
inline int Add(int left, int right) { return left + right; }
If so then no, there is no C# equivalent to this.
Or Do you mean functions that are declared within another function? If so then yes, C# supports this via anonymous methods or lambda expressions.
Example:
static void Example() {
Func<int,int,int> add = (x,y) => x + y;
var result = add(4,6); // 10
}
Yes Exactly, the only distinction is the fact it returns a value.
Simplification (not using expressions):
List<T>.ForEach Takes an action, it doesn't expect a return result.
So an Action<T> delegate would suffice.. say:
List<T>.ForEach(param => Console.WriteLine(param));
is the same as saying:
List<T>.ForEach(delegate(T param) { Console.WriteLine(param); });
the difference is that the param type and delegate decleration are inferred by usage and the braces aren't required on a simple inline method.
Where as
List<T>.Where Takes a function, expecting a result.
So an Function<T, bool> would be expected:
List<T>.Where(param => param.Value == SomeExpectedComparison);
which is the same as:
List<T>.Where(delegate(T param) { return param.Value == SomeExpectedComparison; });
You can also declare these methods inline and asign them to variables IE:
Action myAction = () => Console.WriteLine("I'm doing something Nifty!");
myAction();
or
Function<object, string> myFunction = theObject => theObject.ToString();
string myString = myFunction(someObject);
I hope this helps.
The statement "its best to leave these things alone and let the compiler do the work.." (Cody Brocious) is complete rubish. I have been programming high performance game code for 20 years, and I have yet to come across a compiler that is 'smart enough' to know which code should be inlined (functions) or not. It would be useful to have a "inline" statement in c#, truth is that the compiler just doesnt have all the information it needs to determine which function should be always inlined or not without the "inline" hint. Sure if the function is small (accessor) then it might be automatically inlined, but what if it is a few lines of code? Nonesense, the compiler has no way of knowing, you cant just leave that up to the compiler for optimized code (beyond algorithims).
There are occasions where I do wish to force code to be in-lined.
For example if I have a complex routine where there are a large number of decisions made within a highly iterative block and those decisions result in similar but slightly differing actions to be carried out. Consider for example, a complex (non DB driven) sort comparer where the sorting algorythm sorts the elements according to a number of different unrelated criteria such as one might do if they were sorting words according to gramatical as well as semantic criteria for a fast language recognition system. I would tend to write helper functions to handle those actions in order to maintain the readability and modularity of the source code.
I know that those helper functions should be in-lined because that is the way that the code would be written if it never had to be understood by a human. I would certainly want to ensure in this case that there were no function calling overhead.
I know this question is about C#. However, you can write inline functions in .NET with F#. see: Use of `inline` in F#
No, there is no such construct in C#, but the .NET JIT compiler could decide to do inline function calls on JIT time. But i actually don't know if it is really doing such optimizations.
(I think it should :-))
In case your assemblies will be ngen-ed, you might want to take a look at TargetedPatchingOptOut. This will help ngen decide whether to inline methods. MSDN reference
It is still only a declarative hint to optimize though, not an imperative command.
Lambda expressions are inline functions! I think, that C# doesn`t have a extra attribute like inline or something like that!
I'm doing some post-build CIL weaving that adds CIL to all methods in an assembly (in other words tons of methods). Each method checks if a specific value is null. Example (C# Reflector'd version of CIL code):
// CIL woven region start
if (MyType.Something == null) {
// ... some new stuff
}
// CIL woven region end
What is the performance impact of having MyType.Something as a Property vs. a Field? I know I've read that the C# compiler performs special optimizations and there should be no performance impact in that case...but what about in the case of direct CIL code (no C# compiler)...? Or is it the JIT compiler that allows for these optimizations (so direct CIL code still benefits)?
Will emitting OpCode.Call for the static property's accessor have poorer performance than Ldsfld (bear in mind this is across tens of thousands of invocations since every method in the assembly is woven)?
Thanks.
When developing the math library for SlimDX, we found that, on pre-.NET 3.5 SP1 frameworks, using fields for the members of the math types (such as X, Y, Z for a Vector3) gave a disproportionate performance increase over properties. In other words, the difference was noticeable for small math functions which heavily accessed properties.
This has since been improved since .NET 3.5 SP1 (see JIT inling). While I believe that the JIT prior to that will still inline small methods (properties are simply methods after all), there is a bug in the earlier frameworks that prevented inlining of methods that take or return value types.
Note that the difference, when there, is still quite small. I would still elect to use properties in all but the most performance critical cases.
The C# compiler won't optimize this, no - but the JIT compiler can usually inline trivial (and non-virtual) properties as far as I'm aware.
As with all performance questions though: when in doubt, test!
The effect is minor in either direction. If your properties look like this::
public static SomeType PropertyName
{
get {return MyType.propertyName;}
set {MyType.propertyName = value;}
}
There genuinely should be a very minor difference. The Jit compiler should inline the call MyType.set_Property into a field load, but even if it couldn't due to a bug. I'd personally err on the side of caution and stick with the property setters and getters as potentially the method body might change, and as a result the raw field access/mutation may not be enough.
If you'd like to test you can force the method you emit to use the MethodImpl that turns off inlining or optimizing. And then compare the difference, I really doubt it'll be significant.
ReSharper sometimes hints that I can make some of my random utility methods in my WebForms static. Why would I do this? As far as I can tell, there's no benefit in doing so.. or is there? Am I missing something as far as static members in WebForms goes?
The real reason is not the performance reason -- that will be measured in billionths of a second, if it has any effect at all.
The real reason is that an instance method which makes no use of its instance is logically a design flaw. Suppose I wrote you a method:
class C
{
public int DoubleIt(int x, string y, Type z)
{
return x * 2;
}
}
Is this a well-designed method? No. It takes all kinds of information in which it then ignores and does not use to compute the result or execute a side effect. Why force the caller to pass in an unnecessary string and type?
Now, notice that this method also takes in a C, in the form of the "this" passed into the call. That is also ignored. This method should be static, and take one parameter.
A well-designed method takes in exactly the information it needs to compute its results and execute its side effects, no more, no less. Resharper is telling you that you have a design flaw in your code: you have a method that is taking in information that it is ignoring. Either fix the method so that it starts using that information, or stop passing in useless data by making the method static.
Again, the performance concern is a total red herring; you'll never notice a difference that small unless what you're doing takes on the order of a handful of processor cycles. The reason for the warning is to call your attention to a logical design flaw. Getting the program logic right is far more important than shaving off a nanosecond here and there.
I wouldn't mind any performance improvement, but what you might like is that static methods have no side effect on the instance. So unless you're having a lot of static state (do you?) this gives away your intention that this method is similar to a function, only looking at the parameters and (optional) returning a result.
For me this is a nice hint when I read someone else's code. I don't worry too much about shared state and can see the flow of information more easily. It's much more constrained in what it can do by declaring it static, which is less to worry about for me, the reader.
You will get a performance improvement, FxCop rule CA1822 is the same.
From MSDN:
Methods that do not access instance
data or call instance methods can be
marked as static (Shared in Visual
Basic). After you mark the methods as
static, the compiler will emit
non-virtual call sites to these
members. Emitting non-virtual call
sites will prevent a check at runtime
for each call that ensures that the
current object pointer is non-null.
This can result in a measurable
performance gain for
performance-sensitive code. In some
cases, the failure to access the
current object instance represents a
correctness issue
Resharper suggest to convert methods to static if they don't use any non-static variables or methods from the class.
Benefit could be a minor performance increase (application will use less memory), and there will be one less resharper warning ;)
Do simple lambda expressions get inlined?
I have a tendency (thanks to F# and other functional forays) to encapsulate repeated code present within a single function into a lambda, and call it instead. I'm curious if I'm incurring a run-time overhead as a result:
var foo = a + b;
var bar = a + b;
vs
Func<T1, T2> op = () => a + b;
var foo = op();
var bar = op();
Which one costs more to run?
To answer the performance question: run it a billion times both ways. Measure the cost of each. Then you'll know. We have no idea what hardware you're using, what "noise" is present in your relevant scenarios, or what you consider to be an important performance metric. You're the only person who knows those things, so you're the only person who can answer the question.
To answer your codegen question: Jared is correct but the answer could be expanded upon.
First off, the C# compiler never does inlining of any code. The jit compiler does do inlining of code, but the fact that the C# compiler generates lambdas as delegate instances means that it is unlikely that the jitter can reasonably inline this code. (It is of course possible for the jitter to do this sophisticated analysis to determine that the same code is always in the delegate, but I do not believe that in practice those algorithms have been implemented.)
If you want the code to be inlined then you should write it in line. If you don't want to write it in line but you still want it inlined then you should write it as a static method and hope the jitter inlines it.
But regardless, this sounds like premature optimization. Write the code the way you want to write the code, and then analyze its performance, and then rewrite the slow stuff.
No. Lambda functions are not inlined but instead are stored as delegates under the hood and incur the same cost of execution as other delegates.