Generated IL differences for VB.NET and C#
Today I was playing around with Entity Framework and I've read that the generated IL for C# was different than VB.NET for the following code:
VB.NET:
Dim ctx As New TravelEntities
Sub Main()
CallContext()
CallContext()
CallContext()
End Sub
Private Sub CallContext()
Dim someCustomer = From x In ctx.Customer
Where x.CustomerId.Equals(5)
Select x
Console.WriteLine(someCustomer.Count())
End Sub
C#:
private static TravelEntities ctx = new TravelEntities();
static void Main(string[] args)
{
CallContext();
CallContext();
CallContext();
}
private static void CallContext()
{
var someCustomer = from x in ctx.Customer
where x.CustomerId.Equals(5)
select x;
Console.WriteLine(someCustomer.Count());
}
They produce the following IL:
VB:
.method private static void CallContext() cil managed
{
// Code size 195 (0xc3)
.maxstack 7
.locals init ([0] class [System.Core]System.Linq.IQueryable`1<class VB_IL_Difference.Customer> someCustomer,
[1] class [System.Core]System.Linq.Expressions.ParameterExpression VB$t_ref$S0,
[2] class [System.Core]System.Linq.Expressions.Expression[] VB$t_array$S0,
[3] class [System.Core]System.Linq.Expressions.ParameterExpression[] VB$t_array$S1,
[4] class [System.Core]System.Linq.Expressions.ParameterExpression VB$t_ref$S1,
[5] class [System.Core]System.Linq.Expressions.ParameterExpression[] VB$t_array$S2)
IL_0000: nop
IL_0001: ldsfld class VB_IL_Difference.TravelEntities VB_IL_Difference.Module1::ctx
IL_0006: callvirt instance class [System.Data.Entity]System.Data.Objects.ObjectSet`1<class VB_IL_Difference.Customer> VB_IL_Difference.TravelEntities::get_Customer()
IL_000b: ldtoken VB_IL_Difference.Customer
IL_0010: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_0015: ldstr "x"
IL_001a: call class [System.Core]System.Linq.Expressions.ParameterExpression [System.Core]System.Linq.Expressions.Expression::Parameter(class [mscorlib]System.Type,
string)
IL_001f: stloc.1
IL_0020: ldloc.1
IL_0021: ldtoken method instance int32 VB_IL_Difference.Customer::get_CustomerId()
IL_0026: call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle(valuetype [mscorlib]System.RuntimeMethodHandle)
IL_002b: castclass [mscorlib]System.Reflection.MethodInfo
IL_0030: call class [System.Core]System.Linq.Expressions.MemberExpression [System.Core]System.Linq.Expressions.Expression::Property(class [System.Core]System.Linq.Expressions.Expression,
class [mscorlib]System.Reflection.MethodInfo)
IL_0035: ldtoken method instance bool [mscorlib]System.Int32::Equals(int32)
IL_003a: call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle(valuetype [mscorlib]System.RuntimeMethodHandle)
IL_003f: castclass [mscorlib]System.Reflection.MethodInfo
IL_0044: ldc.i4.1
IL_0045: newarr [System.Core]System.Linq.Expressions.Expression
IL_004a: stloc.2
IL_004b: ldloc.2
IL_004c: ldc.i4.0
IL_004d: ldc.i4.5
IL_004e: box [mscorlib]System.Int32
IL_0053: ldtoken [mscorlib]System.Int32
IL_0058: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_005d: call class [System.Core]System.Linq.Expressions.ConstantExpression [System.Core]System.Linq.Expressions.Expression::Constant(object,
class [mscorlib]System.Type)
IL_0062: stelem.ref
IL_0063: nop
IL_0064: ldloc.2
IL_0065: call class [System.Core]System.Linq.Expressions.MethodCallExpression [System.Core]System.Linq.Expressions.Expression::Call(class [System.Core]System.Linq.Expressions.Expression,
class [mscorlib]System.Reflection.MethodInfo,
class [System.Core]System.Linq.Expressions.Expression[])
IL_006a: ldc.i4.1
IL_006b: newarr [System.Core]System.Linq.Expressions.ParameterExpression
IL_0070: stloc.3
IL_0071: ldloc.3
IL_0072: ldc.i4.0
IL_0073: ldloc.1
IL_0074: stelem.ref
IL_0075: nop
IL_0076: ldloc.3
IL_0077: call class [System.Core]System.Linq.Expressions.Expression`1<!!0> [System.Core]System.Linq.Expressions.Expression::Lambda<class [mscorlib]System.Func`2<class VB_IL_Difference.Customer,bool>>(class [System.Core]System.Linq.Expressions.Expression,
class [System.Core]System.Linq.Expressions.ParameterExpression[])
IL_007c: call class [System.Core]System.Linq.IQueryable`1<!!0> [System.Core]System.Linq.Queryable::Where<class VB_IL_Difference.Customer>(class [System.Core]System.Linq.IQueryable`1<!!0>,
class [System.Core]System.Linq.Expressions.Expression`1<class [mscorlib]System.Func`2<!!0,bool>>)
IL_0081: ldtoken VB_IL_Difference.Customer
IL_0086: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_008b: ldstr "x"
IL_0090: call class [System.Core]System.Linq.Expressions.ParameterExpression [System.Core]System.Linq.Expressions.Expression::Parameter(class [mscorlib]System.Type,
string)
IL_0095: stloc.s VB$t_ref$S1
IL_0097: ldloc.s VB$t_ref$S1
IL_0099: ldc.i4.1
IL_009a: newarr [System.Core]System.Linq.Expressions.ParameterExpression
IL_009f: stloc.s VB$t_array$S2
IL_00a1: ldloc.s VB$t_array$S2
IL_00a3: ldc.i4.0
IL_00a4: ldloc.s VB$t_ref$S1
IL_00a6: stelem.ref
IL_00a7: nop
IL_00a8: ldloc.s VB$t_array$S2
IL_00aa: call class [System.Core]System.Linq.Expressions.Expression`1<!!0> [System.Core]System.Linq.Expressions.Expression::Lambda<class [mscorlib]System.Func`2<class VB_IL_Difference.Customer,class VB_IL_Difference.Customer>>(class [System.Core]System.Linq.Expressions.Expression,
class [System.Core]System.Linq.Expressions.ParameterExpression[])
IL_00af: call class [System.Core]System.Linq.IQueryable`1<!!1> [System.Core]System.Linq.Queryable::Select<class VB_IL_Difference.Customer,class VB_IL_Difference.Customer>(class [System.Core]System.Linq.IQueryable`1<!!0>,
class [System.Core]System.Linq.Expressions.Expression`1<class [mscorlib]System.Func`2<!!0,!!1>>)
IL_00b4: stloc.0
IL_00b5: ldloc.0
IL_00b6: call int32 [System.Core]System.Linq.Queryable::Count<class VB_IL_Difference.Customer>(class [System.Core]System.Linq.IQueryable`1<!!0>)
IL_00bb: call void [mscorlib]System.Console::WriteLine(int32)
IL_00c0: nop
IL_00c1: nop
IL_00c2: ret
} // end of method Module1::CallContext
C#:
.method private hidebysig static void CallContext() cil managed
{
// Code size 141 (0x8d)
.maxstack 7
.locals init ([0] class [System.Core]System.Linq.IQueryable`1<class C_IL_Difference.Customer> someCustomer,
[1] class [System.Core]System.Linq.Expressions.ParameterExpression CS$0$0000,
[2] class [System.Core]System.Linq.Expressions.Expression[] CS$0$0001,
[3] class [System.Core]System.Linq.Expressions.ParameterExpression[] CS$0$0002)
IL_0000: nop
IL_0001: ldsfld class C_IL_Difference.TravelEntities C_IL_Difference.Program::ctx
IL_0006: callvirt instance class [System.Data.Entity]System.Data.Objects.ObjectSet`1<class C_IL_Difference.Customer> C_IL_Difference.TravelEntities::get_Customer()
IL_000b: ldtoken C_IL_Difference.Customer
IL_0010: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_0015: ldstr "x"
IL_001a: call class [System.Core]System.Linq.Expressions.ParameterExpression [System.Core]System.Linq.Expressions.Expression::Parameter(class [mscorlib]System.Type,
string)
IL_001f: stloc.1
IL_0020: ldloc.1
IL_0021: ldtoken method instance int32 C_IL_Difference.Customer::get_CustomerId()
IL_0026: call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle(valuetype [mscorlib]System.RuntimeMethodHandle)
IL_002b: castclass [mscorlib]System.Reflection.MethodInfo
IL_0030: call class [System.Core]System.Linq.Expressions.MemberExpression [System.Core]System.Linq.Expressions.Expression::Property(class [System.Core]System.Linq.Expressions.Expression,
class [mscorlib]System.Reflection.MethodInfo)
IL_0035: ldtoken method instance bool [mscorlib]System.Int32::Equals(int32)
IL_003a: call class [mscorlib]System.Reflection.MethodBase [mscorlib]System.Reflection.MethodBase::GetMethodFromHandle(valuetype [mscorlib]System.RuntimeMethodHandle)
IL_003f: castclass [mscorlib]System.Reflection.MethodInfo
IL_0044: l开发者_JS百科dc.i4.1
IL_0045: newarr [System.Core]System.Linq.Expressions.Expression
IL_004a: stloc.2
IL_004b: ldloc.2
IL_004c: ldc.i4.0
IL_004d: ldc.i4.5
IL_004e: box [mscorlib]System.Int32
IL_0053: ldtoken [mscorlib]System.Int32
IL_0058: call class [mscorlib]System.Type [mscorlib]System.Type::GetTypeFromHandle(valuetype [mscorlib]System.RuntimeTypeHandle)
IL_005d: call class [System.Core]System.Linq.Expressions.ConstantExpression [System.Core]System.Linq.Expressions.Expression::Constant(object,
class [mscorlib]System.Type)
IL_0062: stelem.ref
IL_0063: ldloc.2
IL_0064: call class [System.Core]System.Linq.Expressions.MethodCallExpression [System.Core]System.Linq.Expressions.Expression::Call(class [System.Core]System.Linq.Expressions.Expression,
class [mscorlib]System.Reflection.MethodInfo,
class [System.Core]System.Linq.Expressions.Expression[])
IL_0069: ldc.i4.1
IL_006a: newarr [System.Core]System.Linq.Expressions.ParameterExpression
IL_006f: stloc.3
IL_0070: ldloc.3
IL_0071: ldc.i4.0
IL_0072: ldloc.1
IL_0073: stelem.ref
IL_0074: ldloc.3
IL_0075: call class [System.Core]System.Linq.Expressions.Expression`1<!!0> [System.Core]System.Linq.Expressions.Expression::Lambda<class [mscorlib]System.Func`2<class C_IL_Difference.Customer,bool>>(class [System.Core]System.Linq.Expressions.Expression,
class [System.Core]System.Linq.Expressions.ParameterExpression[])
IL_007a: call class [System.Core]System.Linq.IQueryable`1<!!0> [System.Core]System.Linq.Queryable::Where<class C_IL_Difference.Customer>(class [System.Core]System.Linq.IQueryable`1<!!0>,
class [System.Core]System.Linq.Expressions.Expression`1<class [mscorlib]System.Func`2<!!0,bool>>)
IL_007f: stloc.0
IL_0080: ldloc.0
IL_0081: call int32 [System.Core]System.Linq.Queryable::Count<class C_IL_Difference.Customer>(class [System.Core]System.Linq.IQueryable`1<!!0>)
IL_0086: call void [mscorlib]System.Console::WriteLine(int32)
IL_008b: nop
IL_008c: ret
} // end of method Program::CallContext
As it seems the VB.NET version of this code will contact the database every time the code is executed while the C# version will retrieve the entities from the cache when the code is executed multiple times.
Why would they make both languages behave in such a different manner? It was my misconception that both languages just differed in syntax and had almost exactly the same generated IL.
Are there any more examples where both languages generated such different IL?
Part of the differences you are seeing may be due to calling the end Select x. Since it is not required in the VB query syntax but you are explicitly declaring it, VB includes it in the compilation. You could have stated the VB syntax as follows just as easily:
Dim someCustomer = From x In ctx.Customer
Where x.CustomerId.Equals(5)
Since C# requires the essentially no-oped Select clause at compile time, the compiler optimizes it out in the generated IL.
I suspect in this example, you would see greater differences between the generated expression trees between VB and C# if you used CustomerName =(=) "Foo" because C# and VB have very different handling of string equality. I've seen quite a few LINQ providers (including LINQ to Bing, LINQ to Twitter, EF Sample Query Provider, NOrm) that fail to evaute CustomerName = "Foo" in VB because they only tested their expression tree parsing in C#.
As for your claim that C# caches the results, I'm not seeing that using the following code against Northwind (using LinqPad). It is still calling the database 3 times.
void Main()
{
CallContext();
CallContext();
CallContext();
}
private void CallContext()
{
var someCustomer = from x in Customers
where x.CustomerID.Equals("ALFKI")
select x;
Console.WriteLine(someCustomer.Count());
}
Both the code will call the database each time the CallContext method is called. The difference just in the expression tree generated for the LINQ expression, which in this case is not much of a difference.
As you said in your comment that now you have used LINQ method chaining rather than LINQ syntax, that's why now the generated expression tree will be same.
加载中,请稍侯......
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