.NET9 Pre3 CLR的优化细节

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发布于 2024-04-18 20:10:38

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发布于 2024-04-18 20:10:38

文章被收录于专栏：天下风云天下风云

前言

上一篇:.NET9 Pre3 CLR的改进，讲了下.NET9 Pre3的CLR改进，第二个改进点即是内联。本篇详细看下，略有繁芜。

内联

Pre3里面，哪些代码可以内联优化呢?诸如以下这种：

typeof(T) == obj.GetType()
typeof(T) == typeof(T)
typeof(T) == null
obj1.GetType() == obj2.GetType()

比如其中的typeof，如果出现以下代码：

public static bool Callee<T>() => typeof(T) == typeof(int);

.NET9 Pre3之前呢？typeof函数它实际上是调用了System.Type.GetTypeFromHandle获取到类型，通过System.Type.op_Equality进行类型比较。则比较麻烦。

这里的优化是在JIT层面进行的，如果JIT检测到GetTypeFromHandle和op_Equality标记了Intrincis，则在JIT构建IR的时候，就把这个结果判断出来。

Importing BB01 (PC=000) of 'ConsoleApp3.Program:Callee[int]():ubyte'
    [ 0]   0 (0x000) ldtoken
    [ 1]   5 (0x005) call 0A00000E
In Compiler::impImportCall: opcode is call, kind=0, callRetType is ref, structSize is 0
Named Intrinsic System.Type.GetTypeFromHandle: Recognized

    [ 1]  10 (0x00a) ldtoken
    [ 2]  15 (0x00f) call 0A00000E
In Compiler::impImportCall: opcode is call, kind=0, callRetType is ref, structSize is 0
Named Intrinsic System.Type.GetTypeFromHandle: Recognized

    [ 2]  20 (0x014) call 0A00000F
In Compiler::impImportCall: opcode is call, kind=0, callRetType is ubyte, structSize is 0
Named Intrinsic System.Type.op_Equality: Recognized
Importing Type.op_*Equality intrinsic

Folding call to Type:op_Equality to a simple compare via EQ
Optimizing compare of types-from-handles to instead compare handles
Asking runtime to compare 00007FF89EF9FC30 (System.Int32) and 00007FF89EF9FC30 (System.Int32) for equality
Runtime reports comparison is known at jit time: 0

    [ 1]  25 (0x019) ret

STMT00000 ( 0x000[E-] ... ??? )
               [000008] -----------                         *  RETURN    int
               [000007] -----------                         \--*  CNS_INT   int    1

上面很清晰的看到在JIT Compile的时候就已经判断出了返回的值是0(false)。JIT判断代码：

const bool typesAreEqual = (s == TypeCompareState::Must);
const bool operatorIsEQ  = (oper == GT_EQ);
const int  compareResult = operatorIsEQ ^ typesAreEqual ? 0 : 1;
JITDUMP("Runtime reports comparison is known at jit time: %u\n", compareResult);
GenTree* result = gtNewIconNode(compareResult);                
return result;

减少IR的代码，即如果泛型T与int同类型，则返回true,否则false。而不需要等到JIT生成机器码的时候，生成繁杂的GetTypeFromHandle和op_Equality机器码。

push    rbp
mov     rbp,rsp
mov     eax,1 //类型相同为1,不同为0
pop     rbp
ret

未优化前的：

ConsoleApp3.dll!ConsoleApp3.Program.Callee<T>():
//此处省略，便于观看
00007FF8BCAE22C3 FF 15 07 2C F4 FF    call        qword ptr [System.Type.GetTypeFromHandle(System.RuntimeTypeHandle)+08h (07FF8BCA24ED0h)]  
00007FF8BCAE22C9 48 89 45 E8          mov         qword ptr [rbp-18h],rax  
00007FF8BCAE22CD 48 B9 88 11 A5 BC F8 7F 00 00 mov         rcx,7FF8BCA51188h  
00007FF8BCAE22D7 E8 24 14 AE 5F       call        00007FF91C5C3700  
00007FF8BCAE22DC 48 89 45 E0          mov         qword ptr [rbp-20h],rax  
00007FF8BCAE22E0 48 8B 4D E0          mov         rcx,qword ptr [rbp-20h]  
00007FF8BCAE22E4 FF 15 E6 2B F4 FF    call        qword ptr [System.Type.GetTypeFromHandle(System.RuntimeTypeHandle)+08h (07FF8BCA24ED0h)]  
00007FF8BCAE22EA 48 89 45 D8          mov         qword ptr [rbp-28h],rax  
00007FF8BCAE22EE 48 8B 4D E8          mov         rcx,qword ptr [rbp-18h]  
00007FF8BCAE22F2 48 8B 55 D8          mov         rdx,qword ptr [rbp-28h]  
00007FF8BCAE22F6 FF 15 84 3C F4 FF    call        qword ptr [System.Type.op_Equality(System.Type, System.Type)+08h (07FF8BCA25F80h)]  
//此处省略，便于观看
00007FF8BCAE230B C3                   ret

未优化前，即使是删除了部分代码，依然是比较繁杂。

代码

代码(注意观察需要在Debug模式下开启Debuggable特性,也可以C# Code Relase放到CLR里面)，参考:.NET9极致性能CLR操控MSIL(分层编译)。

可以加特性[assembly: Debuggable(DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints)]
或者dotnet build -c relase 
namespace ConsoleApp3
{
    public class Program
    {
        public static bool Test<T>() => Callee<T>();
        public static bool Callee<T>() => typeof(T) == typeof(int);
        static void Main(string[] args)
        {
            Test<int>();
            Console.ReadLine();
        }
    }
}

原理

通过pMethod->GetMethodSignature().GetToken()获取方法Token
获取到System.Runtime.CompilerServices.IntrinsicAttribute这个特性
通过Token获取到CustomAttribute的IL表里面的Parent字段值，如果相等则表示Intrincis被设置了。此时就可以进行内联优化了。GetTypeFromHandle和op_Equality函数皆是如此。

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原始发表：2024-04-15，如有侵权请联系?cloudcommunity@tencent.com 删除

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