Dependency Injection using ILEmit is generating additional MSIL nop operations in the DynamicMethod

Description

When inspecting MSIL code generated by Dependency Injection dynamic compilation using ILEmit, everytime there is a ldloca.s instruction, 3 nop operations are also generated.

Configuration

Which version of .NET is the code running on? .NET Framework 4.62
What OS and version, and what distro if applicable? Windows 11 (22000.194)
What is the architecture (x64, x86, ARM, ARM64)? x64

Other information

To reproduce the issue, compile Microsoft.Extensions.DependencyInjection using SAVE_ASSEMBLIES symbol. Then run ServiceProviderILEmitContainerTests.ScopedServiceCanBeResolved and inspect MSIL code in artifacts\bin\Microsoft.Extensions.DependencyInjection.Tests\net462-*\Test*.dll

  [...]
  IL_0047: ldloc.2      // sync
  IL_0048: ldloca.s     lockTaken
  IL_004a: nop
  IL_004b: nop
  IL_004c: nop
  IL_004d: call         void [mscorlib]System.Threading.Monitor::Enter(object, bool&)

  IL_0052: ldloc.1      // resolvedServices
  IL_0053: ldloc.0      // key
  IL_0054: ldloca.s     service
  IL_0056: nop
  IL_0057: nop
  IL_0058: nop
  IL_0059: callvirt     instance bool class [mscorlib]System.Collections.Generic.IDictionary`2<valuetype [Microsoft.Extensions.DependencyInjection]Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceCacheKey, object>::TryGetValue(!0/*valuetype [Microsoft.Extensions.DependencyInjection]Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceCacheKey*/, !1/*object*/&)
  IL_005e: brtrue       IL_007c
  [...]

The ldloca.s instruction expects an 1 byte argument (byte), while we are providing a 4 bytes argument (lockTakenLocal.LocalIndex and resultLocal.LocalIndex are int).

runtime/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/ILEmit/ILEmitResolverBuilder.cs

Lines 357 to 366 in dff742a

    
           context.Generator.Emit(OpCodes.Ldloca_S, lockTakenLocal.LocalIndex); 
        
           // Monitor.Enter 
        
           context.Generator.Emit(OpCodes.Call, ServiceLookupHelpers.MonitorEnterMethodInfo); 
        
           // Load resolved services 
        
           Ldloc(context.Generator, resolvedServicesLocal.LocalIndex); 
        
           // Load cache key 
        
           Ldloc(context.Generator, cacheKeyLocal.LocalIndex); 
        
           // Load address of result local 
        
           context.Generator.Emit(OpCodes.Ldloca_S, resultLocal.LocalIndex);

As per documentation, in the remarks section:

If the opcode parameter requires an argument, the caller must ensure that the argument length matches the length of the declared parameter. Otherwise, results will be unpredictable. For example, if the Emit instruction requires a 2-byte operand and the caller supplies a 4-byte operand, the runtime will emit two additional bytes to the instruction stream. These extra bytes will be Nop instructions.

Using optimized ILGenerator.Emit function in Dependency Injection

Using optimized ILGenerator.Emit function in Dependency Injection (#5…

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Dependency Injection using ILEmit is generating additional MSIL nop operations in the DynamicMethod #59624

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	context.Generator.Emit(OpCodes.Ldloca_S, lockTakenLocal.LocalIndex);
	// Monitor.Enter
	context.Generator.Emit(OpCodes.Call, ServiceLookupHelpers.MonitorEnterMethodInfo);

	// Load resolved services
	Ldloc(context.Generator, resolvedServicesLocal.LocalIndex);
	// Load cache key
	Ldloc(context.Generator, cacheKeyLocal.LocalIndex);
	// Load address of result local
	context.Generator.Emit(OpCodes.Ldloca_S, resultLocal.LocalIndex);

Dependency Injection using ILEmit is generating additional MSIL nop operations in the DynamicMethod #59624

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allantargino commented on Sep 26, 2021

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