GDV: don't emit fallback call if classes are "exact"

[EgorBo]

Contributes to #86769 and closes#86235

usingSystem;usingSystem.Runtime.CompilerServices;usingSystem.Threading;publicinterfaceIAnimal{voidMakeSound();}publicclassCat:IAnimal{publicvoidMakeSound()=>Console.WriteLine("Meow!");}publicclassDog:IAnimal{publicvoidMakeSound()=>Console.WriteLine("Woof!");}publicclassCow:IAnimal{publicvoidMakeSound()=>Console.WriteLine("Moo!");}// This class is not used and will be trimmed outpublicclassLion:IAnimal{publicvoidMakeSound()=>Console.WriteLine("Roar!");}publicclassProgram{publicstaticvoidMain(string[]args){Test(newCat());Test(newDog());Test(newCow());}[MethodImpl(MethodImplOptions.NoInlining)]staticvoidTest(IAnimala)=>a.MakeSound();}

NativeAOT codegen for Test:

; Method Program:Test(IAnimal)subrsp,40learax,[(reloc 0x4000000000423000)]cmp qword ptr [rcx],rax ;; is it 'Cat'?jne SHORT G_M31564_IG04learcx, gword ptr [(reloc 0x4000000000423028)] ;; '"Meow!"'call System.Console:WriteLine(System.String)jmp SHORT G_M31564_IG07G_M31564_IG04:learax,[(reloc 0x4000000000423010)]cmp qword ptr [rcx],rax ;; is it 'Dog'?jne SHORT G_M31564_IG06learcx, gword ptr [(reloc 0x4000000000422f98)] ;; '"Woof!"'call System.Console:WriteLine(System.String)jmp SHORT G_M31564_IG07G_M31564_IG06:learcx, gword ptr [(reloc 0x4000000000422f70)] ;; '"Moo!"'call System.Console:WriteLine(System.String)G_M31564_IG07:nopaddrsp,40ret; Total bytes of code: 74

Virtual callback is not emitted since we took care of all possible classes implementing the given interface ("closed world" on NativeAOT). We might still emit it if we e.g. fail to inline one of the candidates (we currently don't do GDV just to devirtualize a call, we only do that when we're able to inline it) -- we might want to do that for cases where interface calls are expensive but that's a different task in #86769

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Issue Details

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usingSystem;usingSystem.Runtime.CompilerServices;usingSystem.Threading;publicinterfaceIAnimal{voidMakeSound();}publicclassCat:IAnimal{publicvoidMakeSound()=>Console.WriteLine("Meow!");}publicclassDog:IAnimal{publicvoidMakeSound()=>Console.WriteLine("Woof!");}publicclassCow:IAnimal{publicvoidMakeSound()=>Console.WriteLine("Moo!");}publicclassProgram{publicstaticvoidMain(string[]args){Test(newCat());Test(newDog());Test(newCow());}[MethodImpl(MethodImplOptions.NoInlining)]staticvoidTest(IAnimala)=>a.MakeSound();}

NativeAOT codegen for Test:

; Method Program:Test(IAnimal)subrsp,40learax,[(reloc 0x4000000000423000)]cmp qword ptr [rcx],rax ;; is it 'Cat'?jne SHORT G_M31564_IG04learcx, gword ptr [(reloc 0x4000000000423028)] ;; '"Meow!"'call System.Console:WriteLine(System.String)jmp SHORT G_M31564_IG07G_M31564_IG04: ;; offset=001EHlearax,[(reloc 0x4000000000423010)]cmp qword ptr [rcx],rax ;; is it 'Dog'?jne SHORT G_M31564_IG06learcx, gword ptr [(reloc 0x4000000000422f98)] ;; '"Woof!"'call System.Console:WriteLine(System.String)jmp SHORT G_M31564_IG07G_M31564_IG06: ;; offset=0038Hlearcx, gword ptr [(reloc 0x4000000000422f70)] ;; '"Moo!"'call System.Console:WriteLine(System.String)G_M31564_IG07: ;; offset=0044Hnopaddrsp,40ret; Total bytes of code: 74

Virtual callback is not emitted since we took care of all possible classes implementing the given interface ("closed world" on NativeAOT). We might still emit it if we e.g. fail to inline one of the candidates (we currently don't do GDV just to devirtualize a call, we only do that when we're able to inline it).

Author:	EgorBo
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[EgorBo]

For reference, codegen for JIT:

staticvoidMain(){for(inti=0;i<200;i++){Test(newCat());Test(newDog());Test(newCow());Thread.Sleep(16);}}[MethodImpl(MethodImplOptions.NoInlining)]staticvoidTest(IAnimala)=>a.MakeSound();

; Assembly listing for method Program:Test(IAnimal)pushrsisubrsp,32movrsi, qword ptr [rcx]movrax,0x7FFF53C41C88 ; Catcmprsi,raxjne SHORT G_M31564_IG04movrcx,0x26780208F80 ; 'Meow!'call[System.Console:WriteLine(System.String)]jmp SHORT G_M31564_IG07G_M31564_IG04:movrax,0x7FFF53C41E48 ; Dogcmprsi,raxjne SHORT G_M31564_IG06movrcx,0x26780209128 ; 'Woof!'call[System.Console:WriteLine(System.String)]jmp SHORT G_M31564_IG07G_M31564_IG06:movrax,0x7FFF53C42008 ; Cowcmprsi,raxjne SHORT G_M31564_IG09movrcx,0x26780209148 ; 'Moo!'call[System.Console:WriteLine(System.String)]G_M31564_IG07:nopaddrsp,32poprsiretG_M31564_IG09:movr11,0x7FFF53130280call[r11]IAnimal:MakeSound():thisjmp SHORT G_M31564_IG07

(PGO-driven)

[EgorBo]

/azp run runtime-extra-platforms, runtime-coreclr pgo

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[EgorBo]

/azp run runtime-extra-platforms

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[EgorBo]

/azp run runtime-extra-platforms

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[EgorBo]

/azp run runtime-extra-platforms

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[EgorBo]

/azp run runtime-extra-platforms

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[EgorBo]

/azp run runtime-extra-platforms

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[EgorBo]

/azp run runtime-extra-platforms

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[EgorBo]

@AndyAyersMS PTAL, it passes NativeAOT outerloop tests + 3 type checks

[EgorBo]

This is an unrelated change, it's just that I used a wrong check in #86965 so it didn't work properly