Rely on PGO for isinst/castclass

[EgorBo]

Follow up to #65460 (and d-o)

Example (with DOTNET_JitCastProfiling=1):

usingSystem.Runtime.CompilerServices;usingSystem.Threading;publicinterfaceIClass{}publicclassClassA:IClass{}publicclassClassB:ClassA{}publicclassProgram{[MethodImpl(MethodImplOptions.NoInlining)]staticClassACastToClassA(objecto)=>(ClassA)o;// currently we always emit a fast path for ClassA here// but in my case o is always ClassB (PGO helps)[MethodImpl(MethodImplOptions.NoInlining)]staticboolIsClassA(objecto)=>oisClassA;// we don't expand it without PGO[MethodImpl(MethodImplOptions.NoInlining)]staticIClassCastToIClass(objecto)=>(IClass)o;// we don't expand it without PGO[MethodImpl(MethodImplOptions.NoInlining)]staticboolIsIClass(objecto)=>oisIClass;// we don't expand it without PGOpublicstaticvoidMain(){// promote methods to tier1varb=newClassB();for(inti=0;i<100;i++){CastToClassA(b);IsClassA(b);CastToIClass(b);IsIClass(b);Thread.Sleep(16);}}}

Codegen diff: https://www.diffchecker.com/RFblv9RB

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Issue Details

---

Follow up to #65460

Example (with DOTNET_JitCastProfiling=1):

usingSystem.Runtime.CompilerServices;usingSystem.Threading;publicinterfaceIClass{}publicclassClassA:IClass{}publicclassClassB:ClassA{}publicclassProgram{[MethodImpl(MethodImplOptions.NoInlining)]staticClassACastToClassA(objecto)=>(ClassA)o;[MethodImpl(MethodImplOptions.NoInlining)]staticboolIsClassA(objecto)=>oisClassA;[MethodImpl(MethodImplOptions.NoInlining)]staticIClassCastToIClass(objecto)=>(IClass)o;[MethodImpl(MethodImplOptions.NoInlining)]staticboolIsIClass(objecto)=>oisIClass;publicstaticvoidMain(){// promote methods to tier1varb=newClassB();for(inti=0;i<100;i++){CastToClassA(b);IsClassA(b);CastToIClass(b);IsIClass(b);Thread.Sleep(16);}}}

Codegen diff: https://www.diffchecker.com/RFblv9RB

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

[EgorBo]

@AndyAyersMS@jakobbotsch PTAL

This PR consumes profile data from mibc for casts/isinst. I guarded it with DOTNET_JitConsumeProfileForCasts just to wait till dotnet-optimization properly propagates mibc with casts/isinst.

Also, I added "random class" stress mode support for it

[EgorBo]

@AndyAyersMS@jakobbotsch PTAL

[jakobbotsch]

Should this rather get its own config variable?

[EgorBo]

Just didn't want to produce even more variables 😄 and the default value for this one was OK to me.
in my other PR to add "multiple guesses" I slightly changed the whole logic so I'll leave it as is for now