JIT: inliner throw with invalid stack check is questionable

[AndyAyersMS]

The JIT won't inline a method with a throw if there are multiple entries on the eval stack at the throw. So a method like:

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    int F(int y)
    {
        int result = x;
        if (y == 33) throw new Exception();
        return result;
    }

won't inline because CSC pends x to the stack before the throw:

  IL_0000:  ldarg.0
  IL_0001:  ldfld      int32 P::x
  IL_0006:  ldarg.1
  IL_0007:  ldc.i4.s   33
  IL_0009:  bne.un.s   IL_0011
  IL_000b:  newobj     instance void [System.Private.CoreLib]System.Exception::.ctor()
  IL_0010:  throw
  IL_0011:  ret

Inlines into 06000004 P:Main():int
  [0 IL=0000 TR=000001 06000003] [FAILED: noinline per IL/cached result] P:M():ref
  [0 IL=0011 TR=000014 06000002] [FAILED: throw with invalid stack] P:F(int):int:this

ECMA-335's only requirement for throw is that the top of stack be an object reference. Seems like this is an unnecessary restriction in the JIT.

category:cq
theme:inlining
skill-level:intermediate
cost:small

[AndyAyersMS]

Fixed via #2232.