Why is this code not verified?

Question

I have a compiler that builds and works correctly, but PEVerify calls it unverifiable at some point. After carefully examining the error, the corresponding source code and ILDasm output for the point in question, I cannot find the problem to the extent that I could suspect the error in PEVerify, except that the versions of .NET and Mono report the same error in same place.

The problematic method reads as follows:

internal static bool InAsyncMethod(Expression value)
{
    INodeWithBody ancestor = value.GetAncestor<BlockExpression>() ?? (INodeWithBody) value.GetAncestor<Method>();
    return ContextAnnotations.IsAsync(ancestor);
}

The error is reported as:

[IL]: Error: [D: \ SDL-1.3.0-4423 \ boo \ build \ Boo.Lang.Compiler.dll: Boo.Lang.Compiler.TypeSystem.AsyncHelper :: InAsyncMethod] [offset 0x00000011] [found ref 'Boo.Lang.Compiler.Ast.Node'] [expected ref Boo.Lang.Compiler.Ast.INodeWithBody '] Unexpected type on the stack.

Offsest 0x11 ??. ILDasm:

.method assembly hidebysig static bool  InAsyncMethod(class Boo.Lang.Compiler.Ast.Expression 'value') cil managed
{
  // Code size       29 (0x1d)
  .maxstack  2
  .locals init ([0] class Boo.Lang.Compiler.Ast.INodeWithBody ancestor,
           [1] bool CS$1$0000)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  callvirt   instance !!0 Boo.Lang.Compiler.Ast.Node::GetAncestor<class Boo.Lang.Compiler.Ast.BlockExpression>()
  IL_0007:  dup
  IL_0008:  brtrue.s   IL_0011
  IL_000a:  pop
  IL_000b:  ldarg.0
  IL_000c:  callvirt   instance !!0 Boo.Lang.Compiler.Ast.Node::GetAncestor<class Boo.Lang.Compiler.Ast.Method>()
  IL_0011:  stloc.0
  IL_0012:  ldloc.0
  IL_0013:  call       bool Boo.Lang.Compiler.Steps.ContextAnnotations::IsAsync(class Boo.Lang.Compiler.Ast.INodeWithBody)
  IL_0018:  stloc.1
  IL_0019:  br.s       IL_001b
  IL_001b:  ldloc.1
  IL_001c:  ret
} // end of method AsyncHelper::InAsyncMethod

Boo.Lang.Compiler.Ast.Node AST. BlockExpression Method node lambdas , , INodeWithBody. , # ( , ), IL ( 000c, GetAncestor<Method> !!0), .)

PEVerify , Node , Method? ?

Answer 1

PEVerify , Node , Method?

, , IL_0011, . Method.

GetAncestor<TAncestor> TAncestor. GetAncestor<BlockExpression> GetAncestor<Method>, BlockExpression, Method. INodeWithBody, - .

, " BlockExpression, Method" . Node ( ), INodeWithBody. . ECMA-335 §III.1.8.1.3:

U (, S := T - , III.1.8.1.2.2):

• if S := T, U=S

• , T := S, U=T

• , S T - , V S T, U=V.

• .

, #, , stloc.0/ldloc.0 INodeWithBody dup. , INodeWithBody Method INodeWithBody.

Answer 2

, 0x11 - ??, 0x08 .

GetAncestor<> a Node, ?? .