Fix incorrect devirtualization in CG2 #37370
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When making a constrained virtual method call on a boxed value type, CG2 devirtualizes the call incorrectly resulting in a direct call. This breaks code patterns like:
```
foreach (TestEnum val in Enum.GetValues(typeof(TestEnum)))
{
buffer += val.ToString();
}
```
In the call to ToString(), `getCallInfo` is passed a boxed `TestEnum` and is calling `object.ToString()`. The constrained type is `TestEnum` so we end up making a direct call to `object.ToString()`. Fixed by removing the constrained type from devirtualization consideration which is how Crossgen treats this call.
MichalStrehovsky
approved these changes
Jun 4, 2020
| @@ -1301,7 +1301,7 @@ private void getFieldInfo(ref CORINFO_RESOLVED_TOKEN pResolvedToken, CORINFO_MET | |||
| // | |||
| // Note that it is safe to devirtualize in the following cases, since a servicing event cannot later modify it | |||
| // 1) Callvirt on a virtual final method of a value type - since value types are sealed types as per ECMA spec | |||
| devirt = (constrainedType ?? targetMethod.OwningType).IsValueType || targetMethod.IsInternalCall; | |||
| devirt = targetMethod.OwningType.IsValueType || targetMethod.IsInternalCall; | |||
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Btw, this code is still different from what crossgen does - the comment above ends at 1), but the VM side special cases 3 things - this seems to be missing an optimization around Delegate.Invoke - we probably generate less efficient code for that as a result.
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I added the two other cases (delegates and intrinsics) so we line with up with CG1
Ensure our devirtualization matches crossgen1's behavior. We were not devirtualizing delegate invoke calls, and we were devirtualizing all internal calls (not just JIT intrinsics) which is not necessarily version resilient.
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When making a constrained virtual method call on a boxed value type, CG2 devirtualizes the call incorrectly resulting in a direct call. This breaks code patterns like:
In the call to ToString(),
getCallInfois passed a boxedTestEnumand is callingobject.ToString(). The constrained type isTestEnumso we end up making a direct call toobject.ToString(). Fixed by removing the constrained type from devirtualization consideration which is how Crossgen treats this call.cc @dotnet/crossgen-contrib