[jogibear9988]

Conversions from Enum or interface references to nullable value types can return incorrect values or mishandle null. Classify the reference conversion using the underlying target type and emit unbox.any for the complete target type.

Parameters and constants; null, matching and incompatible boxed values; checked and unchecked conversions across object, ValueType, Enum and interfaces. Regressions use strict FEC compilation for both Standard and LightExpression.

Validation

Release solution build: zero warnings/errors.

Runtime	TestX groups	Legacy tests
.NET 10	445 passed	1,756 passed
.NET 8	445 passed	1,755 passed
.NET Framework 4.7.2	424 passed	1,639 passed

Measurements

Current master f1d2fb33 → this change, Release, Windows ARM64, .NET 8.0.28 / 10.0.9. Compilation uses prebuilt trees; runtime measures invocation through the same wrapper. Two fresh process rounds with reversed load order, seven samples per round, about 30 ms calibration, one logical CPU and tiered compilation disabled. Tables use the median of the two per-round medians.

The controls below produce correct results on master for their measured inputs. Newly supported trees have no valid before/after execution comparison because master rejects them, produces incorrect results or emits invalid IL. Timings include machine and JIT/code-placement variation; the unchanged add control helps show that variation. These observations do not prove universal performance neutrality.

net8.0 results (master → change)

API / workload	Compile ns	Invoke ns	Compile B/op	Invoke B/op
Standard / add_control	1501.5 → 1463.7	2.6 → 2.6	872.0 → 872.0	0.0 → 0.0
Standard / enum_unbox_value	1527.4 → 1537.2	5.3 → 4.9	912.0 → 912.0	24.0 → 24.0
Standard / nullable_unbox_object	1842.1 → 2162.9	8.4 → 8.5	976.0 → 976.0	0.0 → 0.0
Light / add_control	1348.8 → 1509.9	2.6 → 2.6	872.0 → 872.0	0.0 → 0.0
Light / enum_unbox_value	1621.3 → 1653.8	8.2 → 6.3	912.0 → 912.0	24.0 → 24.0
Light / nullable_unbox_object	1876.9 → 1885.9	8.5 → 8.5	976.0 → 976.0	0.0 → 0.0

net10.0 results (master → change)

API / workload	Compile ns	Invoke ns	Compile B/op	Invoke B/op
Standard / add_control	4096.2 → 4428.1	2.6 → 2.6	872.1 → 872.1	0.0 → 0.0
Standard / enum_unbox_value	4440.7 → 5293.3	6.0 → 5.2	912.0 → 912.0	24.0 → 24.0
Standard / nullable_unbox_object	4917.4 → 4727.2	2.8 → 2.8	976.0 → 976.0	0.0 → 0.0
Light / add_control	3122.5 → 3308.1	2.5 → 2.5	872.0 → 872.0	0.0 → 0.0
Light / enum_unbox_value	3516.0 → 3410.5	4.3 → 4.3	912.0 → 912.0	24.0 → 24.0
Light / nullable_unbox_object	3153.6 → 3180.8	2.3 → 2.3	976.0 → 976.0	0.0 → 0.0

Emitted IL differs in these measured workloads: none.
No measured allocation increase above 0.1 B/op in these controls.