Repository navigation
PHIR classical registers with size 0 are accepted outside the schema and silently zero or sign-fill writes #1348
Description
A classical register declared with "size": 0 is accepted by every PHIR path that does not run the pydantic schema. Writes into it then give silently wrong values. The upstream PHIR schema (size: PositiveInt | None), and so PhirModel.model_validate, rejects the declaration.
Reproduction
The native results below come from the #1314 branch. The size handling involved is the same on dev: Environment::validate_variable_size in crates/pecos-phir-json/src/v0_1/environment.rs (~578 on dev) has no zero check.
src = {"format": "PHIR/JSON", "version": "0.1.0", "ops": [
{"data": "cvar_define", "data_type": "u32", "variable": "a", "size": 0},
{"cop": "=", "args": [5], "returns": ["a"]},
{"cop": "Result", "args": ["a"], "returns": ["out"]},
]}| Path | u32, size 0 | i32, size 0 |
|---|---|---|
pecos_rslib.run_phir_sim (native, no schema) |
{'out': ['']} |
{'out': ['1']} |
HybridEngine, Rust interpreter, phir_validate=False |
a = 0, out = 0 |
a = -1, out = -1 |
HybridEngine, Python interpreter, phir_validate=False |
a = 0, out = 0 |
a = -1, out = -1 |
PhirModel.model_validate |
ValidationError | ValidationError |
a = 5 silently becomes 0 for unsigned registers. For signed registers it becomes -1: a signed size-S register is i(S+1), so size 0 keeps only the sign bit. A measurement into a[0] does fail, with "out of range for a register of declared size 0". The JSON-to-module converter was not checked.
Direction
Reject a classical size of 0 in the shared declaration validation, so every path agrees with the schema. Use a named error ("use a positive integer size that fits the data type"). Add a parity test over native, both interpreters (validation on and off) and the converter. The quantum side already rejects size 0.
Found during the review of the #1314 work.
Activity