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cheriot_instr_auipcc_cross impossibilities #66

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nwf opened this issue Jan 17, 2025 · 1 comment
Open

cheriot_instr_auipcc_cross impossibilities #66

nwf opened this issue Jan 17, 2025 · 1 comment

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@nwf
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nwf commented Jan 17, 2025

@kliuMsft and I spent a while looking and eventually remembered that the cp_cd_pcc_repr_cases component of this cross product is describing whether the result is in bounds of PCC.

This implies that, for any PCC with exponent zero, any non-zero auipcc immediate will always produce a result in cd that is out of bounds (case2 of cp_cd_pcc_repr_cases) and so there needs to be some exclusion from the cross-product here.
@nwf
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nwf commented Jan 17, 2025 •
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Similar observations will hold for cp_cd_cs1_repr_cases / cp_cs1_exp / cp_cheri_imm20 for cheriot_instr_auicgp_cross. A subset will also hold for cheriot_instr_cincaddrimm_cross, I think?

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