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Disallow VTYPE=VILL #454

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Disallow VTYPE=VILL #454

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14 changes: 9 additions & 5 deletions riscv-cc.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -107,7 +107,7 @@ duration in accordance with C11 section 7.6 "Floating-point environment

| v0-v31 | | Temporary registers | No
| vl | | Vector length | No
| vtype | | Vector data type register | No
| vtype | | Vector data type register | No (but never `VILL`)
| vxrm | | Vector fixed-point rounding mode register | No
| vxsat | | Vector fixed-point saturation flag register | No
|===
Expand All @@ -120,7 +120,11 @@ The `vxrm` and `vxsat` fields of `vcsr` are not preserved across calls and their
values are unspecified upon entry.

Procedures may assume that `vstart` is zero upon entry. Procedures may assume
that `vstart` is zero upon return from a procedure call.
that `vstart` is zero upon return from a procedure call. Procedures may assume
that `vtype` is never `VILL`.

NOTE: Versions of the psABI before December 2024 allowed `vtype` to be `VILL`
at arbitrary times.

NOTE: Application software should normally not write `vstart` explicitly.
Any procedure that does explicitly write `vstart` to a nonzero value must zero
Expand All @@ -137,7 +141,7 @@ Any procedure that does explicitly write `vstart` to a nonzero value must zero
| v8-v23 | | Argument registers | No
| v24-v31 | | Callee-saved registers | Yes
| vl | | Vector length | No
| vtype | | Vector data type register | No
| vtype | | Vector data type register | No (but never VILL)
| vxrm | | Vector fixed-point rounding mode register | No
| vxsat | | Vector fixed-point saturation flag register | No
|===
Expand All @@ -150,8 +154,8 @@ attribute `riscv_vector_cc`).
Please refer to the <<Standard Vector Calling Convention Variant>> section for
more details about standard vector calling convention variant.

NOTE: The `vxrm` and `vxsat` fields of `vcsr` follow the same behavior as the
standard calling convention.
NOTE: The `vxrm`, `vxsat` and `vtype` fields of `vcsr` follow the same
behavior as the standard calling convention.

== Procedure Calling Convention

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