mirror of
https://github.com/rust-lang/rust.git
synced 2025-10-28 03:24:11 +00:00
31a72bc45c
rustc_target: Adjust RISC-V feature implication
This commit adjusts feature implication of the RISC-V ISA for better feature detection from the user perspective.
The main rule is:
* If the feature `A` is a functional superset of the feature `B` (`A ⊃ B`),
`A` is to imply `B`, even if this implication is not on the manual.
Such implications (not directly written in the ISA manual) are commented as `A ⊃ B`
which means "`A` is a (functional) superset of `B`".
1. `Zbc` → `Zbkc` (add as a superset)
The `Zbkc` extension is a subset of the `Zbc` extension (`Zbc` minus `clmulr` instruction).
2. `Zkr` → (nothing) (remove dependency to `Zicsr`)
Implication to the `Zicsr` extension is removed because (although nearly harmless), the `Zkr` extension (or the `seed` CSR section) defines its own subset of the `Zicsr` extension (guaranteed to work against the `seed` CSR which needs read/write access).
3. `Zvbb` → `Zvkb` (comment as a superset)
This implication was already there but not denoted as a functional superset. This commit adds the comment.
4. `Zvfh` → `Zvfhmin` (comment as a superset)
This is similar to the case above (`Zvbb` → `Zvkb`).
5. `Zvfh` → `Zve32f` (add implication per the ISA specification)
This dependency is on the ISA manual but was missing (due to the fact that `Zvfh` indirectly implies `Zve32f` on the current implementation through `Zvfh` → `Zvfhmin` which is a functional relation). This commit ensures that this is *also* ISA-compliant in the source code level (there's no functional changes though).
6. `Zvknhb` → `Zvknha` (add as a superset)
The `Zvknhb` extension (SHA-256 / SHA-512) is a functional superset of the `Zvknha` extension (SHA-256 only).
rustc_target contains some very low-level details that are
specific to different compilation targets and so forth.
For more information about how rustc works, see the rustc dev guide.