This commit performs various improvements (better register allocation,
less register clobbering on the worst case and better readability) of
RISC-V inline assembly use cases.
Note that it does not change the `p` module (which defines the "P"
extension draft instructions but very likely to change).
1. Use `lateout` as possible.
Unlike `out(reg)` and `in(reg)` pair, `lateout(reg)` and `in(reg)`
can share the same register because they state that the late-output
register is written after all the reads are performed.
It can improve register allocation.
2. Add `preserves_flags` option as possible.
While RISC-V doesn't have _regular_ condition codes, RISC-V inline
assembly in the Rust language assumes that some registers
(mainly vector state registers) may be overwritten by default.
By adding `preserves_flags` to the intrinsics corresponding
instructions without overwriting them, it can minimize register
clobbering on the worst case.
3. Use trailing semicolon.
As `asm!` declares an action and it doesn't return a value by
itself, it would be better to have trailing semicolon to denote that
an `asm!` call is effectively a statement.
4. Make most of `asm!` calls multi-lined.
`rustfmt` makes some simple (yet long) `asm!` calls multi-lined but
it does not perform formatting of complex `asm!` calls with inputs
and/or outputs. To keep consistency, it makes most of the `asm!`
calls multi-lined.
This instruction is incorrectly categorized as the same one as
`aes64ks1i` and `aes64ks2` (that should require `zkne || zknd` but
currently require `zkne && zknd`) but `aes64im` only requires
the Zknd extension.
This commit fixes the category of this intrinsic (lowering the
requirements from the Rust perspective but it does not actually lower
it from the RISC-V perspective).
They don't need full "Zbc" extension but only its subset: the "Zbkc"
extension. Since the compiler implies `zbkc` from `zbc`, it's safe to
use `#[target_feature(enable = "zbkc")]`.
Changes: 1. Removed `from_c` from the IntrinsicType definition. 2. Moved
the `from_c` arm-specific definition to an ArmIntrinsicType-specific
impl block
Don't special-case llvm.* as nounwind
Certain LLVM intrinsics, such as `llvm.wasm.throw`, can unwind. Marking them as nounwind causes us to skip cleanup of locals and optimize out `catch_unwind` under inlining or when `llvm.wasm.throw` is used directly by user code.
The motivation for forcibly marking llvm.* as nounwind is no longer present: most intrinsics are linked as `extern "C"` or other non-unwinding ABIs, so we won't codegen `invoke` for them anyway.
Closesrust-lang/rust#132416.
`@rustbot` label +T-compiler +A-panic
