bjoernager/rust
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explain PassMode::Cast

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This commit is contained in:
Ralf Jung 2023-09-07 22:06:37 +02:00
parent 9cbc90c0ae
commit 7740476a43
7 changed files with 38 additions and 27 deletions
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25
compiler/rustc_target/src/abi/call/mod.rs
View file

@ -45,10 +45,9 @@ pub enum PassMode {
///
/// The argument has a layout abi of `ScalarPair`.
Pair(ArgAttributes, ArgAttributes),
/// Pass the argument after casting it, to either a single uniform or a
/// pair of registers. The bool indicates if a `Reg::i32()` dummy argument
/// is emitted before the real argument.
Cast(Box<CastTarget>, bool),
/// Pass the argument after casting it. See the `CastTarget` docs for details. The bool
/// indicates if a `Reg::i32()` dummy argument is emitted before the real argument.
Cast { pad_i32: bool, cast: Box<CastTarget> },
/// Pass the argument indirectly via a hidden pointer.
/// The `extra_attrs` value, if any, is for the extra data (vtable or length)
/// which indicates that it refers to an unsized rvalue.
@ -64,10 +63,13 @@ impl PassMode {
/// so that needs to be compared as well!
pub fn eq_abi(&self, other: &Self) -> bool {
match (self, other) {
(PassMode::Ignore, PassMode::Ignore) => true, // can still be reached for the return type
(PassMode::Ignore, PassMode::Ignore) => true,
(PassMode::Direct(a1), PassMode::Direct(a2)) => a1.eq_abi(a2),
(PassMode::Pair(a1, b1), PassMode::Pair(a2, b2)) => a1.eq_abi(a2) && b1.eq_abi(b2),
(PassMode::Cast(c1, pad1), PassMode::Cast(c2, pad2)) => c1.eq_abi(c2) && pad1 == pad2,
(
PassMode::Cast { cast: c1, pad_i32: pad1 },
PassMode::Cast { cast: c2, pad_i32: pad2 },
) => c1.eq_abi(c2) && pad1 == pad2,
(
PassMode::Indirect { attrs: a1, extra_attrs: None, on_stack: s1 },
PassMode::Indirect { attrs: a2, extra_attrs: None, on_stack: s2 },
@ -255,6 +257,13 @@ impl Uniform {
}
}
/// Describes the type used for `PassMode::Cast`.
///
/// Passing arguments in this mode works as follows: the registers in the `prefix` (the ones that
/// are `Some`) get laid out one after the other (using `repr(C)` layout rules). Then the
/// `rest.unit` register type gets repeated often enough to cover `rest.size`. This describes the
/// actual type used for the call; the Rust type of the argument is then transmuted to this ABI type
/// (and all data in the padding between the registers is dropped).
#[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
pub struct CastTarget {
pub prefix: [Option<Reg>; 8],
@ -607,11 +616,11 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
}
pub fn cast_to<T: Into<CastTarget>>(&mut self, target: T) {
self.mode = PassMode::Cast(Box::new(target.into()), false);
self.mode = PassMode::Cast { cast: Box::new(target.into()), pad_i32: false };
}
pub fn cast_to_and_pad_i32<T: Into<CastTarget>>(&mut self, target: T, pad_i32: bool) {
self.mode = PassMode::Cast(Box::new(target.into()), pad_i32);
self.mode = PassMode::Cast { cast: Box::new(target.into()), pad_i32 };
}
pub fn is_indirect(&self) -> bool {

2
compiler/rustc_target/src/abi/call/x86.rs
View file

@ -148,7 +148,7 @@ where
PassMode::Direct(ref mut attrs) => attrs,
PassMode::Pair(..)
| PassMode::Indirect { attrs: _, extra_attrs: Some(_), on_stack: _ }
| PassMode::Cast(..) => {
| PassMode::Cast { .. } => {
unreachable!("x86 shouldn't be passing arguments by {:?}", arg.mode)
}
};