bjoernager/rust
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compiler: rustc_abi::Abi => BackendRepr

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The initial naming of "Abi" was an awful mistake, conveying wrong ideas
about how psABIs worked and even more about what the enum meant.
It was only meant to represent the way the value would be described to
a codegen backend as it was lowered to that intermediate representation.
It was never meant to mean anything about the actual psABI handling!
The conflation is because LLVM typically will associate a certain form
with a certain ABI, but even that does not hold when the special cases
that actually exist arise, plus the IR annotations that modify the ABI.

Reframe `rustc_abi::Abi` as the `BackendRepr` of the type, and rename
`BackendRepr::Aggregate` as `BackendRepr::Memory`. Unfortunately, due to
the persistent misunderstandings, this too is now incorrect:
- Scattered ABI-relevant code is entangled with BackendRepr
- We do not always pre-compute a correct BackendRepr that reflects how
  we "actually" want this value to be handled, so we leave the backend
  interface to also inject various special-cases here
- In some cases `BackendRepr::Memory` is a "real" aggregate, but in
  others it is in fact using memory, and in some cases it is a scalar!

Our rustc-to-backend lowering code handles this sort of thing right now.
That will eventually be addressed by lifting duplicated lowering code
to either rustc_codegen_ssa or rustc_target as appropriate.
This commit is contained in:
Jubilee Young 2024-10-29 13:37:26 -07:00
parent 2dece5bb62
commit 7086dd83cc
51 changed files with 517 additions and 428 deletions
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29
compiler/rustc_target/src/callconv/mod.rs
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@ -6,7 +6,8 @@ use rustc_macros::HashStable_Generic;
use rustc_span::Symbol;
use crate::abi::{
self, Abi, AddressSpace, Align, HasDataLayout, Pointer, Size, TyAbiInterface, TyAndLayout,
self, AddressSpace, Align, BackendRepr, HasDataLayout, Pointer, Size, TyAbiInterface,
TyAndLayout,
};
use crate::spec::abi::Abi as SpecAbi;
use crate::spec::{self, HasTargetSpec, HasWasmCAbiOpt, HasX86AbiOpt, WasmCAbi};
@ -350,15 +351,17 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
layout: TyAndLayout<'a, Ty>,
scalar_attrs: impl Fn(&TyAndLayout<'a, Ty>, abi::Scalar, Size) -> ArgAttributes,
) -> Self {
let mode = match layout.abi {
Abi::Uninhabited => PassMode::Ignore,
Abi::Scalar(scalar) => PassMode::Direct(scalar_attrs(&layout, scalar, Size::ZERO)),
Abi::ScalarPair(a, b) => PassMode::Pair(
let mode = match layout.backend_repr {
BackendRepr::Uninhabited => PassMode::Ignore,
BackendRepr::Scalar(scalar) => {
PassMode::Direct(scalar_attrs(&layout, scalar, Size::ZERO))
}
BackendRepr::ScalarPair(a, b) => PassMode::Pair(
scalar_attrs(&layout, a, Size::ZERO),
scalar_attrs(&layout, b, a.size(cx).align_to(b.align(cx).abi)),
),
Abi::Vector { .. } => PassMode::Direct(ArgAttributes::new()),
Abi::Aggregate { .. } => Self::indirect_pass_mode(&layout),
BackendRepr::Vector { .. } => PassMode::Direct(ArgAttributes::new()),
BackendRepr::Memory { .. } => Self::indirect_pass_mode(&layout),
};
ArgAbi { layout, mode }
}
@ -460,7 +463,7 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
pub fn extend_integer_width_to(&mut self, bits: u64) {
// Only integers have signedness
if let Abi::Scalar(scalar) = self.layout.abi {
if let BackendRepr::Scalar(scalar) = self.layout.backend_repr {
if let abi::Int(i, signed) = scalar.primitive() {
if i.size().bits() < bits {
if let PassMode::Direct(ref mut attrs) = self.mode {
@ -512,7 +515,7 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
// That elevates any type difference to an ABI difference since we just use the
// full Rust type as the LLVM argument/return type.
if matches!(self.mode, PassMode::Direct(..))
&& matches!(self.layout.abi, Abi::Aggregate { .. })
&& matches!(self.layout.backend_repr, BackendRepr::Memory { .. })
{
// For aggregates in `Direct` mode to be compatible, the types need to be equal.
self.layout.ty == other.layout.ty
@ -791,8 +794,8 @@ impl<'a, Ty> FnAbi<'a, Ty> {
continue;
}
match arg.layout.abi {
Abi::Aggregate { .. } => {}
match arg.layout.backend_repr {
BackendRepr::Memory { .. } => {}
// This is a fun case! The gist of what this is doing is
// that we want callers and callees to always agree on the
@ -813,7 +816,9 @@ impl<'a, Ty> FnAbi<'a, Ty> {
// Note that the intrinsic ABI is exempt here as
// that's how we connect up to LLVM and it's unstable
// anyway, we control all calls to it in libstd.
Abi::Vector { .. } if abi != SpecAbi::RustIntrinsic && spec.simd_types_indirect => {
BackendRepr::Vector { .. }
if abi != SpecAbi::RustIntrinsic && spec.simd_types_indirect =>
{
arg.make_indirect();
continue;
}