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Rollup merge of #136985 - zachs18:backend-repr-remove-uninhabited, r=workingjubilee

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Do not ignore uninhabited types for function-call ABI purposes. (Remove BackendRepr::Uninhabited)

Accepted MCP: https://github.com/rust-lang/compiler-team/issues/832

Fixes #135802

Do not consider the inhabitedness of a type for function call ABI purposes.

* Remove the [`rustc_abi::BackendRepr::Uninhabited`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_abi/enum.BackendRepr.html) variant
  * Instead calculate the `BackendRepr` of uninhabited types "normally" (as though they were not uninhabited "at the top level", but still considering inhabitedness of variants to determine enum layout, etc)
* Add an `uninhabited: bool` field to [`rustc_abi::LayoutData`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_abi/struct.LayoutData.html) so inhabitedness of a `LayoutData` can still be queried when necessary (e.g. when determining if an enum variant needs a tag value allocated to it).

This should not affect type layouts (size/align/field offset); this should only affect function call ABI, and only of uninhabited types.

cc ``@RalfJung``
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Jubilee 2025-02-20 14:58:18 -08:00 • committed by GitHub
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49 changed files with 532 additions and 167 deletions
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28
compiler/rustc_codegen_ssa/src/mir/block.rs
View file

@ -4,9 +4,7 @@ use rustc_abi::{BackendRepr, ExternAbi, HasDataLayout, Reg, WrappingRange};
use rustc_ast as ast;
use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
use rustc_hir::lang_items::LangItem;
use rustc_middle::mir::{
self, AssertKind, BasicBlock, InlineAsmMacro, SwitchTargets, UnwindTerminateReason,
};
use rustc_middle::mir::{self, AssertKind, InlineAsmMacro, SwitchTargets, UnwindTerminateReason};
use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, ValidityRequirement};
use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
use rustc_middle::ty::{self, Instance, Ty};
@ -942,7 +940,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
&fn_abi.ret,
&mut llargs,
Some(intrinsic),
target,
);
let dest = match ret_dest {
_ if fn_abi.ret.is_indirect() => llargs[0],
@ -998,19 +995,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
};
let mut llargs = Vec::with_capacity(arg_count);
let destination = target.as_ref().map(|&target| {
(
self.make_return_dest(
bx,
destination,
&fn_abi.ret,
&mut llargs,
None,
Some(target),
),
target,
)
});
// We still need to call `make_return_dest` even if there's no `target`, since
// `fn_abi.ret` could be `PassMode::Indirect`, even if it is uninhabited,
// and `make_return_dest` adds the return-place indirect pointer to `llargs`.
let return_dest = self.make_return_dest(bx, destination, &fn_abi.ret, &mut llargs, None);
let destination = target.map(|target| (return_dest, target));
// Split the rust-call tupled arguments off.
let (first_args, untuple) = if abi == ExternAbi::RustCall && !args.is_empty() {
@ -1813,11 +1803,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
fn_ret: &ArgAbi<'tcx, Ty<'tcx>>,
llargs: &mut Vec<Bx::Value>,
intrinsic: Option<ty::IntrinsicDef>,
target: Option<BasicBlock>,
) -> ReturnDest<'tcx, Bx::Value> {
if target.is_none() {
return ReturnDest::Nothing;
}
// If the return is ignored, we can just return a do-nothing `ReturnDest`.
if fn_ret.is_ignore() {
return ReturnDest::Nothing;

4
compiler/rustc_codegen_ssa/src/mir/operand.rs
View file

@ -422,9 +422,7 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
See <https://github.com/rust-lang/rust/issues/137108>",
);
}
BackendRepr::Uninhabited
| BackendRepr::ScalarPair(_, _)
| BackendRepr::Memory { sized: false } => bug!(),
BackendRepr::ScalarPair(_, _) | BackendRepr::Memory { sized: false } => bug!(),
})
};