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Merged
rust-bors merged 6 commits into from
May 21, 2026
Merged

Remove unsound target_feature_inline_always feature #156242

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c6d2da9
Remove #[inline(always)] + #[target_feature(enable = "<feature>")] su…
Jamesbarford May 7, 2026
52cc7ec
Remove `target_feature_inline_always` from core, std and stdarch `lib…
Jamesbarford May 7, 2026
311cda6
Update tests to reflect changes, deleted ones that are now irrelevant
Jamesbarford May 7, 2026
812e230
PR Feedback - grammatical changes, clear reason for removal and move …
Jamesbarford May 14, 2026
0453288
Fix for new error message
Jamesbarford May 15, 2026
405214d
PR feedback - revert `fn inline_attr(...)` to how it was prior to inl…
Jamesbarford May 15, 2026
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19 changes: 8 additions & 11 deletions compiler/rustc_codegen_llvm/src/attributes.rs
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Expand Up @@ -41,7 +41,8 @@ pub(crate) fn remove_string_attr_from_llfn(llfn: &Value, name: &str) {
}

/// Get LLVM attribute for the provided inline heuristic.
pub(crate) fn inline_attr<'ll, 'tcx>(
#[inline]
fn inline_attr<'ll, 'tcx>(

@RalfJung RalfJung May 13, 2026

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I don't know this function so I have no idea if your changes here make sense.
It seems like before #145932 this didn't have tcx at all. Is it possible to exactly revert the changes from that PR, or would that be a bad idea?

Cc @nikic @dianqk for help with reviewing the codegen_llvm changes.

@Jamesbarford Jamesbarford May 14, 2026

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Happy to revert if you feel it best.

However fn inline_attr(...) as it stands in this PR cleans up the body of fn llfn_attrs_from_instance(...) to be as follows for adding the inline attribute;

if let Some(instance) = instance
    && let Some(inline_attr) = inline_attr(cx, tcx, instance)
{
    to_add.push(inline_attr);
}

It's quite nice the logic is self contained in the fn inline_attr(...) function, this also seems to follow the pattern for the other attributes being added.

@Jamesbarford Jamesbarford May 15, 2026

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405214d I've reverted as best I can. Due to other code changes unrelated to #[inline(always)] + #[target_feature(enable = "...")] it has rendered a 1:1 reversal implausible.

@RalfJung RalfJung May 15, 2026 •
edited
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Okay, so someone will have to actually understand the change to this function then to tell whether this is a clean revert. Without digging into this code (which would take some time as I have no context for it) I can't tell why these lines of code got moved around. I hope one of the people I pinged above can take a look as they might already have this context. (Or maybe @saethlin does.)

@saethlin saethlin May 18, 2026

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The diff here looks okay to me. The code is a bit gnarly but it's always been like that.

@dianqk dianqk May 20, 2026

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LGTM. Btw, the github notification shows me nobody is mentioning me directly.
image

@RalfJung RalfJung May 21, 2026

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@saethlin thanks!

@dianqk odd, as you can see I did mention you directly above... 🤷

cx: &SimpleCx<'ll>,
tcx: TyCtxt<'tcx>,
instance: ty::Instance<'tcx>,
Expand Down Expand Up @@ -418,6 +419,12 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
OptimizeAttr::Speed => {}
}

if let Some(instance) = instance
&& let Some(inline_attr) = inline_attr(cx, tcx, instance)
{
to_add.push(inline_attr);
}

if sess.must_emit_unwind_tables() {
to_add.push(uwtable_attr(cx.llcx, sess.opts.unstable_opts.use_sync_unwind));
}
Expand Down Expand Up @@ -568,16 +575,6 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
let function_features =
codegen_fn_attrs.target_features.iter().map(|f| f.name.as_str()).collect::<Vec<&str>>();

// Apply function attributes as per usual if there are no user defined
// target features otherwise this will get applied at the callsite.
if function_features.is_empty() {
if let Some(instance) = instance
&& let Some(inline_attr) = inline_attr(cx, tcx, instance)
{
to_add.push(inline_attr);
}
}

let function_features = function_features
.iter()
// Convert to LLVMFeatures and filter out unavailable ones
Expand Down
28 changes: 1 addition & 27 deletions compiler/rustc_codegen_llvm/src/builder.rs
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Expand Up @@ -15,7 +15,7 @@ use rustc_codegen_ssa::mir::place::PlaceRef;
use rustc_codegen_ssa::traits::*;
use rustc_data_structures::small_c_str::SmallCStr;
use rustc_hir::def_id::DefId;
use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrs, TargetFeature, TargetFeatureKind};
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
use rustc_middle::ty::layout::{
FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasTypingEnv, LayoutError, LayoutOfHelpers,
TyAndLayout,
Expand Down Expand Up @@ -1419,32 +1419,6 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
)
};

if let Some(callee_instance) = callee_instance {
// Attributes on the function definition being called
let callee_attrs = self.cx.tcx.codegen_fn_attrs(callee_instance.def_id());
if let Some(caller_attrs) = caller_attrs
// If there is an inline attribute and a target feature that matches
// we will add the attribute to the callsite otherwise we'll omit
// this and not add the attribute to prevent soundness issues.
&& let Some(inlining_rule) = attributes::inline_attr(&self.cx, self.cx.tcx, callee_instance)
&& self.cx.tcx.is_target_feature_call_safe(
&callee_attrs.target_features,
&caller_attrs.target_features.iter().cloned().chain(
self.cx.tcx.sess.target_features.iter().map(|feat| TargetFeature {
name: *feat,
kind: TargetFeatureKind::Implied,
})
).collect::<Vec<_>>(),
)
{
attributes::apply_to_callsite(
call,
llvm::AttributePlace::Function,
&[inlining_rule],
);
}
}

if let Some(fn_abi) = fn_abi {
fn_abi.apply_attrs_callsite(self, call);
}
Expand Down
16 changes: 8 additions & 8 deletions compiler/rustc_codegen_ssa/src/codegen_attrs.rs
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Expand Up @@ -419,16 +419,16 @@ fn check_result(
// llvm/llvm-project#70563).
if !codegen_fn_attrs.target_features.is_empty()
&& matches!(codegen_fn_attrs.inline, InlineAttr::Always)
&& !tcx.features().target_feature_inline_always()
&& let Some(span) = interesting_spans.inline
{
feature_err(
tcx.sess,
sym::target_feature_inline_always,
span,
"cannot use `#[inline(always)]` with `#[target_feature]`",
)
.emit();
let mut diag = tcx
.dcx()
.struct_span_err(span, "cannot use `#[inline(always)]` with `#[target_feature]`");
diag.note(
"See issue here for full discussion; \
Comment thread
RalfJung marked this conversation as resolved.
Outdated
https://github.com/rust-lang/rust/issues/145574",
);
diag.emit();
}

// warn that inline has no effect when no_sanitize is present
Expand Down
3 changes: 3 additions & 0 deletions compiler/rustc_feature/src/removed.rs
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Expand Up @@ -282,6 +282,9 @@ declare_features! (
/// Allows string patterns to dereference values to match them.
(removed, string_deref_patterns, "1.94.0", Some(87121), Some("superseded by `deref_patterns`"), 150530),
(removed, struct_inherit, "1.0.0", None, None),
/// Allows the use of target_feature when a function is marked inline(always).
(removed, target_feature_inline_always, "CURRENT_RUSTC_VERSION", Some(145574),
Some("removed because `#[inline(always)]` with `#[target_feature]` is forbidden")),
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(removed, test_removed_feature, "1.0.0", None, None),
/// Allows using items which are missing stability attributes
(removed, unmarked_api, "1.0.0", None, None),
Expand Down
2 changes: 0 additions & 2 deletions compiler/rustc_feature/src/unstable.rs
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Expand Up @@ -725,8 +725,6 @@ declare_features! (
(unstable, super_let, "1.88.0", Some(139076)),
/// Allows subtrait items to shadow supertrait items.
(unstable, supertrait_item_shadowing, "1.86.0", Some(89151)),
/// Allows the use of target_feature when a function is marked inline(always).
(unstable, target_feature_inline_always, "1.91.0", Some(145574)),
/// Allows using `#[thread_local]` on `static` items.
(unstable, thread_local, "1.0.0", Some(29594)),
/// Allows defining `trait X = A + B;` alias items.
Expand Down
4 changes: 4 additions & 0 deletions compiler/rustc_lint/src/lib.rs
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Expand Up @@ -398,6 +398,10 @@ fn register_builtins(store: &mut LintStore) {
store.register_removed("rustdoc", "use `rustdoc::all` instead");

store.register_removed("unknown_features", "replaced by an error");
store.register_removed(
"inline_always_mismatching_target_features",
"replaced by a hard error for `#[inline(always)]` with `#[target_feature]`",
);
Comment thread
RalfJung marked this conversation as resolved.
Outdated
store.register_removed("unsigned_negation", "replaced by negate_unsigned feature gate");
store.register_removed("negate_unsigned", "cast a signed value instead");
store.register_removed("raw_pointer_derive", "using derive with raw pointers is ok");
Expand Down
56 changes: 0 additions & 56 deletions compiler/rustc_lint_defs/src/builtin.rs
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Expand Up @@ -55,7 +55,6 @@ declare_lint_pass! {
ILL_FORMED_ATTRIBUTE_INPUT,
INCOMPLETE_INCLUDE,
INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
INLINE_ALWAYS_MISMATCHING_TARGET_FEATURES,
INLINE_NO_SANITIZE,
INVALID_DOC_ATTRIBUTES,
INVALID_MACRO_EXPORT_ARGUMENTS,
Expand Down Expand Up @@ -5460,61 +5459,6 @@ declare_lint! {
"detects tail calls of functions marked with `#[track_caller]`",
@feature_gate = explicit_tail_calls;
}
declare_lint! {
/// The `inline_always_mismatching_target_features` lint will trigger when a
/// function with the `#[inline(always)]` and `#[target_feature(enable = "...")]`
/// attributes is called and cannot be inlined due to missing target features in the caller.
///
/// ### Example
///
/// ```rust,ignore (fails on x86_64)
/// #[inline(always)]
/// #[target_feature(enable = "fp16")]
/// unsafe fn callee() {
/// // operations using fp16 types
/// }
///
/// // Caller does not enable the required target feature
/// fn caller() {
/// unsafe { callee(); }
/// }
///
/// fn main() {
/// caller();
/// }
/// ```
///
/// This will produce:
///
/// ```text
/// warning: call to `#[inline(always)]`-annotated `callee` requires the same target features. Function will not have `alwaysinline` attribute applied
/// --> $DIR/builtin.rs:5192:14
/// |
/// 10 | unsafe { callee(); }
/// | ^^^^^^^^
/// |
/// note: `fp16` target feature enabled in `callee` here but missing from `caller`
/// --> $DIR/builtin.rs:5185:1
/// |
/// 3 | #[target_feature(enable = "fp16")]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// 4 | unsafe fn callee() {
/// | ------------------
/// = note: `#[warn(inline_always_mismatching_target_features)]` on by default
/// warning: 1 warning emitted
/// ```
///
/// ### Explanation
///
/// Inlining a function with a target feature attribute into a caller that
/// lacks the corresponding target feature can lead to unsound behavior.
/// LLVM may select the wrong instructions or registers, or reorder
/// operations, potentially resulting in runtime errors.
pub INLINE_ALWAYS_MISMATCHING_TARGET_FEATURES,
Warn,
r#"detects when a function annotated with `#[inline(always)]` and `#[target_feature(enable = "..")]` is inlined into a caller without the required target feature"#,
}

declare_lint! {
/// The `repr_c_enums_larger_than_int` lint detects `repr(C)` enums with discriminant
/// values that do not fit into a C `int` or `unsigned int`.
Expand Down
88 changes: 0 additions & 88 deletions compiler/rustc_mir_transform/src/check_inline_always_target_features.rs
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This file was deleted.

41 changes: 0 additions & 41 deletions compiler/rustc_mir_transform/src/errors.rs
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Expand Up @@ -5,52 +5,11 @@ use rustc_errors::{
};
use rustc_macros::{Diagnostic, Subdiagnostic};
use rustc_middle::mir::AssertKind;
use rustc_middle::query::QueryKey;
use rustc_middle::ty::TyCtxt;
use rustc_session::lint::{self, Lint};
use rustc_span::def_id::DefId;
use rustc_span::{Ident, Span, Symbol};

/// Emit diagnostic for calls to `#[inline(always)]`-annotated functions with a
/// `#[target_feature]` attribute where the caller enables a different set of target features.
pub(crate) fn emit_inline_always_target_feature_diagnostic<'a, 'tcx>(
tcx: TyCtxt<'tcx>,
call_span: Span,
callee_def_id: DefId,
caller_def_id: DefId,
callee_only: &[&'a str],
) {
tcx.emit_node_span_lint(
lint::builtin::INLINE_ALWAYS_MISMATCHING_TARGET_FEATURES,
tcx.local_def_id_to_hir_id(caller_def_id.as_local().unwrap()),
call_span,
rustc_errors::DiagDecorator(|lint| {
let callee = tcx.def_path_str(callee_def_id);
let caller = tcx.def_path_str(caller_def_id);

lint.primary_message(format!(
"call to `#[inline(always)]`-annotated `{callee}` \
requires the same target features to be inlined"
));
lint.note("function will not be inlined");

lint.note(format!(
"the following target features are on `{callee}` but missing from `{caller}`: {}",
callee_only.join(", ")
));
lint.span_note(callee_def_id.default_span(tcx), format!("`{callee}` is defined here"));

let feats = callee_only.join(",");
lint.span_suggestion(
tcx.def_span(caller_def_id).shrink_to_lo(),
format!("add `#[target_feature]` attribute to `{caller}`"),
format!("#[target_feature(enable = \"{feats}\")]\n"),
lint::Applicability::MaybeIncorrect,
);
}),
);
}

#[derive(Diagnostic)]
#[diag("function cannot return without recursing")]
#[help("a `loop` may express intention better if this is on purpose")]
Expand Down
4 changes: 0 additions & 4 deletions compiler/rustc_mir_transform/src/lib.rs
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Expand Up @@ -125,7 +125,6 @@ declare_passes! {
mod add_subtyping_projections : Subtyper;
mod check_inline : CheckForceInline;
mod check_call_recursion : CheckCallRecursion, CheckDropRecursion;
mod check_inline_always_target_features: CheckInlineAlwaysTargetFeature;
mod check_alignment : CheckAlignment;
mod check_enums : CheckEnums;
mod check_const_item_mutation : CheckConstItemMutation;
Expand Down Expand Up @@ -407,9 +406,6 @@ fn mir_built(tcx: TyCtxt<'_>, def: LocalDefId) -> &Steal<Body<'_>> {
// MIR-level lints.
&Lint(check_inline::CheckForceInline),
&Lint(check_call_recursion::CheckCallRecursion),
// Check callee's target features match callers target features when
// using `#[inline(always)]`
&Lint(check_inline_always_target_features::CheckInlineAlwaysTargetFeature),
&Lint(check_packed_ref::CheckPackedRef),
&Lint(check_const_item_mutation::CheckConstItemMutation),
&Lint(function_item_references::FunctionItemReferences),
Expand Down
1 change: 0 additions & 1 deletion library/core/src/lib.rs
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Expand Up @@ -167,7 +167,6 @@
#![feature(staged_api)]
#![feature(stmt_expr_attributes)]
#![feature(strict_provenance_lints)]
#![feature(target_feature_inline_always)]
#![feature(trait_alias)]
#![feature(transparent_unions)]
#![feature(try_blocks)]
Expand Down
1 change: 0 additions & 1 deletion library/std/src/lib.rs
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Expand Up @@ -303,7 +303,6 @@
#![feature(staged_api)]
#![feature(stmt_expr_attributes)]
#![feature(strict_provenance_lints)]
#![feature(target_feature_inline_always)]
#![feature(thread_local)]
#![feature(try_blocks)]
#![feature(try_trait_v2)]
Expand Down
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