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Rollup merge of #97389 - m-ou-se:memory-ordering-diagnostics, r=estebank
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Improve memory ordering diagnostics

Before:

![image](https://user-images.githubusercontent.com/783247/170234545-891cac30-eaa2-4186-847b-35cd51e00f2b.png)

After:

![image](https://user-images.githubusercontent.com/783247/170239684-645f186f-5a02-4eb9-8651-2e5fe9591352.png)

---

Before this change, the compiler suggests the failure ordering is too strong and suggests choosing a weaker ordering. After this change, it instead suggests the success ordering is not strong enough, and suggests chosing a stronger one. This is more likely to be correct.

Also, before this change, the compiler suggested downgrading an invalid AcqRel failure ordering to Relaxed, without mentioning Acquire as an option.
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@matthiaskrgr
matthiaskrgr authored Jun 27, 2022
2 parents 7702ae1 + f107923 commit 3694e40
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Showing 7 changed files with 312 additions and 310 deletions.
148 changes: 66 additions & 82 deletions compiler/rustc_lint/src/types.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@ use rustc_attr as attr;
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::{is_range_literal, Expr, ExprKind, Node};
use rustc_middle::ty::layout::{IntegerExt, LayoutOf, SizeSkeleton};
use rustc_middle::ty::subst::SubstsRef;
Expand Down Expand Up @@ -1483,39 +1482,32 @@ impl InvalidAtomicOrdering {
None
}

fn matches_ordering(cx: &LateContext<'_>, did: DefId, orderings: &[Symbol]) -> bool {
fn match_ordering(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<Symbol> {
let ExprKind::Path(ref ord_qpath) = ord_arg.kind else { return None };
let did = cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()?;
let tcx = cx.tcx;
let atomic_ordering = tcx.get_diagnostic_item(sym::Ordering);
orderings.iter().any(|ordering| {
tcx.item_name(did) == *ordering && {
let parent = tcx.parent(did);
Some(parent) == atomic_ordering
// needed in case this is a ctor, not a variant
|| tcx.opt_parent(parent) == atomic_ordering
}
})
}

fn opt_ordering_defid(cx: &LateContext<'_>, ord_arg: &Expr<'_>) -> Option<DefId> {
if let ExprKind::Path(ref ord_qpath) = ord_arg.kind {
cx.qpath_res(ord_qpath, ord_arg.hir_id).opt_def_id()
} else {
None
}
let name = tcx.item_name(did);
let parent = tcx.parent(did);
[sym::Relaxed, sym::Release, sym::Acquire, sym::AcqRel, sym::SeqCst].into_iter().find(
|&ordering| {
name == ordering
&& (Some(parent) == atomic_ordering
// needed in case this is a ctor, not a variant
|| tcx.opt_parent(parent) == atomic_ordering)
},
)
}

fn check_atomic_load_store(cx: &LateContext<'_>, expr: &Expr<'_>) {
use rustc_hir::def::{DefKind, Res};
use rustc_hir::QPath;
if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::load, sym::store])
&& let Some((ordering_arg, invalid_ordering)) = match method {
sym::load => Some((&args[1], sym::Release)),
sym::store => Some((&args[2], sym::Acquire)),
_ => None,
}
&& let ExprKind::Path(QPath::Resolved(_, path)) = ordering_arg.kind
&& let Res::Def(DefKind::Ctor(..), ctor_id) = path.res
&& Self::matches_ordering(cx, ctor_id, &[invalid_ordering, sym::AcqRel])
&& let Some(ordering) = Self::match_ordering(cx, ordering_arg)
&& (ordering == invalid_ordering || ordering == sym::AcqRel)
{
cx.struct_span_lint(INVALID_ATOMIC_ORDERING, ordering_arg.span, |diag| {
if method == sym::load {
Expand All @@ -1537,9 +1529,7 @@ impl InvalidAtomicOrdering {
&& let ExprKind::Path(ref func_qpath) = func.kind
&& let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id()
&& matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::fence | sym::compiler_fence))
&& let ExprKind::Path(ref ordering_qpath) = &args[0].kind
&& let Some(ordering_def_id) = cx.qpath_res(ordering_qpath, args[0].hir_id).opt_def_id()
&& Self::matches_ordering(cx, ordering_def_id, &[sym::Relaxed])
&& Self::match_ordering(cx, &args[0]) == Some(sym::Relaxed)
{
cx.struct_span_lint(INVALID_ATOMIC_ORDERING, args[0].span, |diag| {
diag.build("memory fences cannot have `Relaxed` ordering")
Expand All @@ -1550,62 +1540,56 @@ impl InvalidAtomicOrdering {
}

fn check_atomic_compare_exchange(cx: &LateContext<'_>, expr: &Expr<'_>) {
if let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
&& let Some((success_order_arg, failure_order_arg)) = match method {
sym::fetch_update => Some((&args[1], &args[2])),
sym::compare_exchange | sym::compare_exchange_weak => Some((&args[3], &args[4])),
_ => None,
}
&& let Some(fail_ordering_def_id) = Self::opt_ordering_defid(cx, failure_order_arg)
{
// Helper type holding on to some checking and error reporting data. Has
// - (success ordering,
// - list of failure orderings forbidden by the success order,
// - suggestion message)
type OrdLintInfo = (Symbol, &'static [Symbol], &'static str);
const RELAXED: OrdLintInfo = (sym::Relaxed, &[sym::SeqCst, sym::Acquire], "ordering mode `Relaxed`");
const ACQUIRE: OrdLintInfo = (sym::Acquire, &[sym::SeqCst], "ordering modes `Acquire` or `Relaxed`");
const SEQ_CST: OrdLintInfo = (sym::SeqCst, &[], "ordering modes `Acquire`, `SeqCst` or `Relaxed`");
const RELEASE: OrdLintInfo = (sym::Release, RELAXED.1, RELAXED.2);
const ACQREL: OrdLintInfo = (sym::AcqRel, ACQUIRE.1, ACQUIRE.2);
const SEARCH: [OrdLintInfo; 5] = [RELAXED, ACQUIRE, SEQ_CST, RELEASE, ACQREL];

let success_lint_info = Self::opt_ordering_defid(cx, success_order_arg)
.and_then(|success_ord_def_id| -> Option<OrdLintInfo> {
SEARCH
.iter()
.copied()
.find(|(ordering, ..)| {
Self::matches_ordering(cx, success_ord_def_id, &[*ordering])
})
});
if Self::matches_ordering(cx, fail_ordering_def_id, &[sym::Release, sym::AcqRel]) {
// If we don't know the success order is, use what we'd suggest
// if it were maximally permissive.
let suggested = success_lint_info.unwrap_or(SEQ_CST).2;
cx.struct_span_lint(INVALID_ATOMIC_ORDERING, failure_order_arg.span, |diag| {
let msg = format!(
"{}'s failure ordering may not be `Release` or `AcqRel`",
method,
);
diag.build(&msg)
.help(&format!("consider using {} instead", suggested))
.emit();
});
} else if let Some((success_ord, bad_ords_given_success, suggested)) = success_lint_info {
if Self::matches_ordering(cx, fail_ordering_def_id, bad_ords_given_success) {
cx.struct_span_lint(INVALID_ATOMIC_ORDERING, failure_order_arg.span, |diag| {
let msg = format!(
"{}'s failure ordering may not be stronger than the success ordering of `{}`",
method,
success_ord,
);
diag.build(&msg)
.help(&format!("consider using {} instead", suggested))
.emit();
});
}
}
let Some((method, args)) = Self::inherent_atomic_method_call(cx, expr, &[sym::fetch_update, sym::compare_exchange, sym::compare_exchange_weak])
else {return };

let (success_order_arg, fail_order_arg) = match method {
sym::fetch_update => (&args[1], &args[2]),
sym::compare_exchange | sym::compare_exchange_weak => (&args[3], &args[4]),
_ => return,
};

let Some(fail_ordering) = Self::match_ordering(cx, fail_order_arg) else { return };

if matches!(fail_ordering, sym::Release | sym::AcqRel) {
cx.struct_span_lint(INVALID_ATOMIC_ORDERING, fail_order_arg.span, |diag| {
diag.build(&format!(
"`{method}`'s failure ordering may not be `Release` or `AcqRel`, \
since a failed `{method}` does not result in a write",
))
.span_label(fail_order_arg.span, "invalid failure ordering")
.help("consider using `Acquire` or `Relaxed` failure ordering instead")
.emit();
});
}

let Some(success_ordering) = Self::match_ordering(cx, success_order_arg) else { return };

if matches!(
(success_ordering, fail_ordering),
(sym::Relaxed | sym::Release, sym::Acquire)
| (sym::Relaxed | sym::Release | sym::Acquire | sym::AcqRel, sym::SeqCst)
) {
let success_suggestion =
if success_ordering == sym::Release && fail_ordering == sym::Acquire {
sym::AcqRel
} else {
fail_ordering
};
cx.struct_span_lint(INVALID_ATOMIC_ORDERING, success_order_arg.span, |diag| {
diag.build(&format!(
"`{method}`'s success ordering must be at least as strong as its failure ordering"
))
.span_label(fail_order_arg.span, format!("`{fail_ordering}` failure ordering"))
.span_label(success_order_arg.span, format!("`{success_ordering}` success ordering"))
.span_suggestion_short(
success_order_arg.span,
format!("consider using `{success_suggestion}` success ordering instead"),
format!("std::sync::atomic::Ordering::{success_suggestion}"),
Applicability::MaybeIncorrect,
)
.emit();
});
}
}
}
Expand Down
32 changes: 16 additions & 16 deletions src/test/ui/lint/lint-invalid-atomic-ordering-exchange-weak.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -20,43 +20,43 @@ fn main() {

// AcqRel is always forbidden as a failure ordering
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::Relaxed, Ordering::AcqRel);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::Acquire, Ordering::AcqRel);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::Release, Ordering::AcqRel);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::AcqRel, Ordering::AcqRel);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::SeqCst, Ordering::AcqRel);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`

// Release is always forbidden as a failure ordering
let _ = x.compare_exchange_weak(ptr, ptr2, Ordering::Relaxed, Ordering::Release);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`
let _ = x.compare_exchange_weak(ptr, ptr2, Ordering::Acquire, Ordering::Release);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`
let _ = x.compare_exchange_weak(ptr, ptr2, Ordering::Release, Ordering::Release);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`
let _ = x.compare_exchange_weak(ptr, ptr2, Ordering::AcqRel, Ordering::Release);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`
let _ = x.compare_exchange_weak(ptr, ptr2, Ordering::SeqCst, Ordering::Release);
//~^ ERROR compare_exchange_weak's failure ordering may not be `Release` or `AcqRel`
//~^ ERROR `compare_exchange_weak`'s failure ordering may not be `Release` or `AcqRel`

// Release success order forbids failure order of Acquire or SeqCst
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::Release, Ordering::Acquire);
//~^ ERROR compare_exchange_weak's failure ordering may not be stronger
//~^ ERROR `compare_exchange_weak`'s success ordering must be at least as strong as
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::Release, Ordering::SeqCst);
//~^ ERROR compare_exchange_weak's failure ordering may not be stronger
//~^ ERROR `compare_exchange_weak`'s success ordering must be at least as strong as

// Relaxed success order also forbids failure order of Acquire or SeqCst
let _ = x.compare_exchange_weak(ptr, ptr2, Ordering::Relaxed, Ordering::SeqCst);
//~^ ERROR compare_exchange_weak's failure ordering may not be stronger
//~^ ERROR `compare_exchange_weak`'s success ordering must be at least as strong as
let _ = x.compare_exchange_weak(ptr, ptr2, Ordering::Relaxed, Ordering::Acquire);
//~^ ERROR compare_exchange_weak's failure ordering may not be stronger
//~^ ERROR `compare_exchange_weak`'s success ordering must be at least as strong as

// Acquire/AcqRel forbids failure order of SeqCst
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::Acquire, Ordering::SeqCst);
//~^ ERROR compare_exchange_weak's failure ordering may not be stronger
//~^ ERROR `compare_exchange_weak`'s success ordering must be at least as strong as
let _ = x.compare_exchange_weak(ptr2, ptr, Ordering::AcqRel, Ordering::SeqCst);
//~^ ERROR compare_exchange_weak's failure ordering may not be stronger
//~^ ERROR `compare_exchange_weak`'s success ordering must be at least as strong as
}
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