reduce false positives of tail-expr-drop-order from consumed values

take 2
rust-lang · Oct 6, 2024 · e6641cf · e6641cf
1 parent 68301a6
commit e6641cf
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Showing 60 changed files with 990 additions and 528 deletions.
diff --git a/compiler/rustc_borrowck/src/dataflow.rs b/compiler/rustc_borrowck/src/dataflow.rs
@@ -569,6 +569,7 @@ impl<'tcx> rustc_mir_dataflow::GenKillAnalysis<'tcx> for Borrows<'_, 'tcx> {
             | mir::StatementKind::Coverage(..)
             | mir::StatementKind::Intrinsic(..)
             | mir::StatementKind::ConstEvalCounter
+            | mir::StatementKind::BackwardIncompatibleDropHint { .. }
             | mir::StatementKind::Nop => {}
         }
     }

diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
@@ -655,6 +655,8 @@ impl<'a, 'tcx, R> rustc_mir_dataflow::ResultsVisitor<'a, 'tcx, R>
             | StatementKind::Coverage(..)
             // These do not actually affect borrowck
             | StatementKind::ConstEvalCounter
+            // This do not affect borrowck
+            | StatementKind::BackwardIncompatibleDropHint { .. }
             | StatementKind::StorageLive(..) => {}
             StatementKind::StorageDead(local) => {
                 self.access_place(

diff --git a/compiler/rustc_borrowck/src/polonius/loan_invalidations.rs b/compiler/rustc_borrowck/src/polonius/loan_invalidations.rs
@@ -88,6 +88,7 @@ impl<'a, 'tcx> Visitor<'tcx> for LoanInvalidationsGenerator<'a, 'tcx> {
             | StatementKind::Nop
             | StatementKind::Retag { .. }
             | StatementKind::Deinit(..)
+            | StatementKind::BackwardIncompatibleDropHint { .. }
             | StatementKind::SetDiscriminant { .. } => {
                 bug!("Statement not allowed in this MIR phase")
             }

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -1309,6 +1309,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             | StatementKind::Coverage(..)
             | StatementKind::ConstEvalCounter
             | StatementKind::PlaceMention(..)
+            | StatementKind::BackwardIncompatibleDropHint { .. }
             | StatementKind::Nop => {}
             StatementKind::Deinit(..) | StatementKind::SetDiscriminant { .. } => {
                 bug!("Statement not allowed in this MIR phase")

diff --git a/compiler/rustc_codegen_cranelift/src/base.rs b/compiler/rustc_codegen_cranelift/src/base.rs
@@ -917,6 +917,7 @@ fn codegen_stmt<'tcx>(
         | StatementKind::FakeRead(..)
         | StatementKind::Retag { .. }
         | StatementKind::PlaceMention(..)
+        | StatementKind::BackwardIncompatibleDropHint { .. }
         | StatementKind::AscribeUserType(..) => {}
 
         StatementKind::Coverage { .. } => unreachable!(),

diff --git a/compiler/rustc_codegen_cranelift/src/constant.rs b/compiler/rustc_codegen_cranelift/src/constant.rs
@@ -578,6 +578,7 @@ pub(crate) fn mir_operand_get_const_val<'tcx>(
                         | StatementKind::PlaceMention(..)
                         | StatementKind::Coverage(_)
                         | StatementKind::ConstEvalCounter
+                        | StatementKind::BackwardIncompatibleDropHint { .. }
                         | StatementKind::Nop => {}
                     }
                 }

diff --git a/compiler/rustc_codegen_ssa/src/mir/statement.rs b/compiler/rustc_codegen_ssa/src/mir/statement.rs
@@ -92,7 +92,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             | mir::StatementKind::AscribeUserType(..)
             | mir::StatementKind::ConstEvalCounter
             | mir::StatementKind::PlaceMention(..)
-            | mir::StatementKind::Nop => {}
+            | mir::StatementKind::Nop
+            | mir::StatementKind::BackwardIncompatibleDropHint { .. } => {}
         }
     }
 }
diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -542,6 +542,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
             | StatementKind::Coverage(..)
             | StatementKind::Intrinsic(..)
             | StatementKind::ConstEvalCounter
+            | StatementKind::BackwardIncompatibleDropHint { .. }
             | StatementKind::Nop => {}
         }
     }

diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -143,6 +143,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             // Defined to do nothing. These are added by optimization passes, to avoid changing the
             // size of MIR constantly.
             Nop => {}
+
+            // Only used for temporary lifetime lints
+            BackwardIncompatibleDropHint { .. } => {}
         }
 
         interp_ok(())

diff --git a/compiler/rustc_hir_analysis/src/check/region.rs b/compiler/rustc_hir_analysis/src/check/region.rs
@@ -17,6 +17,7 @@ use rustc_index::Idx;
 use rustc_middle::bug;
 use rustc_middle::middle::region::*;
 use rustc_middle::ty::TyCtxt;
+use rustc_session::lint;
 use rustc_span::source_map;
 use tracing::debug;
 
@@ -167,10 +168,23 @@ fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx h
             }
         }
         if let Some(tail_expr) = blk.expr {
-            if visitor.tcx.features().shorter_tail_lifetimes
-                && blk.span.edition().at_least_rust_2024()
+            let local_id = tail_expr.hir_id.local_id;
+            let edition = blk.span.edition();
+            if visitor.tcx.features().shorter_tail_lifetimes && edition.at_least_rust_2024() {
+                visitor.terminating_scopes.insert(local_id);
+            } else if edition < lint::Edition::Edition2024
+                && !matches!(
+                    visitor.tcx.lint_level_at_node(lint::builtin::TAIL_EXPR_DROP_ORDER, blk.hir_id),
+                    (lint::Level::Allow, _)
+                )
             {
-                visitor.terminating_scopes.insert(tail_expr.hir_id.local_id);
+                // Note: we are unconditionally adding this information so that we can run
+                // migration for Edition lower than 2024.
+                // For future scope changes, we need to extend the mapping with edition information.
+                visitor
+                    .scope_tree
+                    .backwards_incompatible_scope
+                    .insert(local_id, Scope { id: local_id, data: ScopeData::Node });
             }
             visitor.visit_expr(tail_expr);
         }

diff --git a/compiler/rustc_index/src/bit_set.rs b/compiler/rustc_index/src/bit_set.rs
@@ -460,6 +460,10 @@ impl<T: Idx> ChunkedBitSet<T> {
         self.chunks.iter().map(|chunk| chunk.count()).sum()
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.chunks.iter().all(|chunk| matches!(chunk, Chunk::Zeros(..) | Chunk::Ones(0)))
+    }
+
     /// Returns `true` if `self` contains `elem`.
     #[inline]
     pub fn contains(&self, elem: T) -> bool {
@@ -668,12 +672,138 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
         changed
     }
 
-    fn subtract(&mut self, _other: &ChunkedBitSet<T>) -> bool {
-        unimplemented!("implement if/when necessary");
+    fn subtract(&mut self, other: &ChunkedBitSet<T>) -> bool {
+        assert_eq!(self.domain_size, other.domain_size);
+        debug_assert_eq!(self.chunks.len(), other.chunks.len());
+
+        let mut changed = false;
+        for (mut self_chunk, other_chunk) in self.chunks.iter_mut().zip(other.chunks.iter()) {
+            match (&mut self_chunk, &other_chunk) {
+                (Zeros(..), _) | (_, Zeros(..)) => {}
+                (Ones(self_chunk_domain_size), Ones(other_chunk_domain_size)) => {
+                    debug_assert_eq!(self_chunk_domain_size, other_chunk_domain_size);
+                    changed = true;
+                    *self_chunk = Zeros(*self_chunk_domain_size);
+                }
+                (_, Ones(_)) => {}
+                (
+                    Ones(self_chunk_domain_size),
+                    Mixed(other_chunk_domain_size, other_chunk_count, other_chunk_words),
+                ) => {
+                    debug_assert_eq!(self_chunk_domain_size, other_chunk_domain_size);
+                    changed = true;
+                    let num_words = num_words(*self_chunk_domain_size as usize);
+                    debug_assert!(num_words > 0 && num_words <= CHUNK_WORDS);
+                    let mut tail_mask =
+                        1 << (*other_chunk_domain_size - ((num_words - 1) * WORD_BITS) as u16) - 1;
+                    let mut self_chunk_words = **other_chunk_words;
+                    for word in self_chunk_words[0..num_words].iter_mut().rev() {
+                        *word = !*word & tail_mask;
+                        tail_mask = u64::MAX;
+                    }
+                    let self_chunk_count = *self_chunk_domain_size - *other_chunk_count;
+                    debug_assert_eq!(
+                        self_chunk_count,
+                        self_chunk_words[0..num_words]
+                            .iter()
+                            .map(|w| w.count_ones() as ChunkSize)
+                            .sum()
+                    );
+                    *self_chunk =
+                        Mixed(*self_chunk_domain_size, self_chunk_count, Rc::new(self_chunk_words));
+                }
+                (
+                    Mixed(
+                        self_chunk_domain_size,
+                        ref mut self_chunk_count,
+                        ref mut self_chunk_words,
+                    ),
+                    Mixed(_other_chunk_domain_size, _other_chunk_count, other_chunk_words),
+                ) => {
+                    // See [`<Self as BitRelations<ChunkedBitSet<T>>>::union`] for the explanation
+                    let op = |a: u64, b: u64| a & !b;
+                    let num_words = num_words(*self_chunk_domain_size as usize);
+                    if bitwise_changes(
+                        &self_chunk_words[0..num_words],
+                        &other_chunk_words[0..num_words],
+                        op,
+                    ) {
+                        let self_chunk_words = Rc::make_mut(self_chunk_words);
+                        let has_changed = bitwise(
+                            &mut self_chunk_words[0..num_words],
+                            &other_chunk_words[0..num_words],
+                            op,
+                        );
+                        debug_assert!(has_changed);
+                        *self_chunk_count = self_chunk_words[0..num_words]
+                            .iter()
+                            .map(|w| w.count_ones() as ChunkSize)
+                            .sum();
+                        if *self_chunk_count == 0 {
+                            *self_chunk = Zeros(*self_chunk_domain_size);
+                        }
+                        changed = true;
+                    }
+                }
+            }
+        }
+        changed
     }
 
-    fn intersect(&mut self, _other: &ChunkedBitSet<T>) -> bool {
-        unimplemented!("implement if/when necessary");
+    fn intersect(&mut self, other: &ChunkedBitSet<T>) -> bool {
+        assert_eq!(self.domain_size, other.domain_size);
+        debug_assert_eq!(self.chunks.len(), other.chunks.len());
+
+        let mut changed = false;
+        for (mut self_chunk, other_chunk) in self.chunks.iter_mut().zip(other.chunks.iter()) {
+            match (&mut self_chunk, &other_chunk) {
+                (Zeros(..), _) | (_, Ones(..)) => {}
+                (
+                    Ones(self_chunk_domain_size),
+                    Zeros(other_chunk_domain_size) | Mixed(other_chunk_domain_size, ..),
+                )
+                | (Mixed(self_chunk_domain_size, ..), Zeros(other_chunk_domain_size)) => {
+                    debug_assert_eq!(self_chunk_domain_size, other_chunk_domain_size);
+                    changed = true;
+                    *self_chunk = other_chunk.clone();
+                }
+                (
+                    Mixed(
+                        self_chunk_domain_size,
+                        ref mut self_chunk_count,
+                        ref mut self_chunk_words,
+                    ),
+                    Mixed(_other_chunk_domain_size, _other_chunk_count, other_chunk_words),
+                ) => {
+                    // See [`<Self as BitRelations<ChunkedBitSet<T>>>::union`] for the explanation
+                    let op = |a, b| a & b;
+                    let num_words = num_words(*self_chunk_domain_size as usize);
+                    if bitwise_changes(
+                        &self_chunk_words[0..num_words],
+                        &other_chunk_words[0..num_words],
+                        op,
+                    ) {
+                        let self_chunk_words = Rc::make_mut(self_chunk_words);
+                        let has_changed = bitwise(
+                            &mut self_chunk_words[0..num_words],
+                            &other_chunk_words[0..num_words],
+                            op,
+                        );
+                        debug_assert!(has_changed);
+                        *self_chunk_count = self_chunk_words[0..num_words]
+                            .iter()
+                            .map(|w| w.count_ones() as ChunkSize)
+                            .sum();
+                        if *self_chunk_count == 0 {
+                            *self_chunk = Zeros(*self_chunk_domain_size);
+                        }
+                        changed = true;
+                    }
+                }
+            }
+        }
+
+        changed
     }
 }
 

diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
@@ -778,9 +778,6 @@ lint_suspicious_double_ref_clone =
 lint_suspicious_double_ref_deref =
     using `.deref()` on a double reference, which returns `{$ty}` instead of dereferencing the inner type
 
-lint_tail_expr_drop_order = these values and local bindings have significant drop implementation that will have a different drop order from that of Edition 2021
-    .label = these values have significant drop implementation and will observe changes in drop order under Edition 2024
-
 lint_trailing_semi_macro = trailing semicolon in macro used in expression position
     .note1 = macro invocations at the end of a block are treated as expressions
     .note2 = to ignore the value produced by the macro, add a semicolon after the invocation of `{$name}`

diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
@@ -81,7 +81,6 @@ mod redundant_semicolon;
 mod reference_casting;
 mod shadowed_into_iter;
 mod static_mut_refs;
-mod tail_expr_drop_order;
 mod traits;
 mod types;
 mod unit_bindings;
@@ -122,7 +121,6 @@ use rustc_middle::ty::TyCtxt;
 use shadowed_into_iter::ShadowedIntoIter;
 pub use shadowed_into_iter::{ARRAY_INTO_ITER, BOXED_SLICE_INTO_ITER};
 use static_mut_refs::*;
-use tail_expr_drop_order::TailExprDropOrder;
 use traits::*;
 use types::*;
 use unit_bindings::*;
@@ -247,7 +245,6 @@ late_lint_methods!(
             AsyncFnInTrait: AsyncFnInTrait,
             NonLocalDefinitions: NonLocalDefinitions::default(),
             ImplTraitOvercaptures: ImplTraitOvercaptures,
-            TailExprDropOrder: TailExprDropOrder,
             IfLetRescope: IfLetRescope::default(),
             StaticMutRefs: StaticMutRefs,
             UnqualifiedLocalImports: UnqualifiedLocalImports,