Auto merge of #120324 - Nadrieril:remove-interior-mutability, r=<try>

Experiment: track usefulness without interior mutability

This would remove a potential footgun in r-a. Just wanna see if this kills perf

compiler/rustc_pattern_analysis/src/constructor.rs

@@ -162,7 +162,6 @@ use self::MaybeInfiniteInt::*;
 use self::SliceKind::*;
 
 use crate::index;
-use crate::usefulness::PlaceCtxt;
 use crate::TypeCx;
 
 /// Whether we have seen a constructor in the column or not.
@@ -718,21 +717,20 @@ impl<Cx: TypeCx> Constructor<Cx> {
 
     /// The number of fields for this constructor. This must be kept in sync with
     /// `Fields::wildcards`.
-    pub(crate) fn arity(&self, pcx: &PlaceCtxt<'_, Cx>) -> usize {
-        pcx.ctor_arity(self)
+    pub(crate) fn arity(&self, cx: &Cx, ty: &Cx::Ty) -> usize {
+        cx.ctor_arity(self, ty)
     }
 
     /// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
     /// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
     /// this checks for inclusion.
     // We inline because this has a single call site in `Matrix::specialize_constructor`.
     #[inline]
-    pub(crate) fn is_covered_by(&self, pcx: &PlaceCtxt<'_, Cx>, other: &Self) -> bool {
+    pub(crate) fn is_covered_by(&self, cx: &Cx, other: &Self) -> bool {
         match (self, other) {
-            (Wildcard, _) => pcx
-                .mcx
-                .tycx
-                .bug(format_args!("Constructor splitting should not have returned `Wildcard`")),
+            (Wildcard, _) => {
+                cx.bug(format_args!("Constructor splitting should not have returned `Wildcard`"))
+            }
             // Wildcards cover anything
             (_, Wildcard) => true,
             // Only a wildcard pattern can match these special constructors.
@@ -773,7 +771,7 @@ impl<Cx: TypeCx> Constructor<Cx> {
             (Opaque(self_id), Opaque(other_id)) => self_id == other_id,
             (Opaque(..), _) | (_, Opaque(..)) => false,
 
-            _ => pcx.mcx.tycx.bug(format_args!(
+            _ => cx.bug(format_args!(
                 "trying to compare incompatible constructors {self:?} and {other:?}"
             )),
         }
@@ -850,10 +848,10 @@ pub enum ConstructorSet<Cx: TypeCx> {
 /// of the `ConstructorSet` for the type, yet if we forgot to include them in `present` we would be
 /// ignoring any row with `Opaque`s in the algorithm. Hence the importance of point 4.
 #[derive(Debug)]
-pub(crate) struct SplitConstructorSet<Cx: TypeCx> {
-    pub(crate) present: SmallVec<[Constructor<Cx>; 1]>,
-    pub(crate) missing: Vec<Constructor<Cx>>,
-    pub(crate) missing_empty: Vec<Constructor<Cx>>,
+pub struct SplitConstructorSet<Cx: TypeCx> {
+    pub present: SmallVec<[Constructor<Cx>; 1]>,
+    pub missing: Vec<Constructor<Cx>>,
+    pub missing_empty: Vec<Constructor<Cx>>,
 }
 
 impl<Cx: TypeCx> ConstructorSet<Cx> {
@@ -862,7 +860,7 @@ impl<Cx: TypeCx> ConstructorSet<Cx> {
     /// or slices. This can get subtle; see [`SplitConstructorSet`] for details of this operation
     /// and its invariants.
     #[instrument(level = "debug", skip(self, ctors), ret)]
-    pub(crate) fn split<'a>(
+    pub fn split<'a>(
         &self,
         ctors: impl Iterator<Item = &'a Constructor<Cx>> + Clone,
     ) -> SplitConstructorSet<Cx>

compiler/rustc_pattern_analysis/src/lib.rs

@@ -6,6 +6,7 @@ pub mod errors;
 #[cfg(feature = "rustc")]
 pub(crate) mod lints;
 pub mod pat;
+pub mod pat_column;
 #[cfg(feature = "rustc")]
 pub mod rustc;
 pub mod usefulness;
@@ -67,8 +68,9 @@ use rustc_span::ErrorGuaranteed;
 
 use crate::constructor::{Constructor, ConstructorSet, IntRange};
 #[cfg(feature = "rustc")]
-use crate::lints::{lint_nonexhaustive_missing_variants, PatternColumn};
+use crate::lints::lint_nonexhaustive_missing_variants;
 use crate::pat::DeconstructedPat;
+use crate::pat_column::PatternColumn;
 #[cfg(feature = "rustc")]
 use crate::rustc::RustcMatchCheckCtxt;
 #[cfg(feature = "rustc")]
@@ -126,14 +128,6 @@ pub trait TypeCx: Sized + fmt::Debug {
     }
 }
 
-/// Context that provides information global to a match.
-#[derive(derivative::Derivative)]
-#[derivative(Clone(bound = ""), Copy(bound = ""))]
-pub struct MatchCtxt<'a, Cx: TypeCx> {
-    /// The context for type information.
-    pub tycx: &'a Cx,
-}
-
 /// The arm of a match expression.
 #[derive(Debug)]
 #[derive(derivative::Derivative)]
@@ -154,15 +148,13 @@ pub fn analyze_match<'p, 'tcx>(
 ) -> Result<rustc::UsefulnessReport<'p, 'tcx>, ErrorGuaranteed> {
     let scrut_ty = tycx.reveal_opaque_ty(scrut_ty);
     let scrut_validity = ValidityConstraint::from_bool(tycx.known_valid_scrutinee);
-    let cx = MatchCtxt { tycx };
-
-    let report = compute_match_usefulness(cx, arms, scrut_ty, scrut_validity)?;
+    let report = compute_match_usefulness(tycx, arms, scrut_ty, scrut_validity)?;
 
     // Run the non_exhaustive_omitted_patterns lint. Only run on refutable patterns to avoid hitting
     // `if let`s. Only run if the match is exhaustive otherwise the error is redundant.
     if tycx.refutable && report.non_exhaustiveness_witnesses.is_empty() {
         let pat_column = PatternColumn::new(arms);
-        lint_nonexhaustive_missing_variants(cx, arms, &pat_column, scrut_ty)?;
+        lint_nonexhaustive_missing_variants(tycx, arms, &pat_column, scrut_ty)?;
     }
 
     Ok(report)

compiler/rustc_pattern_analysis/src/lints.rs

@@ -1,109 +1,24 @@
 use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
 use rustc_span::ErrorGuaranteed;
 
+use crate::constructor::Constructor;
 use crate::errors::{NonExhaustiveOmittedPattern, NonExhaustiveOmittedPatternLintOnArm, Uncovered};
-use crate::pat::PatOrWild;
-use crate::rustc::{
-    Constructor, DeconstructedPat, MatchArm, MatchCtxt, PlaceCtxt, RevealedTy, RustcMatchCheckCtxt,
-    SplitConstructorSet, WitnessPat,
-};
-
-/// A column of patterns in the matrix, where a column is the intuitive notion of "subpatterns that
-/// inspect the same subvalue/place".
-/// This is used to traverse patterns column-by-column for lints. Despite similarities with the
-/// algorithm in [`crate::usefulness`], this does a different traversal. Notably this is linear in
-/// the depth of patterns, whereas `compute_exhaustiveness_and_usefulness` is worst-case exponential
-/// (exhaustiveness is NP-complete). The core difference is that we treat sub-columns separately.
-///
-/// This must not contain an or-pattern. `expand_and_push` takes care to expand them.
-///
-/// This is not used in the usefulness algorithm; only in lints.
-#[derive(Debug)]
-pub(crate) struct PatternColumn<'p, 'tcx> {
-    patterns: Vec<&'p DeconstructedPat<'p, 'tcx>>,
-}
-
-impl<'p, 'tcx> PatternColumn<'p, 'tcx> {
-    pub(crate) fn new(arms: &[MatchArm<'p, 'tcx>]) -> Self {
-        let patterns = Vec::with_capacity(arms.len());
-        let mut column = PatternColumn { patterns };
-        for arm in arms {
-            column.expand_and_push(PatOrWild::Pat(arm.pat));
-        }
-        column
-    }
-    /// Pushes a pattern onto the column, expanding any or-patterns into its subpatterns.
-    /// Internal method, prefer [`PatternColumn::new`].
-    fn expand_and_push(&mut self, pat: PatOrWild<'p, RustcMatchCheckCtxt<'p, 'tcx>>) {
-        // We flatten or-patterns and skip algorithm-generated wildcards.
-        if pat.is_or_pat() {
-            self.patterns.extend(
-                pat.flatten_or_pat().into_iter().filter_map(|pat_or_wild| pat_or_wild.as_pat()),
-            )
-        } else if let Some(pat) = pat.as_pat() {
-            self.patterns.push(pat)
-        }
-    }
-
-    fn head_ty(&self) -> Option<RevealedTy<'tcx>> {
-        self.patterns.first().map(|pat| *pat.ty())
-    }
-
-    /// Do constructor splitting on the constructors of the column.
-    fn analyze_ctors(
-        &self,
-        pcx: &PlaceCtxt<'_, 'p, 'tcx>,
-    ) -> Result<SplitConstructorSet<'p, 'tcx>, ErrorGuaranteed> {
-        let column_ctors = self.patterns.iter().map(|p| p.ctor());
-        let ctors_for_ty = &pcx.ctors_for_ty()?;
-        Ok(ctors_for_ty.split(column_ctors))
-    }
-
-    /// Does specialization: given a constructor, this takes the patterns from the column that match
-    /// the constructor, and outputs their fields.
-    /// This returns one column per field of the constructor. They usually all have the same length
-    /// (the number of patterns in `self` that matched `ctor`), except that we expand or-patterns
-    /// which may change the lengths.
-    fn specialize(
-        &self,
-        pcx: &PlaceCtxt<'_, 'p, 'tcx>,
-        ctor: &Constructor<'p, 'tcx>,
-    ) -> Vec<PatternColumn<'p, 'tcx>> {
-        let arity = ctor.arity(pcx);
-        if arity == 0 {
-            return Vec::new();
-        }
-
-        // We specialize the column by `ctor`. This gives us `arity`-many columns of patterns. These
-        // columns may have different lengths in the presence of or-patterns (this is why we can't
-        // reuse `Matrix`).
-        let mut specialized_columns: Vec<_> =
-            (0..arity).map(|_| Self { patterns: Vec::new() }).collect();
-        let relevant_patterns =
-            self.patterns.iter().filter(|pat| ctor.is_covered_by(pcx, pat.ctor()));
-        for pat in relevant_patterns {
-            let specialized = pat.specialize(ctor, arity);
-            for (subpat, column) in specialized.into_iter().zip(&mut specialized_columns) {
-                column.expand_and_push(subpat);
-            }
-        }
-        specialized_columns
-    }
-}
+use crate::pat_column::PatternColumn;
+use crate::rustc::{RevealedTy, RustcMatchCheckCtxt, WitnessPat};
+use crate::MatchArm;
 
 /// Traverse the patterns to collect any variants of a non_exhaustive enum that fail to be mentioned
 /// in a given column.
 #[instrument(level = "debug", skip(cx), ret)]
 fn collect_nonexhaustive_missing_variants<'a, 'p, 'tcx>(
-    cx: MatchCtxt<'a, 'p, 'tcx>,
-    column: &PatternColumn<'p, 'tcx>,
+    cx: &RustcMatchCheckCtxt<'p, 'tcx>,
+    column: &PatternColumn<'p, RustcMatchCheckCtxt<'p, 'tcx>>,
 ) -> Result<Vec<WitnessPat<'p, 'tcx>>, ErrorGuaranteed> {
-    let Some(ty) = column.head_ty() else {
+    let Some(&ty) = column.head_ty() else {
         return Ok(Vec::new());
     };
-    let pcx = &PlaceCtxt::new_dummy(cx, &ty);
 
-    let set = column.analyze_ctors(pcx)?;
+    let set = column.analyze_ctors(cx, &ty)?;
     if set.present.is_empty() {
         // We can't consistently handle the case where no constructors are present (since this would
         // require digging deep through any type in case there's a non_exhaustive enum somewhere),
@@ -112,20 +27,20 @@ fn collect_nonexhaustive_missing_variants<'a, 'p, 'tcx>(
     }
 
     let mut witnesses = Vec::new();
-    if cx.tycx.is_foreign_non_exhaustive_enum(ty) {
+    if cx.is_foreign_non_exhaustive_enum(ty) {
         witnesses.extend(
             set.missing
                 .into_iter()
                 // This will list missing visible variants.
                 .filter(|c| !matches!(c, Constructor::Hidden | Constructor::NonExhaustive))
-                .map(|missing_ctor| WitnessPat::wild_from_ctor(pcx, missing_ctor)),
+                .map(|missing_ctor| WitnessPat::wild_from_ctor(cx, missing_ctor, ty)),
         )
     }
 
     // Recurse into the fields.
     for ctor in set.present {
-        let specialized_columns = column.specialize(pcx, &ctor);
-        let wild_pat = WitnessPat::wild_from_ctor(pcx, ctor);
+        let specialized_columns = column.specialize(cx, &ty, &ctor);
+        let wild_pat = WitnessPat::wild_from_ctor(cx, ctor, ty);
         for (i, col_i) in specialized_columns.iter().enumerate() {
             // Compute witnesses for each column.
             let wits_for_col_i = collect_nonexhaustive_missing_variants(cx, col_i)?;
@@ -141,18 +56,17 @@ fn collect_nonexhaustive_missing_variants<'a, 'p, 'tcx>(
     Ok(witnesses)
 }
 
-pub(crate) fn lint_nonexhaustive_missing_variants<'a, 'p, 'tcx>(
-    cx: MatchCtxt<'a, 'p, 'tcx>,
-    arms: &[MatchArm<'p, 'tcx>],
-    pat_column: &PatternColumn<'p, 'tcx>,
+pub(crate) fn lint_nonexhaustive_missing_variants<'p, 'tcx>(
+    rcx: &RustcMatchCheckCtxt<'p, 'tcx>,
+    arms: &[MatchArm<'p, RustcMatchCheckCtxt<'p, 'tcx>>],
+    pat_column: &PatternColumn<'p, RustcMatchCheckCtxt<'p, 'tcx>>,
     scrut_ty: RevealedTy<'tcx>,
 ) -> Result<(), ErrorGuaranteed> {
-    let rcx: &RustcMatchCheckCtxt<'_, '_> = cx.tycx;
     if !matches!(
         rcx.tcx.lint_level_at_node(NON_EXHAUSTIVE_OMITTED_PATTERNS, rcx.match_lint_level).0,
         rustc_session::lint::Level::Allow
     ) {
-        let witnesses = collect_nonexhaustive_missing_variants(cx, pat_column)?;
+        let witnesses = collect_nonexhaustive_missing_variants(rcx, pat_column)?;
         if !witnesses.is_empty() {
             // Report that a match of a `non_exhaustive` enum marked with `non_exhaustive_omitted_patterns`
             // is not exhaustive enough.