Rollup merge of rust-lang#122439 - Nadrieril:store-built-place, r=compiler-errors

match lowering: build the `Place` instead of keeping a `PlaceBuilder` around

Outside of `MatchPair::new` we don't construct new places, so we don't need to keep a `PlaceBuilder` around.

A bit annoyingly we have to store an `Option<Place>` even though it's never `None` after simplification, but the alternative would be to re-entangle `MatchPair` construction and simplification and I'd rather not do that.

Author: matthiaskrgr

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -1111,7 +1111,10 @@ impl<'pat, 'tcx> TestCase<'pat, 'tcx> {
 #[derive(Debug, Clone)]
 pub(crate) struct MatchPair<'pat, 'tcx> {
     /// This place...
-    place: PlaceBuilder<'tcx>,
+    // This can be `None` if it referred to a non-captured place in a closure.
+    // Invariant: place.is_none() => test_case is Irrefutable
+    // In other words this must be `Some(_)` after simplification.
+    place: Option<Place<'tcx>>,
 
     /// ... must pass this test...
     // Invariant: after creation and simplification in `Candidate::new()`, this must not be
@@ -1595,11 +1598,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     fn pick_test(
         &mut self,
         candidates: &mut [&mut Candidate<'_, 'tcx>],
-    ) -> (PlaceBuilder<'tcx>, Test<'tcx>) {
+    ) -> (Place<'tcx>, Test<'tcx>) {
         // Extract the match-pair from the highest priority candidate
         let match_pair = &candidates.first().unwrap().match_pairs[0];
         let test = self.test(match_pair);
-        let match_place = match_pair.place.clone();
+        // Unwrap is ok after simplification.
+        let match_place = match_pair.place.unwrap();
         debug!(?test, ?match_pair);
 
         (match_place, test)
@@ -1640,7 +1644,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// - candidate 1 becomes `[y @ false]` since we know that `x` was `false`.
     fn sort_candidates<'b, 'c, 'pat>(
         &mut self,
-        match_place: &PlaceBuilder<'tcx>,
+        match_place: Place<'tcx>,
         test: &Test<'tcx>,
         mut candidates: &'b mut [&'c mut Candidate<'pat, 'tcx>],
     ) -> (
@@ -1658,7 +1662,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // sorting.
         while let Some(candidate) = candidates.first_mut() {
             let Some(branch) =
-                self.sort_candidate(&match_place, test, candidate, &target_candidates)
+                self.sort_candidate(match_place, test, candidate, &target_candidates)
             else {
                 break;
             };
@@ -1786,7 +1790,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // For each of the N possible test outcomes, build the vector of candidates that applies if
         // the test has that particular outcome.
         let (remaining_candidates, target_candidates) =
-            self.sort_candidates(&match_place, &test, candidates);
+            self.sort_candidates(match_place, &test, candidates);
 
         // The block that we should branch to if none of the
         // `target_candidates` match.
@@ -1826,7 +1830,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             scrutinee_span,
             start_block,
             remainder_start,
-            &match_place,
+            match_place,
             &test,
             target_blocks,
         );

compiler/rustc_mir_build/src/build/matches/test.rs

@@ -5,7 +5,6 @@
 // identify what tests are needed, perform the tests, and then filter
 // the candidates based on the result.
 
-use crate::build::expr::as_place::PlaceBuilder;
 use crate::build::matches::{Candidate, MatchPair, Test, TestBranch, TestCase, TestKind};
 use crate::build::Builder;
 use rustc_data_structures::fx::FxIndexMap;
@@ -55,18 +54,17 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         Test { span: match_pair.pattern.span, kind }
     }
 
-    #[instrument(skip(self, target_blocks, place_builder), level = "debug")]
+    #[instrument(skip(self, target_blocks, place), level = "debug")]
     pub(super) fn perform_test(
         &mut self,
         match_start_span: Span,
         scrutinee_span: Span,
         block: BasicBlock,
         otherwise_block: BasicBlock,
-        place_builder: &PlaceBuilder<'tcx>,
+        place: Place<'tcx>,
         test: &Test<'tcx>,
         target_blocks: FxIndexMap<TestBranch<'tcx>, BasicBlock>,
     ) {
-        let place = place_builder.to_place(self);
         let place_ty = place.ty(&self.local_decls, self.tcx);
         debug!(?place, ?place_ty);
         let target_block = |branch| target_blocks.get(&branch).copied().unwrap_or(otherwise_block);
@@ -475,7 +473,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// tighter match code if we do something a bit different.
     pub(super) fn sort_candidate(
         &mut self,
-        test_place: &PlaceBuilder<'tcx>,
+        test_place: Place<'tcx>,
         test: &Test<'tcx>,
         candidate: &mut Candidate<'_, 'tcx>,
         sorted_candidates: &FxIndexMap<TestBranch<'tcx>, Vec<&mut Candidate<'_, 'tcx>>>,
@@ -486,8 +484,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // than one, but it'd be very unusual to have two sides that
         // both require tests; you'd expect one side to be simplified
         // away.)
-        let (match_pair_index, match_pair) =
-            candidate.match_pairs.iter().enumerate().find(|&(_, mp)| mp.place == *test_place)?;
+        let (match_pair_index, match_pair) = candidate
+            .match_pairs
+            .iter()
+            .enumerate()
+            .find(|&(_, mp)| mp.place == Some(test_place))?;
 
         let fully_matched;
         let ret = match (&test.kind, &match_pair.test_case) {
@@ -521,7 +522,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     candidate
                         .match_pairs
                         .iter()
-                        .any(|mp| mp.place == *test_place && is_covering_range(&mp.test_case))
+                        .any(|mp| mp.place == Some(test_place) && is_covering_range(&mp.test_case))
                 };
                 if sorted_candidates
                     .get(&TestBranch::Failure)

compiler/rustc_mir_build/src/build/matches/util.rs

@@ -95,35 +95,37 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
 impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
     pub(in crate::build) fn new(
-        mut place: PlaceBuilder<'tcx>,
+        mut place_builder: PlaceBuilder<'tcx>,
         pattern: &'pat Pat<'tcx>,
         cx: &mut Builder<'_, 'tcx>,
     ) -> MatchPair<'pat, 'tcx> {
         // Force the place type to the pattern's type.
         // FIXME(oli-obk): can we use this to simplify slice/array pattern hacks?
-        if let Some(resolved) = place.resolve_upvar(cx) {
-            place = resolved;
+        if let Some(resolved) = place_builder.resolve_upvar(cx) {
+            place_builder = resolved;
         }
 
         // Only add the OpaqueCast projection if the given place is an opaque type and the
         // expected type from the pattern is not.
-        let may_need_cast = match place.base() {
+        let may_need_cast = match place_builder.base() {
             PlaceBase::Local(local) => {
-                let ty = Place::ty_from(local, place.projection(), &cx.local_decls, cx.tcx).ty;
+                let ty =
+                    Place::ty_from(local, place_builder.projection(), &cx.local_decls, cx.tcx).ty;
                 ty != pattern.ty && ty.has_opaque_types()
             }
             _ => true,
         };
         if may_need_cast {
-            place = place.project(ProjectionElem::OpaqueCast(pattern.ty));
+            place_builder = place_builder.project(ProjectionElem::OpaqueCast(pattern.ty));
         }
 
+        let place = place_builder.try_to_place(cx);
         let default_irrefutable = || TestCase::Irrefutable { binding: None, ascription: None };
         let mut subpairs = Vec::new();
         let test_case = match pattern.kind {
             PatKind::Never | PatKind::Wild | PatKind::Error(_) => default_irrefutable(),
             PatKind::Or { ref pats } => TestCase::Or {
-                pats: pats.iter().map(|pat| FlatPat::new(place.clone(), pat, cx)).collect(),
+                pats: pats.iter().map(|pat| FlatPat::new(place_builder.clone(), pat, cx)).collect(),
             },
 
             PatKind::Range(ref range) => {
@@ -142,13 +144,13 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
                 ..
             } => {
                 // Apply the type ascription to the value at `match_pair.place`
-                let ascription = place.try_to_place(cx).map(|source| super::Ascription {
+                let ascription = place.map(|source| super::Ascription {
                     annotation: annotation.clone(),
                     source,
                     variance,
                 });
 
-                subpairs.push(MatchPair::new(place.clone(), subpattern, cx));
+                subpairs.push(MatchPair::new(place_builder, subpattern, cx));
                 TestCase::Irrefutable { ascription, binding: None }
             }
 
@@ -161,7 +163,7 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
                 ref subpattern,
                 is_primary: _,
             } => {
-                let binding = place.try_to_place(cx).map(|source| super::Binding {
+                let binding = place.map(|source| super::Binding {
                     span: pattern.span,
                     source,
                     var_id: var,
@@ -170,14 +172,14 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
 
                 if let Some(subpattern) = subpattern.as_ref() {
                     // this is the `x @ P` case; have to keep matching against `P` now
-                    subpairs.push(MatchPair::new(place.clone(), subpattern, cx));
+                    subpairs.push(MatchPair::new(place_builder, subpattern, cx));
                 }
                 TestCase::Irrefutable { ascription: None, binding }
             }
 
             PatKind::InlineConstant { subpattern: ref pattern, def, .. } => {
                 // Apply a type ascription for the inline constant to the value at `match_pair.place`
-                let ascription = place.try_to_place(cx).map(|source| {
+                let ascription = place.map(|source| {
                     let span = pattern.span;
                     let parent_id = cx.tcx.typeck_root_def_id(cx.def_id.to_def_id());
                     let args = ty::InlineConstArgs::new(
@@ -203,16 +205,16 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
                     super::Ascription { annotation, source, variance: ty::Contravariant }
                 });
 
-                subpairs.push(MatchPair::new(place.clone(), pattern, cx));
+                subpairs.push(MatchPair::new(place_builder, pattern, cx));
                 TestCase::Irrefutable { ascription, binding: None }
             }
 
             PatKind::Array { ref prefix, ref slice, ref suffix } => {
-                cx.prefix_slice_suffix(&mut subpairs, &place, prefix, slice, suffix);
+                cx.prefix_slice_suffix(&mut subpairs, &place_builder, prefix, slice, suffix);
                 default_irrefutable()
             }
             PatKind::Slice { ref prefix, ref slice, ref suffix } => {
-                cx.prefix_slice_suffix(&mut subpairs, &place, prefix, slice, suffix);
+                cx.prefix_slice_suffix(&mut subpairs, &place_builder, prefix, slice, suffix);
 
                 if prefix.is_empty() && slice.is_some() && suffix.is_empty() {
                     default_irrefutable()
@@ -225,7 +227,7 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
             }
 
             PatKind::Variant { adt_def, variant_index, args, ref subpatterns } => {
-                let downcast_place = place.clone().downcast(adt_def, variant_index); // `(x as Variant)`
+                let downcast_place = place_builder.downcast(adt_def, variant_index); // `(x as Variant)`
                 subpairs = cx.field_match_pairs(downcast_place, subpatterns);
 
                 let irrefutable = adt_def.variants().iter_enumerated().all(|(i, v)| {
@@ -247,13 +249,12 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
             }
 
             PatKind::Leaf { ref subpatterns } => {
-                subpairs = cx.field_match_pairs(place.clone(), subpatterns);
+                subpairs = cx.field_match_pairs(place_builder, subpatterns);
                 default_irrefutable()
             }
 
             PatKind::Deref { ref subpattern } => {
-                let place_builder = place.clone().deref();
-                subpairs.push(MatchPair::new(place_builder, subpattern, cx));
+                subpairs.push(MatchPair::new(place_builder.deref(), subpattern, cx));
                 default_irrefutable()
             }
 
@@ -310,8 +311,8 @@ impl<'a, 'b, 'tcx> FakeBorrowCollector<'a, 'b, 'tcx> {
             }
         } else {
             // Insert a Shallow borrow of any place that is switched on.
-            if let Some(resolved_place) = match_pair.place.try_to_place(self.cx) {
-                self.fake_borrows.insert(resolved_place);
+            if let Some(place) = match_pair.place {
+                self.fake_borrows.insert(place);
             }
 
             for subpair in &match_pair.subpairs {