Unrolled build for rust-lang#137465

Rollup merge of rust-lang#137465 - Zalathar:visit-primary, r=oli-obk

mir_build: Avoid some useless work when visiting "primary" bindings

While looking over `visit_primary_bindings`, I noticed that it does a bunch of extra work to build up a collection of “user-type projections”, even though 2/3 of its call sites don't even use them. Those callers can get the same result via `thir::Pat::walk_always`.

(And it turns out that doing so also avoids creating some redundant user-type entries in MIR for some binding constructs.)

I also noticed that even when the user-type projections *are* used, the process of building them ends up eagerly cloning some nested vectors at every recursion step, even in cases where they won't be used because the current subpattern has no bindings. To avoid this, the visit method now assembles a linked list on the stack containing the information that *would* be needed to create projections, and only creates the concrete projections as needed when a primary binding is encountered.

Some relevant prior PRs:
- rust-lang#55274
- rust-lang@0bfe184 in rust-lang#55937

---

There should be no user-visible change in compiler output.

Author: rust-timer

compiler/rustc_middle/src/mir/mod.rs

@@ -33,8 +33,8 @@ use crate::mir::interpret::{AllocRange, Scalar};
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::print::{FmtPrinter, Printer, pretty_print_const, with_no_trimmed_paths};
 use crate::ty::{
-    self, AdtDef, GenericArg, GenericArgsRef, Instance, InstanceKind, List, Ty, TyCtxt,
-    TypeVisitableExt, TypingEnv, UserTypeAnnotationIndex,
+    self, GenericArg, GenericArgsRef, Instance, InstanceKind, List, Ty, TyCtxt, TypeVisitableExt,
+    TypingEnv, UserTypeAnnotationIndex,
 };
 
 mod basic_blocks;
@@ -1482,53 +1482,10 @@ pub struct UserTypeProjections {
     pub contents: Vec<UserTypeProjection>,
 }
 
-impl<'tcx> UserTypeProjections {
-    pub fn none() -> Self {
-        UserTypeProjections { contents: vec![] }
-    }
-
-    pub fn is_empty(&self) -> bool {
-        self.contents.is_empty()
-    }
-
+impl UserTypeProjections {
     pub fn projections(&self) -> impl Iterator<Item = &UserTypeProjection> + ExactSizeIterator {
         self.contents.iter()
     }
-
-    pub fn push_user_type(mut self, base_user_type: UserTypeAnnotationIndex) -> Self {
-        self.contents.push(UserTypeProjection { base: base_user_type, projs: vec![] });
-        self
-    }
-
-    fn map_projections(mut self, f: impl FnMut(UserTypeProjection) -> UserTypeProjection) -> Self {
-        self.contents = self.contents.into_iter().map(f).collect();
-        self
-    }
-
-    pub fn index(self) -> Self {
-        self.map_projections(|pat_ty_proj| pat_ty_proj.index())
-    }
-
-    pub fn subslice(self, from: u64, to: u64) -> Self {
-        self.map_projections(|pat_ty_proj| pat_ty_proj.subslice(from, to))
-    }
-
-    pub fn deref(self) -> Self {
-        self.map_projections(|pat_ty_proj| pat_ty_proj.deref())
-    }
-
-    pub fn leaf(self, field: FieldIdx) -> Self {
-        self.map_projections(|pat_ty_proj| pat_ty_proj.leaf(field))
-    }
-
-    pub fn variant(
-        self,
-        adt_def: AdtDef<'tcx>,
-        variant_index: VariantIdx,
-        field_index: FieldIdx,
-    ) -> Self {
-        self.map_projections(|pat_ty_proj| pat_ty_proj.variant(adt_def, variant_index, field_index))
-    }
 }
 
 /// Encodes the effect of a user-supplied type annotation on the
@@ -1553,42 +1510,6 @@ pub struct UserTypeProjection {
     pub projs: Vec<ProjectionKind>,
 }
 
-impl UserTypeProjection {
-    pub(crate) fn index(mut self) -> Self {
-        self.projs.push(ProjectionElem::Index(()));
-        self
-    }
-
-    pub(crate) fn subslice(mut self, from: u64, to: u64) -> Self {
-        self.projs.push(ProjectionElem::Subslice { from, to, from_end: true });
-        self
-    }
-
-    pub(crate) fn deref(mut self) -> Self {
-        self.projs.push(ProjectionElem::Deref);
-        self
-    }
-
-    pub(crate) fn leaf(mut self, field: FieldIdx) -> Self {
-        self.projs.push(ProjectionElem::Field(field, ()));
-        self
-    }
-
-    pub(crate) fn variant(
-        mut self,
-        adt_def: AdtDef<'_>,
-        variant_index: VariantIdx,
-        field_index: FieldIdx,
-    ) -> Self {
-        self.projs.push(ProjectionElem::Downcast(
-            Some(adt_def.variant(variant_index).name),
-            variant_index,
-        ));
-        self.projs.push(ProjectionElem::Field(field_index, ()));
-        self
-    }
-}
-
 rustc_index::newtype_index! {
     #[derive(HashStable)]
     #[encodable]

compiler/rustc_middle/src/thir.rs

@@ -783,8 +783,12 @@ pub enum PatKind<'tcx> {
         var: LocalVarId,
         ty: Ty<'tcx>,
         subpattern: Option<Box<Pat<'tcx>>>,
+
         /// Is this the leftmost occurrence of the binding, i.e., is `var` the
         /// `HirId` of this pattern?
+        ///
+        /// (The same binding can occur multiple times in different branches of
+        /// an or-pattern, but only one of them will be primary.)
         is_primary: bool,
     },
 

compiler/rustc_mir_build/src/builder/block.rs

@@ -199,19 +199,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             None,
                             Some((Some(&destination), initializer_span)),
                         );
-                        this.visit_primary_bindings(
-                            pattern,
-                            UserTypeProjections::none(),
-                            &mut |this, _, _, node, span, _, _| {
-                                this.storage_live_binding(
-                                    block,
-                                    node,
-                                    span,
-                                    OutsideGuard,
-                                    ScheduleDrops::Yes,
-                                );
-                            },
-                        );
+                        this.visit_primary_bindings(pattern, &mut |this, node, span| {
+                            this.storage_live_binding(
+                                block,
+                                node,
+                                span,
+                                OutsideGuard,
+                                ScheduleDrops::Yes,
+                            );
+                        });
                         let else_block_span = this.thir[*else_block].span;
                         let (matching, failure) =
                             this.in_if_then_scope(last_remainder_scope, else_block_span, |this| {
@@ -295,20 +291,16 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         });
 
                         debug!("ast_block_stmts: pattern={:?}", pattern);
-                        this.visit_primary_bindings(
-                            pattern,
-                            UserTypeProjections::none(),
-                            &mut |this, _, _, node, span, _, _| {
-                                this.storage_live_binding(
-                                    block,
-                                    node,
-                                    span,
-                                    OutsideGuard,
-                                    ScheduleDrops::Yes,
-                                );
-                                this.schedule_drop_for_binding(node, span, OutsideGuard);
-                            },
-                        )
+                        this.visit_primary_bindings(pattern, &mut |this, node, span| {
+                            this.storage_live_binding(
+                                block,
+                                node,
+                                span,
+                                OutsideGuard,
+                                ScheduleDrops::Yes,
+                            );
+                            this.schedule_drop_for_binding(node, span, OutsideGuard);
+                        })
                     }
 
                     // Enter the visibility scope, after evaluating the initializer.