Rollup merge of #100034 - tmiasko:elaborate-box-derefs, r=oli-obk

Elaborate all box dereferences in `ElaborateBoxDerefs`

so that it is the only pass responsible for elaboration, instead of
splitting this responsibility between the `StateTransform` and
`ElaborateBoxDerefs`.

compiler/rustc_middle/src/mir/mod.rs

@@ -1531,6 +1531,7 @@ impl<'tcx> Place<'tcx> {
 }
 
 impl From<Local> for Place<'_> {
+    #[inline]
     fn from(local: Local) -> Self {
         Place { local, projection: List::empty() }
     }

compiler/rustc_mir_dataflow/src/impls/liveness.rs

@@ -23,12 +23,6 @@ use crate::{Analysis, AnalysisDomain, Backward, CallReturnPlaces, GenKill, GenKi
 /// [liveness]: https://en.wikipedia.org/wiki/Live_variable_analysis
 pub struct MaybeLiveLocals;
 
-impl MaybeLiveLocals {
-    fn transfer_function<'a, T>(&self, trans: &'a mut T) -> TransferFunction<'a, T> {
-        TransferFunction(trans)
-    }
-}
-
 impl<'tcx> AnalysisDomain<'tcx> for MaybeLiveLocals {
     type Domain = ChunkedBitSet<Local>;
     type Direction = Backward;
@@ -54,7 +48,7 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeLiveLocals {
         statement: &mir::Statement<'tcx>,
         location: Location,
     ) {
-        self.transfer_function(trans).visit_statement(statement, location);
+        TransferFunction(trans).visit_statement(statement, location);
     }
 
     fn terminator_effect(
@@ -63,7 +57,7 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeLiveLocals {
         terminator: &mir::Terminator<'tcx>,
         location: Location,
     ) {
-        self.transfer_function(trans).visit_terminator(terminator, location);
+        TransferFunction(trans).visit_terminator(terminator, location);
     }
 
     fn call_return_effect(
@@ -85,9 +79,11 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeLiveLocals {
         _resume_block: mir::BasicBlock,
         resume_place: mir::Place<'tcx>,
     ) {
-        if let Some(local) = resume_place.as_local() {
-            trans.kill(local);
-        }
+        YieldResumeEffect(trans).visit_place(
+            &resume_place,
+            PlaceContext::MutatingUse(MutatingUseContext::Yield),
+            Location::START,
+        )
     }
 }
 
@@ -98,28 +94,51 @@ where
     T: GenKill<Local>,
 {
     fn visit_place(&mut self, place: &mir::Place<'tcx>, context: PlaceContext, location: Location) {
-        let local = place.local;
-
-        // We purposefully do not call `super_place` here to avoid calling `visit_local` for this
-        // place with one of the `Projection` variants of `PlaceContext`.
-        self.visit_projection(place.as_ref(), context, location);
+        if let PlaceContext::MutatingUse(MutatingUseContext::Yield) = context {
+            // The resume place is evaluated and assigned to only after generator resumes, so its
+            // effect is handled separately in `yield_resume_effect`.
+            return;
+        }
 
         match DefUse::for_place(*place, context) {
-            Some(DefUse::Def) => self.0.kill(local),
-            Some(DefUse::Use) => self.0.gen(local),
+            Some(DefUse::Def) => {
+                if let PlaceContext::MutatingUse(
+                    MutatingUseContext::Call | MutatingUseContext::AsmOutput,
+                ) = context
+                {
+                    // For the associated terminators, this is only a `Def` when the terminator returns
+                    // "successfully." As such, we handle this case separately in `call_return_effect`
+                    // above. However, if the place looks like `*_5`, this is still unconditionally a use of
+                    // `_5`.
+                } else {
+                    self.0.kill(place.local);
+                }
+            }
+            Some(DefUse::Use) => self.0.gen(place.local),
             None => {}
         }
+
+        self.visit_projection(place.as_ref(), context, location);
     }
 
     fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) {
-        // Because we do not call `super_place` above, `visit_local` is only called for locals that
-        // do not appear as part of  a `Place` in the MIR. This handles cases like the implicit use
-        // of the return place in a `Return` terminator or the index in an `Index` projection.
-        match DefUse::for_place(local.into(), context) {
-            Some(DefUse::Def) => self.0.kill(local),
-            Some(DefUse::Use) => self.0.gen(local),
-            None => {}
-        }
+        DefUse::apply(self.0, local.into(), context);
+    }
+}
+
+struct YieldResumeEffect<'a, T>(&'a mut T);
+
+impl<'tcx, T> Visitor<'tcx> for YieldResumeEffect<'_, T>
+where
+    T: GenKill<Local>,
+{
+    fn visit_place(&mut self, place: &mir::Place<'tcx>, context: PlaceContext, location: Location) {
+        DefUse::apply(self.0, *place, context);
+        self.visit_projection(place.as_ref(), context, location);
+    }
+
+    fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) {
+        DefUse::apply(self.0, local.into(), context);
     }
 }
 
@@ -130,11 +149,25 @@ enum DefUse {
 }
 
 impl DefUse {
+    fn apply<'tcx>(trans: &mut impl GenKill<Local>, place: Place<'tcx>, context: PlaceContext) {
+        match DefUse::for_place(place, context) {
+            Some(DefUse::Def) => trans.kill(place.local),
+            Some(DefUse::Use) => trans.gen(place.local),
+            None => {}
+        }
+    }
+
     fn for_place<'tcx>(place: Place<'tcx>, context: PlaceContext) -> Option<DefUse> {
         match context {
             PlaceContext::NonUse(_) => None,
 
-            PlaceContext::MutatingUse(MutatingUseContext::Store | MutatingUseContext::Deinit) => {
+            PlaceContext::MutatingUse(
+                MutatingUseContext::Call
+                | MutatingUseContext::Yield
+                | MutatingUseContext::AsmOutput
+                | MutatingUseContext::Store
+                | MutatingUseContext::Deinit,
+            ) => {
                 if place.is_indirect() {
                     // Treat derefs as a use of the base local. `*p = 4` is not a def of `p` but a
                     // use.
@@ -152,16 +185,6 @@ impl DefUse {
                 place.is_indirect().then_some(DefUse::Use)
             }
 
-            // For the associated terminators, this is only a `Def` when the terminator returns
-            // "successfully." As such, we handle this case separately in `call_return_effect`
-            // above. However, if the place looks like `*_5`, this is still unconditionally a use of
-            // `_5`.
-            PlaceContext::MutatingUse(
-                MutatingUseContext::Call
-                | MutatingUseContext::Yield
-                | MutatingUseContext::AsmOutput,
-            ) => place.is_indirect().then_some(DefUse::Use),
-
             // All other contexts are uses...
             PlaceContext::MutatingUse(
                 MutatingUseContext::AddressOf
@@ -290,8 +313,10 @@ impl<'a, 'tcx> Analysis<'tcx> for MaybeTransitiveLiveLocals<'a> {
         _resume_block: mir::BasicBlock,
         resume_place: mir::Place<'tcx>,
     ) {
-        if let Some(local) = resume_place.as_local() {
-            trans.remove(local);
-        }
+        YieldResumeEffect(trans).visit_place(
+            &resume_place,
+            PlaceContext::MutatingUse(MutatingUseContext::Yield),
+            Location::START,
+        )
     }
 }

compiler/rustc_mir_transform/src/elaborate_box_derefs.rs

@@ -107,27 +107,8 @@ impl<'tcx> MirPass<'tcx> for ElaborateBoxDerefs {
             let mut visitor =
                 ElaborateBoxDerefVisitor { tcx, unique_did, nonnull_did, local_decls, patch };
 
-            for (block, BasicBlockData { statements, terminator, .. }) in
-                body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut()
-            {
-                let mut index = 0;
-                for statement in statements {
-                    let location = Location { block, statement_index: index };
-                    visitor.visit_statement(statement, location);
-                    index += 1;
-                }
-
-                let location = Location { block, statement_index: index };
-                match terminator {
-                    // yielding into a box is handled when lowering generators
-                    Some(Terminator { kind: TerminatorKind::Yield { value, .. }, .. }) => {
-                        visitor.visit_operand(value, location);
-                    }
-                    Some(terminator) => {
-                        visitor.visit_terminator(terminator, location);
-                    }
-                    None => {}
-                }
+            for (block, data) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
+                visitor.visit_basic_block_data(block, data);
             }
 
             visitor.patch.apply(body);

compiler/rustc_mir_transform/src/generator.rs

@@ -1182,8 +1182,6 @@ fn create_cases<'tcx>(
     transform: &TransformVisitor<'tcx>,
     operation: Operation,
 ) -> Vec<(usize, BasicBlock)> {
-    let tcx = transform.tcx;
-
     let source_info = SourceInfo::outermost(body.span);
 
     transform
@@ -1216,85 +1214,13 @@ fn create_cases<'tcx>(
                 if operation == Operation::Resume {
                     // Move the resume argument to the destination place of the `Yield` terminator
                     let resume_arg = Local::new(2); // 0 = return, 1 = self
-
-                    // handle `box yield` properly
-                    let box_place = if let [projection @ .., ProjectionElem::Deref] =
-                        &**point.resume_arg.projection
-                    {
-                        let box_place =
-                            Place::from(point.resume_arg.local).project_deeper(projection, tcx);
-
-                        let box_ty = box_place.ty(&body.local_decls, tcx).ty;
-
-                        if box_ty.is_box() { Some((box_place, box_ty)) } else { None }
-                    } else {
-                        None
-                    };
-
-                    if let Some((box_place, box_ty)) = box_place {
-                        let unique_did = box_ty
-                            .ty_adt_def()
-                            .expect("expected Box to be an Adt")
-                            .non_enum_variant()
-                            .fields[0]
-                            .did;
-
-                        let Some(nonnull_def) = tcx.type_of(unique_did).ty_adt_def() else {
-                            span_bug!(tcx.def_span(unique_did), "expected Box to contain Unique")
-                        };
-
-                        let nonnull_did = nonnull_def.non_enum_variant().fields[0].did;
-
-                        let (unique_ty, nonnull_ty, ptr_ty) =
-                            crate::elaborate_box_derefs::build_ptr_tys(
-                                tcx,
-                                box_ty.boxed_ty(),
-                                unique_did,
-                                nonnull_did,
-                            );
-
-                        let ptr_local = body.local_decls.push(LocalDecl::new(ptr_ty, body.span));
-
-                        statements.push(Statement {
-                            source_info,
-                            kind: StatementKind::StorageLive(ptr_local),
-                        });
-
-                        statements.push(Statement {
-                            source_info,
-                            kind: StatementKind::Assign(Box::new((
-                                Place::from(ptr_local),
-                                Rvalue::Use(Operand::Copy(box_place.project_deeper(
-                                    &crate::elaborate_box_derefs::build_projection(
-                                        unique_ty, nonnull_ty, ptr_ty,
-                                    ),
-                                    tcx,
-                                ))),
-                            ))),
-                        });
-
-                        statements.push(Statement {
-                            source_info,
-                            kind: StatementKind::Assign(Box::new((
-                                Place::from(ptr_local)
-                                    .project_deeper(&[ProjectionElem::Deref], tcx),
-                                Rvalue::Use(Operand::Move(resume_arg.into())),
-                            ))),
-                        });
-
-                        statements.push(Statement {
-                            source_info,
-                            kind: StatementKind::StorageDead(ptr_local),
-                        });
-                    } else {
-                        statements.push(Statement {
-                            source_info,
-                            kind: StatementKind::Assign(Box::new((
-                                point.resume_arg,
-                                Rvalue::Use(Operand::Move(resume_arg.into())),
-                            ))),
-                        });
-                    }
+                    statements.push(Statement {
+                        source_info,
+                        kind: StatementKind::Assign(Box::new((
+                            point.resume_arg,
+                            Rvalue::Use(Operand::Move(resume_arg.into())),
+                        ))),
+                    });
                 }
 
                 // Then jump to the real target