Refactor post borrowck cleanup passes

compiler/rustc_mir_transform/src/cleanup_post_borrowck.rs

@@ -1,59 +1,48 @@
-//! This module provides a pass to replacing the following statements with
-//! [`Nop`]s
+//! This module provides a pass that removes parts of MIR that are no longer relevant after
+//! analysis phase and borrowck. In particular, it removes false edges, user type annotations and
+//! replaces following statements with [`Nop`]s:
 //!
 //!   - [`AscribeUserType`]
 //!   - [`FakeRead`]
 //!   - [`Assign`] statements with a [`Shallow`] borrow
 //!
-//! The `CleanFakeReadsAndBorrows` "pass" is actually implemented as two
-//! traversals (aka visits) of the input MIR. The first traversal,
-//! `DeleteAndRecordFakeReads`, deletes the fake reads and finds the
-//! temporaries read by [`ForMatchGuard`] reads, and `DeleteFakeBorrows`
-//! deletes the initialization of those temporaries.
-//!
 //! [`AscribeUserType`]: rustc_middle::mir::StatementKind::AscribeUserType
-//! [`Shallow`]: rustc_middle::mir::BorrowKind::Shallow
-//! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
 //! [`Assign`]: rustc_middle::mir::StatementKind::Assign
-//! [`ForMatchGuard`]: rustc_middle::mir::FakeReadCause::ForMatchGuard
+//! [`FakeRead`]: rustc_middle::mir::StatementKind::FakeRead
 //! [`Nop`]: rustc_middle::mir::StatementKind::Nop
+//! [`Shallow`]: rustc_middle::mir::BorrowKind::Shallow
 
 use crate::MirPass;
-use rustc_middle::mir::visit::MutVisitor;
-use rustc_middle::mir::{Body, BorrowKind, Location, Rvalue};
-use rustc_middle::mir::{Statement, StatementKind};
+use rustc_middle::mir::{Body, BorrowKind, Rvalue, StatementKind, TerminatorKind};
 use rustc_middle::ty::TyCtxt;
 
-pub struct CleanupNonCodegenStatements;
+pub struct CleanupPostBorrowck;
 
-pub struct DeleteNonCodegenStatements<'tcx> {
-    tcx: TyCtxt<'tcx>,
-}
+impl<'tcx> MirPass<'tcx> for CleanupPostBorrowck {
+    fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        for basic_block in body.basic_blocks.as_mut() {
+            for statement in basic_block.statements.iter_mut() {
+                match statement.kind {
+                    StatementKind::AscribeUserType(..)
+                    | StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Shallow, _)))
+                    | StatementKind::FakeRead(..) => statement.make_nop(),
+                    _ => (),
+                }
+            }
+            let terminator = basic_block.terminator_mut();
+            match terminator.kind {
+                TerminatorKind::FalseEdge { real_target, .. }
+                | TerminatorKind::FalseUnwind { real_target, .. } => {
+                    terminator.kind = TerminatorKind::Goto { target: real_target };
+                }
+                _ => {}
+            }
+        }
 
-impl<'tcx> MirPass<'tcx> for CleanupNonCodegenStatements {
-    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        let mut delete = DeleteNonCodegenStatements { tcx };
-        delete.visit_body_preserves_cfg(body);
         body.user_type_annotations.raw.clear();
 
         for decl in &mut body.local_decls {
             decl.user_ty = None;
         }
     }
 }
-
-impl<'tcx> MutVisitor<'tcx> for DeleteNonCodegenStatements<'tcx> {
-    fn tcx(&self) -> TyCtxt<'tcx> {
-        self.tcx
-    }
-
-    fn visit_statement(&mut self, statement: &mut Statement<'tcx>, location: Location) {
-        match statement.kind {
-            StatementKind::AscribeUserType(..)
-            | StatementKind::Assign(box (_, Rvalue::Ref(_, BorrowKind::Shallow, _)))
-            | StatementKind::FakeRead(..) => statement.make_nop(),
-            _ => (),
-        }
-        self.super_statement(statement, location);
-    }
-}

compiler/rustc_mir_transform/src/lib.rs

@@ -77,8 +77,6 @@ mod match_branches;
 mod multiple_return_terminators;
 mod normalize_array_len;
 mod nrvo;
-// This pass is public to allow external drivers to perform MIR cleanup
-pub mod remove_false_edges;
 mod remove_noop_landing_pads;
 mod remove_storage_markers;
 mod remove_uninit_drops;
@@ -494,10 +492,9 @@ fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>
 /// After this series of passes, no lifetime analysis based on borrowing can be done.
 fn run_analysis_cleanup_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     let passes: &[&dyn MirPass<'tcx>] = &[
-        &remove_false_edges::RemoveFalseEdges,
+        &cleanup_post_borrowck::CleanupPostBorrowck,
         &simplify_branches::SimplifyConstCondition::new("initial"),
         &remove_noop_landing_pads::RemoveNoopLandingPads,
-        &cleanup_post_borrowck::CleanupNonCodegenStatements,
         &simplify::SimplifyCfg::new("early-opt"),
         &deref_separator::Derefer,
     ];

src/test/mir-opt/remove_fake_borrows.match_guard.CleanupNonCodegenStatements.diff → src/test/mir-opt/remove_fake_borrows.match_guard.CleanupPostBorrowck.diff

@@ -1,5 +1,5 @@
-- // MIR for `match_guard` before CleanupNonCodegenStatements
-+ // MIR for `match_guard` after CleanupNonCodegenStatements
+- // MIR for `match_guard` before CleanupPostBorrowck
++ // MIR for `match_guard` after CleanupPostBorrowck
 
   fn match_guard(_1: Option<&&i32>, _2: bool) -> i32 {
       debug x => _1;                       // in scope 0 at $DIR/remove_fake_borrows.rs:+0:16: +0:17
@@ -29,7 +29,8 @@
       }
 
       bb3: {
-          goto -> bb4;                     // scope 0 at $DIR/remove_fake_borrows.rs:+2:9: +2:16
+-         falseEdge -> [real: bb4, imaginary: bb1]; // scope 0 at $DIR/remove_fake_borrows.rs:+2:9: +2:16
++         goto -> bb4;                     // scope 0 at $DIR/remove_fake_borrows.rs:+2:9: +2:16
       }
 
       bb4: {
@@ -62,15 +63,12 @@
 
       bb6: {
           StorageDead(_8);                 // scope 0 at $DIR/remove_fake_borrows.rs:+2:20: +2:21
-          goto -> bb1;                     // scope 0 at $DIR/remove_fake_borrows.rs:+2:20: +2:21
+-         falseEdge -> [real: bb1, imaginary: bb1]; // scope 0 at $DIR/remove_fake_borrows.rs:+2:20: +2:21
++         goto -> bb1;                     // scope 0 at $DIR/remove_fake_borrows.rs:+2:20: +2:21
       }
 
       bb7: {
           return;                          // scope 0 at $DIR/remove_fake_borrows.rs:+5:2: +5:2
       }
-
-      bb8 (cleanup): {
-          resume;                          // scope 0 at $DIR/remove_fake_borrows.rs:+0:1: +5:2
-      }
   }
 

src/test/mir-opt/remove_fake_borrows.rs

@@ -2,7 +2,7 @@
 
 // ignore-wasm32-bare compiled with panic=abort by default
 
-// EMIT_MIR remove_fake_borrows.match_guard.CleanupNonCodegenStatements.diff
+// EMIT_MIR remove_fake_borrows.match_guard.CleanupPostBorrowck.diff
 fn match_guard(x: Option<&&i32>, c: bool) -> i32 {
     match x {
         Some(0) if c => 0,