Rollup merge of #137203 - nnethercote:improve-MIR-modification, r=compiler-errors

Improve MIR modification

A few commits that simplify code that manipulates MIR bodies.

r? `@tmiasko`

Author: matthiaskrgr

compiler/rustc_middle/src/mir/mod.rs

@@ -4,8 +4,8 @@
 
 use std::borrow::Cow;
 use std::fmt::{self, Debug, Formatter};
+use std::iter;
 use std::ops::{Index, IndexMut};
-use std::{iter, mem};
 
 pub use basic_blocks::{BasicBlocks, SwitchTargetValue};
 use either::Either;
@@ -1365,66 +1365,6 @@ impl<'tcx> BasicBlockData<'tcx> {
         self.terminator.as_mut().expect("invalid terminator state")
     }
 
-    pub fn retain_statements<F>(&mut self, mut f: F)
-    where
-        F: FnMut(&mut Statement<'_>) -> bool,
-    {
-        for s in &mut self.statements {
-            if !f(s) {
-                s.make_nop();
-            }
-        }
-    }
-
-    pub fn expand_statements<F, I>(&mut self, mut f: F)
-    where
-        F: FnMut(&mut Statement<'tcx>) -> Option<I>,
-        I: iter::TrustedLen<Item = Statement<'tcx>>,
-    {
-        // Gather all the iterators we'll need to splice in, and their positions.
-        let mut splices: Vec<(usize, I)> = vec![];
-        let mut extra_stmts = 0;
-        for (i, s) in self.statements.iter_mut().enumerate() {
-            if let Some(mut new_stmts) = f(s) {
-                if let Some(first) = new_stmts.next() {
-                    // We can already store the first new statement.
-                    *s = first;
-
-                    // Save the other statements for optimized splicing.
-                    let remaining = new_stmts.size_hint().0;
-                    if remaining > 0 {
-                        splices.push((i + 1 + extra_stmts, new_stmts));
-                        extra_stmts += remaining;
-                    }
-                } else {
-                    s.make_nop();
-                }
-            }
-        }
-
-        // Splice in the new statements, from the end of the block.
-        // FIXME(eddyb) This could be more efficient with a "gap buffer"
-        // where a range of elements ("gap") is left uninitialized, with
-        // splicing adding new elements to the end of that gap and moving
-        // existing elements from before the gap to the end of the gap.
-        // For now, this is safe code, emulating a gap but initializing it.
-        let mut gap = self.statements.len()..self.statements.len() + extra_stmts;
-        self.statements.resize(
-            gap.end,
-            Statement { source_info: SourceInfo::outermost(DUMMY_SP), kind: StatementKind::Nop },
-        );
-        for (splice_start, new_stmts) in splices.into_iter().rev() {
-            let splice_end = splice_start + new_stmts.size_hint().0;
-            while gap.end > splice_end {
-                gap.start -= 1;
-                gap.end -= 1;
-                self.statements.swap(gap.start, gap.end);
-            }
-            self.statements.splice(splice_start..splice_end, new_stmts);
-            gap.end = splice_start;
-        }
-    }
-
     pub fn visitable(&self, index: usize) -> &dyn MirVisitable<'tcx> {
         if index < self.statements.len() { &self.statements[index] } else { &self.terminator }
     }

compiler/rustc_middle/src/mir/statement.rs

@@ -19,15 +19,6 @@ impl Statement<'_> {
     pub fn make_nop(&mut self) {
         self.kind = StatementKind::Nop
     }
-
-    /// Changes a statement to a nop and returns the original statement.
-    #[must_use = "If you don't need the statement, use `make_nop` instead"]
-    pub fn replace_nop(&mut self) -> Self {
-        Statement {
-            source_info: self.source_info,
-            kind: mem::replace(&mut self.kind, StatementKind::Nop),
-        }
-    }
 }
 
 impl<'tcx> StatementKind<'tcx> {

compiler/rustc_mir_transform/src/coroutine.rs

@@ -393,12 +393,13 @@ impl<'tcx> MutVisitor<'tcx> for TransformVisitor<'tcx> {
 
     fn visit_basic_block_data(&mut self, block: BasicBlock, data: &mut BasicBlockData<'tcx>) {
         // Remove StorageLive and StorageDead statements for remapped locals
-        data.retain_statements(|s| match s.kind {
-            StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
-                !self.remap.contains(l)
+        for s in &mut data.statements {
+            if let StatementKind::StorageLive(l) | StatementKind::StorageDead(l) = s.kind
+                && self.remap.contains(l)
+            {
+                s.make_nop();
             }
-            _ => true,
-        });
+        }
 
         let ret_val = match data.terminator().kind {
             TerminatorKind::Return => {

compiler/rustc_mir_transform/src/elaborate_drops.rs

@@ -417,7 +417,7 @@ impl<'a, 'tcx> ElaborateDropsCtxt<'a, 'tcx> {
                 ..
             } = data.terminator().kind
             {
-                assert!(!self.patch.is_patched(bb));
+                assert!(!self.patch.is_term_patched(bb));
 
                 let loc = Location { block: tgt, statement_index: 0 };
                 let path = self.move_data().rev_lookup.find(destination.as_ref());
@@ -462,7 +462,7 @@ impl<'a, 'tcx> ElaborateDropsCtxt<'a, 'tcx> {
                             // a Goto; see `MirPatch::new`).
                         }
                         _ => {
-                            assert!(!self.patch.is_patched(bb));
+                            assert!(!self.patch.is_term_patched(bb));
                         }
                     }
                 }
@@ -486,7 +486,7 @@ impl<'a, 'tcx> ElaborateDropsCtxt<'a, 'tcx> {
                 ..
             } = data.terminator().kind
             {
-                assert!(!self.patch.is_patched(bb));
+                assert!(!self.patch.is_term_patched(bb));
 
                 let loc = Location { block: bb, statement_index: data.statements.len() };
                 let path = self.move_data().rev_lookup.find(destination.as_ref());

compiler/rustc_mir_transform/src/large_enums.rs

@@ -6,6 +6,8 @@ use rustc_middle::ty::util::IntTypeExt;
 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt};
 use rustc_session::Session;
 
+use crate::patch::MirPatch;
+
 /// A pass that seeks to optimize unnecessary moves of large enum types, if there is a large
 /// enough discrepancy between them.
 ///
@@ -41,31 +43,34 @@ impl<'tcx> crate::MirPass<'tcx> for EnumSizeOpt {
         let mut alloc_cache = FxHashMap::default();
         let typing_env = body.typing_env(tcx);
 
-        let blocks = body.basic_blocks.as_mut();
-        let local_decls = &mut body.local_decls;
+        let mut patch = MirPatch::new(body);
 
-        for bb in blocks {
-            bb.expand_statements(|st| {
+        for (block, data) in body.basic_blocks.as_mut().iter_enumerated_mut() {
+            for (statement_index, st) in data.statements.iter_mut().enumerate() {
                 let StatementKind::Assign(box (
                     lhs,
                     Rvalue::Use(Operand::Copy(rhs) | Operand::Move(rhs)),
                 )) = &st.kind
                 else {
-                    return None;
+                    continue;
                 };
 
-                let ty = lhs.ty(local_decls, tcx).ty;
+                let location = Location { block, statement_index };
 
-                let (adt_def, num_variants, alloc_id) =
-                    self.candidate(tcx, typing_env, ty, &mut alloc_cache)?;
+                let ty = lhs.ty(&body.local_decls, tcx).ty;
 
-                let source_info = st.source_info;
-                let span = source_info.span;
+                let Some((adt_def, num_variants, alloc_id)) =
+                    self.candidate(tcx, typing_env, ty, &mut alloc_cache)
+                else {
+                    continue;
+                };
+
+                let span = st.source_info.span;
 
                 let tmp_ty = Ty::new_array(tcx, tcx.types.usize, num_variants as u64);
-                let size_array_local = local_decls.push(LocalDecl::new(tmp_ty, span));
-                let store_live =
-                    Statement { source_info, kind: StatementKind::StorageLive(size_array_local) };
+                let size_array_local = patch.new_temp(tmp_ty, span);
+
+                let store_live = StatementKind::StorageLive(size_array_local);
 
                 let place = Place::from(size_array_local);
                 let constant_vals = ConstOperand {
@@ -77,108 +82,63 @@ impl<'tcx> crate::MirPass<'tcx> for EnumSizeOpt {
                     ),
                 };
                 let rval = Rvalue::Use(Operand::Constant(Box::new(constant_vals)));
-                let const_assign =
-                    Statement { source_info, kind: StatementKind::Assign(Box::new((place, rval))) };
-
-                let discr_place = Place::from(
-                    local_decls.push(LocalDecl::new(adt_def.repr().discr_type().to_ty(tcx), span)),
-                );
-                let store_discr = Statement {
-                    source_info,
-                    kind: StatementKind::Assign(Box::new((
-                        discr_place,
-                        Rvalue::Discriminant(*rhs),
-                    ))),
-                };
-
-                let discr_cast_place =
-                    Place::from(local_decls.push(LocalDecl::new(tcx.types.usize, span)));
-                let cast_discr = Statement {
-                    source_info,
-                    kind: StatementKind::Assign(Box::new((
-                        discr_cast_place,
-                        Rvalue::Cast(
-                            CastKind::IntToInt,
-                            Operand::Copy(discr_place),
-                            tcx.types.usize,
-                        ),
-                    ))),
-                };
-
-                let size_place =
-                    Place::from(local_decls.push(LocalDecl::new(tcx.types.usize, span)));
-                let store_size = Statement {
-                    source_info,
-                    kind: StatementKind::Assign(Box::new((
-                        size_place,
-                        Rvalue::Use(Operand::Copy(Place {
-                            local: size_array_local,
-                            projection: tcx
-                                .mk_place_elems(&[PlaceElem::Index(discr_cast_place.local)]),
-                        })),
-                    ))),
-                };
-
-                let dst =
-                    Place::from(local_decls.push(LocalDecl::new(Ty::new_mut_ptr(tcx, ty), span)));
-                let dst_ptr = Statement {
-                    source_info,
-                    kind: StatementKind::Assign(Box::new((
-                        dst,
-                        Rvalue::RawPtr(RawPtrKind::Mut, *lhs),
-                    ))),
-                };
+                let const_assign = StatementKind::Assign(Box::new((place, rval)));
+
+                let discr_place =
+                    Place::from(patch.new_temp(adt_def.repr().discr_type().to_ty(tcx), span));
+                let store_discr =
+                    StatementKind::Assign(Box::new((discr_place, Rvalue::Discriminant(*rhs))));
+
+                let discr_cast_place = Place::from(patch.new_temp(tcx.types.usize, span));
+                let cast_discr = StatementKind::Assign(Box::new((
+                    discr_cast_place,
+                    Rvalue::Cast(CastKind::IntToInt, Operand::Copy(discr_place), tcx.types.usize),
+                )));
+
+                let size_place = Place::from(patch.new_temp(tcx.types.usize, span));
+                let store_size = StatementKind::Assign(Box::new((
+                    size_place,
+                    Rvalue::Use(Operand::Copy(Place {
+                        local: size_array_local,
+                        projection: tcx.mk_place_elems(&[PlaceElem::Index(discr_cast_place.local)]),
+                    })),
+                )));
+
+                let dst = Place::from(patch.new_temp(Ty::new_mut_ptr(tcx, ty), span));
+                let dst_ptr =
+                    StatementKind::Assign(Box::new((dst, Rvalue::RawPtr(RawPtrKind::Mut, *lhs))));
 
                 let dst_cast_ty = Ty::new_mut_ptr(tcx, tcx.types.u8);
-                let dst_cast_place =
-                    Place::from(local_decls.push(LocalDecl::new(dst_cast_ty, span)));
-                let dst_cast = Statement {
-                    source_info,
-                    kind: StatementKind::Assign(Box::new((
-                        dst_cast_place,
-                        Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(dst), dst_cast_ty),
-                    ))),
-                };
+                let dst_cast_place = Place::from(patch.new_temp(dst_cast_ty, span));
+                let dst_cast = StatementKind::Assign(Box::new((
+                    dst_cast_place,
+                    Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(dst), dst_cast_ty),
+                )));
 
-                let src =
-                    Place::from(local_decls.push(LocalDecl::new(Ty::new_imm_ptr(tcx, ty), span)));
-                let src_ptr = Statement {
-                    source_info,
-                    kind: StatementKind::Assign(Box::new((
-                        src,
-                        Rvalue::RawPtr(RawPtrKind::Const, *rhs),
-                    ))),
-                };
+                let src = Place::from(patch.new_temp(Ty::new_imm_ptr(tcx, ty), span));
+                let src_ptr =
+                    StatementKind::Assign(Box::new((src, Rvalue::RawPtr(RawPtrKind::Const, *rhs))));
 
                 let src_cast_ty = Ty::new_imm_ptr(tcx, tcx.types.u8);
-                let src_cast_place =
-                    Place::from(local_decls.push(LocalDecl::new(src_cast_ty, span)));
-                let src_cast = Statement {
-                    source_info,
-                    kind: StatementKind::Assign(Box::new((
-                        src_cast_place,
-                        Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(src), src_cast_ty),
-                    ))),
-                };
+                let src_cast_place = Place::from(patch.new_temp(src_cast_ty, span));
+                let src_cast = StatementKind::Assign(Box::new((
+                    src_cast_place,
+                    Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(src), src_cast_ty),
+                )));
 
-                let deinit_old =
-                    Statement { source_info, kind: StatementKind::Deinit(Box::new(dst)) };
-
-                let copy_bytes = Statement {
-                    source_info,
-                    kind: StatementKind::Intrinsic(Box::new(
-                        NonDivergingIntrinsic::CopyNonOverlapping(CopyNonOverlapping {
-                            src: Operand::Copy(src_cast_place),
-                            dst: Operand::Copy(dst_cast_place),
-                            count: Operand::Copy(size_place),
-                        }),
-                    )),
-                };
+                let deinit_old = StatementKind::Deinit(Box::new(dst));
+
+                let copy_bytes = StatementKind::Intrinsic(Box::new(
+                    NonDivergingIntrinsic::CopyNonOverlapping(CopyNonOverlapping {
+                        src: Operand::Copy(src_cast_place),
+                        dst: Operand::Copy(dst_cast_place),
+                        count: Operand::Copy(size_place),
+                    }),
+                ));
 
-                let store_dead =
-                    Statement { source_info, kind: StatementKind::StorageDead(size_array_local) };
+                let store_dead = StatementKind::StorageDead(size_array_local);
 
-                let iter = [
+                let stmts = [
                     store_live,
                     const_assign,
                     store_discr,
@@ -191,14 +151,16 @@ impl<'tcx> crate::MirPass<'tcx> for EnumSizeOpt {
                     deinit_old,
                     copy_bytes,
                     store_dead,
-                ]
-                .into_iter();
+                ];
+                for stmt in stmts {
+                    patch.add_statement(location, stmt);
+                }
 
                 st.make_nop();
-
-                Some(iter)
-            });
+            }
         }
+
+        patch.apply(body);
     }
 
     fn is_required(&self) -> bool {