diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/simplify.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/simplify.rs | 155 |
1 files changed, 124 insertions, 31 deletions
diff --git a/compiler/rustc_mir_transform/src/simplify.rs b/compiler/rustc_mir_transform/src/simplify.rs index 75917d23883..8b5efb74205 100644 --- a/compiler/rustc_mir_transform/src/simplify.rs +++ b/compiler/rustc_mir_transform/src/simplify.rs @@ -35,10 +35,12 @@ //! pre-"runtime" MIR! use itertools::Itertools as _; +use rustc_index::bit_set::DenseBitSet; use rustc_index::{Idx, IndexSlice, IndexVec}; use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor}; use rustc_middle::mir::*; use rustc_middle::ty::TyCtxt; +use rustc_mir_dataflow::debuginfo::debuginfo_locals; use rustc_span::DUMMY_SP; use smallvec::SmallVec; use tracing::{debug, trace}; @@ -142,7 +144,7 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { // statements itself to avoid moving the (relatively) large statements twice. // We do not push the statements directly into the target block (`bb`) as that is slower // due to additional reallocations - let mut merged_blocks = Vec::new(); + let mut merged_blocks: Vec<BasicBlock> = Vec::new(); let mut outer_changed = false; loop { let mut changed = false; @@ -157,8 +159,9 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { let mut terminator = self.basic_blocks[bb].terminator.take().expect("invalid terminator state"); - terminator - .successors_mut(|successor| self.collapse_goto_chain(successor, &mut changed)); + terminator.successors_mut(|successor| { + self.collapse_goto_chain(successor, &mut changed); + }); let mut inner_changed = true; merged_blocks.clear(); @@ -175,10 +178,18 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { if statements_to_merge > 0 { let mut statements = std::mem::take(&mut self.basic_blocks[bb].statements); statements.reserve(statements_to_merge); + let mut parent_bb_last_debuginfos = + std::mem::take(&mut self.basic_blocks[bb].after_last_stmt_debuginfos); for &from in &merged_blocks { + if let Some(stmt) = self.basic_blocks[from].statements.first_mut() { + stmt.debuginfos.prepend(&mut parent_bb_last_debuginfos); + } statements.append(&mut self.basic_blocks[from].statements); + parent_bb_last_debuginfos = + std::mem::take(&mut self.basic_blocks[from].after_last_stmt_debuginfos); } self.basic_blocks[bb].statements = statements; + self.basic_blocks[bb].after_last_stmt_debuginfos = parent_bb_last_debuginfos; } self.basic_blocks[bb].terminator = Some(terminator); @@ -218,10 +229,14 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { // goto chains. We should probably benchmark different sizes. let mut terminators: SmallVec<[_; 1]> = Default::default(); let mut current = *start; + // If each successor has only one predecessor, it's a trivial goto chain. + // We can move all debuginfos to the last basic block. + let mut trivial_goto_chain = true; while let Some(terminator) = self.take_terminator_if_simple_goto(current) { let Terminator { kind: TerminatorKind::Goto { target }, .. } = terminator else { unreachable!(); }; + trivial_goto_chain &= self.pred_count[target] == 1; terminators.push((current, terminator)); current = target; } @@ -233,6 +248,17 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { else { unreachable!(); }; + if trivial_goto_chain { + let mut pred_debuginfos = + std::mem::take(&mut self.basic_blocks[current].after_last_stmt_debuginfos); + let debuginfos = if let Some(stmt) = self.basic_blocks[last].statements.first_mut() + { + &mut stmt.debuginfos + } else { + &mut self.basic_blocks[last].after_last_stmt_debuginfos + }; + debuginfos.prepend(&mut pred_debuginfos); + } *changed |= *target != last; *target = last; debug!("collapsing goto chain from {:?} to {:?}", current, target); @@ -303,7 +329,7 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> { fn strip_nops(&mut self) { for blk in self.basic_blocks.iter_mut() { - blk.statements.retain(|stmt| !matches!(stmt.kind, StatementKind::Nop)) + blk.strip_nops(); } } } @@ -476,17 +502,22 @@ fn make_local_map<V>( /// Keeps track of used & unused locals. struct UsedLocals { increment: bool, - arg_count: u32, use_count: IndexVec<Local, u32>, + always_used: DenseBitSet<Local>, } impl UsedLocals { /// Determines which locals are used & unused in the given body. fn new(body: &Body<'_>) -> Self { + let mut always_used = debuginfo_locals(body); + always_used.insert(RETURN_PLACE); + for arg in body.args_iter() { + always_used.insert(arg); + } let mut this = Self { increment: true, - arg_count: body.arg_count.try_into().unwrap(), use_count: IndexVec::from_elem(0, &body.local_decls), + always_used, }; this.visit_body(body); this @@ -494,10 +525,16 @@ impl UsedLocals { /// Checks if local is used. /// - /// Return place and arguments are always considered used. + /// Return place, arguments, var debuginfo are always considered used. fn is_used(&self, local: Local) -> bool { - trace!("is_used({:?}): use_count: {:?}", local, self.use_count[local]); - local.as_u32() <= self.arg_count || self.use_count[local] != 0 + trace!( + "is_used({:?}): use_count: {:?}, always_used: {}", + local, + self.use_count[local], + self.always_used.contains(local) + ); + // To keep things simple, we don't handle debugging information here, these are in DSE. + self.always_used.contains(local) || self.use_count[local] != 0 } /// Updates the use counts to reflect the removal of given statement. @@ -539,10 +576,10 @@ impl<'tcx> Visitor<'tcx> for UsedLocals { self.super_statement(statement, location); } - StatementKind::ConstEvalCounter | StatementKind::Nop => {} - - StatementKind::StorageLive(_local) | StatementKind::StorageDead(_local) => {} - + StatementKind::ConstEvalCounter + | StatementKind::Nop + | StatementKind::StorageLive(..) + | StatementKind::StorageDead(..) => {} StatementKind::Assign(box (ref place, ref rvalue)) => { if rvalue.is_safe_to_remove() { self.visit_lhs(place, location); @@ -560,7 +597,10 @@ impl<'tcx> Visitor<'tcx> for UsedLocals { } } - fn visit_local(&mut self, local: Local, _ctx: PlaceContext, _location: Location) { + fn visit_local(&mut self, local: Local, ctx: PlaceContext, _location: Location) { + if matches!(ctx, PlaceContext::NonUse(_)) { + return; + } if self.increment { self.use_count[local] += 1; } else { @@ -583,28 +623,26 @@ fn remove_unused_definitions_helper(used_locals: &mut UsedLocals, body: &mut Bod for data in body.basic_blocks.as_mut_preserves_cfg() { // Remove unnecessary StorageLive and StorageDead annotations. - data.statements.retain(|statement| { - let keep = match &statement.kind { + for statement in data.statements.iter_mut() { + let keep_statement = match &statement.kind { StatementKind::StorageLive(local) | StatementKind::StorageDead(local) => { used_locals.is_used(*local) } - StatementKind::Assign(box (place, _)) => used_locals.is_used(place.local), - - StatementKind::SetDiscriminant { place, .. } - | StatementKind::BackwardIncompatibleDropHint { place, reason: _ } - | StatementKind::Deinit(place) => used_locals.is_used(place.local), - StatementKind::Nop => false, - _ => true, + StatementKind::Assign(box (place, _)) + | StatementKind::SetDiscriminant { box place, .. } + | StatementKind::BackwardIncompatibleDropHint { box place, .. } + | StatementKind::Deinit(box place) => used_locals.is_used(place.local), + _ => continue, }; - - if !keep { - trace!("removing statement {:?}", statement); - modified = true; - used_locals.statement_removed(statement); + if keep_statement { + continue; } - - keep - }); + trace!("removing statement {:?}", statement); + modified = true; + used_locals.statement_removed(statement); + statement.make_nop(true); + } + data.strip_nops(); } } } @@ -619,7 +657,62 @@ impl<'tcx> MutVisitor<'tcx> for LocalUpdater<'tcx> { self.tcx } + fn visit_statement_debuginfo( + &mut self, + stmt_debuginfo: &mut StmtDebugInfo<'tcx>, + location: Location, + ) { + match stmt_debuginfo { + StmtDebugInfo::AssignRef(local, place) => { + if place.as_ref().accessed_locals().any(|local| self.map[local].is_none()) { + *stmt_debuginfo = StmtDebugInfo::InvalidAssign(*local); + } + } + StmtDebugInfo::InvalidAssign(_) => {} + } + self.super_statement_debuginfo(stmt_debuginfo, location); + } + fn visit_local(&mut self, l: &mut Local, _: PlaceContext, _: Location) { *l = self.map[*l].unwrap(); } } + +pub(crate) struct UsedInStmtLocals { + pub(crate) locals: DenseBitSet<Local>, +} + +impl UsedInStmtLocals { + pub(crate) fn new(body: &Body<'_>) -> Self { + let mut this = Self { locals: DenseBitSet::new_empty(body.local_decls.len()) }; + this.visit_body(body); + this + } + + pub(crate) fn remove_unused_storage_annotations<'tcx>(&self, body: &mut Body<'tcx>) { + for data in body.basic_blocks.as_mut_preserves_cfg() { + // Remove unnecessary StorageLive and StorageDead annotations. + for statement in data.statements.iter_mut() { + let keep_statement = match &statement.kind { + StatementKind::StorageLive(local) | StatementKind::StorageDead(local) => { + self.locals.contains(*local) + } + _ => continue, + }; + if keep_statement { + continue; + } + statement.make_nop(true); + } + } + } +} + +impl<'tcx> Visitor<'tcx> for UsedInStmtLocals { + fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) { + if matches!(context, PlaceContext::NonUse(_)) { + return; + } + self.locals.insert(local); + } +} |