diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/rustc_mir_transform/src/const_debuginfo.rs | 102 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/lib.rs | 4 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/single_use_consts.rs | 199 |
3 files changed, 201 insertions, 104 deletions
diff --git a/compiler/rustc_mir_transform/src/const_debuginfo.rs b/compiler/rustc_mir_transform/src/const_debuginfo.rs deleted file mode 100644 index e4e4270c499..00000000000 --- a/compiler/rustc_mir_transform/src/const_debuginfo.rs +++ /dev/null @@ -1,102 +0,0 @@ -//! Finds locals which are assigned once to a const and unused except for debuginfo and converts -//! their debuginfo to use the const directly, allowing the local to be removed. - -use rustc_middle::{ - mir::{ - visit::{PlaceContext, Visitor}, - Body, ConstOperand, Local, Location, Operand, Rvalue, StatementKind, VarDebugInfoContents, - }, - ty::TyCtxt, -}; - -use crate::MirPass; -use rustc_index::{bit_set::BitSet, IndexVec}; - -pub struct ConstDebugInfo; - -impl<'tcx> MirPass<'tcx> for ConstDebugInfo { - fn is_enabled(&self, sess: &rustc_session::Session) -> bool { - sess.mir_opt_level() > 0 - } - - fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { - trace!("running ConstDebugInfo on {:?}", body.source); - - for (local, constant) in find_optimization_opportunities(body) { - for debuginfo in &mut body.var_debug_info { - if let VarDebugInfoContents::Place(p) = debuginfo.value { - if p.local == local && p.projection.is_empty() { - trace!( - "changing debug info for {:?} from place {:?} to constant {:?}", - debuginfo.name, - p, - constant - ); - debuginfo.value = VarDebugInfoContents::Const(constant); - } - } - } - } - } -} - -struct LocalUseVisitor { - local_mutating_uses: IndexVec<Local, u8>, - local_assignment_locations: IndexVec<Local, Option<Location>>, -} - -fn find_optimization_opportunities<'tcx>(body: &Body<'tcx>) -> Vec<(Local, ConstOperand<'tcx>)> { - let mut visitor = LocalUseVisitor { - local_mutating_uses: IndexVec::from_elem(0, &body.local_decls), - local_assignment_locations: IndexVec::from_elem(None, &body.local_decls), - }; - - visitor.visit_body(body); - - let mut locals_to_debuginfo = BitSet::new_empty(body.local_decls.len()); - for debuginfo in &body.var_debug_info { - if let VarDebugInfoContents::Place(p) = debuginfo.value - && let Some(l) = p.as_local() - { - locals_to_debuginfo.insert(l); - } - } - - let mut eligible_locals = Vec::new(); - for (local, mutating_uses) in visitor.local_mutating_uses.drain_enumerated(..) { - if mutating_uses != 1 || !locals_to_debuginfo.contains(local) { - continue; - } - - if let Some(location) = visitor.local_assignment_locations[local] { - let bb = &body[location.block]; - - // The value is assigned as the result of a call, not a constant - if bb.statements.len() == location.statement_index { - continue; - } - - if let StatementKind::Assign(box (p, Rvalue::Use(Operand::Constant(box c)))) = - &bb.statements[location.statement_index].kind - { - if let Some(local) = p.as_local() { - eligible_locals.push((local, *c)); - } - } - } - } - - eligible_locals -} - -impl Visitor<'_> for LocalUseVisitor { - fn visit_local(&mut self, local: Local, context: PlaceContext, location: Location) { - if context.is_mutating_use() { - self.local_mutating_uses[local] = self.local_mutating_uses[local].saturating_add(1); - - if context.is_place_assignment() { - self.local_assignment_locations[local] = Some(location); - } - } - } -} diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs index e4670633914..551760f4703 100644 --- a/compiler/rustc_mir_transform/src/lib.rs +++ b/compiler/rustc_mir_transform/src/lib.rs @@ -55,7 +55,6 @@ mod remove_place_mention; // This pass is public to allow external drivers to perform MIR cleanup mod add_subtyping_projections; pub mod cleanup_post_borrowck; -mod const_debuginfo; mod copy_prop; mod coroutine; mod cost_checker; @@ -106,6 +105,7 @@ mod check_alignment; pub mod simplify; mod simplify_branches; mod simplify_comparison_integral; +mod single_use_consts; mod sroa; mod unreachable_enum_branching; mod unreachable_prop; @@ -593,7 +593,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { &gvn::GVN, &simplify::SimplifyLocals::AfterGVN, &dataflow_const_prop::DataflowConstProp, - &const_debuginfo::ConstDebugInfo, + &single_use_consts::SingleUseConsts, &o1(simplify_branches::SimplifyConstCondition::AfterConstProp), &jump_threading::JumpThreading, &early_otherwise_branch::EarlyOtherwiseBranch, diff --git a/compiler/rustc_mir_transform/src/single_use_consts.rs b/compiler/rustc_mir_transform/src/single_use_consts.rs new file mode 100644 index 00000000000..93736e55996 --- /dev/null +++ b/compiler/rustc_mir_transform/src/single_use_consts.rs @@ -0,0 +1,199 @@ +use rustc_index::{bit_set::BitSet, IndexVec}; +use rustc_middle::bug; +use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor}; +use rustc_middle::mir::*; +use rustc_middle::ty::TyCtxt; + +/// Various parts of MIR building introduce temporaries that are commonly not needed. +/// +/// Notably, `if CONST` and `match CONST` end up being used-once temporaries, which +/// obfuscates the structure for other passes and codegen, which would like to always +/// be able to just see the constant directly. +/// +/// At higher optimization levels fancier passes like GVN will take care of this +/// in a more general fashion, but this handles the easy cases so can run in debug. +/// +/// This only removes constants with a single-use because re-evaluating constants +/// isn't always an improvement, especially for large ones. +/// +/// It also removes *never*-used constants, since it had all the information +/// needed to do that too, including updating the debug info. +pub struct SingleUseConsts; + +impl<'tcx> MirPass<'tcx> for SingleUseConsts { + fn is_enabled(&self, sess: &rustc_session::Session) -> bool { + sess.mir_opt_level() > 0 + } + + fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { + let mut finder = SingleUseConstsFinder { + ineligible_locals: BitSet::new_empty(body.local_decls.len()), + locations: IndexVec::from_elem(LocationPair::new(), &body.local_decls), + locals_in_debug_info: BitSet::new_empty(body.local_decls.len()), + }; + + finder.ineligible_locals.insert_range(..=Local::from_usize(body.arg_count)); + + finder.visit_body(body); + + for (local, locations) in finder.locations.iter_enumerated() { + if finder.ineligible_locals.contains(local) { + continue; + } + + let Some(init_loc) = locations.init_loc else { + continue; + }; + + // We're only changing an operand, not the terminator kinds or successors + let basic_blocks = body.basic_blocks.as_mut_preserves_cfg(); + let init_statement = + basic_blocks[init_loc.block].statements[init_loc.statement_index].replace_nop(); + let StatementKind::Assign(place_and_rvalue) = init_statement.kind else { + bug!("No longer an assign?"); + }; + let (place, rvalue) = *place_and_rvalue; + assert_eq!(place.as_local(), Some(local)); + let Rvalue::Use(operand) = rvalue else { bug!("No longer a use?") }; + + let mut replacer = LocalReplacer { tcx, local, operand: Some(operand) }; + + if finder.locals_in_debug_info.contains(local) { + for var_debug_info in &mut body.var_debug_info { + replacer.visit_var_debug_info(var_debug_info); + } + } + + let Some(use_loc) = locations.use_loc else { continue }; + + let use_block = &mut basic_blocks[use_loc.block]; + if let Some(use_statement) = use_block.statements.get_mut(use_loc.statement_index) { + replacer.visit_statement(use_statement, use_loc); + } else { + replacer.visit_terminator(use_block.terminator_mut(), use_loc); + } + + if replacer.operand.is_some() { + bug!( + "operand wasn't used replacing local {local:?} with locations {locations:?} in body {body:#?}" + ); + } + } + } +} + +#[derive(Copy, Clone, Debug)] +struct LocationPair { + init_loc: Option<Location>, + use_loc: Option<Location>, +} + +impl LocationPair { + fn new() -> Self { + Self { init_loc: None, use_loc: None } + } +} + +struct SingleUseConstsFinder { + ineligible_locals: BitSet<Local>, + locations: IndexVec<Local, LocationPair>, + locals_in_debug_info: BitSet<Local>, +} + +impl<'tcx> Visitor<'tcx> for SingleUseConstsFinder { + fn visit_assign(&mut self, place: &Place<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) { + if let Some(local) = place.as_local() + && let Rvalue::Use(operand) = rvalue + && let Operand::Constant(_) = operand + { + let locations = &mut self.locations[local]; + if locations.init_loc.is_some() { + self.ineligible_locals.insert(local); + } else { + locations.init_loc = Some(location); + } + } else { + self.super_assign(place, rvalue, location); + } + } + + fn visit_operand(&mut self, operand: &Operand<'tcx>, location: Location) { + if let Some(place) = operand.place() + && let Some(local) = place.as_local() + { + let locations = &mut self.locations[local]; + if locations.use_loc.is_some() { + self.ineligible_locals.insert(local); + } else { + locations.use_loc = Some(location); + } + } else { + self.super_operand(operand, location); + } + } + + fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) { + match &statement.kind { + // Storage markers are irrelevant to this. + StatementKind::StorageLive(_) | StatementKind::StorageDead(_) => {} + _ => self.super_statement(statement, location), + } + } + + fn visit_var_debug_info(&mut self, var_debug_info: &VarDebugInfo<'tcx>) { + if let VarDebugInfoContents::Place(place) = &var_debug_info.value + && let Some(local) = place.as_local() + { + self.locals_in_debug_info.insert(local); + } else { + self.super_var_debug_info(var_debug_info); + } + } + + fn visit_local(&mut self, local: Local, _context: PlaceContext, _location: Location) { + // If there's any path that gets here, rather than being understood elsewhere, + // then we'd better not do anything with this local. + self.ineligible_locals.insert(local); + } +} + +struct LocalReplacer<'tcx> { + tcx: TyCtxt<'tcx>, + local: Local, + operand: Option<Operand<'tcx>>, +} + +impl<'tcx> MutVisitor<'tcx> for LocalReplacer<'tcx> { + fn tcx(&self) -> TyCtxt<'tcx> { + self.tcx + } + + fn visit_operand(&mut self, operand: &mut Operand<'tcx>, _location: Location) { + if let Operand::Copy(place) | Operand::Move(place) = operand + && let Some(local) = place.as_local() + && local == self.local + { + *operand = self.operand.take().unwrap_or_else(|| { + bug!("there was a second use of the operand"); + }); + } + } + + fn visit_var_debug_info(&mut self, var_debug_info: &mut VarDebugInfo<'tcx>) { + if let VarDebugInfoContents::Place(place) = &var_debug_info.value + && let Some(local) = place.as_local() + && local == self.local + { + let const_op = self + .operand + .as_ref() + .unwrap_or_else(|| { + bug!("the operand was already stolen"); + }) + .constant() + .unwrap() + .clone(); + var_debug_info.value = VarDebugInfoContents::Const(const_op); + } + } +} |