diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/simplify_try.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/simplify_try.rs | 822 |
1 files changed, 0 insertions, 822 deletions
diff --git a/compiler/rustc_mir_transform/src/simplify_try.rs b/compiler/rustc_mir_transform/src/simplify_try.rs deleted file mode 100644 index e4f3ace9a..000000000 --- a/compiler/rustc_mir_transform/src/simplify_try.rs +++ /dev/null @@ -1,822 +0,0 @@ -//! The general point of the optimizations provided here is to simplify something like: -//! -//! ```rust -//! # fn foo<T, E>(x: Result<T, E>) -> Result<T, E> { -//! match x { -//! Ok(x) => Ok(x), -//! Err(x) => Err(x) -//! } -//! # } -//! ``` -//! -//! into just `x`. - -use crate::{simplify, MirPass}; -use itertools::Itertools as _; -use rustc_index::{bit_set::BitSet, vec::IndexVec}; -use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor}; -use rustc_middle::mir::*; -use rustc_middle::ty::{self, List, Ty, TyCtxt}; -use rustc_target::abi::VariantIdx; -use std::iter::{once, Enumerate, Peekable}; -use std::slice::Iter; - -/// Simplifies arms of form `Variant(x) => Variant(x)` to just a move. -/// -/// This is done by transforming basic blocks where the statements match: -/// -/// ```ignore (MIR) -/// _LOCAL_TMP = ((_LOCAL_1 as Variant ).FIELD: TY ); -/// _TMP_2 = _LOCAL_TMP; -/// ((_LOCAL_0 as Variant).FIELD: TY) = move _TMP_2; -/// discriminant(_LOCAL_0) = VAR_IDX; -/// ``` -/// -/// into: -/// -/// ```ignore (MIR) -/// _LOCAL_0 = move _LOCAL_1 -/// ``` -pub struct SimplifyArmIdentity; - -#[derive(Debug)] -struct ArmIdentityInfo<'tcx> { - /// Storage location for the variant's field - local_temp_0: Local, - /// Storage location holding the variant being read from - local_1: Local, - /// The variant field being read from - vf_s0: VarField<'tcx>, - /// Index of the statement which loads the variant being read - get_variant_field_stmt: usize, - - /// Tracks each assignment to a temporary of the variant's field - field_tmp_assignments: Vec<(Local, Local)>, - - /// Storage location holding the variant's field that was read from - local_tmp_s1: Local, - /// Storage location holding the enum that we are writing to - local_0: Local, - /// The variant field being written to - vf_s1: VarField<'tcx>, - - /// Storage location that the discriminant is being written to - set_discr_local: Local, - /// The variant being written - set_discr_var_idx: VariantIdx, - - /// Index of the statement that should be overwritten as a move - stmt_to_overwrite: usize, - /// SourceInfo for the new move - source_info: SourceInfo, - - /// Indices of matching Storage{Live,Dead} statements encountered. - /// (StorageLive index,, StorageDead index, Local) - storage_stmts: Vec<(usize, usize, Local)>, - - /// The statements that should be removed (turned into nops) - stmts_to_remove: Vec<usize>, - - /// Indices of debug variables that need to be adjusted to point to - // `{local_0}.{dbg_projection}`. - dbg_info_to_adjust: Vec<usize>, - - /// The projection used to rewrite debug info. - dbg_projection: &'tcx List<PlaceElem<'tcx>>, -} - -fn get_arm_identity_info<'a, 'tcx>( - stmts: &'a [Statement<'tcx>], - locals_count: usize, - debug_info: &'a [VarDebugInfo<'tcx>], -) -> Option<ArmIdentityInfo<'tcx>> { - // This can't possibly match unless there are at least 3 statements in the block - // so fail fast on tiny blocks. - if stmts.len() < 3 { - return None; - } - - let mut tmp_assigns = Vec::new(); - let mut nop_stmts = Vec::new(); - let mut storage_stmts = Vec::new(); - let mut storage_live_stmts = Vec::new(); - let mut storage_dead_stmts = Vec::new(); - - type StmtIter<'a, 'tcx> = Peekable<Enumerate<Iter<'a, Statement<'tcx>>>>; - - fn is_storage_stmt(stmt: &Statement<'_>) -> bool { - matches!(stmt.kind, StatementKind::StorageLive(_) | StatementKind::StorageDead(_)) - } - - /// Eats consecutive Statements which match `test`, performing the specified `action` for each. - /// The iterator `stmt_iter` is not advanced if none were matched. - fn try_eat<'a, 'tcx>( - stmt_iter: &mut StmtIter<'a, 'tcx>, - test: impl Fn(&'a Statement<'tcx>) -> bool, - mut action: impl FnMut(usize, &'a Statement<'tcx>), - ) { - while stmt_iter.peek().map_or(false, |(_, stmt)| test(stmt)) { - let (idx, stmt) = stmt_iter.next().unwrap(); - - action(idx, stmt); - } - } - - /// Eats consecutive `StorageLive` and `StorageDead` Statements. - /// The iterator `stmt_iter` is not advanced if none were found. - fn try_eat_storage_stmts( - stmt_iter: &mut StmtIter<'_, '_>, - storage_live_stmts: &mut Vec<(usize, Local)>, - storage_dead_stmts: &mut Vec<(usize, Local)>, - ) { - try_eat(stmt_iter, is_storage_stmt, |idx, stmt| { - if let StatementKind::StorageLive(l) = stmt.kind { - storage_live_stmts.push((idx, l)); - } else if let StatementKind::StorageDead(l) = stmt.kind { - storage_dead_stmts.push((idx, l)); - } - }) - } - - fn is_tmp_storage_stmt(stmt: &Statement<'_>) -> bool { - use rustc_middle::mir::StatementKind::Assign; - if let Assign(box (place, Rvalue::Use(Operand::Copy(p) | Operand::Move(p)))) = &stmt.kind { - place.as_local().is_some() && p.as_local().is_some() - } else { - false - } - } - - /// Eats consecutive `Assign` Statements. - // The iterator `stmt_iter` is not advanced if none were found. - fn try_eat_assign_tmp_stmts( - stmt_iter: &mut StmtIter<'_, '_>, - tmp_assigns: &mut Vec<(Local, Local)>, - nop_stmts: &mut Vec<usize>, - ) { - try_eat(stmt_iter, is_tmp_storage_stmt, |idx, stmt| { - use rustc_middle::mir::StatementKind::Assign; - if let Assign(box (place, Rvalue::Use(Operand::Copy(p) | Operand::Move(p)))) = - &stmt.kind - { - tmp_assigns.push((place.as_local().unwrap(), p.as_local().unwrap())); - nop_stmts.push(idx); - } - }) - } - - fn find_storage_live_dead_stmts_for_local( - local: Local, - stmts: &[Statement<'_>], - ) -> Option<(usize, usize)> { - trace!("looking for {:?}", local); - let mut storage_live_stmt = None; - let mut storage_dead_stmt = None; - for (idx, stmt) in stmts.iter().enumerate() { - if stmt.kind == StatementKind::StorageLive(local) { - storage_live_stmt = Some(idx); - } else if stmt.kind == StatementKind::StorageDead(local) { - storage_dead_stmt = Some(idx); - } - } - - Some((storage_live_stmt?, storage_dead_stmt.unwrap_or(usize::MAX))) - } - - // Try to match the expected MIR structure with the basic block we're processing. - // We want to see something that looks like: - // ``` - // (StorageLive(_) | StorageDead(_));* - // _LOCAL_INTO = ((_LOCAL_FROM as Variant).FIELD: TY); - // (StorageLive(_) | StorageDead(_));* - // (tmp_n+1 = tmp_n);* - // (StorageLive(_) | StorageDead(_));* - // (tmp_n+1 = tmp_n);* - // ((LOCAL_FROM as Variant).FIELD: TY) = move tmp; - // discriminant(LOCAL_FROM) = VariantIdx; - // (StorageLive(_) | StorageDead(_));* - // ``` - let mut stmt_iter = stmts.iter().enumerate().peekable(); - - try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts); - - let (get_variant_field_stmt, stmt) = stmt_iter.next()?; - let (local_tmp_s0, local_1, vf_s0, dbg_projection) = match_get_variant_field(stmt)?; - - try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts); - - try_eat_assign_tmp_stmts(&mut stmt_iter, &mut tmp_assigns, &mut nop_stmts); - - try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts); - - try_eat_assign_tmp_stmts(&mut stmt_iter, &mut tmp_assigns, &mut nop_stmts); - - let (idx, stmt) = stmt_iter.next()?; - let (local_tmp_s1, local_0, vf_s1) = match_set_variant_field(stmt)?; - nop_stmts.push(idx); - - let (idx, stmt) = stmt_iter.next()?; - let (set_discr_local, set_discr_var_idx) = match_set_discr(stmt)?; - let discr_stmt_source_info = stmt.source_info; - nop_stmts.push(idx); - - try_eat_storage_stmts(&mut stmt_iter, &mut storage_live_stmts, &mut storage_dead_stmts); - - for (live_idx, live_local) in storage_live_stmts { - if let Some(i) = storage_dead_stmts.iter().rposition(|(_, l)| *l == live_local) { - let (dead_idx, _) = storage_dead_stmts.swap_remove(i); - storage_stmts.push((live_idx, dead_idx, live_local)); - - if live_local == local_tmp_s0 { - nop_stmts.push(get_variant_field_stmt); - } - } - } - // We sort primitive usize here so we can use unstable sort - nop_stmts.sort_unstable(); - - // Use one of the statements we're going to discard between the point - // where the storage location for the variant field becomes live and - // is killed. - let (live_idx, dead_idx) = find_storage_live_dead_stmts_for_local(local_tmp_s0, stmts)?; - let stmt_to_overwrite = - nop_stmts.iter().find(|stmt_idx| live_idx < **stmt_idx && **stmt_idx < dead_idx); - - let mut tmp_assigned_vars = BitSet::new_empty(locals_count); - for (l, r) in &tmp_assigns { - tmp_assigned_vars.insert(*l); - tmp_assigned_vars.insert(*r); - } - - let dbg_info_to_adjust: Vec<_> = debug_info - .iter() - .enumerate() - .filter_map(|(i, var_info)| { - if let VarDebugInfoContents::Place(p) = var_info.value { - if tmp_assigned_vars.contains(p.local) { - return Some(i); - } - } - - None - }) - .collect(); - - Some(ArmIdentityInfo { - local_temp_0: local_tmp_s0, - local_1, - vf_s0, - get_variant_field_stmt, - field_tmp_assignments: tmp_assigns, - local_tmp_s1, - local_0, - vf_s1, - set_discr_local, - set_discr_var_idx, - stmt_to_overwrite: *stmt_to_overwrite?, - source_info: discr_stmt_source_info, - storage_stmts, - stmts_to_remove: nop_stmts, - dbg_info_to_adjust, - dbg_projection, - }) -} - -fn optimization_applies<'tcx>( - opt_info: &ArmIdentityInfo<'tcx>, - local_decls: &IndexVec<Local, LocalDecl<'tcx>>, - local_uses: &IndexVec<Local, usize>, - var_debug_info: &[VarDebugInfo<'tcx>], -) -> bool { - trace!("testing if optimization applies..."); - - // FIXME(wesleywiser): possibly relax this restriction? - if opt_info.local_0 == opt_info.local_1 { - trace!("NO: moving into ourselves"); - return false; - } else if opt_info.vf_s0 != opt_info.vf_s1 { - trace!("NO: the field-and-variant information do not match"); - return false; - } else if local_decls[opt_info.local_0].ty != local_decls[opt_info.local_1].ty { - // FIXME(Centril,oli-obk): possibly relax to same layout? - trace!("NO: source and target locals have different types"); - return false; - } else if (opt_info.local_0, opt_info.vf_s0.var_idx) - != (opt_info.set_discr_local, opt_info.set_discr_var_idx) - { - trace!("NO: the discriminants do not match"); - return false; - } - - // Verify the assignment chain consists of the form b = a; c = b; d = c; etc... - if opt_info.field_tmp_assignments.is_empty() { - trace!("NO: no assignments found"); - return false; - } - let mut last_assigned_to = opt_info.field_tmp_assignments[0].1; - let source_local = last_assigned_to; - for (l, r) in &opt_info.field_tmp_assignments { - if *r != last_assigned_to { - trace!("NO: found unexpected assignment {:?} = {:?}", l, r); - return false; - } - - last_assigned_to = *l; - } - - // Check that the first and last used locals are only used twice - // since they are of the form: - // - // ``` - // _first = ((_x as Variant).n: ty); - // _n = _first; - // ... - // ((_y as Variant).n: ty) = _n; - // discriminant(_y) = z; - // ``` - for (l, r) in &opt_info.field_tmp_assignments { - if local_uses[*l] != 2 { - warn!("NO: FAILED assignment chain local {:?} was used more than twice", l); - return false; - } else if local_uses[*r] != 2 { - warn!("NO: FAILED assignment chain local {:?} was used more than twice", r); - return false; - } - } - - // Check that debug info only points to full Locals and not projections. - for dbg_idx in &opt_info.dbg_info_to_adjust { - let dbg_info = &var_debug_info[*dbg_idx]; - if let VarDebugInfoContents::Place(p) = dbg_info.value { - if !p.projection.is_empty() { - trace!("NO: debug info for {:?} had a projection {:?}", dbg_info.name, p); - return false; - } - } - } - - if source_local != opt_info.local_temp_0 { - trace!( - "NO: start of assignment chain does not match enum variant temp: {:?} != {:?}", - source_local, - opt_info.local_temp_0 - ); - return false; - } else if last_assigned_to != opt_info.local_tmp_s1 { - trace!( - "NO: end of assignment chain does not match written enum temp: {:?} != {:?}", - last_assigned_to, - opt_info.local_tmp_s1 - ); - return false; - } - - trace!("SUCCESS: optimization applies!"); - true -} - -impl<'tcx> MirPass<'tcx> for SimplifyArmIdentity { - fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { - // FIXME(77359): This optimization can result in unsoundness. - if !tcx.sess.opts.unstable_opts.unsound_mir_opts { - return; - } - - let source = body.source; - trace!("running SimplifyArmIdentity on {:?}", source); - - let local_uses = LocalUseCounter::get_local_uses(body); - for bb in body.basic_blocks.as_mut() { - if let Some(opt_info) = - get_arm_identity_info(&bb.statements, body.local_decls.len(), &body.var_debug_info) - { - trace!("got opt_info = {:#?}", opt_info); - if !optimization_applies( - &opt_info, - &body.local_decls, - &local_uses, - &body.var_debug_info, - ) { - debug!("optimization skipped for {:?}", source); - continue; - } - - // Also remove unused Storage{Live,Dead} statements which correspond - // to temps used previously. - for (live_idx, dead_idx, local) in &opt_info.storage_stmts { - // The temporary that we've read the variant field into is scoped to this block, - // so we can remove the assignment. - if *local == opt_info.local_temp_0 { - bb.statements[opt_info.get_variant_field_stmt].make_nop(); - } - - for (left, right) in &opt_info.field_tmp_assignments { - if local == left || local == right { - bb.statements[*live_idx].make_nop(); - bb.statements[*dead_idx].make_nop(); - } - } - } - - // Right shape; transform - for stmt_idx in opt_info.stmts_to_remove { - bb.statements[stmt_idx].make_nop(); - } - - let stmt = &mut bb.statements[opt_info.stmt_to_overwrite]; - stmt.source_info = opt_info.source_info; - stmt.kind = StatementKind::Assign(Box::new(( - opt_info.local_0.into(), - Rvalue::Use(Operand::Move(opt_info.local_1.into())), - ))); - - bb.statements.retain(|stmt| stmt.kind != StatementKind::Nop); - - // Fix the debug info to point to the right local - for dbg_index in opt_info.dbg_info_to_adjust { - let dbg_info = &mut body.var_debug_info[dbg_index]; - assert!( - matches!(dbg_info.value, VarDebugInfoContents::Place(_)), - "value was not a Place" - ); - if let VarDebugInfoContents::Place(p) = &mut dbg_info.value { - assert!(p.projection.is_empty()); - p.local = opt_info.local_0; - p.projection = opt_info.dbg_projection; - } - } - - trace!("block is now {:?}", bb.statements); - } - } - } -} - -struct LocalUseCounter { - local_uses: IndexVec<Local, usize>, -} - -impl LocalUseCounter { - fn get_local_uses(body: &Body<'_>) -> IndexVec<Local, usize> { - let mut counter = LocalUseCounter { local_uses: IndexVec::from_elem(0, &body.local_decls) }; - counter.visit_body(body); - counter.local_uses - } -} - -impl Visitor<'_> for LocalUseCounter { - fn visit_local(&mut self, local: Local, context: PlaceContext, _location: Location) { - if context.is_storage_marker() - || context == PlaceContext::NonUse(NonUseContext::VarDebugInfo) - { - return; - } - - self.local_uses[local] += 1; - } -} - -/// Match on: -/// ```ignore (MIR) -/// _LOCAL_INTO = ((_LOCAL_FROM as Variant).FIELD: TY); -/// ``` -fn match_get_variant_field<'tcx>( - stmt: &Statement<'tcx>, -) -> Option<(Local, Local, VarField<'tcx>, &'tcx List<PlaceElem<'tcx>>)> { - match &stmt.kind { - StatementKind::Assign(box ( - place_into, - Rvalue::Use(Operand::Copy(pf) | Operand::Move(pf)), - )) => { - let local_into = place_into.as_local()?; - let (local_from, vf) = match_variant_field_place(*pf)?; - Some((local_into, local_from, vf, pf.projection)) - } - _ => None, - } -} - -/// Match on: -/// ```ignore (MIR) -/// ((_LOCAL_FROM as Variant).FIELD: TY) = move _LOCAL_INTO; -/// ``` -fn match_set_variant_field<'tcx>(stmt: &Statement<'tcx>) -> Option<(Local, Local, VarField<'tcx>)> { - match &stmt.kind { - StatementKind::Assign(box (place_from, Rvalue::Use(Operand::Move(place_into)))) => { - let local_into = place_into.as_local()?; - let (local_from, vf) = match_variant_field_place(*place_from)?; - Some((local_into, local_from, vf)) - } - _ => None, - } -} - -/// Match on: -/// ```ignore (MIR) -/// discriminant(_LOCAL_TO_SET) = VAR_IDX; -/// ``` -fn match_set_discr(stmt: &Statement<'_>) -> Option<(Local, VariantIdx)> { - match &stmt.kind { - StatementKind::SetDiscriminant { place, variant_index } => { - Some((place.as_local()?, *variant_index)) - } - _ => None, - } -} - -#[derive(PartialEq, Debug)] -struct VarField<'tcx> { - field: Field, - field_ty: Ty<'tcx>, - var_idx: VariantIdx, -} - -/// Match on `((_LOCAL as Variant).FIELD: TY)`. -fn match_variant_field_place(place: Place<'_>) -> Option<(Local, VarField<'_>)> { - match place.as_ref() { - PlaceRef { - local, - projection: &[ProjectionElem::Downcast(_, var_idx), ProjectionElem::Field(field, ty)], - } => Some((local, VarField { field, field_ty: ty, var_idx })), - _ => None, - } -} - -/// Simplifies `SwitchInt(_) -> [targets]`, -/// where all the `targets` have the same form, -/// into `goto -> target_first`. -pub struct SimplifyBranchSame; - -impl<'tcx> MirPass<'tcx> for SimplifyBranchSame { - fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { - // This optimization is disabled by default for now due to - // soundness concerns; see issue #89485 and PR #89489. - if !tcx.sess.opts.unstable_opts.unsound_mir_opts { - return; - } - - trace!("Running SimplifyBranchSame on {:?}", body.source); - let finder = SimplifyBranchSameOptimizationFinder { body, tcx }; - let opts = finder.find(); - - let did_remove_blocks = opts.len() > 0; - for opt in opts.iter() { - trace!("SUCCESS: Applying optimization {:?}", opt); - // Replace `SwitchInt(..) -> [bb_first, ..];` with a `goto -> bb_first;`. - body.basic_blocks_mut()[opt.bb_to_opt_terminator].terminator_mut().kind = - TerminatorKind::Goto { target: opt.bb_to_goto }; - } - - if did_remove_blocks { - // We have dead blocks now, so remove those. - simplify::remove_dead_blocks(tcx, body); - } - } -} - -#[derive(Debug)] -struct SimplifyBranchSameOptimization { - /// All basic blocks are equal so go to this one - bb_to_goto: BasicBlock, - /// Basic block where the terminator can be simplified to a goto - bb_to_opt_terminator: BasicBlock, -} - -struct SwitchTargetAndValue { - target: BasicBlock, - // None in case of the `otherwise` case - value: Option<u128>, -} - -struct SimplifyBranchSameOptimizationFinder<'a, 'tcx> { - body: &'a Body<'tcx>, - tcx: TyCtxt<'tcx>, -} - -impl<'tcx> SimplifyBranchSameOptimizationFinder<'_, 'tcx> { - fn find(&self) -> Vec<SimplifyBranchSameOptimization> { - self.body - .basic_blocks - .iter_enumerated() - .filter_map(|(bb_idx, bb)| { - let (discr_switched_on, targets_and_values) = match &bb.terminator().kind { - TerminatorKind::SwitchInt { targets, discr, .. } => { - let targets_and_values: Vec<_> = targets.iter() - .map(|(val, target)| SwitchTargetAndValue { target, value: Some(val) }) - .chain(once(SwitchTargetAndValue { target: targets.otherwise(), value: None })) - .collect(); - (discr, targets_and_values) - }, - _ => return None, - }; - - // find the adt that has its discriminant read - // assuming this must be the last statement of the block - let adt_matched_on = match &bb.statements.last()?.kind { - StatementKind::Assign(box (place, rhs)) - if Some(*place) == discr_switched_on.place() => - { - match rhs { - Rvalue::Discriminant(adt_place) if adt_place.ty(self.body, self.tcx).ty.is_enum() => adt_place, - _ => { - trace!("NO: expected a discriminant read of an enum instead of: {:?}", rhs); - return None; - } - } - } - other => { - trace!("NO: expected an assignment of a discriminant read to a place. Found: {:?}", other); - return None - }, - }; - - let mut iter_bbs_reachable = targets_and_values - .iter() - .map(|target_and_value| (target_and_value, &self.body.basic_blocks[target_and_value.target])) - .filter(|(_, bb)| { - // Reaching `unreachable` is UB so assume it doesn't happen. - bb.terminator().kind != TerminatorKind::Unreachable - }) - .peekable(); - - let bb_first = iter_bbs_reachable.peek().map_or(&targets_and_values[0], |(idx, _)| *idx); - let mut all_successors_equivalent = StatementEquality::TrivialEqual; - - // All successor basic blocks must be equal or contain statements that are pairwise considered equal. - for ((target_and_value_l,bb_l), (target_and_value_r,bb_r)) in iter_bbs_reachable.tuple_windows() { - let trivial_checks = bb_l.is_cleanup == bb_r.is_cleanup - && bb_l.terminator().kind == bb_r.terminator().kind - && bb_l.statements.len() == bb_r.statements.len(); - let statement_check = || { - bb_l.statements.iter().zip(&bb_r.statements).try_fold(StatementEquality::TrivialEqual, |acc,(l,r)| { - let stmt_equality = self.statement_equality(*adt_matched_on, &l, target_and_value_l, &r, target_and_value_r); - if matches!(stmt_equality, StatementEquality::NotEqual) { - // short circuit - None - } else { - Some(acc.combine(&stmt_equality)) - } - }) - .unwrap_or(StatementEquality::NotEqual) - }; - if !trivial_checks { - all_successors_equivalent = StatementEquality::NotEqual; - break; - } - all_successors_equivalent = all_successors_equivalent.combine(&statement_check()); - }; - - match all_successors_equivalent{ - StatementEquality::TrivialEqual => { - // statements are trivially equal, so just take first - trace!("Statements are trivially equal"); - Some(SimplifyBranchSameOptimization { - bb_to_goto: bb_first.target, - bb_to_opt_terminator: bb_idx, - }) - } - StatementEquality::ConsideredEqual(bb_to_choose) => { - trace!("Statements are considered equal"); - Some(SimplifyBranchSameOptimization { - bb_to_goto: bb_to_choose, - bb_to_opt_terminator: bb_idx, - }) - } - StatementEquality::NotEqual => { - trace!("NO: not all successors of basic block {:?} were equivalent", bb_idx); - None - } - } - }) - .collect() - } - - /// Tests if two statements can be considered equal - /// - /// Statements can be trivially equal if the kinds match. - /// But they can also be considered equal in the following case A: - /// ```ignore (MIR) - /// discriminant(_0) = 0; // bb1 - /// _0 = move _1; // bb2 - /// ``` - /// In this case the two statements are equal iff - /// - `_0` is an enum where the variant index 0 is fieldless, and - /// - bb1 was targeted by a switch where the discriminant of `_1` was switched on - fn statement_equality( - &self, - adt_matched_on: Place<'tcx>, - x: &Statement<'tcx>, - x_target_and_value: &SwitchTargetAndValue, - y: &Statement<'tcx>, - y_target_and_value: &SwitchTargetAndValue, - ) -> StatementEquality { - let helper = |rhs: &Rvalue<'tcx>, - place: &Place<'tcx>, - variant_index: VariantIdx, - switch_value: u128, - side_to_choose| { - let place_type = place.ty(self.body, self.tcx).ty; - let adt = match *place_type.kind() { - ty::Adt(adt, _) if adt.is_enum() => adt, - _ => return StatementEquality::NotEqual, - }; - // We need to make sure that the switch value that targets the bb with - // SetDiscriminant is the same as the variant discriminant. - let variant_discr = adt.discriminant_for_variant(self.tcx, variant_index).val; - if variant_discr != switch_value { - trace!( - "NO: variant discriminant {} does not equal switch value {}", - variant_discr, - switch_value - ); - return StatementEquality::NotEqual; - } - let variant_is_fieldless = adt.variant(variant_index).fields.is_empty(); - if !variant_is_fieldless { - trace!("NO: variant {:?} was not fieldless", variant_index); - return StatementEquality::NotEqual; - } - - match rhs { - Rvalue::Use(operand) if operand.place() == Some(adt_matched_on) => { - StatementEquality::ConsideredEqual(side_to_choose) - } - _ => { - trace!( - "NO: RHS of assignment was {:?}, but expected it to match the adt being matched on in the switch, which is {:?}", - rhs, - adt_matched_on - ); - StatementEquality::NotEqual - } - } - }; - match (&x.kind, &y.kind) { - // trivial case - (x, y) if x == y => StatementEquality::TrivialEqual, - - // check for case A - ( - StatementKind::Assign(box (_, rhs)), - &StatementKind::SetDiscriminant { ref place, variant_index }, - ) if y_target_and_value.value.is_some() => { - // choose basic block of x, as that has the assign - helper( - rhs, - place, - variant_index, - y_target_and_value.value.unwrap(), - x_target_and_value.target, - ) - } - ( - &StatementKind::SetDiscriminant { ref place, variant_index }, - &StatementKind::Assign(box (_, ref rhs)), - ) if x_target_and_value.value.is_some() => { - // choose basic block of y, as that has the assign - helper( - rhs, - place, - variant_index, - x_target_and_value.value.unwrap(), - y_target_and_value.target, - ) - } - _ => { - trace!("NO: statements `{:?}` and `{:?}` not considered equal", x, y); - StatementEquality::NotEqual - } - } - } -} - -#[derive(Copy, Clone, Eq, PartialEq)] -enum StatementEquality { - /// The two statements are trivially equal; same kind - TrivialEqual, - /// The two statements are considered equal, but may be of different kinds. The BasicBlock field is the basic block to jump to when performing the branch-same optimization. - /// For example, `_0 = _1` and `discriminant(_0) = discriminant(0)` are considered equal if 0 is a fieldless variant of an enum. But we don't want to jump to the basic block with the SetDiscriminant, as that is not legal if _1 is not the 0 variant index - ConsideredEqual(BasicBlock), - /// The two statements are not equal - NotEqual, -} - -impl StatementEquality { - fn combine(&self, other: &StatementEquality) -> StatementEquality { - use StatementEquality::*; - match (self, other) { - (TrivialEqual, TrivialEqual) => TrivialEqual, - (TrivialEqual, ConsideredEqual(b)) | (ConsideredEqual(b), TrivialEqual) => { - ConsideredEqual(*b) - } - (ConsideredEqual(b1), ConsideredEqual(b2)) => { - if b1 == b2 { - ConsideredEqual(*b1) - } else { - NotEqual - } - } - (_, NotEqual) | (NotEqual, _) => NotEqual, - } - } -} |