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Rollup merge of #107172 - cjgillot:no-nal, r=nagisa
Reimplement NormalizeArrayLen based on SsaLocals Based on #106908 Fixes #105929 Only the last commit "Reimplement NormalizeArrayLen" is relevant.
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322 changes: 69 additions & 253 deletions
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compiler/rustc_mir_transform/src/normalize_array_len.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,288 +1,104 @@ | ||
| //! This pass eliminates casting of arrays into slices when their length | ||
| //! is taken using `.len()` method. Handy to preserve information in MIR for const prop | ||
|
|
||
| use crate::ssa::SsaLocals; | ||
| use crate::MirPass; | ||
| use rustc_data_structures::fx::FxIndexMap; | ||
| use rustc_data_structures::intern::Interned; | ||
| use rustc_index::bit_set::BitSet; | ||
| use rustc_index::vec::IndexVec; | ||
| use rustc_middle::mir::visit::*; | ||
| use rustc_middle::mir::*; | ||
| use rustc_middle::ty::{self, ReErased, Region, TyCtxt}; | ||
|
|
||
| const MAX_NUM_BLOCKS: usize = 800; | ||
| const MAX_NUM_LOCALS: usize = 3000; | ||
| use rustc_middle::ty::{self, TyCtxt}; | ||
| use rustc_mir_dataflow::impls::borrowed_locals; | ||
|
|
||
| pub struct NormalizeArrayLen; | ||
|
|
||
| impl<'tcx> MirPass<'tcx> for NormalizeArrayLen { | ||
| fn is_enabled(&self, sess: &rustc_session::Session) -> bool { | ||
| // See #105929 | ||
| sess.mir_opt_level() >= 4 && sess.opts.unstable_opts.unsound_mir_opts | ||
| sess.mir_opt_level() >= 3 | ||
| } | ||
|
|
||
| #[instrument(level = "trace", skip(self, tcx, body))] | ||
| fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { | ||
| // early returns for edge cases of highly unrolled functions | ||
| if body.basic_blocks.len() > MAX_NUM_BLOCKS { | ||
| return; | ||
| } | ||
| if body.local_decls.len() > MAX_NUM_LOCALS { | ||
| return; | ||
| } | ||
| debug!(def_id = ?body.source.def_id()); | ||
| normalize_array_len_calls(tcx, body) | ||
| } | ||
| } | ||
|
|
||
| pub fn normalize_array_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { | ||
| // We don't ever touch terminators, so no need to invalidate the CFG cache | ||
| let basic_blocks = body.basic_blocks.as_mut_preserves_cfg(); | ||
| let local_decls = &mut body.local_decls; | ||
| fn normalize_array_len_calls<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { | ||
| let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id()); | ||
| let borrowed_locals = borrowed_locals(body); | ||
| let ssa = SsaLocals::new(tcx, param_env, body, &borrowed_locals); | ||
|
|
||
| // do a preliminary analysis to see if we ever have locals of type `[T;N]` or `&[T;N]` | ||
| let mut interesting_locals = BitSet::new_empty(local_decls.len()); | ||
| for (local, decl) in local_decls.iter_enumerated() { | ||
| match decl.ty.kind() { | ||
| ty::Array(..) => { | ||
| interesting_locals.insert(local); | ||
| } | ||
| ty::Ref(.., ty, Mutability::Not) => match ty.kind() { | ||
| ty::Array(..) => { | ||
| interesting_locals.insert(local); | ||
| } | ||
| _ => {} | ||
| }, | ||
| _ => {} | ||
| } | ||
| } | ||
| if interesting_locals.is_empty() { | ||
| // we have found nothing to analyze | ||
| return; | ||
| } | ||
| let num_intesting_locals = interesting_locals.count(); | ||
| let mut state = FxIndexMap::with_capacity_and_hasher(num_intesting_locals, Default::default()); | ||
| let mut patches_scratchpad = | ||
| FxIndexMap::with_capacity_and_hasher(num_intesting_locals, Default::default()); | ||
| let mut replacements_scratchpad = | ||
| FxIndexMap::with_capacity_and_hasher(num_intesting_locals, Default::default()); | ||
| for block in basic_blocks { | ||
| // make length calls for arrays [T; N] not to decay into length calls for &[T] | ||
| // that forbids constant propagation | ||
| normalize_array_len_call( | ||
| tcx, | ||
| block, | ||
| local_decls, | ||
| &interesting_locals, | ||
| &mut state, | ||
| &mut patches_scratchpad, | ||
| &mut replacements_scratchpad, | ||
| ); | ||
| state.clear(); | ||
| patches_scratchpad.clear(); | ||
| replacements_scratchpad.clear(); | ||
| } | ||
| } | ||
| let slice_lengths = compute_slice_length(tcx, &ssa, body); | ||
| debug!(?slice_lengths); | ||
|
|
||
| struct Patcher<'a, 'tcx> { | ||
| tcx: TyCtxt<'tcx>, | ||
| patches_scratchpad: &'a FxIndexMap<usize, usize>, | ||
| replacements_scratchpad: &'a mut FxIndexMap<usize, Local>, | ||
| local_decls: &'a mut IndexVec<Local, LocalDecl<'tcx>>, | ||
| statement_idx: usize, | ||
| Replacer { tcx, slice_lengths }.visit_body_preserves_cfg(body); | ||
| } | ||
|
|
||
| impl<'tcx> Patcher<'_, 'tcx> { | ||
| fn patch_expand_statement( | ||
| &mut self, | ||
| statement: &mut Statement<'tcx>, | ||
| ) -> Option<std::vec::IntoIter<Statement<'tcx>>> { | ||
| let idx = self.statement_idx; | ||
| if let Some(len_statemnt_idx) = self.patches_scratchpad.get(&idx).copied() { | ||
| let mut statements = Vec::with_capacity(2); | ||
|
|
||
| // we are at statement that performs a cast. The only sound way is | ||
| // to create another local that performs a similar copy without a cast and then | ||
| // use this copy in the Len operation | ||
|
|
||
| match &statement.kind { | ||
| StatementKind::Assign(box ( | ||
| .., | ||
| Rvalue::Cast( | ||
| CastKind::Pointer(ty::adjustment::PointerCast::Unsize), | ||
| operand, | ||
| _, | ||
| ), | ||
| )) => { | ||
| match operand { | ||
| Operand::Copy(place) | Operand::Move(place) => { | ||
| // create new local | ||
| let ty = operand.ty(self.local_decls, self.tcx); | ||
| let local_decl = LocalDecl::with_source_info(ty, statement.source_info); | ||
| let local = self.local_decls.push(local_decl); | ||
| // make it live | ||
| let mut make_live_statement = statement.clone(); | ||
| make_live_statement.kind = StatementKind::StorageLive(local); | ||
| statements.push(make_live_statement); | ||
| // copy into it | ||
|
|
||
| let operand = Operand::Copy(*place); | ||
| let mut make_copy_statement = statement.clone(); | ||
| let assign_to = Place::from(local); | ||
| let rvalue = Rvalue::Use(operand); | ||
| make_copy_statement.kind = | ||
| StatementKind::Assign(Box::new((assign_to, rvalue))); | ||
| statements.push(make_copy_statement); | ||
|
|
||
| // to reorder we have to copy and make NOP | ||
| statements.push(statement.clone()); | ||
| statement.make_nop(); | ||
|
|
||
| self.replacements_scratchpad.insert(len_statemnt_idx, local); | ||
| } | ||
| _ => { | ||
| unreachable!("it's a bug in the implementation") | ||
| } | ||
| } | ||
| } | ||
| _ => { | ||
| unreachable!("it's a bug in the implementation") | ||
| fn compute_slice_length<'tcx>( | ||
| tcx: TyCtxt<'tcx>, | ||
| ssa: &SsaLocals, | ||
| body: &Body<'tcx>, | ||
| ) -> IndexVec<Local, Option<ty::Const<'tcx>>> { | ||
| let mut slice_lengths = IndexVec::from_elem(None, &body.local_decls); | ||
|
|
||
| for (local, rvalue) in ssa.assignments(body) { | ||
| match rvalue { | ||
| Rvalue::Cast( | ||
| CastKind::Pointer(ty::adjustment::PointerCast::Unsize), | ||
| operand, | ||
| cast_ty, | ||
| ) => { | ||
| let operand_ty = operand.ty(body, tcx); | ||
| debug!(?operand_ty); | ||
| if let Some(operand_ty) = operand_ty.builtin_deref(true) | ||
| && let ty::Array(_, len) = operand_ty.ty.kind() | ||
| && let Some(cast_ty) = cast_ty.builtin_deref(true) | ||
| && let ty::Slice(..) = cast_ty.ty.kind() | ||
| { | ||
| slice_lengths[local] = Some(*len); | ||
| } | ||
| } | ||
|
|
||
| self.statement_idx += 1; | ||
|
|
||
| Some(statements.into_iter()) | ||
| } else if let Some(local) = self.replacements_scratchpad.get(&idx).copied() { | ||
| let mut statements = Vec::with_capacity(2); | ||
|
|
||
| match &statement.kind { | ||
| StatementKind::Assign(box (into, Rvalue::Len(place))) => { | ||
| let add_deref = if let Some(..) = place.as_local() { | ||
| false | ||
| } else if let Some(..) = place.local_or_deref_local() { | ||
| true | ||
| } else { | ||
| unreachable!("it's a bug in the implementation") | ||
| }; | ||
| // replace len statement | ||
| let mut len_statement = statement.clone(); | ||
| let mut place = Place::from(local); | ||
| if add_deref { | ||
| place = self.tcx.mk_place_deref(place); | ||
| } | ||
| len_statement.kind = | ||
| StatementKind::Assign(Box::new((*into, Rvalue::Len(place)))); | ||
| statements.push(len_statement); | ||
|
|
||
| // make temporary dead | ||
| let mut make_dead_statement = statement.clone(); | ||
| make_dead_statement.kind = StatementKind::StorageDead(local); | ||
| statements.push(make_dead_statement); | ||
|
|
||
| // make original statement NOP | ||
| statement.make_nop(); | ||
| // The length information is stored in the fat pointer, so we treat `operand` as a value. | ||
| Rvalue::Use(operand) => { | ||
| if let Some(rhs) = operand.place() && let Some(rhs) = rhs.as_local() { | ||
| slice_lengths[local] = slice_lengths[rhs]; | ||
| } | ||
| _ => { | ||
| unreachable!("it's a bug in the implementation") | ||
| } | ||
| // The length information is stored in the fat pointer. | ||
| // Reborrowing copies length information from one pointer to the other. | ||
| Rvalue::Ref(_, _, rhs) | Rvalue::AddressOf(_, rhs) => { | ||
| if let [PlaceElem::Deref] = rhs.projection[..] { | ||
| slice_lengths[local] = slice_lengths[rhs.local]; | ||
| } | ||
| } | ||
|
|
||
| self.statement_idx += 1; | ||
|
|
||
| Some(statements.into_iter()) | ||
| } else { | ||
| self.statement_idx += 1; | ||
| None | ||
| _ => {} | ||
| } | ||
| } | ||
|
|
||
| slice_lengths | ||
| } | ||
|
|
||
| fn normalize_array_len_call<'tcx>( | ||
| struct Replacer<'tcx> { | ||
| tcx: TyCtxt<'tcx>, | ||
| block: &mut BasicBlockData<'tcx>, | ||
| local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>, | ||
| interesting_locals: &BitSet<Local>, | ||
| state: &mut FxIndexMap<Local, usize>, | ||
| patches_scratchpad: &mut FxIndexMap<usize, usize>, | ||
| replacements_scratchpad: &mut FxIndexMap<usize, Local>, | ||
| ) { | ||
| for (statement_idx, statement) in block.statements.iter_mut().enumerate() { | ||
| match &mut statement.kind { | ||
| StatementKind::Assign(box (place, rvalue)) => { | ||
| match rvalue { | ||
| Rvalue::Cast( | ||
| CastKind::Pointer(ty::adjustment::PointerCast::Unsize), | ||
| operand, | ||
| cast_ty, | ||
| ) => { | ||
| let Some(local) = place.as_local() else { return }; | ||
| match operand { | ||
| Operand::Copy(place) | Operand::Move(place) => { | ||
| let Some(operand_local) = place.local_or_deref_local() else { return; }; | ||
| if !interesting_locals.contains(operand_local) { | ||
| return; | ||
| } | ||
| let operand_ty = local_decls[operand_local].ty; | ||
| match (operand_ty.kind(), cast_ty.kind()) { | ||
| (ty::Array(of_ty_src, ..), ty::Slice(of_ty_dst)) => { | ||
| if of_ty_src == of_ty_dst { | ||
| // this is a cast from [T; N] into [T], so we are good | ||
| state.insert(local, statement_idx); | ||
| } | ||
| } | ||
| // current way of patching doesn't allow to work with `mut` | ||
| ( | ||
| ty::Ref( | ||
| Region(Interned(ReErased, _)), | ||
| operand_ty, | ||
| Mutability::Not, | ||
| ), | ||
| ty::Ref( | ||
| Region(Interned(ReErased, _)), | ||
| cast_ty, | ||
| Mutability::Not, | ||
| ), | ||
| ) => { | ||
| match (operand_ty.kind(), cast_ty.kind()) { | ||
| // current way of patching doesn't allow to work with `mut` | ||
| (ty::Array(of_ty_src, ..), ty::Slice(of_ty_dst)) => { | ||
| if of_ty_src == of_ty_dst { | ||
| // this is a cast from [T; N] into [T], so we are good | ||
| state.insert(local, statement_idx); | ||
| } | ||
| } | ||
| _ => {} | ||
| } | ||
| } | ||
| _ => {} | ||
| } | ||
| } | ||
| _ => {} | ||
| } | ||
| } | ||
| Rvalue::Len(place) => { | ||
| let Some(local) = place.local_or_deref_local() else { | ||
| return; | ||
| }; | ||
| if let Some(cast_statement_idx) = state.get(&local).copied() { | ||
| patches_scratchpad.insert(cast_statement_idx, statement_idx); | ||
| } | ||
| } | ||
| _ => { | ||
| // invalidate | ||
| state.remove(&place.local); | ||
| } | ||
| } | ||
| } | ||
| _ => {} | ||
| } | ||
| } | ||
| slice_lengths: IndexVec<Local, Option<ty::Const<'tcx>>>, | ||
| } | ||
|
|
||
| let mut patcher = Patcher { | ||
| tcx, | ||
| patches_scratchpad: &*patches_scratchpad, | ||
| replacements_scratchpad, | ||
| local_decls, | ||
| statement_idx: 0, | ||
| }; | ||
| impl<'tcx> MutVisitor<'tcx> for Replacer<'tcx> { | ||
| fn tcx(&self) -> TyCtxt<'tcx> { | ||
| self.tcx | ||
| } | ||
|
|
||
| block.expand_statements(|st| patcher.patch_expand_statement(st)); | ||
| fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, loc: Location) { | ||
| if let Rvalue::Len(place) = rvalue | ||
| && let [PlaceElem::Deref] = &place.projection[..] | ||
| && let Some(len) = self.slice_lengths[place.local] | ||
| { | ||
| *rvalue = Rvalue::Use(Operand::Constant(Box::new(Constant { | ||
| span: rustc_span::DUMMY_SP, | ||
| user_ty: None, | ||
| literal: ConstantKind::from_const(len, self.tcx), | ||
| }))); | ||
| } | ||
| self.super_rvalue(rvalue, loc); | ||
| } | ||
| } |
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