diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src')
10 files changed, 1000 insertions, 66 deletions
diff --git a/compiler/rustc_mir_transform/src/const_goto.rs b/compiler/rustc_mir_transform/src/const_goto.rs index 3884346076e..cb5b66b314d 100644 --- a/compiler/rustc_mir_transform/src/const_goto.rs +++ b/compiler/rustc_mir_transform/src/const_goto.rs @@ -51,7 +51,7 @@ impl<'tcx> MirPass<'tcx> for ConstGoto { // if we applied optimizations, we potentially have some cfg to cleanup to // make it easier for further passes if should_simplify { - simplify_cfg(tcx, body); + simplify_cfg(body); simplify_locals(body, tcx); } } diff --git a/compiler/rustc_mir_transform/src/deduplicate_blocks.rs b/compiler/rustc_mir_transform/src/deduplicate_blocks.rs index b40b2ec8bfd..824974970bb 100644 --- a/compiler/rustc_mir_transform/src/deduplicate_blocks.rs +++ b/compiler/rustc_mir_transform/src/deduplicate_blocks.rs @@ -25,7 +25,7 @@ impl<'tcx> MirPass<'tcx> for DeduplicateBlocks { if has_opts_to_apply { let mut opt_applier = OptApplier { tcx, duplicates }; opt_applier.visit_body(body); - simplify_cfg(tcx, body); + simplify_cfg(body); } } } diff --git a/compiler/rustc_mir_transform/src/early_otherwise_branch.rs b/compiler/rustc_mir_transform/src/early_otherwise_branch.rs index 6eb6cb069fe..0d600f0f937 100644 --- a/compiler/rustc_mir_transform/src/early_otherwise_branch.rs +++ b/compiler/rustc_mir_transform/src/early_otherwise_branch.rs @@ -212,7 +212,7 @@ impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch { // Since this optimization adds new basic blocks and invalidates others, // clean up the cfg to make it nicer for other passes if should_cleanup { - simplify_cfg(tcx, body); + simplify_cfg(body); } } } diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs index 8ad804bf3e7..ebefc3b47cc 100644 --- a/compiler/rustc_mir_transform/src/inline.rs +++ b/compiler/rustc_mir_transform/src/inline.rs @@ -15,7 +15,7 @@ use rustc_target::abi::FieldIdx; use rustc_target::spec::abi::Abi; use crate::cost_checker::CostChecker; -use crate::simplify::{remove_dead_blocks, CfgSimplifier}; +use crate::simplify::simplify_cfg; use crate::util; use std::iter; use std::ops::{Range, RangeFrom}; @@ -56,8 +56,7 @@ impl<'tcx> MirPass<'tcx> for Inline { let _guard = span.enter(); if inline(tcx, body) { debug!("running simplify cfg on {:?}", body.source); - CfgSimplifier::new(body).simplify(); - remove_dead_blocks(body); + simplify_cfg(body); deref_finder(tcx, body); } } diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs index 2c1602dadc1..43c5b3873b9 100644 --- a/compiler/rustc_mir_transform/src/lib.rs +++ b/compiler/rustc_mir_transform/src/lib.rs @@ -1,5 +1,6 @@ #![deny(rustc::untranslatable_diagnostic)] #![deny(rustc::diagnostic_outside_of_impl)] +#![feature(assert_matches)] #![feature(box_patterns)] #![feature(cow_is_borrowed)] #![feature(decl_macro)] @@ -94,6 +95,7 @@ mod multiple_return_terminators; mod normalize_array_len; mod nrvo; mod prettify; +mod promote_consts; mod ref_prop; mod remove_noop_landing_pads; mod remove_storage_markers; @@ -115,7 +117,6 @@ mod uninhabited_enum_branching; mod unreachable_prop; use rustc_const_eval::transform::check_consts::{self, ConstCx}; -use rustc_const_eval::transform::promote_consts; use rustc_const_eval::transform::validate; use rustc_mir_dataflow::rustc_peek; diff --git a/compiler/rustc_mir_transform/src/match_branches.rs b/compiler/rustc_mir_transform/src/match_branches.rs index 1c4aa37d57f..6d4332793af 100644 --- a/compiler/rustc_mir_transform/src/match_branches.rs +++ b/compiler/rustc_mir_transform/src/match_branches.rs @@ -174,7 +174,7 @@ impl<'tcx> MirPass<'tcx> for MatchBranchSimplification { } if should_cleanup { - simplify_cfg(tcx, body); + simplify_cfg(body); } } } diff --git a/compiler/rustc_mir_transform/src/promote_consts.rs b/compiler/rustc_mir_transform/src/promote_consts.rs new file mode 100644 index 00000000000..841b86fed45 --- /dev/null +++ b/compiler/rustc_mir_transform/src/promote_consts.rs @@ -0,0 +1,952 @@ +//! A pass that promotes borrows of constant rvalues. +//! +//! The rvalues considered constant are trees of temps, +//! each with exactly one initialization, and holding +//! a constant value with no interior mutability. +//! They are placed into a new MIR constant body in +//! `promoted` and the borrow rvalue is replaced with +//! a `Literal::Promoted` using the index into `promoted` +//! of that constant MIR. +//! +//! This pass assumes that every use is dominated by an +//! initialization and can otherwise silence errors, if +//! move analysis runs after promotion on broken MIR. + +use either::{Left, Right}; +use rustc_hir as hir; +use rustc_middle::mir; +use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor}; +use rustc_middle::mir::*; +use rustc_middle::ty::GenericArgs; +use rustc_middle::ty::{self, List, Ty, TyCtxt, TypeVisitableExt}; +use rustc_span::Span; + +use rustc_index::{Idx, IndexSlice, IndexVec}; + +use std::assert_matches::assert_matches; +use std::cell::Cell; +use std::{cmp, iter, mem}; + +use rustc_const_eval::transform::check_consts::{qualifs, ConstCx}; + +/// A `MirPass` for promotion. +/// +/// Promotion is the extraction of promotable temps into separate MIR bodies so they can have +/// `'static` lifetime. +/// +/// After this pass is run, `promoted_fragments` will hold the MIR body corresponding to each +/// newly created `Constant`. +#[derive(Default)] +pub struct PromoteTemps<'tcx> { + pub promoted_fragments: Cell<IndexVec<Promoted, Body<'tcx>>>, +} + +impl<'tcx> MirPass<'tcx> for PromoteTemps<'tcx> { + fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { + // There's not really any point in promoting errorful MIR. + // + // This does not include MIR that failed const-checking, which we still try to promote. + if let Err(_) = body.return_ty().error_reported() { + debug!("PromoteTemps: MIR had errors"); + return; + } + if body.source.promoted.is_some() { + return; + } + + let ccx = ConstCx::new(tcx, body); + let (mut temps, all_candidates) = collect_temps_and_candidates(&ccx); + + let promotable_candidates = validate_candidates(&ccx, &mut temps, &all_candidates); + + let promoted = promote_candidates(body, tcx, temps, promotable_candidates); + self.promoted_fragments.set(promoted); + } +} + +/// State of a temporary during collection and promotion. +#[derive(Copy, Clone, PartialEq, Eq, Debug)] +enum TempState { + /// No references to this temp. + Undefined, + /// One direct assignment and any number of direct uses. + /// A borrow of this temp is promotable if the assigned + /// value is qualified as constant. + Defined { location: Location, uses: usize, valid: Result<(), ()> }, + /// Any other combination of assignments/uses. + Unpromotable, + /// This temp was part of an rvalue which got extracted + /// during promotion and needs cleanup. + PromotedOut, +} + +/// A "root candidate" for promotion, which will become the +/// returned value in a promoted MIR, unless it's a subset +/// of a larger candidate. +#[derive(Copy, Clone, PartialEq, Eq, Debug)] +struct Candidate { + location: Location, +} + +struct Collector<'a, 'tcx> { + ccx: &'a ConstCx<'a, 'tcx>, + temps: IndexVec<Local, TempState>, + candidates: Vec<Candidate>, +} + +impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> { + fn visit_local(&mut self, index: Local, context: PlaceContext, location: Location) { + debug!("visit_local: index={:?} context={:?} location={:?}", index, context, location); + // We're only interested in temporaries and the return place + match self.ccx.body.local_kind(index) { + LocalKind::Arg => return, + LocalKind::Temp if self.ccx.body.local_decls[index].is_user_variable() => return, + LocalKind::ReturnPointer | LocalKind::Temp => {} + } + + // Ignore drops, if the temp gets promoted, + // then it's constant and thus drop is noop. + // Non-uses are also irrelevant. + if context.is_drop() || !context.is_use() { + debug!( + "visit_local: context.is_drop={:?} context.is_use={:?}", + context.is_drop(), + context.is_use(), + ); + return; + } + + let temp = &mut self.temps[index]; + debug!("visit_local: temp={:?}", temp); + *temp = match *temp { + TempState::Undefined => match context { + PlaceContext::MutatingUse(MutatingUseContext::Store) + | PlaceContext::MutatingUse(MutatingUseContext::Call) => { + TempState::Defined { location, uses: 0, valid: Err(()) } + } + _ => TempState::Unpromotable, + }, + TempState::Defined { ref mut uses, .. } => { + // We always allow borrows, even mutable ones, as we need + // to promote mutable borrows of some ZSTs e.g., `&mut []`. + let allowed_use = match context { + PlaceContext::MutatingUse(MutatingUseContext::Borrow) + | PlaceContext::NonMutatingUse(_) => true, + PlaceContext::MutatingUse(_) | PlaceContext::NonUse(_) => false, + }; + debug!("visit_local: allowed_use={:?}", allowed_use); + if allowed_use { + *uses += 1; + return; + } + TempState::Unpromotable + } + TempState::Unpromotable | TempState::PromotedOut => TempState::Unpromotable, + }; + } + + fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) { + self.super_rvalue(rvalue, location); + + if let Rvalue::Ref(..) = *rvalue { + self.candidates.push(Candidate { location }); + } + } +} + +fn collect_temps_and_candidates<'tcx>( + ccx: &ConstCx<'_, 'tcx>, +) -> (IndexVec<Local, TempState>, Vec<Candidate>) { + let mut collector = Collector { + temps: IndexVec::from_elem(TempState::Undefined, &ccx.body.local_decls), + candidates: vec![], + ccx, + }; + for (bb, data) in traversal::reverse_postorder(ccx.body) { + collector.visit_basic_block_data(bb, data); + } + (collector.temps, collector.candidates) +} + +/// Checks whether locals that appear in a promotion context (`Candidate`) are actually promotable. +/// +/// This wraps an `Item`, and has access to all fields of that `Item` via `Deref` coercion. +struct Validator<'a, 'tcx> { + ccx: &'a ConstCx<'a, 'tcx>, + temps: &'a mut IndexSlice<Local, TempState>, +} + +impl<'a, 'tcx> std::ops::Deref for Validator<'a, 'tcx> { + type Target = ConstCx<'a, 'tcx>; + + fn deref(&self) -> &Self::Target { + self.ccx + } +} + +struct Unpromotable; + +impl<'tcx> Validator<'_, 'tcx> { + fn validate_candidate(&mut self, candidate: Candidate) -> Result<(), Unpromotable> { + let Left(statement) = self.body.stmt_at(candidate.location) else { bug!() }; + let Some((_, Rvalue::Ref(_, kind, place))) = statement.kind.as_assign() else { bug!() }; + + // We can only promote interior borrows of promotable temps (non-temps + // don't get promoted anyway). + self.validate_local(place.local)?; + + // The reference operation itself must be promotable. + // (Needs to come after `validate_local` to avoid ICEs.) + self.validate_ref(*kind, place)?; + + // We do not check all the projections (they do not get promoted anyway), + // but we do stay away from promoting anything involving a dereference. + if place.projection.contains(&ProjectionElem::Deref) { + return Err(Unpromotable); + } + + Ok(()) + } + + // FIXME(eddyb) maybe cache this? + fn qualif_local<Q: qualifs::Qualif>(&mut self, local: Local) -> bool { + let TempState::Defined { location: loc, .. } = self.temps[local] else { + return false; + }; + + let stmt_or_term = self.body.stmt_at(loc); + match stmt_or_term { + Left(statement) => { + let Some((_, rhs)) = statement.kind.as_assign() else { + span_bug!(statement.source_info.span, "{:?} is not an assignment", statement) + }; + qualifs::in_rvalue::<Q, _>(self.ccx, &mut |l| self.qualif_local::<Q>(l), rhs) + } + Right(terminator) => { + assert_matches!(terminator.kind, TerminatorKind::Call { .. }); + let return_ty = self.body.local_decls[local].ty; + Q::in_any_value_of_ty(self.ccx, return_ty) + } + } + } + + fn validate_local(&mut self, local: Local) -> Result<(), Unpromotable> { + let TempState::Defined { location: loc, uses, valid } = self.temps[local] else { + return Err(Unpromotable); + }; + + // We cannot promote things that need dropping, since the promoted value would not get + // dropped. + if self.qualif_local::<qualifs::NeedsDrop>(local) { + return Err(Unpromotable); + } + + if valid.is_ok() { + return Ok(()); + } + + let ok = { + let stmt_or_term = self.body.stmt_at(loc); + match stmt_or_term { + Left(statement) => { + let Some((_, rhs)) = statement.kind.as_assign() else { + span_bug!( + statement.source_info.span, + "{:?} is not an assignment", + statement + ) + }; + self.validate_rvalue(rhs) + } + Right(terminator) => match &terminator.kind { + TerminatorKind::Call { func, args, .. } => self.validate_call(func, args), + TerminatorKind::Yield { .. } => Err(Unpromotable), + kind => { + span_bug!(terminator.source_info.span, "{:?} not promotable", kind); + } + }, + } + }; + + self.temps[local] = match ok { + Ok(()) => TempState::Defined { location: loc, uses, valid: Ok(()) }, + Err(_) => TempState::Unpromotable, + }; + + ok + } + + fn validate_place(&mut self, place: PlaceRef<'tcx>) -> Result<(), Unpromotable> { + let Some((place_base, elem)) = place.last_projection() else { + return self.validate_local(place.local); + }; + + // Validate topmost projection, then recurse. + match elem { + // Recurse directly. + ProjectionElem::ConstantIndex { .. } + | ProjectionElem::Subtype(_) + | ProjectionElem::Subslice { .. } => {} + + // Never recurse. + ProjectionElem::OpaqueCast(..) | ProjectionElem::Downcast(..) => { + return Err(Unpromotable); + } + + ProjectionElem::Deref => { + // When a static is used by-value, that gets desugared to `*STATIC_ADDR`, + // and we need to be able to promote this. So check if this deref matches + // that specific pattern. + + // We need to make sure this is a `Deref` of a local with no further projections. + // Discussion can be found at + // https://github.com/rust-lang/rust/pull/74945#discussion_r463063247 + if let Some(local) = place_base.as_local() + && let TempState::Defined { location, .. } = self.temps[local] + && let Left(def_stmt) = self.body.stmt_at(location) + && let Some((_, Rvalue::Use(Operand::Constant(c)))) = def_stmt.kind.as_assign() + && let Some(did) = c.check_static_ptr(self.tcx) + // Evaluating a promoted may not read statics except if it got + // promoted from a static (this is a CTFE check). So we + // can only promote static accesses inside statics. + && let Some(hir::ConstContext::Static(..)) = self.const_kind + && !self.tcx.is_thread_local_static(did) + { + // Recurse. + } else { + return Err(Unpromotable); + } + } + ProjectionElem::Index(local) => { + // Only accept if we can predict the index and are indexing an array. + if let TempState::Defined { location: loc, .. } = self.temps[local] + && let Left(statement) = self.body.stmt_at(loc) + && let Some((_, Rvalue::Use(Operand::Constant(c)))) = statement.kind.as_assign() + && let Some(idx) = c.const_.try_eval_target_usize(self.tcx, self.param_env) + // Determine the type of the thing we are indexing. + && let ty::Array(_, len) = place_base.ty(self.body, self.tcx).ty.kind() + // It's an array; determine its length. + && let Some(len) = len.try_eval_target_usize(self.tcx, self.param_env) + // If the index is in-bounds, go ahead. + && idx < len + { + self.validate_local(local)?; + // Recurse. + } else { + return Err(Unpromotable); + } + } + + ProjectionElem::Field(..) => { + let base_ty = place_base.ty(self.body, self.tcx).ty; + if base_ty.is_union() { + // No promotion of union field accesses. + return Err(Unpromotable); + } + } + } + + self.validate_place(place_base) + } + + fn validate_operand(&mut self, operand: &Operand<'tcx>) -> Result<(), Unpromotable> { + match operand { + Operand::Copy(place) | Operand::Move(place) => self.validate_place(place.as_ref()), + + // The qualifs for a constant (e.g. `HasMutInterior`) are checked in + // `validate_rvalue` upon access. + Operand::Constant(c) => { + if let Some(def_id) = c.check_static_ptr(self.tcx) { + // Only allow statics (not consts) to refer to other statics. + // FIXME(eddyb) does this matter at all for promotion? + // FIXME(RalfJung) it makes little sense to not promote this in `fn`/`const fn`, + // and in `const` this cannot occur anyway. The only concern is that we might + // promote even `let x = &STATIC` which would be useless, but this applies to + // promotion inside statics as well. + let is_static = matches!(self.const_kind, Some(hir::ConstContext::Static(_))); + if !is_static { + return Err(Unpromotable); + } + + let is_thread_local = self.tcx.is_thread_local_static(def_id); + if is_thread_local { + return Err(Unpromotable); + } + } + + Ok(()) + } + } + } + + fn validate_ref(&mut self, kind: BorrowKind, place: &Place<'tcx>) -> Result<(), Unpromotable> { + match kind { + // Reject these borrow types just to be safe. + // FIXME(RalfJung): could we allow them? Should we? No point in it until we have a usecase. + BorrowKind::Fake | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => { + return Err(Unpromotable); + } + + BorrowKind::Shared => { + let has_mut_interior = self.qualif_local::<qualifs::HasMutInterior>(place.local); + if has_mut_interior { + return Err(Unpromotable); + } + } + + // FIXME: consider changing this to only promote &mut [] for default borrows, + // also forbidding two phase borrows + BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow } => { + let ty = place.ty(self.body, self.tcx).ty; + + // In theory, any zero-sized value could be borrowed + // mutably without consequences. However, only &mut [] + // is allowed right now. + if let ty::Array(_, len) = ty.kind() { + match len.try_eval_target_usize(self.tcx, self.param_env) { + Some(0) => {} + _ => return Err(Unpromotable), + } + } else { + return Err(Unpromotable); + } + } + } + + Ok(()) + } + + fn validate_rvalue(&mut self, rvalue: &Rvalue<'tcx>) -> Result<(), Unpromotable> { + match rvalue { + Rvalue::Use(operand) | Rvalue::Repeat(operand, _) => { + self.validate_operand(operand)?; + } + Rvalue::CopyForDeref(place) => { + let op = &Operand::Copy(*place); + self.validate_operand(op)? + } + + Rvalue::Discriminant(place) | Rvalue::Len(place) => { + self.validate_place(place.as_ref())? + } + + Rvalue::ThreadLocalRef(_) => return Err(Unpromotable), + + // ptr-to-int casts are not possible in consts and thus not promotable + Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => return Err(Unpromotable), + + // all other casts including int-to-ptr casts are fine, they just use the integer value + // at pointer type. + Rvalue::Cast(_, operand, _) => { + self.validate_operand(operand)?; + } + + Rvalue::NullaryOp(op, _) => match op { + NullOp::SizeOf => {} + NullOp::AlignOf => {} + NullOp::OffsetOf(_) => {} + }, + + Rvalue::ShallowInitBox(_, _) => return Err(Unpromotable), + + Rvalue::UnaryOp(op, operand) => { + match op { + // These operations can never fail. + UnOp::Neg | UnOp::Not => {} + } + + self.validate_operand(operand)?; + } + + Rvalue::BinaryOp(op, box (lhs, rhs)) | Rvalue::CheckedBinaryOp(op, box (lhs, rhs)) => { + let op = *op; + let lhs_ty = lhs.ty(self.body, self.tcx); + + if let ty::RawPtr(_) | ty::FnPtr(..) = lhs_ty.kind() { + // Raw and fn pointer operations are not allowed inside consts and thus not promotable. + assert!(matches!( + op, + BinOp::Eq + | BinOp::Ne + | BinOp::Le + | BinOp::Lt + | BinOp::Ge + | BinOp::Gt + | BinOp::Offset + )); + return Err(Unpromotable); + } + + match op { + BinOp::Div | BinOp::Rem => { + if lhs_ty.is_integral() { + // Integer division: the RHS must be a non-zero const. + let const_val = match rhs { + Operand::Constant(c) => { + c.const_.try_eval_bits(self.tcx, self.param_env) + } + _ => None, + }; + match const_val { + Some(x) if x != 0 => {} // okay + _ => return Err(Unpromotable), // value not known or 0 -- not okay + } + } + } + // The remaining operations can never fail. + BinOp::Eq + | BinOp::Ne + | BinOp::Le + | BinOp::Lt + | BinOp::Ge + | BinOp::Gt + | BinOp::Offset + | BinOp::Add + | BinOp::AddUnchecked + | BinOp::Sub + | BinOp::SubUnchecked + | BinOp::Mul + | BinOp::MulUnchecked + | BinOp::BitXor + | BinOp::BitAnd + | BinOp::BitOr + | BinOp::Shl + | BinOp::ShlUnchecked + | BinOp::Shr + | BinOp::ShrUnchecked => {} + } + + self.validate_operand(lhs)?; + self.validate_operand(rhs)?; + } + + Rvalue::AddressOf(_, place) => { + // We accept `&raw *`, i.e., raw reborrows -- creating a raw pointer is + // no problem, only using it is. + if let Some((place_base, ProjectionElem::Deref)) = place.as_ref().last_projection() + { + let base_ty = place_base.ty(self.body, self.tcx).ty; + if let ty::Ref(..) = base_ty.kind() { + return self.validate_place(place_base); + } + } + return Err(Unpromotable); + } + + Rvalue::Ref(_, kind, place) => { + // Special-case reborrows to be more like a copy of the reference. + let mut place_simplified = place.as_ref(); + if let Some((place_base, ProjectionElem::Deref)) = + place_simplified.last_projection() + { + let base_ty = place_base.ty(self.body, self.tcx).ty; + if let ty::Ref(..) = base_ty.kind() { + place_simplified = place_base; + } + } + + self.validate_place(place_simplified)?; + + // Check that the reference is fine (using the original place!). + // (Needs to come after `validate_place` to avoid ICEs.) + self.validate_ref(*kind, place)?; + } + + Rvalue::Aggregate(_, operands) => { + for o in operands { + self.validate_operand(o)?; + } + } + } + + Ok(()) + } + + fn validate_call( + &mut self, + callee: &Operand<'tcx>, + args: &[Operand<'tcx>], + ) -> Result<(), Unpromotable> { + let fn_ty = callee.ty(self.body, self.tcx); + + // Inside const/static items, we promote all (eligible) function calls. + // Everywhere else, we require `#[rustc_promotable]` on the callee. + let promote_all_const_fn = matches!( + self.const_kind, + Some(hir::ConstContext::Static(_) | hir::ConstContext::Const { inline: false }) + ); + if !promote_all_const_fn { + if let ty::FnDef(def_id, _) = *fn_ty.kind() { + // Never promote runtime `const fn` calls of + // functions without `#[rustc_promotable]`. + if !self.tcx.is_promotable_const_fn(def_id) { + return Err(Unpromotable); + } + } + } + + let is_const_fn = match *fn_ty.kind() { + ty::FnDef(def_id, _) => self.tcx.is_const_fn_raw(def_id), + _ => false, + }; + if !is_const_fn { + return Err(Unpromotable); + } + + self.validate_operand(callee)?; + for arg in args { + self.validate_operand(arg)?; + } + + Ok(()) + } +} + +// FIXME(eddyb) remove the differences for promotability in `static`, `const`, `const fn`. +fn validate_candidates( + ccx: &ConstCx<'_, '_>, + temps: &mut IndexSlice<Local, TempState>, + candidates: &[Candidate], +) -> Vec<Candidate> { + let mut validator = Validator { ccx, temps }; + + candidates + .iter() + .copied() + .filter(|&candidate| validator.validate_candidate(candidate).is_ok()) + .collect() +} + +struct Promoter<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + source: &'a mut Body<'tcx>, + promoted: Body<'tcx>, + temps: &'a mut IndexVec<Local, TempState>, + extra_statements: &'a mut Vec<(Location, Statement<'tcx>)>, + + /// If true, all nested temps are also kept in the + /// source MIR, not moved to the promoted MIR. + keep_original: bool, +} + +impl<'a, 'tcx> Promoter<'a, 'tcx> { + fn new_block(&mut self) -> BasicBlock { + let span = self.promoted.span; + self.promoted.basic_blocks_mut().push(BasicBlockData { + statements: vec![], + terminator: Some(Terminator { + source_info: SourceInfo::outermost(span), + kind: TerminatorKind::Return, + }), + is_cleanup: false, + }) + } + + fn assign(&mut self, dest: Local, rvalue: Rvalue<'tcx>, span: Span) { + let last = self.promoted.basic_blocks.last_index().unwrap(); + let data = &mut self.promoted[last]; + data.statements.push(Statement { + source_info: SourceInfo::outermost(span), + kind: StatementKind::Assign(Box::new((Place::from(dest), rvalue))), + }); + } + + fn is_temp_kind(&self, local: Local) -> bool { + self.source.local_kind(local) == LocalKind::Temp + } + + /// Copies the initialization of this temp to the + /// promoted MIR, recursing through temps. + fn promote_temp(&mut self, temp: Local) -> Local { + let old_keep_original = self.keep_original; + let loc = match self.temps[temp] { + TempState::Defined { location, uses, .. } if uses > 0 => { + if uses > 1 { + self.keep_original = true; + } + location + } + state => { + span_bug!(self.promoted.span, "{:?} not promotable: {:?}", temp, state); + } + }; + if !self.keep_original { + self.temps[temp] = TempState::PromotedOut; + } + + let num_stmts = self.source[loc.block].statements.len(); + let new_temp = self.promoted.local_decls.push(LocalDecl::new( + self.source.local_decls[temp].ty, + self.source.local_decls[temp].source_info.span, + )); + + debug!("promote({:?} @ {:?}/{:?}, {:?})", temp, loc, num_stmts, self.keep_original); + + // First, take the Rvalue or Call out of the source MIR, + // or duplicate it, depending on keep_original. + if loc.statement_index < num_stmts { + let (mut rvalue, source_info) = { + let statement = &mut self.source[loc.block].statements[loc.statement_index]; + let StatementKind::Assign(box (_, rhs)) = &mut statement.kind else { + span_bug!(statement.source_info.span, "{:?} is not an assignment", statement); + }; + + ( + if self.keep_original { + rhs.clone() + } else { + let unit = Rvalue::Use(Operand::Constant(Box::new(ConstOperand { + span: statement.source_info.span, + user_ty: None, + const_: Const::zero_sized(self.tcx.types.unit), + }))); + mem::replace(rhs, unit) + }, + statement.source_info, + ) + }; + + self.visit_rvalue(&mut rvalue, loc); + self.assign(new_temp, rvalue, source_info.span); + } else { + let terminator = if self.keep_original { + self.source[loc.block].terminator().clone() + } else { + let terminator = self.source[loc.block].terminator_mut(); + let target = match &terminator.kind { + TerminatorKind::Call { target: Some(target), .. } => *target, + kind => { + span_bug!(terminator.source_info.span, "{:?} not promotable", kind); + } + }; + Terminator { + source_info: terminator.source_info, + kind: mem::replace(&mut terminator.kind, TerminatorKind::Goto { target }), + } + }; + + match terminator.kind { + TerminatorKind::Call { + mut func, mut args, call_source: desugar, fn_span, .. + } => { + self.visit_operand(&mut func, loc); + for arg in &mut args { + self.visit_operand(arg, loc); + } + + let last = self.promoted.basic_blocks.last_index().unwrap(); + let new_target = self.new_block(); + + *self.promoted[last].terminator_mut() = Terminator { + kind: TerminatorKind::Call { + func, + args, + unwind: UnwindAction::Continue, + destination: Place::from(new_temp), + target: Some(new_target), + call_source: desugar, + fn_span, + }, + source_info: SourceInfo::outermost(terminator.source_info.span), + ..terminator + }; + } + kind => { + span_bug!(terminator.source_info.span, "{:?} not promotable", kind); + } + }; + }; + + self.keep_original = old_keep_original; + new_temp + } + + fn promote_candidate(mut self, candidate: Candidate, next_promoted_id: usize) -> Body<'tcx> { + let def = self.source.source.def_id(); + let mut rvalue = { + let promoted = &mut self.promoted; + let promoted_id = Promoted::new(next_promoted_id); + let tcx = self.tcx; + let mut promoted_operand = |ty, span| { + promoted.span = span; + promoted.local_decls[RETURN_PLACE] = LocalDecl::new(ty, span); + let args = tcx.erase_regions(GenericArgs::identity_for_item(tcx, def)); + let uneval = mir::UnevaluatedConst { def, args, promoted: Some(promoted_id) }; + + Operand::Constant(Box::new(ConstOperand { + span, + user_ty: None, + const_: Const::Unevaluated(uneval, ty), + })) + }; + + let blocks = self.source.basic_blocks.as_mut(); + let local_decls = &mut self.source.local_decls; + let loc = candidate.location; + let statement = &mut blocks[loc.block].statements[loc.statement_index]; + let StatementKind::Assign(box (_, Rvalue::Ref(region, borrow_kind, place))) = + &mut statement.kind + else { + bug!() + }; + + // Use the underlying local for this (necessarily interior) borrow. + debug_assert!(region.is_erased()); + let ty = local_decls[place.local].ty; + let span = statement.source_info.span; + + let ref_ty = Ty::new_ref( + tcx, + tcx.lifetimes.re_erased, + ty::TypeAndMut { ty, mutbl: borrow_kind.to_mutbl_lossy() }, + ); + + let mut projection = vec![PlaceElem::Deref]; + projection.extend(place.projection); + place.projection = tcx.mk_place_elems(&projection); + + // Create a temp to hold the promoted reference. + // This is because `*r` requires `r` to be a local, + // otherwise we would use the `promoted` directly. + let mut promoted_ref = LocalDecl::new(ref_ty, span); + promoted_ref.source_info = statement.source_info; + let promoted_ref = local_decls.push(promoted_ref); + assert_eq!(self.temps.push(TempState::Unpromotable), promoted_ref); + + let promoted_ref_statement = Statement { + source_info: statement.source_info, + kind: StatementKind::Assign(Box::new(( + Place::from(promoted_ref), + Rvalue::Use(promoted_operand(ref_ty, span)), + ))), + }; + self.extra_statements.push((loc, promoted_ref_statement)); + + Rvalue::Ref( + tcx.lifetimes.re_erased, + *borrow_kind, + Place { + local: mem::replace(&mut place.local, promoted_ref), + projection: List::empty(), + }, + ) + }; + + assert_eq!(self.new_block(), START_BLOCK); + self.visit_rvalue( + &mut rvalue, + Location { block: START_BLOCK, statement_index: usize::MAX }, + ); + + let span = self.promoted.span; + self.assign(RETURN_PLACE, rvalue, span); + self.promoted + } +} + +/// Replaces all temporaries with their promoted counterparts. +impl<'a, 'tcx> MutVisitor<'tcx> for Promoter<'a, 'tcx> { + fn tcx(&self) -> TyCtxt<'tcx> { + self.tcx + } + + fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) { + if self.is_temp_kind(*local) { + *local = self.promote_temp(*local); + } + } +} + +fn promote_candidates<'tcx>( + body: &mut Body<'tcx>, + tcx: TyCtxt<'tcx>, + mut temps: IndexVec<Local, TempState>, + candidates: Vec<Candidate>, +) -> IndexVec<Promoted, Body<'tcx>> { + // Visit candidates in reverse, in case they're nested. + debug!("promote_candidates({:?})", candidates); + + let mut promotions = IndexVec::new(); + + let mut extra_statements = vec![]; + for candidate in candidates.into_iter().rev() { + let Location { block, statement_index } = candidate.location; + if let StatementKind::Assign(box (place, _)) = &body[block].statements[statement_index].kind + { + if let Some(local) = place.as_local() { + if temps[local] == TempState::PromotedOut { + // Already promoted. + continue; + } + } + } + + // Declare return place local so that `mir::Body::new` doesn't complain. + let initial_locals = iter::once(LocalDecl::new(tcx.types.never, body.span)).collect(); + + let mut scope = body.source_scopes[body.source_info(candidate.location).scope].clone(); + scope.parent_scope = None; + + let mut promoted = Body::new( + body.source, // `promoted` gets filled in below + IndexVec::new(), + IndexVec::from_elem_n(scope, 1), + initial_locals, + IndexVec::new(), + 0, + vec![], + body.span, + None, + body.tainted_by_errors, + ); + promoted.phase = MirPhase::Analysis(AnalysisPhase::Initial); + + let promoter = Promoter { + promoted, + tcx, + source: body, + temps: &mut temps, + extra_statements: &mut extra_statements, + keep_original: false, + }; + + let mut promoted = promoter.promote_candidate(candidate, promotions.len()); + promoted.source.promoted = Some(promotions.next_index()); + promotions.push(promoted); + } + + // Insert each of `extra_statements` before its indicated location, which + // has to be done in reverse location order, to not invalidate the rest. + extra_statements.sort_by_key(|&(loc, _)| cmp::Reverse(loc)); + for (loc, statement) in extra_statements { + body[loc.block].statements.insert(loc.statement_index, statement); + } + + // Eliminate assignments to, and drops of promoted temps. + let promoted = |index: Local| temps[index] == TempState::PromotedOut; + for block in body.basic_blocks_mut() { + block.statements.retain(|statement| match &statement.kind { + StatementKind::Assign(box (place, _)) => { + if let Some(index) = place.as_local() { + !promoted(index) + } else { + true + } + } + StatementKind::StorageLive(index) | StatementKind::StorageDead(index) => { + !promoted(*index) + } + _ => true, + }); + let terminator = block.terminator_mut(); + if let TerminatorKind::Drop { place, target, .. } = &terminator.kind { + if let Some(index) = place.as_local() { + if promoted(index) { + terminator.kind = TerminatorKind::Goto { target: *target }; + } + } + } + } + + promotions +} diff --git a/compiler/rustc_mir_transform/src/remove_unneeded_drops.rs b/compiler/rustc_mir_transform/src/remove_unneeded_drops.rs index 5d528bed356..2778d91e17b 100644 --- a/compiler/rustc_mir_transform/src/remove_unneeded_drops.rs +++ b/compiler/rustc_mir_transform/src/remove_unneeded_drops.rs @@ -38,7 +38,7 @@ impl<'tcx> MirPass<'tcx> for RemoveUnneededDrops { // if we applied optimizations, we potentially have some cfg to cleanup to // make it easier for further passes if should_simplify { - simplify_cfg(tcx, body); + simplify_cfg(body); } } } diff --git a/compiler/rustc_mir_transform/src/separate_const_switch.rs b/compiler/rustc_mir_transform/src/separate_const_switch.rs index 6e22690d8da..7120ef72142 100644 --- a/compiler/rustc_mir_transform/src/separate_const_switch.rs +++ b/compiler/rustc_mir_transform/src/separate_const_switch.rs @@ -50,11 +50,11 @@ impl<'tcx> MirPass<'tcx> for SeparateConstSwitch { sess.mir_opt_level() >= 2 && sess.opts.unstable_opts.unsound_mir_opts } - fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { + fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) { // If execution did something, applying a simplification layer // helps later passes optimize the copy away. if separate_const_switch(body) > 0 { - super::simplify::simplify_cfg(tcx, body); + super::simplify::simplify_cfg(body); } } } diff --git a/compiler/rustc_mir_transform/src/simplify.rs b/compiler/rustc_mir_transform/src/simplify.rs index 856a0f22771..8c8818bd68e 100644 --- a/compiler/rustc_mir_transform/src/simplify.rs +++ b/compiler/rustc_mir_transform/src/simplify.rs @@ -27,7 +27,6 @@ //! naively generate still contains the `_a = ()` write in the unreachable block "after" the //! return. -use rustc_data_structures::fx::FxIndexSet; use rustc_index::{Idx, IndexSlice, IndexVec}; use rustc_middle::mir::visit::{MutVisitor, MutatingUseContext, PlaceContext, Visitor}; use rustc_middle::mir::*; @@ -62,9 +61,8 @@ impl SimplifyCfg { } } -pub fn simplify_cfg<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { +pub(crate) fn simplify_cfg(body: &mut Body<'_>) { CfgSimplifier::new(body).simplify(); - remove_duplicate_unreachable_blocks(tcx, body); remove_dead_blocks(body); // FIXME: Should probably be moved into some kind of pass manager @@ -76,9 +74,9 @@ impl<'tcx> MirPass<'tcx> for SimplifyCfg { self.name() } - fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { + fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) { debug!("SimplifyCfg({:?}) - simplifying {:?}", self.name(), body.source); - simplify_cfg(tcx, body); + simplify_cfg(body); } } @@ -289,55 +287,25 @@ pub fn simplify_duplicate_switch_targets(terminator: &mut Terminator<'_>) { } } -pub fn remove_duplicate_unreachable_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { - struct OptApplier<'tcx> { - tcx: TyCtxt<'tcx>, - duplicates: FxIndexSet<BasicBlock>, - } - - impl<'tcx> MutVisitor<'tcx> for OptApplier<'tcx> { - fn tcx(&self) -> TyCtxt<'tcx> { - self.tcx - } - - fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Location) { - for target in terminator.successors_mut() { - // We don't have to check whether `target` is a cleanup block, because have - // entirely excluded cleanup blocks in building the set of duplicates. - if self.duplicates.contains(target) { - *target = self.duplicates[0]; - } - } - - simplify_duplicate_switch_targets(terminator); - - self.super_terminator(terminator, location); - } - } +pub(crate) fn remove_dead_blocks(body: &mut Body<'_>) { + let should_deduplicate_unreachable = |bbdata: &BasicBlockData<'_>| { + // CfgSimplifier::simplify leaves behind some unreachable basic blocks without a + // terminator. Those blocks will be deleted by remove_dead_blocks, but we run just + // before then so we need to handle missing terminators. + // We also need to prevent confusing cleanup and non-cleanup blocks. In practice we + // don't emit empty unreachable cleanup blocks, so this simple check suffices. + bbdata.terminator.is_some() && bbdata.is_empty_unreachable() && !bbdata.is_cleanup + }; - let unreachable_blocks = body + let reachable = traversal::reachable_as_bitset(body); + let empty_unreachable_blocks = body .basic_blocks .iter_enumerated() - .filter(|(_, bb)| { - // CfgSimplifier::simplify leaves behind some unreachable basic blocks without a - // terminator. Those blocks will be deleted by remove_dead_blocks, but we run just - // before then so we need to handle missing terminators. - // We also need to prevent confusing cleanup and non-cleanup blocks. In practice we - // don't emit empty unreachable cleanup blocks, so this simple check suffices. - bb.terminator.is_some() && bb.is_empty_unreachable() && !bb.is_cleanup - }) - .map(|(block, _)| block) - .collect::<FxIndexSet<_>>(); - - if unreachable_blocks.len() > 1 { - OptApplier { tcx, duplicates: unreachable_blocks }.visit_body(body); - } -} + .filter(|(bb, bbdata)| should_deduplicate_unreachable(bbdata) && reachable.contains(*bb)) + .count(); -pub fn remove_dead_blocks(body: &mut Body<'_>) { - let reachable = traversal::reachable_as_bitset(body); let num_blocks = body.basic_blocks.len(); - if num_blocks == reachable.count() { + if num_blocks == reachable.count() && empty_unreachable_blocks <= 1 { return; } @@ -346,14 +314,28 @@ pub fn remove_dead_blocks(body: &mut Body<'_>) { let mut replacements: Vec<_> = (0..num_blocks).map(BasicBlock::new).collect(); let mut orig_index = 0; let mut used_index = 0; - basic_blocks.raw.retain(|_| { - let keep = reachable.contains(BasicBlock::new(orig_index)); - if keep { - replacements[orig_index] = BasicBlock::new(used_index); - used_index += 1; + let mut kept_unreachable = None; + basic_blocks.raw.retain(|bbdata| { + let orig_bb = BasicBlock::new(orig_index); + if !reachable.contains(orig_bb) { + orig_index += 1; + return false; + } + + let used_bb = BasicBlock::new(used_index); + if should_deduplicate_unreachable(bbdata) { + let kept_unreachable = *kept_unreachable.get_or_insert(used_bb); + if kept_unreachable != used_bb { + replacements[orig_index] = kept_unreachable; + orig_index += 1; + return false; + } } + + replacements[orig_index] = used_bb; + used_index += 1; orig_index += 1; - keep + true }); for block in basic_blocks { |