diff options
Diffstat (limited to 'compiler/rustc_mir_build/src/build/expr/as_rvalue.rs')
| -rw-r--r-- | compiler/rustc_mir_build/src/build/expr/as_rvalue.rs | 694 |
1 files changed, 694 insertions, 0 deletions
diff --git a/compiler/rustc_mir_build/src/build/expr/as_rvalue.rs b/compiler/rustc_mir_build/src/build/expr/as_rvalue.rs new file mode 100644 index 000000000..15f2d17c4 --- /dev/null +++ b/compiler/rustc_mir_build/src/build/expr/as_rvalue.rs @@ -0,0 +1,694 @@ +//! See docs in `build/expr/mod.rs`. + +use rustc_index::vec::Idx; +use rustc_middle::ty::util::IntTypeExt; + +use crate::build::expr::as_place::PlaceBase; +use crate::build::expr::category::{Category, RvalueFunc}; +use crate::build::{BlockAnd, BlockAndExtension, Builder, NeedsTemporary}; +use rustc_hir::lang_items::LangItem; +use rustc_middle::middle::region; +use rustc_middle::mir::AssertKind; +use rustc_middle::mir::Place; +use rustc_middle::mir::*; +use rustc_middle::thir::*; +use rustc_middle::ty::cast::CastTy; +use rustc_middle::ty::{self, Ty, UpvarSubsts}; +use rustc_span::Span; + +impl<'a, 'tcx> Builder<'a, 'tcx> { + /// Returns an rvalue suitable for use until the end of the current + /// scope expression. + /// + /// The operand returned from this function will *not be valid* after + /// an ExprKind::Scope is passed, so please do *not* return it from + /// functions to avoid bad miscompiles. + pub(crate) fn as_local_rvalue( + &mut self, + block: BasicBlock, + expr: &Expr<'tcx>, + ) -> BlockAnd<Rvalue<'tcx>> { + let local_scope = self.local_scope(); + self.as_rvalue(block, Some(local_scope), expr) + } + + /// Compile `expr`, yielding an rvalue. + pub(crate) fn as_rvalue( + &mut self, + mut block: BasicBlock, + scope: Option<region::Scope>, + expr: &Expr<'tcx>, + ) -> BlockAnd<Rvalue<'tcx>> { + debug!("expr_as_rvalue(block={:?}, scope={:?}, expr={:?})", block, scope, expr); + + let this = self; + let expr_span = expr.span; + let source_info = this.source_info(expr_span); + + match expr.kind { + ExprKind::ThreadLocalRef(did) => block.and(Rvalue::ThreadLocalRef(did)), + ExprKind::Scope { region_scope, lint_level, value } => { + let region_scope = (region_scope, source_info); + this.in_scope(region_scope, lint_level, |this| { + this.as_rvalue(block, scope, &this.thir[value]) + }) + } + ExprKind::Repeat { value, count } => { + if Some(0) == count.try_eval_usize(this.tcx, this.param_env) { + this.build_zero_repeat(block, value, scope, source_info) + } else { + let value_operand = unpack!( + block = this.as_operand( + block, + scope, + &this.thir[value], + None, + NeedsTemporary::No + ) + ); + block.and(Rvalue::Repeat(value_operand, count)) + } + } + ExprKind::Binary { op, lhs, rhs } => { + let lhs = unpack!( + block = + this.as_operand(block, scope, &this.thir[lhs], None, NeedsTemporary::Maybe) + ); + let rhs = unpack!( + block = + this.as_operand(block, scope, &this.thir[rhs], None, NeedsTemporary::No) + ); + this.build_binary_op(block, op, expr_span, expr.ty, lhs, rhs) + } + ExprKind::Unary { op, arg } => { + let arg = unpack!( + block = + this.as_operand(block, scope, &this.thir[arg], None, NeedsTemporary::No) + ); + // Check for -MIN on signed integers + if this.check_overflow && op == UnOp::Neg && expr.ty.is_signed() { + let bool_ty = this.tcx.types.bool; + + let minval = this.minval_literal(expr_span, expr.ty); + let is_min = this.temp(bool_ty, expr_span); + + this.cfg.push_assign( + block, + source_info, + is_min, + Rvalue::BinaryOp(BinOp::Eq, Box::new((arg.to_copy(), minval))), + ); + + block = this.assert( + block, + Operand::Move(is_min), + false, + AssertKind::OverflowNeg(arg.to_copy()), + expr_span, + ); + } + block.and(Rvalue::UnaryOp(op, arg)) + } + ExprKind::Box { value } => { + let value = &this.thir[value]; + let tcx = this.tcx; + + // `exchange_malloc` is unsafe but box is safe, so need a new scope. + let synth_scope = this.new_source_scope( + expr_span, + LintLevel::Inherited, + Some(Safety::BuiltinUnsafe), + ); + let synth_info = SourceInfo { span: expr_span, scope: synth_scope }; + + let size = this.temp(tcx.types.usize, expr_span); + this.cfg.push_assign( + block, + synth_info, + size, + Rvalue::NullaryOp(NullOp::SizeOf, value.ty), + ); + + let align = this.temp(tcx.types.usize, expr_span); + this.cfg.push_assign( + block, + synth_info, + align, + Rvalue::NullaryOp(NullOp::AlignOf, value.ty), + ); + + // malloc some memory of suitable size and align: + let exchange_malloc = Operand::function_handle( + tcx, + tcx.require_lang_item(LangItem::ExchangeMalloc, Some(expr_span)), + ty::List::empty(), + expr_span, + ); + let storage = this.temp(tcx.mk_mut_ptr(tcx.types.u8), expr_span); + let success = this.cfg.start_new_block(); + this.cfg.terminate( + block, + synth_info, + TerminatorKind::Call { + func: exchange_malloc, + args: vec![Operand::Move(size), Operand::Move(align)], + destination: storage, + target: Some(success), + cleanup: None, + from_hir_call: false, + fn_span: expr_span, + }, + ); + this.diverge_from(block); + block = success; + + // The `Box<T>` temporary created here is not a part of the HIR, + // and therefore is not considered during generator auto-trait + // determination. See the comment about `box` at `yield_in_scope`. + let result = this.local_decls.push(LocalDecl::new(expr.ty, expr_span).internal()); + this.cfg.push( + block, + Statement { source_info, kind: StatementKind::StorageLive(result) }, + ); + if let Some(scope) = scope { + // schedule a shallow free of that memory, lest we unwind: + this.schedule_drop_storage_and_value(expr_span, scope, result); + } + + // Transmute `*mut u8` to the box (thus far, uninitialized): + let box_ = Rvalue::ShallowInitBox(Operand::Move(storage), value.ty); + this.cfg.push_assign(block, source_info, Place::from(result), box_); + + // initialize the box contents: + unpack!( + block = this.expr_into_dest( + this.tcx.mk_place_deref(Place::from(result)), + block, + value + ) + ); + block.and(Rvalue::Use(Operand::Move(Place::from(result)))) + } + ExprKind::Cast { source } => { + let source = &this.thir[source]; + + // Casting an enum to an integer is equivalent to computing the discriminant and casting the + // discriminant. Previously every backend had to repeat the logic for this operation. Now we + // create all the steps directly in MIR with operations all backends need to support anyway. + let (source, ty) = if let ty::Adt(adt_def, ..) = source.ty.kind() && adt_def.is_enum() { + let discr_ty = adt_def.repr().discr_type().to_ty(this.tcx); + let place = unpack!(block = this.as_place(block, source)); + let discr = this.temp(discr_ty, source.span); + this.cfg.push_assign( + block, + source_info, + discr, + Rvalue::Discriminant(place), + ); + + (Operand::Move(discr), discr_ty) + } else { + let ty = source.ty; + let source = unpack!( + block = this.as_operand(block, scope, source, None, NeedsTemporary::No) + ); + (source, ty) + }; + let from_ty = CastTy::from_ty(ty); + let cast_ty = CastTy::from_ty(expr.ty); + let cast_kind = match (from_ty, cast_ty) { + (Some(CastTy::Ptr(_) | CastTy::FnPtr), Some(CastTy::Int(_))) => { + CastKind::PointerExposeAddress + } + (Some(CastTy::Int(_)), Some(CastTy::Ptr(_))) => { + CastKind::PointerFromExposedAddress + } + (_, _) => CastKind::Misc, + }; + block.and(Rvalue::Cast(cast_kind, source, expr.ty)) + } + ExprKind::Pointer { cast, source } => { + let source = unpack!( + block = + this.as_operand(block, scope, &this.thir[source], None, NeedsTemporary::No) + ); + block.and(Rvalue::Cast(CastKind::Pointer(cast), source, expr.ty)) + } + ExprKind::Array { ref fields } => { + // (*) We would (maybe) be closer to codegen if we + // handled this and other aggregate cases via + // `into()`, not `as_rvalue` -- in that case, instead + // of generating + // + // let tmp1 = ...1; + // let tmp2 = ...2; + // dest = Rvalue::Aggregate(Foo, [tmp1, tmp2]) + // + // we could just generate + // + // dest.f = ...1; + // dest.g = ...2; + // + // The problem is that then we would need to: + // + // (a) have a more complex mechanism for handling + // partial cleanup; + // (b) distinguish the case where the type `Foo` has a + // destructor, in which case creating an instance + // as a whole "arms" the destructor, and you can't + // write individual fields; and, + // (c) handle the case where the type Foo has no + // fields. We don't want `let x: ();` to compile + // to the same MIR as `let x = ();`. + + // first process the set of fields + let el_ty = expr.ty.sequence_element_type(this.tcx); + let fields: Vec<_> = fields + .into_iter() + .copied() + .map(|f| { + unpack!( + block = this.as_operand( + block, + scope, + &this.thir[f], + None, + NeedsTemporary::Maybe + ) + ) + }) + .collect(); + + block.and(Rvalue::Aggregate(Box::new(AggregateKind::Array(el_ty)), fields)) + } + ExprKind::Tuple { ref fields } => { + // see (*) above + // first process the set of fields + let fields: Vec<_> = fields + .into_iter() + .copied() + .map(|f| { + unpack!( + block = this.as_operand( + block, + scope, + &this.thir[f], + None, + NeedsTemporary::Maybe + ) + ) + }) + .collect(); + + block.and(Rvalue::Aggregate(Box::new(AggregateKind::Tuple), fields)) + } + ExprKind::Closure { closure_id, substs, ref upvars, movability, ref fake_reads } => { + // Convert the closure fake reads, if any, from `ExprRef` to mir `Place` + // and push the fake reads. + // This must come before creating the operands. This is required in case + // there is a fake read and a borrow of the same path, since otherwise the + // fake read might interfere with the borrow. Consider an example like this + // one: + // ``` + // let mut x = 0; + // let c = || { + // &mut x; // mutable borrow of `x` + // match x { _ => () } // fake read of `x` + // }; + // ``` + // + for (thir_place, cause, hir_id) in fake_reads.into_iter() { + let place_builder = + unpack!(block = this.as_place_builder(block, &this.thir[*thir_place])); + + if let Ok(place_builder_resolved) = + place_builder.try_upvars_resolved(this.tcx, this.typeck_results) + { + let mir_place = + place_builder_resolved.into_place(this.tcx, this.typeck_results); + this.cfg.push_fake_read( + block, + this.source_info(this.tcx.hir().span(*hir_id)), + *cause, + mir_place, + ); + } + } + + // see (*) above + let operands: Vec<_> = upvars + .into_iter() + .copied() + .map(|upvar| { + let upvar = &this.thir[upvar]; + match Category::of(&upvar.kind) { + // Use as_place to avoid creating a temporary when + // moving a variable into a closure, so that + // borrowck knows which variables to mark as being + // used as mut. This is OK here because the upvar + // expressions have no side effects and act on + // disjoint places. + // This occurs when capturing by copy/move, while + // by reference captures use as_operand + Some(Category::Place) => { + let place = unpack!(block = this.as_place(block, upvar)); + this.consume_by_copy_or_move(place) + } + _ => { + // Turn mutable borrow captures into unique + // borrow captures when capturing an immutable + // variable. This is sound because the mutation + // that caused the capture will cause an error. + match upvar.kind { + ExprKind::Borrow { + borrow_kind: + BorrowKind::Mut { allow_two_phase_borrow: false }, + arg, + } => unpack!( + block = this.limit_capture_mutability( + upvar.span, + upvar.ty, + scope, + block, + &this.thir[arg], + ) + ), + _ => { + unpack!( + block = this.as_operand( + block, + scope, + upvar, + None, + NeedsTemporary::Maybe + ) + ) + } + } + } + } + }) + .collect(); + + let result = match substs { + UpvarSubsts::Generator(substs) => { + // We implicitly set the discriminant to 0. See + // librustc_mir/transform/deaggregator.rs for details. + let movability = movability.unwrap(); + Box::new(AggregateKind::Generator(closure_id, substs, movability)) + } + UpvarSubsts::Closure(substs) => { + Box::new(AggregateKind::Closure(closure_id, substs)) + } + }; + block.and(Rvalue::Aggregate(result, operands)) + } + ExprKind::Assign { .. } | ExprKind::AssignOp { .. } => { + block = unpack!(this.stmt_expr(block, expr, None)); + block.and(Rvalue::Use(Operand::Constant(Box::new(Constant { + span: expr_span, + user_ty: None, + literal: ConstantKind::zero_sized(this.tcx.types.unit), + })))) + } + + ExprKind::Literal { .. } + | ExprKind::NamedConst { .. } + | ExprKind::NonHirLiteral { .. } + | ExprKind::ZstLiteral { .. } + | ExprKind::ConstParam { .. } + | ExprKind::ConstBlock { .. } + | ExprKind::StaticRef { .. } => { + let constant = this.as_constant(expr); + block.and(Rvalue::Use(Operand::Constant(Box::new(constant)))) + } + + ExprKind::Yield { .. } + | ExprKind::Block { .. } + | ExprKind::Match { .. } + | ExprKind::If { .. } + | ExprKind::NeverToAny { .. } + | ExprKind::Use { .. } + | ExprKind::Borrow { .. } + | ExprKind::AddressOf { .. } + | ExprKind::Adt { .. } + | ExprKind::Loop { .. } + | ExprKind::LogicalOp { .. } + | ExprKind::Call { .. } + | ExprKind::Field { .. } + | ExprKind::Let { .. } + | ExprKind::Deref { .. } + | ExprKind::Index { .. } + | ExprKind::VarRef { .. } + | ExprKind::UpvarRef { .. } + | ExprKind::Break { .. } + | ExprKind::Continue { .. } + | ExprKind::Return { .. } + | ExprKind::InlineAsm { .. } + | ExprKind::PlaceTypeAscription { .. } + | ExprKind::ValueTypeAscription { .. } => { + // these do not have corresponding `Rvalue` variants, + // so make an operand and then return that + debug_assert!(!matches!( + Category::of(&expr.kind), + Some(Category::Rvalue(RvalueFunc::AsRvalue) | Category::Constant) + )); + let operand = + unpack!(block = this.as_operand(block, scope, expr, None, NeedsTemporary::No)); + block.and(Rvalue::Use(operand)) + } + } + } + + pub(crate) fn build_binary_op( + &mut self, + mut block: BasicBlock, + op: BinOp, + span: Span, + ty: Ty<'tcx>, + lhs: Operand<'tcx>, + rhs: Operand<'tcx>, + ) -> BlockAnd<Rvalue<'tcx>> { + let source_info = self.source_info(span); + let bool_ty = self.tcx.types.bool; + if self.check_overflow && op.is_checkable() && ty.is_integral() { + let result_tup = self.tcx.intern_tup(&[ty, bool_ty]); + let result_value = self.temp(result_tup, span); + + self.cfg.push_assign( + block, + source_info, + result_value, + Rvalue::CheckedBinaryOp(op, Box::new((lhs.to_copy(), rhs.to_copy()))), + ); + let val_fld = Field::new(0); + let of_fld = Field::new(1); + + let tcx = self.tcx; + let val = tcx.mk_place_field(result_value, val_fld, ty); + let of = tcx.mk_place_field(result_value, of_fld, bool_ty); + + let err = AssertKind::Overflow(op, lhs, rhs); + + block = self.assert(block, Operand::Move(of), false, err, span); + + block.and(Rvalue::Use(Operand::Move(val))) + } else { + if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) { + // Checking division and remainder is more complex, since we 1. always check + // and 2. there are two possible failure cases, divide-by-zero and overflow. + + let zero_err = if op == BinOp::Div { + AssertKind::DivisionByZero(lhs.to_copy()) + } else { + AssertKind::RemainderByZero(lhs.to_copy()) + }; + let overflow_err = AssertKind::Overflow(op, lhs.to_copy(), rhs.to_copy()); + + // Check for / 0 + let is_zero = self.temp(bool_ty, span); + let zero = self.zero_literal(span, ty); + self.cfg.push_assign( + block, + source_info, + is_zero, + Rvalue::BinaryOp(BinOp::Eq, Box::new((rhs.to_copy(), zero))), + ); + + block = self.assert(block, Operand::Move(is_zero), false, zero_err, span); + + // We only need to check for the overflow in one case: + // MIN / -1, and only for signed values. + if ty.is_signed() { + let neg_1 = self.neg_1_literal(span, ty); + let min = self.minval_literal(span, ty); + + let is_neg_1 = self.temp(bool_ty, span); + let is_min = self.temp(bool_ty, span); + let of = self.temp(bool_ty, span); + + // this does (rhs == -1) & (lhs == MIN). It could short-circuit instead + + self.cfg.push_assign( + block, + source_info, + is_neg_1, + Rvalue::BinaryOp(BinOp::Eq, Box::new((rhs.to_copy(), neg_1))), + ); + self.cfg.push_assign( + block, + source_info, + is_min, + Rvalue::BinaryOp(BinOp::Eq, Box::new((lhs.to_copy(), min))), + ); + + let is_neg_1 = Operand::Move(is_neg_1); + let is_min = Operand::Move(is_min); + self.cfg.push_assign( + block, + source_info, + of, + Rvalue::BinaryOp(BinOp::BitAnd, Box::new((is_neg_1, is_min))), + ); + + block = self.assert(block, Operand::Move(of), false, overflow_err, span); + } + } + + block.and(Rvalue::BinaryOp(op, Box::new((lhs, rhs)))) + } + } + + fn build_zero_repeat( + &mut self, + mut block: BasicBlock, + value: ExprId, + scope: Option<region::Scope>, + outer_source_info: SourceInfo, + ) -> BlockAnd<Rvalue<'tcx>> { + let this = self; + let value = &this.thir[value]; + let elem_ty = value.ty; + if let Some(Category::Constant) = Category::of(&value.kind) { + // Repeating a const does nothing + } else { + // For a non-const, we may need to generate an appropriate `Drop` + let value_operand = + unpack!(block = this.as_operand(block, scope, value, None, NeedsTemporary::No)); + if let Operand::Move(to_drop) = value_operand { + let success = this.cfg.start_new_block(); + this.cfg.terminate( + block, + outer_source_info, + TerminatorKind::Drop { place: to_drop, target: success, unwind: None }, + ); + this.diverge_from(block); + block = success; + } + this.record_operands_moved(&[value_operand]); + } + block.and(Rvalue::Aggregate(Box::new(AggregateKind::Array(elem_ty)), Vec::new())) + } + + fn limit_capture_mutability( + &mut self, + upvar_span: Span, + upvar_ty: Ty<'tcx>, + temp_lifetime: Option<region::Scope>, + mut block: BasicBlock, + arg: &Expr<'tcx>, + ) -> BlockAnd<Operand<'tcx>> { + let this = self; + + let source_info = this.source_info(upvar_span); + let temp = this.local_decls.push(LocalDecl::new(upvar_ty, upvar_span)); + + this.cfg.push(block, Statement { source_info, kind: StatementKind::StorageLive(temp) }); + + let arg_place_builder = unpack!(block = this.as_place_builder(block, arg)); + + let mutability = match arg_place_builder.base() { + // We are capturing a path that starts off a local variable in the parent. + // The mutability of the current capture is same as the mutability + // of the local declaration in the parent. + PlaceBase::Local(local) => this.local_decls[local].mutability, + // Parent is a closure and we are capturing a path that is captured + // by the parent itself. The mutability of the current capture + // is same as that of the capture in the parent closure. + PlaceBase::Upvar { .. } => { + let enclosing_upvars_resolved = + arg_place_builder.clone().into_place(this.tcx, this.typeck_results); + + match enclosing_upvars_resolved.as_ref() { + PlaceRef { + local, + projection: &[ProjectionElem::Field(upvar_index, _), ..], + } + | PlaceRef { + local, + projection: + &[ProjectionElem::Deref, ProjectionElem::Field(upvar_index, _), ..], + } => { + // Not in a closure + debug_assert!( + local == ty::CAPTURE_STRUCT_LOCAL, + "Expected local to be Local(1), found {:?}", + local + ); + // Not in a closure + debug_assert!( + this.upvar_mutbls.len() > upvar_index.index(), + "Unexpected capture place, upvar_mutbls={:#?}, upvar_index={:?}", + this.upvar_mutbls, + upvar_index + ); + this.upvar_mutbls[upvar_index.index()] + } + _ => bug!("Unexpected capture place"), + } + } + }; + + let borrow_kind = match mutability { + Mutability::Not => BorrowKind::Unique, + Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false }, + }; + + let arg_place = arg_place_builder.into_place(this.tcx, this.typeck_results); + + this.cfg.push_assign( + block, + source_info, + Place::from(temp), + Rvalue::Ref(this.tcx.lifetimes.re_erased, borrow_kind, arg_place), + ); + + // See the comment in `expr_as_temp` and on the `rvalue_scopes` field for why + // this can be `None`. + if let Some(temp_lifetime) = temp_lifetime { + this.schedule_drop_storage_and_value(upvar_span, temp_lifetime, temp); + } + + block.and(Operand::Move(Place::from(temp))) + } + + // Helper to get a `-1` value of the appropriate type + fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> { + let param_ty = ty::ParamEnv::empty().and(ty); + let size = self.tcx.layout_of(param_ty).unwrap().size; + let literal = ConstantKind::from_bits(self.tcx, size.unsigned_int_max(), param_ty); + + self.literal_operand(span, literal) + } + + // Helper to get the minimum value of the appropriate type + fn minval_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> { + assert!(ty.is_signed()); + let param_ty = ty::ParamEnv::empty().and(ty); + let bits = self.tcx.layout_of(param_ty).unwrap().size.bits(); + let n = 1 << (bits - 1); + let literal = ConstantKind::from_bits(self.tcx, n, param_ty); + + self.literal_operand(span, literal) + } +} |