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Diffstat (limited to 'compiler/stable_mir/src/mir/visit.rs')
-rw-r--r-- | compiler/stable_mir/src/mir/visit.rs | 414 |
1 files changed, 414 insertions, 0 deletions
diff --git a/compiler/stable_mir/src/mir/visit.rs b/compiler/stable_mir/src/mir/visit.rs new file mode 100644 index 000000000..806dced71 --- /dev/null +++ b/compiler/stable_mir/src/mir/visit.rs @@ -0,0 +1,414 @@ +//! # The Stable MIR Visitor +//! +//! ## Overview +//! +//! We currently only support an immutable visitor. +//! The structure of this visitor is similar to the ones internal to `rustc`, +//! and it follows the following conventions: +//! +//! For every mir item, the trait has a `visit_<item>` and a `super_<item>` method. +//! - `visit_<item>`, by default, calls `super_<item>` +//! - `super_<item>`, by default, destructures the `<item>` and calls `visit_<sub_item>` for +//! all sub-items that compose the original item. +//! +//! In order to implement a visitor, override the `visit_*` methods for the types you are +//! interested in analyzing, and invoke (within that method call) +//! `self.super_*` to continue to the traverse. +//! Avoid calling `super` methods in other circumstances. +//! +//! For the most part, we do not destructure things external to the +//! MIR, e.g., types, spans, etc, but simply visit them and stop. +//! This avoids duplication with other visitors like `TypeFoldable`. +//! +//! ## Updating +//! +//! The code is written in a very deliberate style intended to minimize +//! the chance of things being overlooked. +//! +//! Use pattern matching to reference fields and ensure that all +//! matches are exhaustive. +//! +//! For this to work, ALL MATCHES MUST BE EXHAUSTIVE IN FIELDS AND VARIANTS. +//! That means you never write `..` to skip over fields, nor do you write `_` +//! to skip over variants in a `match`. +//! +//! The only place that `_` is acceptable is to match a field (or +//! variant argument) that does not require visiting. + +use crate::mir::*; +use crate::ty::{Const, GenericArgs, Region, Ty}; +use crate::{Opaque, Span}; + +pub trait MirVisitor { + fn visit_body(&mut self, body: &Body) { + self.super_body(body) + } + + fn visit_basic_block(&mut self, bb: &BasicBlock) { + self.super_basic_block(bb) + } + + fn visit_ret_decl(&mut self, local: Local, decl: &LocalDecl) { + self.super_ret_decl(local, decl) + } + + fn visit_arg_decl(&mut self, local: Local, decl: &LocalDecl) { + self.super_arg_decl(local, decl) + } + + fn visit_local_decl(&mut self, local: Local, decl: &LocalDecl) { + self.super_local_decl(local, decl) + } + + fn visit_statement(&mut self, stmt: &Statement, location: Location) { + self.super_statement(stmt, location) + } + + fn visit_terminator(&mut self, term: &Terminator, location: Location) { + self.super_terminator(term, location) + } + + fn visit_span(&mut self, span: &Span) { + self.super_span(span) + } + + fn visit_place(&mut self, place: &Place, ptx: PlaceContext, location: Location) { + self.super_place(place, ptx, location) + } + + fn visit_local(&mut self, local: &Local, ptx: PlaceContext, location: Location) { + let _ = (local, ptx, location); + } + + fn visit_rvalue(&mut self, rvalue: &Rvalue, location: Location) { + self.super_rvalue(rvalue, location) + } + + fn visit_operand(&mut self, operand: &Operand, location: Location) { + self.super_operand(operand, location) + } + + fn visit_user_type_projection(&mut self, projection: &UserTypeProjection) { + self.super_user_type_projection(projection) + } + + fn visit_ty(&mut self, ty: &Ty, location: Location) { + let _ = location; + self.super_ty(ty) + } + + fn visit_constant(&mut self, constant: &Constant, location: Location) { + self.super_constant(constant, location) + } + + fn visit_const(&mut self, constant: &Const, location: Location) { + self.super_const(constant, location) + } + + fn visit_region(&mut self, region: &Region, location: Location) { + let _ = location; + self.super_region(region) + } + + fn visit_args(&mut self, args: &GenericArgs, location: Location) { + let _ = location; + self.super_args(args) + } + + fn visit_assert_msg(&mut self, msg: &AssertMessage, location: Location) { + self.super_assert_msg(msg, location) + } + + fn super_body(&mut self, body: &Body) { + let Body { blocks, locals: _, arg_count } = body; + + for bb in blocks { + self.visit_basic_block(bb); + } + + self.visit_ret_decl(RETURN_LOCAL, body.ret_local()); + + for (idx, arg) in body.arg_locals().iter().enumerate() { + self.visit_arg_decl(idx + 1, arg) + } + + let local_start = arg_count + 1; + for (idx, arg) in body.arg_locals().iter().enumerate() { + self.visit_local_decl(idx + local_start, arg) + } + } + + fn super_basic_block(&mut self, bb: &BasicBlock) { + let BasicBlock { statements, terminator } = bb; + for stmt in statements { + self.visit_statement(stmt, Location(stmt.span)); + } + self.visit_terminator(terminator, Location(terminator.span)); + } + + fn super_local_decl(&mut self, local: Local, decl: &LocalDecl) { + let _ = local; + let LocalDecl { ty, span } = decl; + self.visit_ty(ty, Location(*span)); + } + + fn super_ret_decl(&mut self, local: Local, decl: &LocalDecl) { + self.super_local_decl(local, decl) + } + + fn super_arg_decl(&mut self, local: Local, decl: &LocalDecl) { + self.super_local_decl(local, decl) + } + + fn super_statement(&mut self, stmt: &Statement, location: Location) { + let Statement { kind, span } = stmt; + self.visit_span(span); + match kind { + StatementKind::Assign(place, rvalue) => { + self.visit_place(place, PlaceContext::MUTATING, location); + self.visit_rvalue(rvalue, location); + } + StatementKind::FakeRead(_, place) => { + self.visit_place(place, PlaceContext::NON_MUTATING, location); + } + StatementKind::SetDiscriminant { place, .. } => { + self.visit_place(place, PlaceContext::MUTATING, location); + } + StatementKind::Deinit(place) => { + self.visit_place(place, PlaceContext::MUTATING, location); + } + StatementKind::StorageLive(local) => { + self.visit_local(local, PlaceContext::NON_USE, location); + } + StatementKind::StorageDead(local) => { + self.visit_local(local, PlaceContext::NON_USE, location); + } + StatementKind::Retag(_, place) => { + self.visit_place(place, PlaceContext::MUTATING, location); + } + StatementKind::PlaceMention(place) => { + self.visit_place(place, PlaceContext::NON_MUTATING, location); + } + StatementKind::AscribeUserType { place, projections, variance: _ } => { + self.visit_place(place, PlaceContext::NON_USE, location); + self.visit_user_type_projection(projections); + } + StatementKind::Coverage(coverage) => visit_opaque(coverage), + StatementKind::Intrinsic(intrisic) => match intrisic { + NonDivergingIntrinsic::Assume(operand) => { + self.visit_operand(operand, location); + } + NonDivergingIntrinsic::CopyNonOverlapping(CopyNonOverlapping { + src, + dst, + count, + }) => { + self.visit_operand(src, location); + self.visit_operand(dst, location); + self.visit_operand(count, location); + } + }, + StatementKind::ConstEvalCounter => {} + StatementKind::Nop => {} + } + } + + fn super_terminator(&mut self, term: &Terminator, location: Location) { + let Terminator { kind, span } = term; + self.visit_span(&span); + match kind { + TerminatorKind::Goto { .. } + | TerminatorKind::Resume + | TerminatorKind::Abort + | TerminatorKind::Unreachable + | TerminatorKind::CoroutineDrop => {} + TerminatorKind::Assert { cond, expected: _, msg, target: _, unwind: _ } => { + self.visit_operand(cond, location); + self.visit_assert_msg(msg, location); + } + TerminatorKind::Drop { place, target: _, unwind: _ } => { + self.visit_place(place, PlaceContext::MUTATING, location); + } + TerminatorKind::Call { func, args, destination, target: _, unwind: _ } => { + self.visit_operand(func, location); + for arg in args { + self.visit_operand(arg, location); + } + self.visit_place(destination, PlaceContext::MUTATING, location); + } + TerminatorKind::InlineAsm { operands, .. } => { + for op in operands { + let InlineAsmOperand { in_value, out_place, raw_rpr: _ } = op; + if let Some(input) = in_value { + self.visit_operand(input, location); + } + if let Some(output) = out_place { + self.visit_place(output, PlaceContext::MUTATING, location); + } + } + } + TerminatorKind::Return => { + let local = RETURN_LOCAL; + self.visit_local(&local, PlaceContext::NON_MUTATING, location); + } + TerminatorKind::SwitchInt { discr, targets: _, otherwise: _ } => { + self.visit_operand(discr, location); + } + } + } + + fn super_span(&mut self, span: &Span) { + let _ = span; + } + + fn super_place(&mut self, place: &Place, ptx: PlaceContext, location: Location) { + let _ = location; + let _ = ptx; + visit_opaque(&Opaque(place.projection.clone())); + } + + fn super_rvalue(&mut self, rvalue: &Rvalue, location: Location) { + match rvalue { + Rvalue::AddressOf(mutability, place) => { + let pcx = PlaceContext { is_mut: *mutability == Mutability::Mut }; + self.visit_place(place, pcx, location); + } + Rvalue::Aggregate(_, operands) => { + for op in operands { + self.visit_operand(op, location); + } + } + Rvalue::BinaryOp(_, lhs, rhs) | Rvalue::CheckedBinaryOp(_, lhs, rhs) => { + self.visit_operand(lhs, location); + self.visit_operand(rhs, location); + } + Rvalue::Cast(_, op, ty) => { + self.visit_operand(op, location); + self.visit_ty(ty, location); + } + Rvalue::CopyForDeref(place) | Rvalue::Discriminant(place) | Rvalue::Len(place) => { + self.visit_place(place, PlaceContext::NON_MUTATING, location); + } + Rvalue::Ref(region, kind, place) => { + self.visit_region(region, location); + let pcx = PlaceContext { is_mut: matches!(kind, BorrowKind::Mut { .. }) }; + self.visit_place(place, pcx, location); + } + Rvalue::Repeat(op, constant) => { + self.visit_operand(op, location); + self.visit_const(constant, location); + } + Rvalue::ShallowInitBox(op, ty) => { + self.visit_ty(ty, location); + self.visit_operand(op, location) + } + Rvalue::ThreadLocalRef(_) => {} + Rvalue::NullaryOp(_, ty) => { + self.visit_ty(ty, location); + } + Rvalue::UnaryOp(_, op) | Rvalue::Use(op) => { + self.visit_operand(op, location); + } + } + } + + fn super_operand(&mut self, operand: &Operand, location: Location) { + match operand { + Operand::Copy(place) | Operand::Move(place) => { + self.visit_place(place, PlaceContext::NON_MUTATING, location) + } + Operand::Constant(constant) => { + self.visit_constant(constant, location); + } + } + } + + fn super_user_type_projection(&mut self, projection: &UserTypeProjection) { + // This is a no-op on mir::Visitor. + let _ = projection; + } + + fn super_ty(&mut self, ty: &Ty) { + let _ = ty; + } + + fn super_constant(&mut self, constant: &Constant, location: Location) { + let Constant { span, user_ty: _, literal } = constant; + self.visit_span(span); + self.visit_const(literal, location); + } + + fn super_const(&mut self, constant: &Const, location: Location) { + let Const { kind: _, ty, id: _ } = constant; + self.visit_ty(ty, location); + } + + fn super_region(&mut self, region: &Region) { + let _ = region; + } + + fn super_args(&mut self, args: &GenericArgs) { + let _ = args; + } + + fn super_assert_msg(&mut self, msg: &AssertMessage, location: Location) { + match msg { + AssertMessage::BoundsCheck { len, index } => { + self.visit_operand(len, location); + self.visit_operand(index, location); + } + AssertMessage::Overflow(_, left, right) => { + self.visit_operand(left, location); + self.visit_operand(right, location); + } + AssertMessage::OverflowNeg(op) + | AssertMessage::DivisionByZero(op) + | AssertMessage::RemainderByZero(op) => { + self.visit_operand(op, location); + } + AssertMessage::ResumedAfterReturn(_) | AssertMessage::ResumedAfterPanic(_) => { //nothing to visit + } + AssertMessage::MisalignedPointerDereference { required, found } => { + self.visit_operand(required, location); + self.visit_operand(found, location); + } + } + } +} + +/// This function is a no-op that gets used to ensure this visitor is kept up-to-date. +/// +/// The idea is that whenever we replace an Opaque type by a real type, the compiler will fail +/// when trying to invoke `visit_opaque`. +/// +/// If you are here because your compilation is broken, replace the failing call to `visit_opaque()` +/// by a `visit_<CONSTRUCT>` for your construct. +fn visit_opaque(_: &Opaque) {} + +/// The location of a statement / terminator in the code and the CFG. +#[derive(Clone, Copy, PartialEq, Eq)] +pub struct Location(Span); + +impl Location { + pub fn span(&self) -> Span { + self.0 + } +} + +/// Information about a place's usage. +#[derive(Copy, Clone, PartialEq, Eq, Hash)] +pub struct PlaceContext { + /// Whether the access is mutable or not. Keep this private so we can increment the type in a + /// backward compatible manner. + is_mut: bool, +} + +impl PlaceContext { + const MUTATING: Self = PlaceContext { is_mut: true }; + const NON_MUTATING: Self = PlaceContext { is_mut: false }; + const NON_USE: Self = PlaceContext { is_mut: false }; + + pub fn is_mutating(&self) -> bool { + self.is_mut + } +} |