1998 lines
80 KiB
Rust
1998 lines
80 KiB
Rust
//! Code related to match expressions. These are sufficiently complex to
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//! warrant their own module and submodules. :) This main module includes the
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//! high-level algorithm, the submodules contain the details.
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//!
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//! This also includes code for pattern bindings in `let` statements and
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//! function parameters.
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use crate::build::scope::DropKind;
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use crate::build::ForGuard::{self, OutsideGuard, RefWithinGuard};
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use crate::build::{BlockAnd, BlockAndExtension, Builder};
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use crate::build::{GuardFrame, GuardFrameLocal, LocalsForNode};
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use crate::hair::{self, *};
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use rustc_data_structures::fx::{FxHashMap, FxHashSet};
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use rustc_hir::HirId;
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use rustc_index::bit_set::BitSet;
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use rustc_middle::middle::region;
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use rustc_middle::mir::*;
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use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty};
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use rustc_span::Span;
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use rustc_span::symbol::Symbol;
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use rustc_target::abi::VariantIdx;
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use smallvec::{smallvec, SmallVec};
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// helper functions, broken out by category:
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mod simplify;
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mod test;
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mod util;
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use std::borrow::Borrow;
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use std::convert::TryFrom;
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use std::mem;
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impl<'a, 'tcx> Builder<'a, 'tcx> {
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/// Generates MIR for a `match` expression.
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///
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/// The MIR that we generate for a match looks like this.
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///
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/// ```text
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/// [ 0. Pre-match ]
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/// |
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/// [ 1. Evaluate Scrutinee (expression being matched on) ]
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/// [ (fake read of scrutinee) ]
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/// |
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/// [ 2. Decision tree -- check discriminants ] <--------+
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/// | |
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/// | (once a specific arm is chosen) |
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/// | |
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/// [pre_binding_block] [otherwise_block]
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/// | |
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/// [ 3. Create "guard bindings" for arm ] |
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/// [ (create fake borrows) ] |
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/// | |
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/// [ 4. Execute guard code ] |
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/// [ (read fake borrows) ] --(guard is false)-----------+
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/// |
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/// | (guard results in true)
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/// |
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/// [ 5. Create real bindings and execute arm ]
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/// |
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/// [ Exit match ]
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/// ```
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///
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/// All of the different arms have been stacked on top of each other to
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/// simplify the diagram. For an arm with no guard the blocks marked 3 and
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/// 4 and the fake borrows are omitted.
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///
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/// We generate MIR in the following steps:
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///
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/// 1. Evaluate the scrutinee and add the fake read of it ([Builder::lower_scrutinee]).
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/// 2. Create the decision tree ([Builder::lower_match_tree]).
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/// 3. Determine the fake borrows that are needed from the places that were
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/// matched against and create the required temporaries for them
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/// ([Builder::calculate_fake_borrows]).
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/// 4. Create everything else: the guards and the arms ([Builder::lower_match_arms]).
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///
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/// ## False edges
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///
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/// We don't want to have the exact structure of the decision tree be
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/// visible through borrow checking. False edges ensure that the CFG as
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/// seen by borrow checking doesn't encode this. False edges are added:
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///
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/// * From each prebinding block to the next prebinding block.
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/// * From each otherwise block to the next prebinding block.
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crate fn match_expr(
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&mut self,
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destination: Place<'tcx>,
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span: Span,
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mut block: BasicBlock,
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scrutinee: ExprRef<'tcx>,
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arms: Vec<Arm<'tcx>>,
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) -> BlockAnd<()> {
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let scrutinee_span = scrutinee.span();
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let scrutinee_place =
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unpack!(block = self.lower_scrutinee(block, scrutinee, scrutinee_span,));
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let mut arm_candidates = self.create_match_candidates(scrutinee_place, &arms);
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let match_has_guard = arms.iter().any(|arm| arm.guard.is_some());
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let mut candidates =
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arm_candidates.iter_mut().map(|(_, candidate)| candidate).collect::<Vec<_>>();
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let fake_borrow_temps =
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self.lower_match_tree(block, scrutinee_span, match_has_guard, &mut candidates);
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self.lower_match_arms(
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destination,
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scrutinee_place,
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scrutinee_span,
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arm_candidates,
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self.source_info(span),
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fake_borrow_temps,
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)
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}
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/// Evaluate the scrutinee and add the fake read of it.
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fn lower_scrutinee(
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&mut self,
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mut block: BasicBlock,
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scrutinee: ExprRef<'tcx>,
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scrutinee_span: Span,
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) -> BlockAnd<Place<'tcx>> {
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let scrutinee_place = unpack!(block = self.as_place(block, scrutinee));
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// Matching on a `scrutinee_place` with an uninhabited type doesn't
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// generate any memory reads by itself, and so if the place "expression"
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// contains unsafe operations like raw pointer dereferences or union
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// field projections, we wouldn't know to require an `unsafe` block
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// around a `match` equivalent to `std::intrinsics::unreachable()`.
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// See issue #47412 for this hole being discovered in the wild.
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//
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// HACK(eddyb) Work around the above issue by adding a dummy inspection
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// of `scrutinee_place`, specifically by applying `ReadForMatch`.
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//
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// NOTE: ReadForMatch also checks that the scrutinee is initialized.
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// This is currently needed to not allow matching on an uninitialized,
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// uninhabited value. If we get never patterns, those will check that
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// the place is initialized, and so this read would only be used to
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// check safety.
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let cause_matched_place = FakeReadCause::ForMatchedPlace;
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let source_info = self.source_info(scrutinee_span);
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self.cfg.push_fake_read(block, source_info, cause_matched_place, scrutinee_place);
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block.and(scrutinee_place)
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}
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/// Create the initial `Candidate`s for a `match` expression.
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fn create_match_candidates<'pat>(
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&mut self,
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scrutinee: Place<'tcx>,
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arms: &'pat [Arm<'tcx>],
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) -> Vec<(&'pat Arm<'tcx>, Candidate<'pat, 'tcx>)> {
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// Assemble a list of candidates: there is one candidate per pattern,
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// which means there may be more than one candidate *per arm*.
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arms.iter()
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.map(|arm| {
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let arm_has_guard = arm.guard.is_some();
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let arm_candidate = Candidate::new(scrutinee, &arm.pattern, arm_has_guard);
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(arm, arm_candidate)
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})
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.collect()
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}
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/// Create the decision tree for the match expression, starting from `block`.
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///
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/// Modifies `candidates` to store the bindings and type ascriptions for
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/// that candidate.
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///
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/// Returns the places that need fake borrows because we bind or test them.
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fn lower_match_tree<'pat>(
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&mut self,
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block: BasicBlock,
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scrutinee_span: Span,
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match_has_guard: bool,
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candidates: &mut [&mut Candidate<'pat, 'tcx>],
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) -> Vec<(Place<'tcx>, Local)> {
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// The set of places that we are creating fake borrows of. If there are
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// no match guards then we don't need any fake borrows, so don't track
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// them.
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let mut fake_borrows = if match_has_guard { Some(FxHashSet::default()) } else { None };
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let mut otherwise = None;
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// This will generate code to test scrutinee_place and
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// branch to the appropriate arm block
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self.match_candidates(scrutinee_span, block, &mut otherwise, candidates, &mut fake_borrows);
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if let Some(otherwise_block) = otherwise {
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// See the doc comment on `match_candidates` for why we may have an
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// otherwise block. Match checking will ensure this is actually
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// unreachable.
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let source_info = self.source_info(scrutinee_span);
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self.cfg.terminate(otherwise_block, source_info, TerminatorKind::Unreachable);
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}
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// Link each leaf candidate to the `pre_binding_block` of the next one.
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let mut previous_candidate: Option<&mut Candidate<'_, '_>> = None;
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for candidate in candidates {
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candidate.visit_leaves(|leaf_candidate| {
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if let Some(ref mut prev) = previous_candidate {
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prev.next_candidate_pre_binding_block = leaf_candidate.pre_binding_block;
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}
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previous_candidate = Some(leaf_candidate);
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});
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}
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if let Some(ref borrows) = fake_borrows {
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self.calculate_fake_borrows(borrows, scrutinee_span)
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} else {
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Vec::new()
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}
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}
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/// Lower the bindings, guards and arm bodies of a `match` expression.
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///
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/// The decision tree should have already been created
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/// (by [Builder::lower_match_tree]).
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///
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/// `outer_source_info` is the SourceInfo for the whole match.
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fn lower_match_arms(
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&mut self,
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destination: Place<'tcx>,
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scrutinee_place: Place<'tcx>,
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scrutinee_span: Span,
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arm_candidates: Vec<(&'_ Arm<'tcx>, Candidate<'_, 'tcx>)>,
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outer_source_info: SourceInfo,
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fake_borrow_temps: Vec<(Place<'tcx>, Local)>,
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) -> BlockAnd<()> {
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let match_scope = self.scopes.topmost();
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let arm_end_blocks: Vec<_> = arm_candidates
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.into_iter()
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.map(|(arm, candidate)| {
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debug!("lowering arm {:?}\ncanidate = {:?}", arm, candidate);
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let arm_source_info = self.source_info(arm.span);
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let arm_scope = (arm.scope, arm_source_info);
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self.in_scope(arm_scope, arm.lint_level, |this| {
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let body = this.hir.mirror(arm.body.clone());
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let scope = this.declare_bindings(
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None,
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arm.span,
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&arm.pattern,
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ArmHasGuard(arm.guard.is_some()),
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Some((Some(&scrutinee_place), scrutinee_span)),
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);
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let arm_block = this.bind_pattern(
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outer_source_info,
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candidate,
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arm.guard.as_ref().map(|g| (g, match_scope)),
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&fake_borrow_temps,
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scrutinee_span,
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Some(arm.scope),
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);
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if let Some(source_scope) = scope {
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this.source_scope = source_scope;
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}
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this.into(destination, arm_block, body)
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})
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})
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.collect();
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// all the arm blocks will rejoin here
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let end_block = self.cfg.start_new_block();
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for arm_block in arm_end_blocks {
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self.cfg.goto(unpack!(arm_block), outer_source_info, end_block);
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}
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self.source_scope = outer_source_info.scope;
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end_block.unit()
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}
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/// Binds the variables and ascribes types for a given `match` arm or
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/// `let` binding.
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///
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/// Also check if the guard matches, if it's provided.
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/// `arm_scope` should be `Some` if and only if this is called for a
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/// `match` arm.
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fn bind_pattern(
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&mut self,
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outer_source_info: SourceInfo,
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candidate: Candidate<'_, 'tcx>,
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guard: Option<(&Guard<'tcx>, region::Scope)>,
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fake_borrow_temps: &Vec<(Place<'tcx>, Local)>,
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scrutinee_span: Span,
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arm_scope: Option<region::Scope>,
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) -> BasicBlock {
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if candidate.subcandidates.is_empty() {
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// Avoid generating another `BasicBlock` when we only have one
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// candidate.
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self.bind_and_guard_matched_candidate(
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candidate,
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&[],
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guard,
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fake_borrow_temps,
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scrutinee_span,
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true,
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)
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} else {
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// It's helpful to avoid scheduling drops multiple times to save
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// drop elaboration from having to clean up the extra drops.
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//
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// If we are in a `let` then we only schedule drops for the first
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// candidate.
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//
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// If we're in a `match` arm then we could have a case like so:
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//
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// Ok(x) | Err(x) if return => { /* ... */ }
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//
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// In this case we don't want a drop of `x` scheduled when we
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// return: it isn't bound by move until right before enter the arm.
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// To handle this we instead unschedule it's drop after each time
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// we lower the guard.
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let target_block = self.cfg.start_new_block();
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let mut schedule_drops = true;
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// We keep a stack of all of the bindings and type asciptions
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// from the the parent candidates that we visit, that also need to
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// be bound for each candidate.
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traverse_candidate(
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candidate,
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&mut Vec::new(),
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&mut |leaf_candidate, parent_bindings| {
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if let Some(arm_scope) = arm_scope {
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self.clear_top_scope(arm_scope);
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}
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let binding_end = self.bind_and_guard_matched_candidate(
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leaf_candidate,
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parent_bindings,
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guard,
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&fake_borrow_temps,
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scrutinee_span,
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schedule_drops,
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);
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if arm_scope.is_none() {
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schedule_drops = false;
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}
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self.cfg.goto(binding_end, outer_source_info, target_block);
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},
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|inner_candidate, parent_bindings| {
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parent_bindings.push((inner_candidate.bindings, inner_candidate.ascriptions));
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inner_candidate.subcandidates.into_iter()
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},
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|parent_bindings| {
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parent_bindings.pop();
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},
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);
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target_block
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}
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}
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pub(super) fn expr_into_pattern(
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&mut self,
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mut block: BasicBlock,
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irrefutable_pat: Pat<'tcx>,
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initializer: ExprRef<'tcx>,
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) -> BlockAnd<()> {
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match *irrefutable_pat.kind {
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// Optimize the case of `let x = ...` to write directly into `x`
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PatKind::Binding { mode: BindingMode::ByValue, var, subpattern: None, .. } => {
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let place =
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self.storage_live_binding(block, var, irrefutable_pat.span, OutsideGuard, true);
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unpack!(block = self.into(place, block, initializer));
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// Inject a fake read, see comments on `FakeReadCause::ForLet`.
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let source_info = self.source_info(irrefutable_pat.span);
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self.cfg.push_fake_read(block, source_info, FakeReadCause::ForLet, place);
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self.schedule_drop_for_binding(var, irrefutable_pat.span, OutsideGuard);
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block.unit()
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}
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// Optimize the case of `let x: T = ...` to write directly
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// into `x` and then require that `T == typeof(x)`.
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//
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// Weirdly, this is needed to prevent the
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// `intrinsic-move-val.rs` test case from crashing. That
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// test works with uninitialized values in a rather
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// dubious way, so it may be that the test is kind of
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// broken.
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PatKind::AscribeUserType {
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subpattern:
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Pat {
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kind:
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box PatKind::Binding {
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mode: BindingMode::ByValue,
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var,
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subpattern: None,
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..
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},
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..
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},
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ascription:
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hair::pattern::Ascription { user_ty: pat_ascription_ty, variance: _, user_ty_span },
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} => {
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let place =
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self.storage_live_binding(block, var, irrefutable_pat.span, OutsideGuard, true);
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unpack!(block = self.into(place, block, initializer));
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// Inject a fake read, see comments on `FakeReadCause::ForLet`.
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let pattern_source_info = self.source_info(irrefutable_pat.span);
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let cause_let = FakeReadCause::ForLet;
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self.cfg.push_fake_read(block, pattern_source_info, cause_let, place);
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let ty_source_info = self.source_info(user_ty_span);
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let user_ty = pat_ascription_ty.user_ty(
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&mut self.canonical_user_type_annotations,
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place.ty(&self.local_decls, self.hir.tcx()).ty,
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ty_source_info.span,
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);
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self.cfg.push(
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block,
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Statement {
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source_info: ty_source_info,
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kind: StatementKind::AscribeUserType(
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box (place, user_ty),
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// We always use invariant as the variance here. This is because the
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// variance field from the ascription refers to the variance to use
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// when applying the type to the value being matched, but this
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// ascription applies rather to the type of the binding. e.g., in this
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// example:
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//
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// ```
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// let x: T = <expr>
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// ```
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//
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// We are creating an ascription that defines the type of `x` to be
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// exactly `T` (i.e., with invariance). The variance field, in
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// contrast, is intended to be used to relate `T` to the type of
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// `<expr>`.
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ty::Variance::Invariant,
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),
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},
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);
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self.schedule_drop_for_binding(var, irrefutable_pat.span, OutsideGuard);
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block.unit()
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}
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_ => {
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let place = unpack!(block = self.as_place(block, initializer));
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self.place_into_pattern(block, irrefutable_pat, place, true)
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}
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}
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}
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crate fn place_into_pattern(
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&mut self,
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block: BasicBlock,
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irrefutable_pat: Pat<'tcx>,
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initializer: Place<'tcx>,
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set_match_place: bool,
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) -> BlockAnd<()> {
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let mut candidate = Candidate::new(initializer, &irrefutable_pat, false);
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let fake_borrow_temps =
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self.lower_match_tree(block, irrefutable_pat.span, false, &mut [&mut candidate]);
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// For matches and function arguments, the place that is being matched
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// can be set when creating the variables. But the place for
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// let PATTERN = ... might not even exist until we do the assignment.
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// so we set it here instead.
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if set_match_place {
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let mut candidate_ref = &candidate;
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while let Some(next) = {
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for binding in &candidate_ref.bindings {
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let local = self.var_local_id(binding.var_id, OutsideGuard);
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if let Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(
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VarBindingForm { opt_match_place: Some((ref mut match_place, _)), .. },
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)))) = self.local_decls[local].local_info
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{
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*match_place = Some(initializer);
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} else {
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bug!("Let binding to non-user variable.")
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}
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}
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// All of the subcandidates should bind the same locals, so we
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// only visit the first one.
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candidate_ref.subcandidates.get(0)
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} {
|
|
candidate_ref = next;
|
|
}
|
|
}
|
|
|
|
self.bind_pattern(
|
|
self.source_info(irrefutable_pat.span),
|
|
candidate,
|
|
None,
|
|
&fake_borrow_temps,
|
|
irrefutable_pat.span,
|
|
None,
|
|
)
|
|
.unit()
|
|
}
|
|
|
|
/// Declares the bindings of the given patterns and returns the visibility
|
|
/// scope for the bindings in these patterns, if such a scope had to be
|
|
/// created. NOTE: Declaring the bindings should always be done in their
|
|
/// drop scope.
|
|
crate fn declare_bindings(
|
|
&mut self,
|
|
mut visibility_scope: Option<SourceScope>,
|
|
scope_span: Span,
|
|
pattern: &Pat<'tcx>,
|
|
has_guard: ArmHasGuard,
|
|
opt_match_place: Option<(Option<&Place<'tcx>>, Span)>,
|
|
) -> Option<SourceScope> {
|
|
debug!("declare_bindings: pattern={:?}", pattern);
|
|
self.visit_bindings(
|
|
&pattern,
|
|
UserTypeProjections::none(),
|
|
&mut |this, mutability, name, mode, var, span, ty, user_ty| {
|
|
if visibility_scope.is_none() {
|
|
visibility_scope =
|
|
Some(this.new_source_scope(scope_span, LintLevel::Inherited, None));
|
|
}
|
|
let source_info = SourceInfo { span, scope: this.source_scope };
|
|
let visibility_scope = visibility_scope.unwrap();
|
|
this.declare_binding(
|
|
source_info,
|
|
visibility_scope,
|
|
mutability,
|
|
name,
|
|
mode,
|
|
var,
|
|
ty,
|
|
user_ty,
|
|
has_guard,
|
|
opt_match_place.map(|(x, y)| (x.cloned(), y)),
|
|
pattern.span,
|
|
);
|
|
},
|
|
);
|
|
visibility_scope
|
|
}
|
|
|
|
crate fn storage_live_binding(
|
|
&mut self,
|
|
block: BasicBlock,
|
|
var: HirId,
|
|
span: Span,
|
|
for_guard: ForGuard,
|
|
schedule_drop: bool,
|
|
) -> Place<'tcx> {
|
|
let local_id = self.var_local_id(var, for_guard);
|
|
let source_info = self.source_info(span);
|
|
self.cfg.push(block, Statement { source_info, kind: StatementKind::StorageLive(local_id) });
|
|
let region_scope = self.hir.region_scope_tree.var_scope(var.local_id);
|
|
if schedule_drop {
|
|
self.schedule_drop(span, region_scope, local_id, DropKind::Storage);
|
|
}
|
|
Place::from(local_id)
|
|
}
|
|
|
|
crate fn schedule_drop_for_binding(&mut self, var: HirId, span: Span, for_guard: ForGuard) {
|
|
let local_id = self.var_local_id(var, for_guard);
|
|
let region_scope = self.hir.region_scope_tree.var_scope(var.local_id);
|
|
self.schedule_drop(span, region_scope, local_id, DropKind::Value);
|
|
}
|
|
|
|
pub(super) fn visit_bindings(
|
|
&mut self,
|
|
pattern: &Pat<'tcx>,
|
|
pattern_user_ty: UserTypeProjections,
|
|
f: &mut impl FnMut(
|
|
&mut Self,
|
|
Mutability,
|
|
Symbol,
|
|
BindingMode,
|
|
HirId,
|
|
Span,
|
|
Ty<'tcx>,
|
|
UserTypeProjections,
|
|
),
|
|
) {
|
|
debug!("visit_bindings: pattern={:?} pattern_user_ty={:?}", pattern, pattern_user_ty);
|
|
match *pattern.kind {
|
|
PatKind::Binding { mutability, name, mode, var, ty, ref subpattern, .. } => {
|
|
f(self, mutability, name, mode, var, pattern.span, ty, pattern_user_ty.clone());
|
|
if let Some(subpattern) = subpattern.as_ref() {
|
|
self.visit_bindings(subpattern, pattern_user_ty, f);
|
|
}
|
|
}
|
|
|
|
PatKind::Array { ref prefix, ref slice, ref suffix }
|
|
| PatKind::Slice { ref prefix, ref slice, ref suffix } => {
|
|
let from = u32::try_from(prefix.len()).unwrap();
|
|
let to = u32::try_from(suffix.len()).unwrap();
|
|
for subpattern in prefix {
|
|
self.visit_bindings(subpattern, pattern_user_ty.clone().index(), f);
|
|
}
|
|
for subpattern in slice {
|
|
self.visit_bindings(subpattern, pattern_user_ty.clone().subslice(from, to), f);
|
|
}
|
|
for subpattern in suffix {
|
|
self.visit_bindings(subpattern, pattern_user_ty.clone().index(), f);
|
|
}
|
|
}
|
|
|
|
PatKind::Constant { .. } | PatKind::Range { .. } | PatKind::Wild => {}
|
|
|
|
PatKind::Deref { ref subpattern } => {
|
|
self.visit_bindings(subpattern, pattern_user_ty.deref(), f);
|
|
}
|
|
|
|
PatKind::AscribeUserType {
|
|
ref subpattern,
|
|
ascription: hair::pattern::Ascription { ref user_ty, user_ty_span, variance: _ },
|
|
} => {
|
|
// This corresponds to something like
|
|
//
|
|
// ```
|
|
// let A::<'a>(_): A<'static> = ...;
|
|
// ```
|
|
//
|
|
// Note that the variance doesn't apply here, as we are tracking the effect
|
|
// of `user_ty` on any bindings contained with subpattern.
|
|
let annotation = CanonicalUserTypeAnnotation {
|
|
span: user_ty_span,
|
|
user_ty: user_ty.user_ty,
|
|
inferred_ty: subpattern.ty,
|
|
};
|
|
let projection = UserTypeProjection {
|
|
base: self.canonical_user_type_annotations.push(annotation),
|
|
projs: Vec::new(),
|
|
};
|
|
let subpattern_user_ty = pattern_user_ty.push_projection(&projection, user_ty_span);
|
|
self.visit_bindings(subpattern, subpattern_user_ty, f)
|
|
}
|
|
|
|
PatKind::Leaf { ref subpatterns } => {
|
|
for subpattern in subpatterns {
|
|
let subpattern_user_ty = pattern_user_ty.clone().leaf(subpattern.field);
|
|
debug!("visit_bindings: subpattern_user_ty={:?}", subpattern_user_ty);
|
|
self.visit_bindings(&subpattern.pattern, subpattern_user_ty, f);
|
|
}
|
|
}
|
|
|
|
PatKind::Variant { adt_def, substs: _, variant_index, ref subpatterns } => {
|
|
for subpattern in subpatterns {
|
|
let subpattern_user_ty =
|
|
pattern_user_ty.clone().variant(adt_def, variant_index, subpattern.field);
|
|
self.visit_bindings(&subpattern.pattern, subpattern_user_ty, f);
|
|
}
|
|
}
|
|
PatKind::Or { ref pats } => {
|
|
self.visit_bindings(&pats[0], pattern_user_ty, f);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
#[derive(Debug)]
|
|
struct Candidate<'pat, 'tcx> {
|
|
/// `Span` of the original pattern that gave rise to this candidate
|
|
span: Span,
|
|
|
|
/// This `Candidate` has a guard.
|
|
has_guard: bool,
|
|
|
|
/// All of these must be satisfied...
|
|
match_pairs: SmallVec<[MatchPair<'pat, 'tcx>; 1]>,
|
|
|
|
/// ...these bindings established...
|
|
bindings: Vec<Binding<'tcx>>,
|
|
|
|
/// ...and these types asserted...
|
|
ascriptions: Vec<Ascription<'tcx>>,
|
|
|
|
/// ... and if this is non-empty, one of these subcandidates also has to match ...
|
|
subcandidates: Vec<Candidate<'pat, 'tcx>>,
|
|
|
|
/// ...and the guard must be evaluated, if false branch to Block...
|
|
otherwise_block: Option<BasicBlock>,
|
|
|
|
/// ...and the blocks for add false edges between candidates
|
|
pre_binding_block: Option<BasicBlock>,
|
|
next_candidate_pre_binding_block: Option<BasicBlock>,
|
|
}
|
|
|
|
impl<'tcx, 'pat> Candidate<'pat, 'tcx> {
|
|
fn new(place: Place<'tcx>, pattern: &'pat Pat<'tcx>, has_guard: bool) -> Self {
|
|
Candidate {
|
|
span: pattern.span,
|
|
has_guard,
|
|
match_pairs: smallvec![MatchPair { place, pattern }],
|
|
bindings: Vec::new(),
|
|
ascriptions: Vec::new(),
|
|
subcandidates: Vec::new(),
|
|
otherwise_block: None,
|
|
pre_binding_block: None,
|
|
next_candidate_pre_binding_block: None,
|
|
}
|
|
}
|
|
|
|
/// Visit the leaf candidates (those with no subcandidates) contained in
|
|
/// this candidate.
|
|
fn visit_leaves<'a>(&'a mut self, mut visit_leaf: impl FnMut(&'a mut Self)) {
|
|
traverse_candidate(
|
|
self,
|
|
&mut (),
|
|
&mut move |c, _| visit_leaf(c),
|
|
move |c, _| c.subcandidates.iter_mut(),
|
|
|_| {},
|
|
);
|
|
}
|
|
}
|
|
|
|
/// A depth-first traversal of the `Candidate` and all of its recursive
|
|
/// subcandidates.
|
|
fn traverse_candidate<'pat, 'tcx: 'pat, C, T, I>(
|
|
candidate: C,
|
|
context: &mut T,
|
|
visit_leaf: &mut impl FnMut(C, &mut T),
|
|
get_children: impl Copy + Fn(C, &mut T) -> I,
|
|
complete_children: impl Copy + Fn(&mut T),
|
|
) where
|
|
C: Borrow<Candidate<'pat, 'tcx>>,
|
|
I: Iterator<Item = C>,
|
|
{
|
|
if candidate.borrow().subcandidates.is_empty() {
|
|
visit_leaf(candidate, context)
|
|
} else {
|
|
for child in get_children(candidate, context) {
|
|
traverse_candidate(child, context, visit_leaf, get_children, complete_children);
|
|
}
|
|
complete_children(context)
|
|
}
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
struct Binding<'tcx> {
|
|
span: Span,
|
|
source: Place<'tcx>,
|
|
name: Symbol,
|
|
var_id: HirId,
|
|
var_ty: Ty<'tcx>,
|
|
mutability: Mutability,
|
|
binding_mode: BindingMode,
|
|
}
|
|
|
|
/// Indicates that the type of `source` must be a subtype of the
|
|
/// user-given type `user_ty`; this is basically a no-op but can
|
|
/// influence region inference.
|
|
#[derive(Clone, Debug)]
|
|
struct Ascription<'tcx> {
|
|
span: Span,
|
|
source: Place<'tcx>,
|
|
user_ty: PatTyProj<'tcx>,
|
|
variance: ty::Variance,
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
crate struct MatchPair<'pat, 'tcx> {
|
|
// this place...
|
|
place: Place<'tcx>,
|
|
|
|
// ... must match this pattern.
|
|
pattern: &'pat Pat<'tcx>,
|
|
}
|
|
|
|
#[derive(Clone, Debug, PartialEq)]
|
|
enum TestKind<'tcx> {
|
|
/// Test the branches of enum.
|
|
Switch {
|
|
/// The enum being tested
|
|
adt_def: &'tcx ty::AdtDef,
|
|
/// The set of variants that we should create a branch for. We also
|
|
/// create an additional "otherwise" case.
|
|
variants: BitSet<VariantIdx>,
|
|
},
|
|
|
|
/// Test what value an `integer`, `bool` or `char` has.
|
|
SwitchInt {
|
|
/// The type of the value that we're testing.
|
|
switch_ty: Ty<'tcx>,
|
|
/// The (ordered) set of values that we test for.
|
|
///
|
|
/// For integers and `char`s we create a branch to each of the values in
|
|
/// `options`, as well as an "otherwise" branch for all other values, even
|
|
/// in the (rare) case that options is exhaustive.
|
|
///
|
|
/// For `bool` we always generate two edges, one for `true` and one for
|
|
/// `false`.
|
|
options: Vec<u128>,
|
|
/// Reverse map used to ensure that the values in `options` are unique.
|
|
indices: FxHashMap<&'tcx ty::Const<'tcx>, usize>,
|
|
},
|
|
|
|
/// Test for equality with value, possibly after an unsizing coercion to
|
|
/// `ty`,
|
|
Eq {
|
|
value: &'tcx ty::Const<'tcx>,
|
|
// Integer types are handled by `SwitchInt`, and constants with ADT
|
|
// types are converted back into patterns, so this can only be `&str`,
|
|
// `&[T]`, `f32` or `f64`.
|
|
ty: Ty<'tcx>,
|
|
},
|
|
|
|
/// Test whether the value falls within an inclusive or exclusive range
|
|
Range(PatRange<'tcx>),
|
|
|
|
/// Test length of the slice is equal to len
|
|
Len { len: u64, op: BinOp },
|
|
}
|
|
|
|
#[derive(Debug)]
|
|
crate struct Test<'tcx> {
|
|
span: Span,
|
|
kind: TestKind<'tcx>,
|
|
}
|
|
|
|
/// ArmHasGuard is isomorphic to a boolean flag. It indicates whether
|
|
/// a match arm has a guard expression attached to it.
|
|
#[derive(Copy, Clone, Debug)]
|
|
crate struct ArmHasGuard(crate bool);
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// Main matching algorithm
|
|
|
|
impl<'a, 'tcx> Builder<'a, 'tcx> {
|
|
/// The main match algorithm. It begins with a set of candidates
|
|
/// `candidates` and has the job of generating code to determine
|
|
/// which of these candidates, if any, is the correct one. The
|
|
/// candidates are sorted such that the first item in the list
|
|
/// has the highest priority. When a candidate is found to match
|
|
/// the value, we will set and generate a branch to the appropriate
|
|
/// prebinding block.
|
|
///
|
|
/// If we find that *NONE* of the candidates apply, we branch to the
|
|
/// `otherwise_block`, setting it to `Some` if required. In principle, this
|
|
/// means that the input list was not exhaustive, though at present we
|
|
/// sometimes are not smart enough to recognize all exhaustive inputs.
|
|
///
|
|
/// It might be surprising that the input can be inexhaustive.
|
|
/// Indeed, initially, it is not, because all matches are
|
|
/// exhaustive in Rust. But during processing we sometimes divide
|
|
/// up the list of candidates and recurse with a non-exhaustive
|
|
/// list. This is important to keep the size of the generated code
|
|
/// under control. See `test_candidates` for more details.
|
|
///
|
|
/// If `fake_borrows` is Some, then places which need fake borrows
|
|
/// will be added to it.
|
|
///
|
|
/// For an example of a case where we set `otherwise_block`, even for an
|
|
/// exhaustive match consider:
|
|
///
|
|
/// match x {
|
|
/// (true, true) => (),
|
|
/// (_, false) => (),
|
|
/// (false, true) => (),
|
|
/// }
|
|
///
|
|
/// For this match, we check if `x.0` matches `true` (for the first
|
|
/// arm). If that's false, we check `x.1`. If it's `true` we check if
|
|
/// `x.0` matches `false` (for the third arm). In the (impossible at
|
|
/// runtime) case when `x.0` is now `true`, we branch to
|
|
/// `otherwise_block`.
|
|
fn match_candidates<'pat>(
|
|
&mut self,
|
|
span: Span,
|
|
start_block: BasicBlock,
|
|
otherwise_block: &mut Option<BasicBlock>,
|
|
candidates: &mut [&mut Candidate<'pat, 'tcx>],
|
|
fake_borrows: &mut Option<FxHashSet<Place<'tcx>>>,
|
|
) {
|
|
debug!(
|
|
"matched_candidate(span={:?}, candidates={:?}, start_block={:?}, otherwise_block={:?})",
|
|
span, candidates, start_block, otherwise_block,
|
|
);
|
|
|
|
// Start by simplifying candidates. Once this process is complete, all
|
|
// the match pairs which remain require some form of test, whether it
|
|
// be a switch or pattern comparison.
|
|
let mut split_or_candidate = false;
|
|
for candidate in &mut *candidates {
|
|
split_or_candidate |= self.simplify_candidate(candidate);
|
|
}
|
|
|
|
if split_or_candidate {
|
|
// At least one of the candidates has been split into subcandidates.
|
|
// We need to change the candidate list to include those.
|
|
let mut new_candidates = Vec::new();
|
|
|
|
for candidate in candidates {
|
|
candidate.visit_leaves(|leaf_candidate| new_candidates.push(leaf_candidate));
|
|
}
|
|
self.match_simplified_candidates(
|
|
span,
|
|
start_block,
|
|
otherwise_block,
|
|
&mut *new_candidates,
|
|
fake_borrows,
|
|
);
|
|
} else {
|
|
self.match_simplified_candidates(
|
|
span,
|
|
start_block,
|
|
otherwise_block,
|
|
candidates,
|
|
fake_borrows,
|
|
);
|
|
};
|
|
}
|
|
|
|
fn match_simplified_candidates(
|
|
&mut self,
|
|
span: Span,
|
|
start_block: BasicBlock,
|
|
otherwise_block: &mut Option<BasicBlock>,
|
|
candidates: &mut [&mut Candidate<'_, 'tcx>],
|
|
fake_borrows: &mut Option<FxHashSet<Place<'tcx>>>,
|
|
) {
|
|
// The candidates are sorted by priority. Check to see whether the
|
|
// higher priority candidates (and hence at the front of the slice)
|
|
// have satisfied all their match pairs.
|
|
let fully_matched = candidates.iter().take_while(|c| c.match_pairs.is_empty()).count();
|
|
debug!("match_candidates: {:?} candidates fully matched", fully_matched);
|
|
let (matched_candidates, unmatched_candidates) = candidates.split_at_mut(fully_matched);
|
|
|
|
let block = if !matched_candidates.is_empty() {
|
|
let otherwise_block =
|
|
self.select_matched_candidates(matched_candidates, start_block, fake_borrows);
|
|
|
|
if let Some(last_otherwise_block) = otherwise_block {
|
|
last_otherwise_block
|
|
} else {
|
|
// Any remaining candidates are unreachable.
|
|
if unmatched_candidates.is_empty() {
|
|
return;
|
|
}
|
|
self.cfg.start_new_block()
|
|
}
|
|
} else {
|
|
start_block
|
|
};
|
|
|
|
// If there are no candidates that still need testing, we're
|
|
// done. Since all matches are exhaustive, execution should
|
|
// never reach this point.
|
|
if unmatched_candidates.is_empty() {
|
|
let source_info = self.source_info(span);
|
|
if let Some(otherwise) = *otherwise_block {
|
|
self.cfg.goto(block, source_info, otherwise);
|
|
} else {
|
|
*otherwise_block = Some(block);
|
|
}
|
|
return;
|
|
}
|
|
|
|
// Test for the remaining candidates.
|
|
self.test_candidates_with_or(
|
|
span,
|
|
unmatched_candidates,
|
|
block,
|
|
otherwise_block,
|
|
fake_borrows,
|
|
);
|
|
}
|
|
|
|
/// Link up matched candidates. For example, if we have something like
|
|
/// this:
|
|
///
|
|
/// ...
|
|
/// Some(x) if cond => ...
|
|
/// Some(x) => ...
|
|
/// Some(x) if cond => ...
|
|
/// ...
|
|
///
|
|
/// We generate real edges from:
|
|
/// * `start_block` to the `prebinding_block` of the first pattern,
|
|
/// * the otherwise block of the first pattern to the second pattern,
|
|
/// * the otherwise block of the third pattern to the a block with an
|
|
/// Unreachable terminator.
|
|
///
|
|
/// As well as that we add fake edges from the otherwise blocks to the
|
|
/// prebinding block of the next candidate in the original set of
|
|
/// candidates.
|
|
fn select_matched_candidates(
|
|
&mut self,
|
|
matched_candidates: &mut [&mut Candidate<'_, 'tcx>],
|
|
start_block: BasicBlock,
|
|
fake_borrows: &mut Option<FxHashSet<Place<'tcx>>>,
|
|
) -> Option<BasicBlock> {
|
|
debug_assert!(
|
|
!matched_candidates.is_empty(),
|
|
"select_matched_candidates called with no candidates",
|
|
);
|
|
debug_assert!(
|
|
matched_candidates.iter().all(|c| c.subcandidates.is_empty()),
|
|
"subcandidates should be empty in select_matched_candidates",
|
|
);
|
|
|
|
// Insert a borrows of prefixes of places that are bound and are
|
|
// behind a dereference projection.
|
|
//
|
|
// These borrows are taken to avoid situations like the following:
|
|
//
|
|
// match x[10] {
|
|
// _ if { x = &[0]; false } => (),
|
|
// y => (), // Out of bounds array access!
|
|
// }
|
|
//
|
|
// match *x {
|
|
// // y is bound by reference in the guard and then by copy in the
|
|
// // arm, so y is 2 in the arm!
|
|
// y if { y == 1 && (x = &2) == () } => y,
|
|
// _ => 3,
|
|
// }
|
|
if let Some(fake_borrows) = fake_borrows {
|
|
for Binding { source, .. } in
|
|
matched_candidates.iter().flat_map(|candidate| &candidate.bindings)
|
|
{
|
|
if let Some(i) =
|
|
source.projection.iter().rposition(|elem| *elem == ProjectionElem::Deref)
|
|
{
|
|
let proj_base = &source.projection[..i];
|
|
|
|
fake_borrows.insert(Place {
|
|
local: source.local,
|
|
projection: self.hir.tcx().intern_place_elems(proj_base),
|
|
});
|
|
}
|
|
}
|
|
}
|
|
|
|
let fully_matched_with_guard = matched_candidates
|
|
.iter()
|
|
.position(|c| !c.has_guard)
|
|
.unwrap_or(matched_candidates.len() - 1);
|
|
|
|
let (reachable_candidates, unreachable_candidates) =
|
|
matched_candidates.split_at_mut(fully_matched_with_guard + 1);
|
|
|
|
let mut next_prebinding = start_block;
|
|
|
|
for candidate in reachable_candidates.iter_mut() {
|
|
assert!(candidate.otherwise_block.is_none());
|
|
assert!(candidate.pre_binding_block.is_none());
|
|
candidate.pre_binding_block = Some(next_prebinding);
|
|
if candidate.has_guard {
|
|
// Create the otherwise block for this candidate, which is the
|
|
// pre-binding block for the next candidate.
|
|
next_prebinding = self.cfg.start_new_block();
|
|
candidate.otherwise_block = Some(next_prebinding);
|
|
}
|
|
}
|
|
|
|
debug!(
|
|
"match_candidates: add pre_binding_blocks for unreachable {:?}",
|
|
unreachable_candidates,
|
|
);
|
|
for candidate in unreachable_candidates {
|
|
assert!(candidate.pre_binding_block.is_none());
|
|
candidate.pre_binding_block = Some(self.cfg.start_new_block());
|
|
}
|
|
|
|
reachable_candidates.last_mut().unwrap().otherwise_block
|
|
}
|
|
|
|
/// Tests a candidate where there are only or-patterns left to test, or
|
|
/// forwards to [Builder::test_candidates].
|
|
///
|
|
/// Given a pattern `(P | Q, R | S)` we (in principle) generate a CFG like
|
|
/// so
|
|
///
|
|
/// ```text
|
|
/// [ start ]
|
|
/// |
|
|
/// [ match P, Q ]
|
|
/// |
|
|
/// +----------------------------------------+------------------------------------+
|
|
/// | | |
|
|
/// V V V
|
|
/// [ P matches ] [ Q matches ] [ otherwise ]
|
|
/// | | |
|
|
/// V V |
|
|
/// [ match R, S ] [ match R, S ] |
|
|
/// | | |
|
|
/// +--------------+------------+ +--------------+------------+ |
|
|
/// | | | | | | |
|
|
/// V V V V V V |
|
|
/// [ R matches ] [ S matches ] [otherwise ] [ R matches ] [ S matches ] [otherwise ] |
|
|
/// | | | | | | |
|
|
/// +--------------+------------|------------+--------------+ | |
|
|
/// | | | |
|
|
/// | +----------------------------------------+--------+
|
|
/// | |
|
|
/// V V
|
|
/// [ Success ] [ Failure ]
|
|
/// ```
|
|
///
|
|
/// In practice there are some complications:
|
|
///
|
|
/// * If there's a guard, then the otherwise branch of the first match on
|
|
/// `R | S` goes to a test for whether `Q` matches, and the control flow
|
|
/// doesn't merge into a single success block until after the guard is
|
|
/// tested.
|
|
/// * If neither `P` or `Q` has any bindings or type ascriptions and there
|
|
/// isn't a match guard, then we create a smaller CFG like:
|
|
///
|
|
/// ```text
|
|
/// ...
|
|
/// +---------------+------------+
|
|
/// | | |
|
|
/// [ P matches ] [ Q matches ] [ otherwise ]
|
|
/// | | |
|
|
/// +---------------+ |
|
|
/// | ...
|
|
/// [ match R, S ]
|
|
/// |
|
|
/// ...
|
|
/// ```
|
|
fn test_candidates_with_or(
|
|
&mut self,
|
|
span: Span,
|
|
candidates: &mut [&mut Candidate<'_, 'tcx>],
|
|
block: BasicBlock,
|
|
otherwise_block: &mut Option<BasicBlock>,
|
|
fake_borrows: &mut Option<FxHashSet<Place<'tcx>>>,
|
|
) {
|
|
let (first_candidate, remaining_candidates) = candidates.split_first_mut().unwrap();
|
|
|
|
// All of the or-patterns have been sorted to the end, so if the first
|
|
// pattern is an or-pattern we only have or-patterns.
|
|
match *first_candidate.match_pairs[0].pattern.kind {
|
|
PatKind::Or { .. } => (),
|
|
_ => {
|
|
self.test_candidates(span, candidates, block, otherwise_block, fake_borrows);
|
|
return;
|
|
}
|
|
}
|
|
|
|
let match_pairs = mem::take(&mut first_candidate.match_pairs);
|
|
first_candidate.pre_binding_block = Some(block);
|
|
|
|
let mut otherwise = None;
|
|
for match_pair in match_pairs {
|
|
if let PatKind::Or { ref pats } = *match_pair.pattern.kind {
|
|
let or_span = match_pair.pattern.span;
|
|
let place = match_pair.place;
|
|
|
|
first_candidate.visit_leaves(|leaf_candidate| {
|
|
self.test_or_pattern(
|
|
leaf_candidate,
|
|
&mut otherwise,
|
|
pats,
|
|
or_span,
|
|
place,
|
|
fake_borrows,
|
|
);
|
|
});
|
|
} else {
|
|
bug!("Or-patterns should have been sorted to the end");
|
|
}
|
|
}
|
|
|
|
let remainder_start = otherwise.unwrap_or_else(|| self.cfg.start_new_block());
|
|
|
|
self.match_candidates(
|
|
span,
|
|
remainder_start,
|
|
otherwise_block,
|
|
remaining_candidates,
|
|
fake_borrows,
|
|
)
|
|
}
|
|
|
|
fn test_or_pattern<'pat>(
|
|
&mut self,
|
|
candidate: &mut Candidate<'pat, 'tcx>,
|
|
otherwise: &mut Option<BasicBlock>,
|
|
pats: &'pat [Pat<'tcx>],
|
|
or_span: Span,
|
|
place: Place<'tcx>,
|
|
fake_borrows: &mut Option<FxHashSet<Place<'tcx>>>,
|
|
) {
|
|
debug!("test_or_pattern:\ncandidate={:#?}\npats={:#?}", candidate, pats);
|
|
let mut or_candidates: Vec<_> =
|
|
pats.iter().map(|pat| Candidate::new(place, pat, candidate.has_guard)).collect();
|
|
let mut or_candidate_refs: Vec<_> = or_candidates.iter_mut().collect();
|
|
let otherwise = if candidate.otherwise_block.is_some() {
|
|
&mut candidate.otherwise_block
|
|
} else {
|
|
otherwise
|
|
};
|
|
self.match_candidates(
|
|
or_span,
|
|
candidate.pre_binding_block.unwrap(),
|
|
otherwise,
|
|
&mut or_candidate_refs,
|
|
fake_borrows,
|
|
);
|
|
candidate.subcandidates = or_candidates;
|
|
self.merge_trivial_subcandidates(candidate, self.source_info(or_span));
|
|
}
|
|
|
|
/// Try to merge all of the subcandidates of the given candidate into one.
|
|
/// This avoids exponentially large CFGs in cases like `(1 | 2, 3 | 4, ...)`.
|
|
fn merge_trivial_subcandidates(
|
|
&mut self,
|
|
candidate: &mut Candidate<'_, 'tcx>,
|
|
source_info: SourceInfo,
|
|
) {
|
|
if candidate.subcandidates.is_empty() || candidate.has_guard {
|
|
// FIXME(or_patterns; matthewjasper) Don't give up if we have a guard.
|
|
return;
|
|
}
|
|
|
|
let mut can_merge = true;
|
|
|
|
// Not `Iterator::all` because we don't want to short-circuit.
|
|
for subcandidate in &mut candidate.subcandidates {
|
|
self.merge_trivial_subcandidates(subcandidate, source_info);
|
|
|
|
// FIXME(or_patterns; matthewjasper) Try to be more aggressive here.
|
|
can_merge &= subcandidate.subcandidates.is_empty()
|
|
&& subcandidate.bindings.is_empty()
|
|
&& subcandidate.ascriptions.is_empty();
|
|
}
|
|
|
|
if can_merge {
|
|
let any_matches = self.cfg.start_new_block();
|
|
for subcandidate in mem::take(&mut candidate.subcandidates) {
|
|
let or_block = subcandidate.pre_binding_block.unwrap();
|
|
self.cfg.goto(or_block, source_info, any_matches);
|
|
}
|
|
candidate.pre_binding_block = Some(any_matches);
|
|
}
|
|
}
|
|
|
|
/// This is the most subtle part of the matching algorithm. At
|
|
/// this point, the input candidates have been fully simplified,
|
|
/// and so we know that all remaining match-pairs require some
|
|
/// sort of test. To decide what test to do, we take the highest
|
|
/// priority candidate (last one in the list) and extract the
|
|
/// first match-pair from the list. From this we decide what kind
|
|
/// of test is needed using `test`, defined in the `test` module.
|
|
///
|
|
/// *Note:* taking the first match pair is somewhat arbitrary, and
|
|
/// we might do better here by choosing more carefully what to
|
|
/// test.
|
|
///
|
|
/// For example, consider the following possible match-pairs:
|
|
///
|
|
/// 1. `x @ Some(P)` -- we will do a `Switch` to decide what variant `x` has
|
|
/// 2. `x @ 22` -- we will do a `SwitchInt`
|
|
/// 3. `x @ 3..5` -- we will do a range test
|
|
/// 4. etc.
|
|
///
|
|
/// Once we know what sort of test we are going to perform, this
|
|
/// Tests may also help us with other candidates. So we walk over
|
|
/// the candidates (from high to low priority) and check. This
|
|
/// gives us, for each outcome of the test, a transformed list of
|
|
/// candidates. For example, if we are testing the current
|
|
/// variant of `x.0`, and we have a candidate `{x.0 @ Some(v), x.1
|
|
/// @ 22}`, then we would have a resulting candidate of `{(x.0 as
|
|
/// Some).0 @ v, x.1 @ 22}`. Note that the first match-pair is now
|
|
/// simpler (and, in fact, irrefutable).
|
|
///
|
|
/// But there may also be candidates that the test just doesn't
|
|
/// apply to. The classical example involves wildcards:
|
|
///
|
|
/// ```
|
|
/// # let (x, y, z) = (true, true, true);
|
|
/// match (x, y, z) {
|
|
/// (true, _, true) => true, // (0)
|
|
/// (_, true, _) => true, // (1)
|
|
/// (false, false, _) => false, // (2)
|
|
/// (true, _, false) => false, // (3)
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// In that case, after we test on `x`, there are 2 overlapping candidate
|
|
/// sets:
|
|
///
|
|
/// - If the outcome is that `x` is true, candidates 0, 1, and 3
|
|
/// - If the outcome is that `x` is false, candidates 1 and 2
|
|
///
|
|
/// Here, the traditional "decision tree" method would generate 2
|
|
/// separate code-paths for the 2 separate cases.
|
|
///
|
|
/// In some cases, this duplication can create an exponential amount of
|
|
/// code. This is most easily seen by noticing that this method terminates
|
|
/// with precisely the reachable arms being reachable - but that problem
|
|
/// is trivially NP-complete:
|
|
///
|
|
/// ```rust
|
|
/// match (var0, var1, var2, var3, ..) {
|
|
/// (true, _, _, false, true, ...) => false,
|
|
/// (_, true, true, false, _, ...) => false,
|
|
/// (false, _, false, false, _, ...) => false,
|
|
/// ...
|
|
/// _ => true
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// Here the last arm is reachable only if there is an assignment to
|
|
/// the variables that does not match any of the literals. Therefore,
|
|
/// compilation would take an exponential amount of time in some cases.
|
|
///
|
|
/// That kind of exponential worst-case might not occur in practice, but
|
|
/// our simplistic treatment of constants and guards would make it occur
|
|
/// in very common situations - for example #29740:
|
|
///
|
|
/// ```rust
|
|
/// match x {
|
|
/// "foo" if foo_guard => ...,
|
|
/// "bar" if bar_guard => ...,
|
|
/// "baz" if baz_guard => ...,
|
|
/// ...
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// Here we first test the match-pair `x @ "foo"`, which is an `Eq` test.
|
|
///
|
|
/// It might seem that we would end up with 2 disjoint candidate
|
|
/// sets, consisting of the first candidate or the other 3, but our
|
|
/// algorithm doesn't reason about "foo" being distinct from the other
|
|
/// constants; it considers the latter arms to potentially match after
|
|
/// both outcomes, which obviously leads to an exponential amount
|
|
/// of tests.
|
|
///
|
|
/// To avoid these kinds of problems, our algorithm tries to ensure
|
|
/// the amount of generated tests is linear. When we do a k-way test,
|
|
/// we return an additional "unmatched" set alongside the obvious `k`
|
|
/// sets. When we encounter a candidate that would be present in more
|
|
/// than one of the sets, we put it and all candidates below it into the
|
|
/// "unmatched" set. This ensures these `k+1` sets are disjoint.
|
|
///
|
|
/// After we perform our test, we branch into the appropriate candidate
|
|
/// set and recurse with `match_candidates`. These sub-matches are
|
|
/// obviously inexhaustive - as we discarded our otherwise set - so
|
|
/// we set their continuation to do `match_candidates` on the
|
|
/// "unmatched" set (which is again inexhaustive).
|
|
///
|
|
/// If you apply this to the above test, you basically wind up
|
|
/// with an if-else-if chain, testing each candidate in turn,
|
|
/// which is precisely what we want.
|
|
///
|
|
/// In addition to avoiding exponential-time blowups, this algorithm
|
|
/// also has nice property that each guard and arm is only generated
|
|
/// once.
|
|
fn test_candidates<'pat, 'b, 'c>(
|
|
&mut self,
|
|
span: Span,
|
|
mut candidates: &'b mut [&'c mut Candidate<'pat, 'tcx>],
|
|
block: BasicBlock,
|
|
otherwise_block: &mut Option<BasicBlock>,
|
|
fake_borrows: &mut Option<FxHashSet<Place<'tcx>>>,
|
|
) {
|
|
// extract the match-pair from the highest priority candidate
|
|
let match_pair = &candidates.first().unwrap().match_pairs[0];
|
|
let mut test = self.test(match_pair);
|
|
let match_place = match_pair.place;
|
|
|
|
// most of the time, the test to perform is simply a function
|
|
// of the main candidate; but for a test like SwitchInt, we
|
|
// may want to add cases based on the candidates that are
|
|
// available
|
|
match test.kind {
|
|
TestKind::SwitchInt { switch_ty, ref mut options, ref mut indices } => {
|
|
for candidate in candidates.iter() {
|
|
if !self.add_cases_to_switch(
|
|
&match_place,
|
|
candidate,
|
|
switch_ty,
|
|
options,
|
|
indices,
|
|
) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
TestKind::Switch { adt_def: _, ref mut variants } => {
|
|
for candidate in candidates.iter() {
|
|
if !self.add_variants_to_switch(&match_place, candidate, variants) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
_ => {}
|
|
}
|
|
|
|
// Insert a Shallow borrow of any places that is switched on.
|
|
if let Some(fb) = fake_borrows {
|
|
fb.insert(match_place);
|
|
}
|
|
|
|
// perform the test, branching to one of N blocks. For each of
|
|
// those N possible outcomes, create a (initially empty)
|
|
// vector of candidates. Those are the candidates that still
|
|
// apply if the test has that particular outcome.
|
|
debug!("match_candidates: test={:?} match_pair={:?}", test, match_pair);
|
|
let mut target_candidates: Vec<Vec<&mut Candidate<'pat, 'tcx>>> = vec![];
|
|
target_candidates.resize_with(test.targets(), Default::default);
|
|
|
|
let total_candidate_count = candidates.len();
|
|
|
|
// Sort the candidates into the appropriate vector in
|
|
// `target_candidates`. Note that at some point we may
|
|
// encounter a candidate where the test is not relevant; at
|
|
// that point, we stop sorting.
|
|
while let Some(candidate) = candidates.first_mut() {
|
|
if let Some(idx) = self.sort_candidate(&match_place, &test, candidate) {
|
|
let (candidate, rest) = candidates.split_first_mut().unwrap();
|
|
target_candidates[idx].push(candidate);
|
|
candidates = rest;
|
|
} else {
|
|
break;
|
|
}
|
|
}
|
|
// at least the first candidate ought to be tested
|
|
assert!(total_candidate_count > candidates.len());
|
|
debug!("tested_candidates: {}", total_candidate_count - candidates.len());
|
|
debug!("untested_candidates: {}", candidates.len());
|
|
|
|
// HACK(matthewjasper) This is a closure so that we can let the test
|
|
// create its blocks before the rest of the match. This currently
|
|
// improves the speed of llvm when optimizing long string literal
|
|
// matches
|
|
let make_target_blocks = move |this: &mut Self| -> Vec<BasicBlock> {
|
|
// The block that we should branch to if none of the
|
|
// `target_candidates` match. This is either the block where we
|
|
// start matching the untested candidates if there are any,
|
|
// otherwise it's the `otherwise_block`.
|
|
let remainder_start = &mut None;
|
|
let remainder_start =
|
|
if candidates.is_empty() { &mut *otherwise_block } else { remainder_start };
|
|
|
|
// For each outcome of test, process the candidates that still
|
|
// apply. Collect a list of blocks where control flow will
|
|
// branch if one of the `target_candidate` sets is not
|
|
// exhaustive.
|
|
let target_blocks: Vec<_> = target_candidates
|
|
.into_iter()
|
|
.map(|mut candidates| {
|
|
if !candidates.is_empty() {
|
|
let candidate_start = this.cfg.start_new_block();
|
|
this.match_candidates(
|
|
span,
|
|
candidate_start,
|
|
remainder_start,
|
|
&mut *candidates,
|
|
fake_borrows,
|
|
);
|
|
candidate_start
|
|
} else {
|
|
*remainder_start.get_or_insert_with(|| this.cfg.start_new_block())
|
|
}
|
|
})
|
|
.collect();
|
|
|
|
if !candidates.is_empty() {
|
|
let remainder_start = remainder_start.unwrap_or_else(|| this.cfg.start_new_block());
|
|
this.match_candidates(
|
|
span,
|
|
remainder_start,
|
|
otherwise_block,
|
|
candidates,
|
|
fake_borrows,
|
|
);
|
|
};
|
|
|
|
target_blocks
|
|
};
|
|
|
|
self.perform_test(block, match_place, &test, make_target_blocks);
|
|
}
|
|
|
|
/// Determine the fake borrows that are needed from a set of places that
|
|
/// have to be stable across match guards.
|
|
///
|
|
/// Returns a list of places that need a fake borrow and the temporary
|
|
/// that's used to store the fake borrow.
|
|
///
|
|
/// Match exhaustiveness checking is not able to handle the case where the
|
|
/// place being matched on is mutated in the guards. We add "fake borrows"
|
|
/// to the guards that prevent any mutation of the place being matched.
|
|
/// There are a some subtleties:
|
|
///
|
|
/// 1. Borrowing `*x` doesn't prevent assigning to `x`. If `x` is a shared
|
|
/// reference, the borrow isn't even tracked. As such we have to add fake
|
|
/// borrows of any prefixes of a place
|
|
/// 2. We don't want `match x { _ => (), }` to conflict with mutable
|
|
/// borrows of `x`, so we only add fake borrows for places which are
|
|
/// bound or tested by the match.
|
|
/// 3. We don't want the fake borrows to conflict with `ref mut` bindings,
|
|
/// so we use a special BorrowKind for them.
|
|
/// 4. The fake borrows may be of places in inactive variants, so it would
|
|
/// be UB to generate code for them. They therefore have to be removed
|
|
/// by a MIR pass run after borrow checking.
|
|
fn calculate_fake_borrows<'b>(
|
|
&mut self,
|
|
fake_borrows: &'b FxHashSet<Place<'tcx>>,
|
|
temp_span: Span,
|
|
) -> Vec<(Place<'tcx>, Local)> {
|
|
let tcx = self.hir.tcx();
|
|
|
|
debug!("add_fake_borrows fake_borrows = {:?}", fake_borrows);
|
|
|
|
let mut all_fake_borrows = Vec::with_capacity(fake_borrows.len());
|
|
|
|
// Insert a Shallow borrow of the prefixes of any fake borrows.
|
|
for place in fake_borrows {
|
|
let mut cursor = place.projection.as_ref();
|
|
while let [proj_base @ .., elem] = cursor {
|
|
cursor = proj_base;
|
|
|
|
if let ProjectionElem::Deref = elem {
|
|
// Insert a shallow borrow after a deref. For other
|
|
// projections the borrow of prefix_cursor will
|
|
// conflict with any mutation of base.
|
|
all_fake_borrows.push(PlaceRef { local: place.local, projection: proj_base });
|
|
}
|
|
}
|
|
|
|
all_fake_borrows.push(place.as_ref());
|
|
}
|
|
|
|
// Deduplicate and ensure a deterministic order.
|
|
all_fake_borrows.sort();
|
|
all_fake_borrows.dedup();
|
|
|
|
debug!("add_fake_borrows all_fake_borrows = {:?}", all_fake_borrows);
|
|
|
|
all_fake_borrows
|
|
.into_iter()
|
|
.map(|matched_place_ref| {
|
|
let matched_place = Place {
|
|
local: matched_place_ref.local,
|
|
projection: tcx.intern_place_elems(matched_place_ref.projection),
|
|
};
|
|
let fake_borrow_deref_ty = matched_place.ty(&self.local_decls, tcx).ty;
|
|
let fake_borrow_ty = tcx.mk_imm_ref(tcx.lifetimes.re_erased, fake_borrow_deref_ty);
|
|
let fake_borrow_temp =
|
|
self.local_decls.push(LocalDecl::new(fake_borrow_ty, temp_span));
|
|
|
|
(matched_place, fake_borrow_temp)
|
|
})
|
|
.collect()
|
|
}
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// Pat binding - used for `let` and function parameters as well.
|
|
|
|
impl<'a, 'tcx> Builder<'a, 'tcx> {
|
|
/// Initializes each of the bindings from the candidate by
|
|
/// moving/copying/ref'ing the source as appropriate. Tests the guard, if
|
|
/// any, and then branches to the arm. Returns the block for the case where
|
|
/// the guard fails.
|
|
///
|
|
/// Note: we do not check earlier that if there is a guard,
|
|
/// there cannot be move bindings. We avoid a use-after-move by only
|
|
/// moving the binding once the guard has evaluated to true (see below).
|
|
fn bind_and_guard_matched_candidate<'pat>(
|
|
&mut self,
|
|
candidate: Candidate<'pat, 'tcx>,
|
|
parent_bindings: &[(Vec<Binding<'tcx>>, Vec<Ascription<'tcx>>)],
|
|
guard: Option<(&Guard<'tcx>, region::Scope)>,
|
|
fake_borrows: &Vec<(Place<'tcx>, Local)>,
|
|
scrutinee_span: Span,
|
|
schedule_drops: bool,
|
|
) -> BasicBlock {
|
|
debug!("bind_and_guard_matched_candidate(candidate={:?})", candidate);
|
|
|
|
debug_assert!(candidate.match_pairs.is_empty());
|
|
|
|
let candidate_source_info = self.source_info(candidate.span);
|
|
|
|
let mut block = candidate.pre_binding_block.unwrap();
|
|
|
|
if candidate.next_candidate_pre_binding_block.is_some() {
|
|
let fresh_block = self.cfg.start_new_block();
|
|
self.false_edges(
|
|
block,
|
|
fresh_block,
|
|
candidate.next_candidate_pre_binding_block,
|
|
candidate_source_info,
|
|
);
|
|
block = fresh_block;
|
|
}
|
|
|
|
self.ascribe_types(
|
|
block,
|
|
parent_bindings
|
|
.iter()
|
|
.flat_map(|(_, ascriptions)| ascriptions)
|
|
.chain(&candidate.ascriptions),
|
|
);
|
|
|
|
// rust-lang/rust#27282: The `autoref` business deserves some
|
|
// explanation here.
|
|
//
|
|
// The intent of the `autoref` flag is that when it is true,
|
|
// then any pattern bindings of type T will map to a `&T`
|
|
// within the context of the guard expression, but will
|
|
// continue to map to a `T` in the context of the arm body. To
|
|
// avoid surfacing this distinction in the user source code
|
|
// (which would be a severe change to the language and require
|
|
// far more revision to the compiler), when `autoref` is true,
|
|
// then any occurrence of the identifier in the guard
|
|
// expression will automatically get a deref op applied to it.
|
|
//
|
|
// So an input like:
|
|
//
|
|
// ```
|
|
// let place = Foo::new();
|
|
// match place { foo if inspect(foo)
|
|
// => feed(foo), ... }
|
|
// ```
|
|
//
|
|
// will be treated as if it were really something like:
|
|
//
|
|
// ```
|
|
// let place = Foo::new();
|
|
// match place { Foo { .. } if { let tmp1 = &place; inspect(*tmp1) }
|
|
// => { let tmp2 = place; feed(tmp2) }, ... }
|
|
//
|
|
// And an input like:
|
|
//
|
|
// ```
|
|
// let place = Foo::new();
|
|
// match place { ref mut foo if inspect(foo)
|
|
// => feed(foo), ... }
|
|
// ```
|
|
//
|
|
// will be treated as if it were really something like:
|
|
//
|
|
// ```
|
|
// let place = Foo::new();
|
|
// match place { Foo { .. } if { let tmp1 = & &mut place; inspect(*tmp1) }
|
|
// => { let tmp2 = &mut place; feed(tmp2) }, ... }
|
|
// ```
|
|
//
|
|
// In short, any pattern binding will always look like *some*
|
|
// kind of `&T` within the guard at least in terms of how the
|
|
// MIR-borrowck views it, and this will ensure that guard
|
|
// expressions cannot mutate their the match inputs via such
|
|
// bindings. (It also ensures that guard expressions can at
|
|
// most *copy* values from such bindings; non-Copy things
|
|
// cannot be moved via pattern bindings in guard expressions.)
|
|
//
|
|
// ----
|
|
//
|
|
// Implementation notes (under assumption `autoref` is true).
|
|
//
|
|
// To encode the distinction above, we must inject the
|
|
// temporaries `tmp1` and `tmp2`.
|
|
//
|
|
// There are two cases of interest: binding by-value, and binding by-ref.
|
|
//
|
|
// 1. Binding by-value: Things are simple.
|
|
//
|
|
// * Establishing `tmp1` creates a reference into the
|
|
// matched place. This code is emitted by
|
|
// bind_matched_candidate_for_guard.
|
|
//
|
|
// * `tmp2` is only initialized "lazily", after we have
|
|
// checked the guard. Thus, the code that can trigger
|
|
// moves out of the candidate can only fire after the
|
|
// guard evaluated to true. This initialization code is
|
|
// emitted by bind_matched_candidate_for_arm.
|
|
//
|
|
// 2. Binding by-reference: Things are tricky.
|
|
//
|
|
// * Here, the guard expression wants a `&&` or `&&mut`
|
|
// into the original input. This means we need to borrow
|
|
// the reference that we create for the arm.
|
|
// * So we eagerly create the reference for the arm and then take a
|
|
// reference to that.
|
|
if let Some((guard, region_scope)) = guard {
|
|
let tcx = self.hir.tcx();
|
|
let bindings = parent_bindings
|
|
.iter()
|
|
.flat_map(|(bindings, _)| bindings)
|
|
.chain(&candidate.bindings);
|
|
|
|
self.bind_matched_candidate_for_guard(block, schedule_drops, bindings.clone());
|
|
let guard_frame = GuardFrame {
|
|
locals: bindings.map(|b| GuardFrameLocal::new(b.var_id, b.binding_mode)).collect(),
|
|
};
|
|
debug!("entering guard building context: {:?}", guard_frame);
|
|
self.guard_context.push(guard_frame);
|
|
|
|
let re_erased = tcx.lifetimes.re_erased;
|
|
let scrutinee_source_info = self.source_info(scrutinee_span);
|
|
for &(place, temp) in fake_borrows {
|
|
let borrow = Rvalue::Ref(re_erased, BorrowKind::Shallow, place);
|
|
self.cfg.push_assign(block, scrutinee_source_info, Place::from(temp), borrow);
|
|
}
|
|
|
|
// the block to branch to if the guard fails; if there is no
|
|
// guard, this block is simply unreachable
|
|
let guard = match guard {
|
|
Guard::If(e) => self.hir.mirror(e.clone()),
|
|
};
|
|
let source_info = self.source_info(guard.span);
|
|
let guard_end = self.source_info(tcx.sess.source_map().end_point(guard.span));
|
|
let (post_guard_block, otherwise_post_guard_block) =
|
|
self.test_bool(block, guard, source_info);
|
|
let guard_frame = self.guard_context.pop().unwrap();
|
|
debug!("Exiting guard building context with locals: {:?}", guard_frame);
|
|
|
|
for &(_, temp) in fake_borrows {
|
|
let cause = FakeReadCause::ForMatchGuard;
|
|
self.cfg.push_fake_read(post_guard_block, guard_end, cause, Place::from(temp));
|
|
}
|
|
|
|
let otherwise_block = candidate.otherwise_block.unwrap_or_else(|| {
|
|
let unreachable = self.cfg.start_new_block();
|
|
self.cfg.terminate(unreachable, source_info, TerminatorKind::Unreachable);
|
|
unreachable
|
|
});
|
|
let outside_scope = self.cfg.start_new_block();
|
|
self.exit_scope(
|
|
source_info.span,
|
|
region_scope,
|
|
otherwise_post_guard_block,
|
|
outside_scope,
|
|
);
|
|
self.false_edges(
|
|
outside_scope,
|
|
otherwise_block,
|
|
candidate.next_candidate_pre_binding_block,
|
|
source_info,
|
|
);
|
|
|
|
// We want to ensure that the matched candidates are bound
|
|
// after we have confirmed this candidate *and* any
|
|
// associated guard; Binding them on `block` is too soon,
|
|
// because that would be before we've checked the result
|
|
// from the guard.
|
|
//
|
|
// But binding them on the arm is *too late*, because
|
|
// then all of the candidates for a single arm would be
|
|
// bound in the same place, that would cause a case like:
|
|
//
|
|
// ```rust
|
|
// match (30, 2) {
|
|
// (mut x, 1) | (2, mut x) if { true } => { ... }
|
|
// ... // ^^^^^^^ (this is `arm_block`)
|
|
// }
|
|
// ```
|
|
//
|
|
// would yield a `arm_block` something like:
|
|
//
|
|
// ```
|
|
// StorageLive(_4); // _4 is `x`
|
|
// _4 = &mut (_1.0: i32); // this is handling `(mut x, 1)` case
|
|
// _4 = &mut (_1.1: i32); // this is handling `(2, mut x)` case
|
|
// ```
|
|
//
|
|
// and that is clearly not correct.
|
|
let by_value_bindings =
|
|
parent_bindings
|
|
.iter()
|
|
.flat_map(|(bindings, _)| bindings)
|
|
.chain(&candidate.bindings)
|
|
.filter(|binding| {
|
|
if let BindingMode::ByValue = binding.binding_mode { true } else { false }
|
|
});
|
|
// Read all of the by reference bindings to ensure that the
|
|
// place they refer to can't be modified by the guard.
|
|
for binding in by_value_bindings.clone() {
|
|
let local_id = self.var_local_id(binding.var_id, RefWithinGuard);
|
|
let cause = FakeReadCause::ForGuardBinding;
|
|
self.cfg.push_fake_read(post_guard_block, guard_end, cause, Place::from(local_id));
|
|
}
|
|
assert!(schedule_drops, "patterns with guards must schedule drops");
|
|
self.bind_matched_candidate_for_arm_body(post_guard_block, true, by_value_bindings);
|
|
|
|
post_guard_block
|
|
} else {
|
|
// (Here, it is not too early to bind the matched
|
|
// candidate on `block`, because there is no guard result
|
|
// that we have to inspect before we bind them.)
|
|
self.bind_matched_candidate_for_arm_body(
|
|
block,
|
|
schedule_drops,
|
|
parent_bindings
|
|
.iter()
|
|
.flat_map(|(bindings, _)| bindings)
|
|
.chain(&candidate.bindings),
|
|
);
|
|
block
|
|
}
|
|
}
|
|
|
|
/// Append `AscribeUserType` statements onto the end of `block`
|
|
/// for each ascription
|
|
fn ascribe_types<'b>(
|
|
&mut self,
|
|
block: BasicBlock,
|
|
ascriptions: impl IntoIterator<Item = &'b Ascription<'tcx>>,
|
|
) where
|
|
'tcx: 'b,
|
|
{
|
|
for ascription in ascriptions {
|
|
let source_info = self.source_info(ascription.span);
|
|
|
|
debug!(
|
|
"adding user ascription at span {:?} of place {:?} and {:?}",
|
|
source_info.span, ascription.source, ascription.user_ty,
|
|
);
|
|
|
|
let user_ty = ascription.user_ty.clone().user_ty(
|
|
&mut self.canonical_user_type_annotations,
|
|
ascription.source.ty(&self.local_decls, self.hir.tcx()).ty,
|
|
source_info.span,
|
|
);
|
|
self.cfg.push(
|
|
block,
|
|
Statement {
|
|
source_info,
|
|
kind: StatementKind::AscribeUserType(
|
|
box (ascription.source, user_ty),
|
|
ascription.variance,
|
|
),
|
|
},
|
|
);
|
|
}
|
|
}
|
|
|
|
fn bind_matched_candidate_for_guard<'b>(
|
|
&mut self,
|
|
block: BasicBlock,
|
|
schedule_drops: bool,
|
|
bindings: impl IntoIterator<Item = &'b Binding<'tcx>>,
|
|
) where
|
|
'tcx: 'b,
|
|
{
|
|
debug!("bind_matched_candidate_for_guard(block={:?})", block);
|
|
|
|
// Assign each of the bindings. Since we are binding for a
|
|
// guard expression, this will never trigger moves out of the
|
|
// candidate.
|
|
let re_erased = self.hir.tcx().lifetimes.re_erased;
|
|
for binding in bindings {
|
|
debug!("bind_matched_candidate_for_guard(binding={:?})", binding);
|
|
let source_info = self.source_info(binding.span);
|
|
|
|
// For each pattern ident P of type T, `ref_for_guard` is
|
|
// a reference R: &T pointing to the location matched by
|
|
// the pattern, and every occurrence of P within a guard
|
|
// denotes *R.
|
|
let ref_for_guard = self.storage_live_binding(
|
|
block,
|
|
binding.var_id,
|
|
binding.span,
|
|
RefWithinGuard,
|
|
schedule_drops,
|
|
);
|
|
match binding.binding_mode {
|
|
BindingMode::ByValue => {
|
|
let rvalue = Rvalue::Ref(re_erased, BorrowKind::Shared, binding.source);
|
|
self.cfg.push_assign(block, source_info, ref_for_guard, rvalue);
|
|
}
|
|
BindingMode::ByRef(borrow_kind) => {
|
|
let value_for_arm = self.storage_live_binding(
|
|
block,
|
|
binding.var_id,
|
|
binding.span,
|
|
OutsideGuard,
|
|
schedule_drops,
|
|
);
|
|
|
|
let rvalue = Rvalue::Ref(re_erased, borrow_kind, binding.source);
|
|
self.cfg.push_assign(block, source_info, value_for_arm, rvalue);
|
|
let rvalue = Rvalue::Ref(re_erased, BorrowKind::Shared, value_for_arm);
|
|
self.cfg.push_assign(block, source_info, ref_for_guard, rvalue);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
fn bind_matched_candidate_for_arm_body<'b>(
|
|
&mut self,
|
|
block: BasicBlock,
|
|
schedule_drops: bool,
|
|
bindings: impl IntoIterator<Item = &'b Binding<'tcx>>,
|
|
) where
|
|
'tcx: 'b,
|
|
{
|
|
debug!("bind_matched_candidate_for_arm_body(block={:?})", block);
|
|
|
|
let re_erased = self.hir.tcx().lifetimes.re_erased;
|
|
// Assign each of the bindings. This may trigger moves out of the candidate.
|
|
for binding in bindings {
|
|
let source_info = self.source_info(binding.span);
|
|
let local = self.storage_live_binding(
|
|
block,
|
|
binding.var_id,
|
|
binding.span,
|
|
OutsideGuard,
|
|
schedule_drops,
|
|
);
|
|
if schedule_drops {
|
|
self.schedule_drop_for_binding(binding.var_id, binding.span, OutsideGuard);
|
|
}
|
|
let rvalue = match binding.binding_mode {
|
|
BindingMode::ByValue => Rvalue::Use(self.consume_by_copy_or_move(binding.source)),
|
|
BindingMode::ByRef(borrow_kind) => {
|
|
Rvalue::Ref(re_erased, borrow_kind, binding.source)
|
|
}
|
|
};
|
|
self.cfg.push_assign(block, source_info, local, rvalue);
|
|
}
|
|
}
|
|
|
|
/// Each binding (`ref mut var`/`ref var`/`mut var`/`var`, where the bound
|
|
/// `var` has type `T` in the arm body) in a pattern maps to 2 locals. The
|
|
/// first local is a binding for occurrences of `var` in the guard, which
|
|
/// will have type `&T`. The second local is a binding for occurrences of
|
|
/// `var` in the arm body, which will have type `T`.
|
|
fn declare_binding(
|
|
&mut self,
|
|
source_info: SourceInfo,
|
|
visibility_scope: SourceScope,
|
|
mutability: Mutability,
|
|
name: Symbol,
|
|
mode: BindingMode,
|
|
var_id: HirId,
|
|
var_ty: Ty<'tcx>,
|
|
user_ty: UserTypeProjections,
|
|
has_guard: ArmHasGuard,
|
|
opt_match_place: Option<(Option<Place<'tcx>>, Span)>,
|
|
pat_span: Span,
|
|
) {
|
|
debug!(
|
|
"declare_binding(var_id={:?}, name={:?}, mode={:?}, var_ty={:?}, \
|
|
visibility_scope={:?}, source_info={:?})",
|
|
var_id, name, mode, var_ty, visibility_scope, source_info
|
|
);
|
|
|
|
let tcx = self.hir.tcx();
|
|
let debug_source_info = SourceInfo { span: source_info.span, scope: visibility_scope };
|
|
let binding_mode = match mode {
|
|
BindingMode::ByValue => ty::BindingMode::BindByValue(mutability),
|
|
BindingMode::ByRef(_) => ty::BindingMode::BindByReference(mutability),
|
|
};
|
|
debug!("declare_binding: user_ty={:?}", user_ty);
|
|
let local = LocalDecl::<'tcx> {
|
|
mutability,
|
|
ty: var_ty,
|
|
user_ty: if user_ty.is_empty() { None } else { Some(box user_ty) },
|
|
source_info,
|
|
internal: false,
|
|
is_block_tail: None,
|
|
local_info: Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
|
|
binding_mode,
|
|
// hypothetically, `visit_bindings` could try to unzip
|
|
// an outermost hir::Ty as we descend, matching up
|
|
// idents in pat; but complex w/ unclear UI payoff.
|
|
// Instead, just abandon providing diagnostic info.
|
|
opt_ty_info: None,
|
|
opt_match_place,
|
|
pat_span,
|
|
})))),
|
|
};
|
|
let for_arm_body = self.local_decls.push(local);
|
|
self.var_debug_info.push(VarDebugInfo {
|
|
name,
|
|
source_info: debug_source_info,
|
|
place: for_arm_body.into(),
|
|
});
|
|
let locals = if has_guard.0 {
|
|
let ref_for_guard = self.local_decls.push(LocalDecl::<'tcx> {
|
|
// This variable isn't mutated but has a name, so has to be
|
|
// immutable to avoid the unused mut lint.
|
|
mutability: Mutability::Not,
|
|
ty: tcx.mk_imm_ref(tcx.lifetimes.re_erased, var_ty),
|
|
user_ty: None,
|
|
source_info,
|
|
internal: false,
|
|
is_block_tail: None,
|
|
local_info: Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::RefForGuard))),
|
|
});
|
|
self.var_debug_info.push(VarDebugInfo {
|
|
name,
|
|
source_info: debug_source_info,
|
|
place: ref_for_guard.into(),
|
|
});
|
|
LocalsForNode::ForGuard { ref_for_guard, for_arm_body }
|
|
} else {
|
|
LocalsForNode::One(for_arm_body)
|
|
};
|
|
debug!("declare_binding: vars={:?}", locals);
|
|
self.var_indices.insert(var_id, locals);
|
|
}
|
|
}
|