1642 lines
64 KiB
Rust
1642 lines
64 KiB
Rust
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Code related to match expressions. These are sufficiently complex
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//! to warrant their own module and submodules. :) This main module
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//! includes the high-level algorithm, the submodules contain the
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//! details.
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use build::scope::{CachedBlock, DropKind};
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use build::ForGuard::{self, OutsideGuard, RefWithinGuard, ValWithinGuard};
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use build::{BlockAnd, BlockAndExtension, Builder};
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use build::{GuardFrame, GuardFrameLocal, LocalsForNode};
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use hair::*;
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use hair::pattern::PatternTypeProjections;
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use rustc::hir;
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use rustc::mir::*;
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use rustc::ty::{self, Ty};
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use rustc::ty::layout::VariantIdx;
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use rustc_data_structures::bit_set::BitSet;
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use rustc_data_structures::fx::FxHashMap;
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use syntax::ast::{Name, NodeId};
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use syntax_pos::Span;
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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::convert::TryFrom;
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/// ArmHasGuard is isomorphic to a boolean flag. It indicates whether
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/// a match arm has a guard expression attached to it.
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#[derive(Copy, Clone, Debug)]
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pub(crate) struct ArmHasGuard(pub bool);
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impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
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pub 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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discriminant: ExprRef<'tcx>,
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arms: Vec<Arm<'tcx>>,
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) -> BlockAnd<()> {
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let tcx = self.hir.tcx();
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let discriminant_span = discriminant.span();
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let discriminant_place = unpack!(block = self.as_place(block, discriminant));
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// Matching on a `discriminant_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 `discriminant_place`, specifically by applying `ReadForMatch`.
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//
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// NOTE: ReadForMatch also checks that the discriminant 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 source_info = self.source_info(discriminant_span);
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self.cfg.push(block, Statement {
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source_info,
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kind: StatementKind::FakeRead(
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FakeReadCause::ForMatchedPlace,
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discriminant_place.clone(),
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),
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});
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let mut arm_blocks = ArmBlocks {
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blocks: arms.iter().map(|_| self.cfg.start_new_block()).collect(),
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};
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// Get the arm bodies and their scopes, while declaring bindings.
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let arm_bodies: Vec<_> = arms.iter()
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.map(|arm| {
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// BUG: use arm lint level
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let body = self.hir.mirror(arm.body.clone());
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let scope = self.declare_bindings(
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None,
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body.span,
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LintLevel::Inherited,
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&arm.patterns[..],
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ArmHasGuard(arm.guard.is_some()),
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Some((Some(&discriminant_place), discriminant_span)),
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);
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(body, scope.unwrap_or(self.source_scope))
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})
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.collect();
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// create binding start block for link them by false edges
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let candidate_count = arms.iter().fold(0, |ac, c| ac + c.patterns.len());
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let pre_binding_blocks: Vec<_> = (0..candidate_count + 1)
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.map(|_| self.cfg.start_new_block())
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.collect();
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let mut has_guard = false;
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// assemble a list of candidates: there is one candidate per
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// pattern, which means there may be more than one candidate
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// *per arm*. These candidates are kept sorted such that the
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// highest priority candidate comes first in the list.
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// (i.e. same order as in source)
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let candidates: Vec<_> = arms.iter()
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.enumerate()
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.flat_map(|(arm_index, arm)| {
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arm.patterns
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.iter()
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.enumerate()
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.map(move |(pat_index, pat)| (arm_index, pat_index, pat, arm.guard.clone()))
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})
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.zip(
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pre_binding_blocks
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.iter()
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.zip(pre_binding_blocks.iter().skip(1)),
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)
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.map(
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|(
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(arm_index, pat_index, pattern, guard),
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(pre_binding_block, next_candidate_pre_binding_block)
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)| {
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has_guard |= guard.is_some();
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// One might ask: why not build up the match pair such that it
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// matches via `borrowed_input_temp.deref()` instead of
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// using the `discriminant_place` directly, as it is doing here?
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//
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// The basic answer is that if you do that, then you end up with
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// accceses to a shared borrow of the input and that conflicts with
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// any arms that look like e.g.
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//
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// match Some(&4) {
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// ref mut foo => {
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// ... /* mutate `foo` in arm body */ ...
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// }
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// }
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//
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// (Perhaps we could further revise the MIR
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// construction here so that it only does a
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// shared borrow at the outset and delays doing
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// the mutable borrow until after the pattern is
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// matched *and* the guard (if any) for the arm
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// has been run.)
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Candidate {
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span: pattern.span,
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match_pairs: vec![MatchPair::new(discriminant_place.clone(), pattern)],
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bindings: vec![],
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ascriptions: vec![],
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guard,
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arm_index,
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pat_index,
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pre_binding_block: *pre_binding_block,
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next_candidate_pre_binding_block: *next_candidate_pre_binding_block,
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}
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},
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)
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.collect();
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let outer_source_info = self.source_info(span);
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self.cfg.terminate(
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*pre_binding_blocks.last().unwrap(),
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outer_source_info,
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TerminatorKind::Unreachable,
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);
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// Maps a place to the kind of Fake borrow that we want to perform on
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// it: either Shallow or Shared, depending on whether the place is
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// bound in the match, or just switched on.
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// If there are no match guards then we don't need any fake borrows,
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// so don't track them.
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let mut fake_borrows = if has_guard && tcx.generate_borrow_of_any_match_input() {
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Some(FxHashMap::default())
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} else {
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None
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};
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let pre_binding_blocks: Vec<_> = candidates
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.iter()
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.map(|cand| (cand.pre_binding_block, cand.span))
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.collect();
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// this will generate code to test discriminant_place and
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// branch to the appropriate arm block
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let otherwise = self.match_candidates(
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discriminant_span,
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&mut arm_blocks,
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candidates,
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block,
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&mut fake_borrows,
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);
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if !otherwise.is_empty() {
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// All matches are exhaustive. However, because some matches
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// only have exponentially-large exhaustive decision trees, we
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// sometimes generate an inexhaustive decision tree.
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//
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// In that case, the inexhaustive tips of the decision tree
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// can't be reached - terminate them with an `unreachable`.
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let source_info = self.source_info(span);
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let mut otherwise = otherwise;
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otherwise.sort();
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otherwise.dedup(); // variant switches can introduce duplicate target blocks
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for block in otherwise {
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self.cfg
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.terminate(block, source_info, TerminatorKind::Unreachable);
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}
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}
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if let Some(fake_borrows) = fake_borrows {
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self.add_fake_borrows(&pre_binding_blocks, fake_borrows, source_info, block);
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}
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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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let outer_source_info = self.source_info(span);
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for (arm_index, (body, source_scope)) in arm_bodies.into_iter().enumerate() {
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let mut arm_block = arm_blocks.blocks[arm_index];
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// Re-enter the source scope we created the bindings in.
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self.source_scope = source_scope;
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unpack!(arm_block = self.into(destination, arm_block, body));
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self.cfg.terminate(
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arm_block,
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outer_source_info,
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TerminatorKind::Goto { target: end_block },
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);
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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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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: Pattern<'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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PatternKind::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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let place =
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self.storage_live_binding(block, var, irrefutable_pat.span, OutsideGuard);
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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(
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block,
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Statement {
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source_info,
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kind: StatementKind::FakeRead(FakeReadCause::ForLet, place),
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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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// 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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PatternKind::AscribeUserType {
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subpattern: Pattern {
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kind: box PatternKind::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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user_ty: pat_ascription_ty,
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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);
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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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self.cfg.push(
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block,
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Statement {
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source_info: pattern_source_info,
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kind: StatementKind::FakeRead(FakeReadCause::ForLet, place.clone()),
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},
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);
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let ty_source_info = self.source_info(user_ty_span);
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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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place,
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ty::Variance::Invariant,
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box pat_ascription_ty.user_ty(),
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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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pub fn place_into_pattern(
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&mut self,
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mut block: BasicBlock,
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irrefutable_pat: Pattern<'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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// create a dummy candidate
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let mut candidate = Candidate {
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span: irrefutable_pat.span,
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match_pairs: vec![MatchPair::new(initializer.clone(), &irrefutable_pat)],
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bindings: vec![],
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ascriptions: vec![],
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guard: None,
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// since we don't call `match_candidates`, next fields is unused
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arm_index: 0,
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pat_index: 0,
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pre_binding_block: block,
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next_candidate_pre_binding_block: block,
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};
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// Simplify the candidate. Since the pattern is irrefutable, this should
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// always convert all match-pairs into bindings.
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unpack!(block = self.simplify_candidate(block, &mut candidate));
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if !candidate.match_pairs.is_empty() {
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span_bug!(
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candidate.match_pairs[0].pattern.span,
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"match pairs {:?} remaining after simplifying \
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irrefutable pattern",
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candidate.match_pairs
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);
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}
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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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for binding in &candidate.bindings {
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let local = self.var_local_id(binding.var_id, OutsideGuard);
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if let Some(ClearCrossCrate::Set(BindingForm::Var(VarBindingForm {
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opt_match_place: Some((ref mut match_place, _)),
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..
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}))) = self.local_decls[local].is_user_variable
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{
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*match_place = Some(initializer.clone());
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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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}
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self.ascribe_types(block, &candidate.ascriptions);
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// now apply the bindings, which will also declare the variables
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self.bind_matched_candidate_for_arm_body(block, &candidate.bindings);
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block.unit()
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}
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/// Declares the bindings of the given patterns and returns the visibility
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/// scope for the bindings in these patterns, if such a scope had to be
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/// created. NOTE: Declaring the bindings should always be done in their
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/// drop scope.
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pub fn declare_bindings(
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&mut self,
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mut visibility_scope: Option<SourceScope>,
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scope_span: Span,
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lint_level: LintLevel,
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patterns: &[Pattern<'tcx>],
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has_guard: ArmHasGuard,
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opt_match_place: Option<(Option<&Place<'tcx>>, Span)>,
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) -> Option<SourceScope> {
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assert!(
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!(visibility_scope.is_some() && lint_level.is_explicit()),
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"can't have both a visibility and a lint scope at the same time"
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);
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let mut scope = self.source_scope;
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let num_patterns = patterns.len();
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self.visit_bindings(
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&patterns[0],
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&PatternTypeProjections::none(),
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&mut |this, mutability, name, mode, var, span, ty, user_ty| {
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if visibility_scope.is_none() {
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visibility_scope =
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Some(this.new_source_scope(scope_span, LintLevel::Inherited, None));
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// If we have lints, create a new source scope
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// that marks the lints for the locals. See the comment
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// on the `source_info` field for why this is needed.
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if lint_level.is_explicit() {
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scope = this.new_source_scope(scope_span, lint_level, None);
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}
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}
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let source_info = SourceInfo { span, scope };
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let visibility_scope = visibility_scope.unwrap();
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this.declare_binding(
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source_info,
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visibility_scope,
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mutability,
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name,
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mode,
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num_patterns,
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var,
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ty,
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user_ty,
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has_guard,
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opt_match_place.map(|(x, y)| (x.cloned(), y)),
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patterns[0].span,
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);
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},
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);
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visibility_scope
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}
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|
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pub fn storage_live_binding(
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&mut self,
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block: BasicBlock,
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var: NodeId,
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span: Span,
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for_guard: ForGuard,
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) -> Place<'tcx> {
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let local_id = self.var_local_id(var, for_guard);
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let source_info = self.source_info(span);
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self.cfg.push(
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block,
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Statement {
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source_info,
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kind: StatementKind::StorageLive(local_id),
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},
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);
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let place = Place::Local(local_id);
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let var_ty = self.local_decls[local_id].ty;
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let hir_id = self.hir.tcx().hir.node_to_hir_id(var);
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let region_scope = self.hir.region_scope_tree.var_scope(hir_id.local_id);
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self.schedule_drop(span, region_scope, &place, var_ty, DropKind::Storage);
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place
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}
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pub fn schedule_drop_for_binding(&mut self, var: NodeId, span: Span, for_guard: ForGuard) {
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let local_id = self.var_local_id(var, for_guard);
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let var_ty = self.local_decls[local_id].ty;
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let hir_id = self.hir.tcx().hir.node_to_hir_id(var);
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let region_scope = self.hir.region_scope_tree.var_scope(hir_id.local_id);
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self.schedule_drop(
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span,
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region_scope,
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&Place::Local(local_id),
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var_ty,
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DropKind::Value {
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cached_block: CachedBlock::default(),
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},
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);
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}
|
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|
|
pub(super) fn visit_bindings(
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&mut self,
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pattern: &Pattern<'tcx>,
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pattern_user_ty: &PatternTypeProjections<'tcx>,
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|
f: &mut impl FnMut(
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|
&mut Self,
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|
Mutability,
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Name,
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BindingMode,
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NodeId,
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Span,
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|
Ty<'tcx>,
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&PatternTypeProjections<'tcx>,
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),
|
|
) {
|
|
match *pattern.kind {
|
|
PatternKind::Binding {
|
|
mutability,
|
|
name,
|
|
mode,
|
|
var,
|
|
ty,
|
|
ref subpattern,
|
|
..
|
|
} => {
|
|
let pattern_ref_binding; // sidestep temp lifetime limitations.
|
|
let binding_user_ty = match mode {
|
|
BindingMode::ByValue => { pattern_user_ty }
|
|
BindingMode::ByRef(..) => {
|
|
// If this is a `ref` binding (e.g., `let ref
|
|
// x: T = ..`), then the type of `x` is not
|
|
// `T` but rather `&T`.
|
|
pattern_ref_binding = pattern_user_ty.ref_binding();
|
|
&pattern_ref_binding
|
|
}
|
|
};
|
|
|
|
f(self, mutability, name, mode, var, pattern.span, ty, binding_user_ty);
|
|
if let Some(subpattern) = subpattern.as_ref() {
|
|
self.visit_bindings(subpattern, pattern_user_ty, f);
|
|
}
|
|
}
|
|
PatternKind::Array {
|
|
ref prefix,
|
|
ref slice,
|
|
ref suffix,
|
|
}
|
|
| PatternKind::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.index(), f);
|
|
}
|
|
for subpattern in slice {
|
|
self.visit_bindings(subpattern, &pattern_user_ty.subslice(from, to), f);
|
|
}
|
|
for subpattern in suffix {
|
|
self.visit_bindings(subpattern, &pattern_user_ty.index(), f);
|
|
}
|
|
}
|
|
PatternKind::Constant { .. } | PatternKind::Range { .. } | PatternKind::Wild => {}
|
|
PatternKind::Deref { ref subpattern } => {
|
|
self.visit_bindings(subpattern, &pattern_user_ty.deref(), f);
|
|
}
|
|
PatternKind::AscribeUserType { ref subpattern, ref user_ty, user_ty_span } => {
|
|
// This corresponds to something like
|
|
//
|
|
// ```
|
|
// let A::<'a>(_): A<'static> = ...;
|
|
// ```
|
|
let subpattern_user_ty = pattern_user_ty.add_user_type(user_ty, user_ty_span);
|
|
self.visit_bindings(subpattern, &subpattern_user_ty, f)
|
|
}
|
|
|
|
PatternKind::Leaf { ref subpatterns } => {
|
|
for subpattern in subpatterns {
|
|
let subpattern_user_ty = pattern_user_ty.leaf(subpattern.field);
|
|
self.visit_bindings(&subpattern.pattern, &subpattern_user_ty, f);
|
|
}
|
|
}
|
|
|
|
PatternKind::Variant { adt_def, substs: _, variant_index, ref subpatterns } => {
|
|
for subpattern in subpatterns {
|
|
let subpattern_user_ty = pattern_user_ty.variant(
|
|
adt_def, variant_index, subpattern.field);
|
|
self.visit_bindings(&subpattern.pattern, &subpattern_user_ty, f);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// List of blocks for each arm (and potentially other metadata in the
|
|
/// future).
|
|
struct ArmBlocks {
|
|
blocks: Vec<BasicBlock>,
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
pub struct Candidate<'pat, 'tcx: 'pat> {
|
|
// span of the original pattern that gave rise to this candidate
|
|
span: Span,
|
|
|
|
// all of these must be satisfied...
|
|
match_pairs: Vec<MatchPair<'pat, 'tcx>>,
|
|
|
|
// ...these bindings established...
|
|
bindings: Vec<Binding<'tcx>>,
|
|
|
|
// ...these types asserted...
|
|
ascriptions: Vec<Ascription<'tcx>>,
|
|
|
|
// ...and the guard must be evaluated...
|
|
guard: Option<Guard<'tcx>>,
|
|
|
|
// ...and then we branch to arm with this index.
|
|
arm_index: usize,
|
|
|
|
// ...and the blocks for add false edges between candidates
|
|
pre_binding_block: BasicBlock,
|
|
next_candidate_pre_binding_block: BasicBlock,
|
|
|
|
// This uniquely identifies this candidate *within* the arm.
|
|
pat_index: usize,
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
struct Binding<'tcx> {
|
|
span: Span,
|
|
source: Place<'tcx>,
|
|
name: Name,
|
|
var_id: NodeId,
|
|
var_ty: Ty<'tcx>,
|
|
mutability: Mutability,
|
|
binding_mode: BindingMode<'tcx>,
|
|
}
|
|
|
|
/// 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: PatternTypeProjection<'tcx>,
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
pub struct MatchPair<'pat, 'tcx: 'pat> {
|
|
// this place...
|
|
place: Place<'tcx>,
|
|
|
|
// ... must match this pattern.
|
|
pattern: &'pat Pattern<'tcx>,
|
|
|
|
// HACK(eddyb) This is used to toggle whether a Slice pattern
|
|
// has had its length checked. This is only necessary because
|
|
// the "rest" part of the pattern right now has type &[T] and
|
|
// as such, it requires an Rvalue::Slice to be generated.
|
|
// See RFC 495 / issue #23121 for the eventual (proper) solution.
|
|
slice_len_checked: bool,
|
|
}
|
|
|
|
#[derive(Clone, Debug, PartialEq)]
|
|
enum TestKind<'tcx> {
|
|
// test the branches of enum
|
|
Switch {
|
|
adt_def: &'tcx ty::AdtDef,
|
|
variants: BitSet<VariantIdx>,
|
|
},
|
|
|
|
// test the branches of enum
|
|
SwitchInt {
|
|
switch_ty: Ty<'tcx>,
|
|
options: Vec<u128>,
|
|
indices: FxHashMap<&'tcx ty::Const<'tcx>, usize>,
|
|
},
|
|
|
|
// test for equality
|
|
Eq {
|
|
value: &'tcx ty::Const<'tcx>,
|
|
ty: Ty<'tcx>,
|
|
},
|
|
|
|
// test whether the value falls within an inclusive or exclusive range
|
|
Range {
|
|
lo: &'tcx ty::Const<'tcx>,
|
|
hi: &'tcx ty::Const<'tcx>,
|
|
ty: Ty<'tcx>,
|
|
end: hir::RangeEnd,
|
|
},
|
|
|
|
// test length of the slice is equal to len
|
|
Len {
|
|
len: u64,
|
|
op: BinOp,
|
|
},
|
|
}
|
|
|
|
#[derive(Debug)]
|
|
pub struct Test<'tcx> {
|
|
span: Span,
|
|
kind: TestKind<'tcx>,
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// Main matching algorithm
|
|
|
|
impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, '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 generate a branch to the appropriate
|
|
/// block found in `arm_blocks`.
|
|
///
|
|
/// The return value is a list of "otherwise" blocks. These are
|
|
/// points in execution where we found that *NONE* of the
|
|
/// candidates apply. 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 `add_fake_borrows` is true, then places which need fake borrows
|
|
/// will be added to it.
|
|
fn match_candidates<'pat>(
|
|
&mut self,
|
|
span: Span,
|
|
arm_blocks: &mut ArmBlocks,
|
|
mut candidates: Vec<Candidate<'pat, 'tcx>>,
|
|
mut block: BasicBlock,
|
|
fake_borrows: &mut Option<FxHashMap<Place<'tcx>, BorrowKind>>,
|
|
) -> Vec<BasicBlock> {
|
|
debug!(
|
|
"matched_candidate(span={:?}, block={:?}, candidates={:?})",
|
|
span, block, candidates
|
|
);
|
|
|
|
// 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.
|
|
for candidate in &mut candidates {
|
|
unpack!(block = self.simplify_candidate(block, candidate));
|
|
}
|
|
|
|
// The candidates are sorted by priority. Check to see
|
|
// whether the higher priority candidates (and hence at
|
|
// the front of the vec) 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 mut unmatched_candidates = candidates.split_off(fully_matched);
|
|
|
|
// Insert a *Shared* borrow of any places that are bound.
|
|
if let Some(fake_borrows) = fake_borrows {
|
|
for Binding { source, .. }
|
|
in candidates.iter().flat_map(|candidate| &candidate.bindings)
|
|
{
|
|
fake_borrows.insert(source.clone(), BorrowKind::Shared);
|
|
}
|
|
}
|
|
|
|
let fully_matched_with_guard = candidates.iter().take_while(|c| c.guard.is_some()).count();
|
|
|
|
let unreachable_candidates = if fully_matched_with_guard + 1 < candidates.len() {
|
|
candidates.split_off(fully_matched_with_guard + 1)
|
|
} else {
|
|
vec![]
|
|
};
|
|
|
|
for candidate in candidates {
|
|
// If so, apply any bindings, test the guard (if any), and
|
|
// branch to the arm.
|
|
if let Some(b) = self.bind_and_guard_matched_candidate(block, arm_blocks, candidate) {
|
|
block = b;
|
|
} else {
|
|
// if None is returned, then any remaining candidates
|
|
// are unreachable (at least not through this path).
|
|
// Link them with false edges.
|
|
debug!(
|
|
"match_candidates: add false edges for unreachable {:?} and unmatched {:?}",
|
|
unreachable_candidates, unmatched_candidates
|
|
);
|
|
for candidate in unreachable_candidates {
|
|
let source_info = self.source_info(candidate.span);
|
|
let target = self.cfg.start_new_block();
|
|
if let Some(otherwise) =
|
|
self.bind_and_guard_matched_candidate(target, arm_blocks, candidate)
|
|
{
|
|
self.cfg
|
|
.terminate(otherwise, source_info, TerminatorKind::Unreachable);
|
|
}
|
|
}
|
|
|
|
if unmatched_candidates.is_empty() {
|
|
return vec![];
|
|
} else {
|
|
let target = self.cfg.start_new_block();
|
|
return self.match_candidates(
|
|
span,
|
|
arm_blocks,
|
|
unmatched_candidates,
|
|
target,
|
|
&mut None,
|
|
);
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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() {
|
|
return vec![block];
|
|
}
|
|
|
|
// Test candidates where possible.
|
|
let (otherwise, tested_candidates) =
|
|
self.test_candidates(span, arm_blocks, &unmatched_candidates, block, fake_borrows);
|
|
|
|
// If the target candidates were exhaustive, then we are done.
|
|
// But for borrowck continue build decision tree.
|
|
|
|
// If all candidates were sorted into `target_candidates` somewhere, then
|
|
// the initial set was inexhaustive.
|
|
let untested_candidates = unmatched_candidates.split_off(tested_candidates);
|
|
if untested_candidates.len() == 0 {
|
|
return otherwise;
|
|
}
|
|
|
|
// Otherwise, let's process those remaining candidates.
|
|
let join_block = self.join_otherwise_blocks(span, otherwise);
|
|
self.match_candidates(span, arm_blocks, untested_candidates, join_block, &mut None)
|
|
}
|
|
|
|
fn join_otherwise_blocks(&mut self, span: Span, mut otherwise: Vec<BasicBlock>) -> BasicBlock {
|
|
let source_info = self.source_info(span);
|
|
otherwise.sort();
|
|
otherwise.dedup(); // variant switches can introduce duplicate target blocks
|
|
if otherwise.len() == 1 {
|
|
otherwise[0]
|
|
} else {
|
|
let join_block = self.cfg.start_new_block();
|
|
for block in otherwise {
|
|
self.cfg.terminate(
|
|
block,
|
|
source_info,
|
|
TerminatorKind::Goto { target: join_block },
|
|
);
|
|
}
|
|
join_block
|
|
}
|
|
}
|
|
|
|
/// 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
|
|
/// test 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>(
|
|
&mut self,
|
|
span: Span,
|
|
arm_blocks: &mut ArmBlocks,
|
|
candidates: &[Candidate<'pat, 'tcx>],
|
|
block: BasicBlock,
|
|
fake_borrows: &mut Option<FxHashMap<Place<'tcx>, BorrowKind>>,
|
|
) -> (Vec<BasicBlock>, usize) {
|
|
// 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);
|
|
|
|
// 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_pair.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_pair.place, candidate, variants) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
_ => {}
|
|
}
|
|
|
|
// Insert a Shallow borrow of any places that is switched on.
|
|
fake_borrows.as_mut().map(|fb| {
|
|
fb.entry(match_pair.place.clone()).or_insert(BorrowKind::Shallow)
|
|
});
|
|
|
|
// 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 target_blocks = self.perform_test(block, &match_pair.place, &test);
|
|
let mut target_candidates: Vec<_> = (0..target_blocks.len()).map(|_| vec![]).collect();
|
|
|
|
// 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.
|
|
let tested_candidates = candidates
|
|
.iter()
|
|
.take_while(|c| {
|
|
self.sort_candidate(&match_pair.place, &test, c, &mut target_candidates)
|
|
})
|
|
.count();
|
|
assert!(tested_candidates > 0); // at least the last candidate ought to be tested
|
|
debug!("tested_candidates: {}", tested_candidates);
|
|
debug!(
|
|
"untested_candidates: {}",
|
|
candidates.len() - tested_candidates
|
|
);
|
|
|
|
// 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 otherwise: Vec<_> = target_blocks
|
|
.into_iter()
|
|
.zip(target_candidates)
|
|
.flat_map(|(target_block, target_candidates)| {
|
|
self.match_candidates(
|
|
span,
|
|
arm_blocks,
|
|
target_candidates,
|
|
target_block,
|
|
fake_borrows,
|
|
)
|
|
})
|
|
.collect();
|
|
|
|
(otherwise, tested_candidates)
|
|
}
|
|
|
|
/// 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 check earlier that if there is a guard, there cannot
|
|
/// be move bindings. This isn't really important for the
|
|
/// self-consistency of this fn, but the reason for it should be
|
|
/// clear: after we've done the assignments, if there were move
|
|
/// bindings, further tests would be a use-after-move (which would
|
|
/// in turn be detected by the borrowck code that runs on the
|
|
/// MIR).
|
|
fn bind_and_guard_matched_candidate<'pat>(
|
|
&mut self,
|
|
mut block: BasicBlock,
|
|
arm_blocks: &mut ArmBlocks,
|
|
candidate: Candidate<'pat, 'tcx>,
|
|
) -> Option<BasicBlock> {
|
|
debug!(
|
|
"bind_and_guard_matched_candidate(block={:?}, candidate={:?})",
|
|
block, candidate
|
|
);
|
|
|
|
debug_assert!(candidate.match_pairs.is_empty());
|
|
|
|
self.ascribe_types(block, &candidate.ascriptions);
|
|
|
|
let arm_block = arm_blocks.blocks[candidate.arm_index];
|
|
let candidate_source_info = self.source_info(candidate.span);
|
|
|
|
self.cfg.terminate(
|
|
block,
|
|
candidate_source_info,
|
|
TerminatorKind::Goto {
|
|
target: candidate.pre_binding_block,
|
|
},
|
|
);
|
|
|
|
block = self.cfg.start_new_block();
|
|
self.cfg.terminate(
|
|
candidate.pre_binding_block,
|
|
candidate_source_info,
|
|
TerminatorKind::FalseEdges {
|
|
real_target: block,
|
|
imaginary_targets: vec![candidate.next_candidate_pre_binding_block],
|
|
},
|
|
);
|
|
|
|
// 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
|
|
// a reference that we do not immediately have at hand
|
|
// (because all we have is the places associated with the
|
|
// match input itself; it is up to us to create a place
|
|
// holding a `&` or `&mut` that we can then borrow).
|
|
|
|
let autoref = self.hir
|
|
.tcx()
|
|
.all_pat_vars_are_implicit_refs_within_guards();
|
|
if let Some(guard) = candidate.guard {
|
|
if autoref {
|
|
self.bind_matched_candidate_for_guard(
|
|
block,
|
|
candidate.pat_index,
|
|
&candidate.bindings,
|
|
);
|
|
let guard_frame = GuardFrame {
|
|
locals: candidate
|
|
.bindings
|
|
.iter()
|
|
.map(|b| GuardFrameLocal::new(b.var_id, b.binding_mode))
|
|
.collect(),
|
|
};
|
|
debug!("Entering guard building context: {:?}", guard_frame);
|
|
self.guard_context.push(guard_frame);
|
|
} else {
|
|
self.bind_matched_candidate_for_arm_body(block, &candidate.bindings);
|
|
}
|
|
|
|
// 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),
|
|
};
|
|
let source_info = self.source_info(guard.span);
|
|
let cond = unpack!(block = self.as_local_operand(block, guard));
|
|
if autoref {
|
|
let guard_frame = self.guard_context.pop().unwrap();
|
|
debug!(
|
|
"Exiting guard building context with locals: {:?}",
|
|
guard_frame
|
|
);
|
|
}
|
|
|
|
let false_edge_block = self.cfg.start_new_block();
|
|
|
|
// 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 `arm_block` 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 post_guard_block = self.cfg.start_new_block();
|
|
self.cfg.terminate(
|
|
block,
|
|
source_info,
|
|
TerminatorKind::if_(self.hir.tcx(), cond, post_guard_block, false_edge_block),
|
|
);
|
|
|
|
if autoref {
|
|
self.bind_matched_candidate_for_arm_body(post_guard_block, &candidate.bindings);
|
|
}
|
|
|
|
self.cfg.terminate(
|
|
post_guard_block,
|
|
source_info,
|
|
TerminatorKind::Goto { target: arm_block },
|
|
);
|
|
|
|
let otherwise = self.cfg.start_new_block();
|
|
|
|
self.cfg.terminate(
|
|
false_edge_block,
|
|
source_info,
|
|
TerminatorKind::FalseEdges {
|
|
real_target: otherwise,
|
|
imaginary_targets: vec![candidate.next_candidate_pre_binding_block],
|
|
},
|
|
);
|
|
Some(otherwise)
|
|
} 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, &candidate.bindings);
|
|
self.cfg.terminate(
|
|
block,
|
|
candidate_source_info,
|
|
TerminatorKind::Goto { target: arm_block },
|
|
);
|
|
None
|
|
}
|
|
}
|
|
|
|
/// Append `AscribeUserType` statements onto the end of `block`
|
|
/// for each ascription
|
|
fn ascribe_types<'pat>(
|
|
&mut self,
|
|
block: BasicBlock,
|
|
ascriptions: &[Ascription<'tcx>],
|
|
) {
|
|
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,
|
|
);
|
|
|
|
self.cfg.push(
|
|
block,
|
|
Statement {
|
|
source_info,
|
|
kind: StatementKind::AscribeUserType(
|
|
ascription.source.clone(),
|
|
ty::Variance::Covariant,
|
|
box ascription.user_ty.clone().user_ty(),
|
|
),
|
|
},
|
|
);
|
|
}
|
|
}
|
|
|
|
// Only called when all_pat_vars_are_implicit_refs_within_guards,
|
|
// and thus all code/comments assume we are in that context.
|
|
fn bind_matched_candidate_for_guard(
|
|
&mut self,
|
|
block: BasicBlock,
|
|
pat_index: usize,
|
|
bindings: &[Binding<'tcx>],
|
|
) {
|
|
debug!(
|
|
"bind_matched_candidate_for_guard(block={:?}, pat_index={:?}, bindings={:?})",
|
|
block, pat_index, bindings
|
|
);
|
|
|
|
// Assign each of the bindings. Since we are binding for a
|
|
// guard expression, this will never trigger moves out of the
|
|
// candidate.
|
|
let re_empty = self.hir.tcx().types.re_empty;
|
|
for binding in bindings {
|
|
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);
|
|
// Question: Why schedule drops if bindings are all
|
|
// shared-&'s? Answer: Because schedule_drop_for_binding
|
|
// also emits StorageDead's for those locals.
|
|
self.schedule_drop_for_binding(binding.var_id, binding.span, RefWithinGuard);
|
|
match binding.binding_mode {
|
|
BindingMode::ByValue => {
|
|
let rvalue = Rvalue::Ref(re_empty, BorrowKind::Shared, binding.source.clone());
|
|
self.cfg
|
|
.push_assign(block, source_info, &ref_for_guard, rvalue);
|
|
}
|
|
BindingMode::ByRef(region, borrow_kind) => {
|
|
// Tricky business: For `ref id` and `ref mut id`
|
|
// patterns, we want `id` within the guard to
|
|
// correspond to a temp of type `& &T` or `& &mut
|
|
// T` (i.e. a "borrow of a borrow") that is
|
|
// implicitly dereferenced.
|
|
//
|
|
// To borrow a borrow, we need that inner borrow
|
|
// to point to. So, create a temp for the inner
|
|
// borrow, and then take a reference to it.
|
|
//
|
|
// Note: the temp created here is *not* the one
|
|
// used by the arm body itself. This eases
|
|
// observing two-phase borrow restrictions.
|
|
let val_for_guard = self.storage_live_binding(
|
|
block,
|
|
binding.var_id,
|
|
binding.span,
|
|
ValWithinGuard(pat_index),
|
|
);
|
|
self.schedule_drop_for_binding(
|
|
binding.var_id,
|
|
binding.span,
|
|
ValWithinGuard(pat_index),
|
|
);
|
|
|
|
// rust-lang/rust#27282: We reuse the two-phase
|
|
// borrow infrastructure so that the mutable
|
|
// borrow (whose mutabilty is *unusable* within
|
|
// the guard) does not conflict with the implicit
|
|
// borrow of the whole match input. See additional
|
|
// discussion on rust-lang/rust#49870.
|
|
let borrow_kind = match borrow_kind {
|
|
BorrowKind::Shared
|
|
| BorrowKind::Shallow
|
|
| BorrowKind::Unique => borrow_kind,
|
|
BorrowKind::Mut { .. } => BorrowKind::Mut {
|
|
allow_two_phase_borrow: true,
|
|
},
|
|
};
|
|
let rvalue = Rvalue::Ref(region, borrow_kind, binding.source.clone());
|
|
self.cfg
|
|
.push_assign(block, source_info, &val_for_guard, rvalue);
|
|
let rvalue = Rvalue::Ref(region, BorrowKind::Shared, val_for_guard);
|
|
self.cfg
|
|
.push_assign(block, source_info, &ref_for_guard, rvalue);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
fn bind_matched_candidate_for_arm_body(
|
|
&mut self,
|
|
block: BasicBlock,
|
|
bindings: &[Binding<'tcx>],
|
|
) {
|
|
debug!(
|
|
"bind_matched_candidate_for_arm_body(block={:?}, bindings={:?}",
|
|
block, bindings
|
|
);
|
|
|
|
// 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);
|
|
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.clone()))
|
|
}
|
|
BindingMode::ByRef(region, borrow_kind) => {
|
|
Rvalue::Ref(region, borrow_kind, binding.source.clone())
|
|
}
|
|
};
|
|
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+N` locals. The first local is a binding for
|
|
/// occurrences of `var` in the guard, which will all have type
|
|
/// `&T`. The N locals are bindings for the `T` that is referenced
|
|
/// by the first local; they are not used outside of the
|
|
/// guard. The last local is a binding for occurrences of `var` in
|
|
/// the arm body, which will have type `T`.
|
|
///
|
|
/// The reason we have N locals rather than just 1 is to
|
|
/// accommodate rust-lang/rust#51348: If the arm has N candidate
|
|
/// patterns, then in general they can correspond to distinct
|
|
/// parts of the matched data, and we want them to be distinct
|
|
/// temps in order to simplify checks performed by our internal
|
|
/// leveraging of two-phase borrows).
|
|
fn declare_binding(
|
|
&mut self,
|
|
source_info: SourceInfo,
|
|
visibility_scope: SourceScope,
|
|
mutability: Mutability,
|
|
name: Name,
|
|
mode: BindingMode,
|
|
num_patterns: usize,
|
|
var_id: NodeId,
|
|
var_ty: Ty<'tcx>,
|
|
user_var_ty: &PatternTypeProjections<'tcx>,
|
|
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 binding_mode = match mode {
|
|
BindingMode::ByValue => ty::BindingMode::BindByValue(mutability.into()),
|
|
BindingMode::ByRef { .. } => ty::BindingMode::BindByReference(mutability.into()),
|
|
};
|
|
let local = LocalDecl::<'tcx> {
|
|
mutability,
|
|
ty: var_ty,
|
|
user_ty: user_var_ty.clone().user_ty(),
|
|
name: Some(name),
|
|
source_info,
|
|
visibility_scope,
|
|
internal: false,
|
|
is_block_tail: None,
|
|
is_user_variable: Some(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.clone());
|
|
let locals = if has_guard.0 && tcx.all_pat_vars_are_implicit_refs_within_guards() {
|
|
let mut vals_for_guard = Vec::with_capacity(num_patterns);
|
|
for _ in 0..num_patterns {
|
|
let val_for_guard_idx = self.local_decls.push(LocalDecl {
|
|
// This variable isn't mutated but has a name, so has to be
|
|
// immutable to avoid the unused mut lint.
|
|
mutability: Mutability::Not,
|
|
..local.clone()
|
|
});
|
|
vals_for_guard.push(val_for_guard_idx);
|
|
}
|
|
let ref_for_guard = self.local_decls.push(LocalDecl::<'tcx> {
|
|
// See previous comment.
|
|
mutability: Mutability::Not,
|
|
ty: tcx.mk_imm_ref(tcx.types.re_empty, var_ty),
|
|
user_ty: UserTypeProjections::none(),
|
|
name: Some(name),
|
|
source_info,
|
|
visibility_scope,
|
|
// FIXME: should these secretly injected ref_for_guard's be marked as `internal`?
|
|
internal: false,
|
|
is_block_tail: None,
|
|
is_user_variable: Some(ClearCrossCrate::Set(BindingForm::RefForGuard)),
|
|
});
|
|
LocalsForNode::ForGuard {
|
|
vals_for_guard,
|
|
ref_for_guard,
|
|
for_arm_body,
|
|
}
|
|
} else {
|
|
LocalsForNode::One(for_arm_body)
|
|
};
|
|
debug!("declare_binding: vars={:?}", locals);
|
|
self.var_indices.insert(var_id, locals);
|
|
}
|
|
|
|
// Determine the fake borrows that are needed to ensure that the place
|
|
// will evaluate to the same thing until an arm has been chosen.
|
|
fn add_fake_borrows<'pat>(
|
|
&mut self,
|
|
pre_binding_blocks: &[(BasicBlock, Span)],
|
|
fake_borrows: FxHashMap<Place<'tcx>, BorrowKind>,
|
|
source_info: SourceInfo,
|
|
start_block: BasicBlock,
|
|
) {
|
|
let tcx = self.hir.tcx();
|
|
|
|
debug!("add_fake_borrows pre_binding_blocks = {:?}, fake_borrows = {:?}",
|
|
pre_binding_blocks, 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, borrow_kind) in fake_borrows
|
|
{
|
|
{
|
|
let mut prefix_cursor = &place;
|
|
while let Place::Projection(box Projection { base, elem }) = prefix_cursor {
|
|
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((base.clone(), BorrowKind::Shallow));
|
|
}
|
|
prefix_cursor = base;
|
|
}
|
|
}
|
|
|
|
all_fake_borrows.push((place, borrow_kind));
|
|
}
|
|
|
|
// Deduplicate and ensure a deterministic order.
|
|
all_fake_borrows.sort();
|
|
all_fake_borrows.dedup();
|
|
|
|
debug!("add_fake_borrows all_fake_borrows = {:?}", all_fake_borrows);
|
|
|
|
// Add fake borrows to the start of the match and reads of them before
|
|
// the start of each arm.
|
|
let mut borrowed_input_temps = Vec::with_capacity(all_fake_borrows.len());
|
|
|
|
for (matched_place, borrow_kind) in all_fake_borrows {
|
|
let borrowed_input =
|
|
Rvalue::Ref(tcx.types.re_empty, borrow_kind, matched_place.clone());
|
|
let borrowed_input_ty = borrowed_input.ty(&self.local_decls, tcx);
|
|
let borrowed_input_temp = self.temp(borrowed_input_ty, source_info.span);
|
|
self.cfg.push_assign(
|
|
start_block,
|
|
source_info,
|
|
&borrowed_input_temp,
|
|
borrowed_input
|
|
);
|
|
borrowed_input_temps.push(borrowed_input_temp);
|
|
}
|
|
|
|
// FIXME: This could be a lot of reads (#fake borrows * #patterns).
|
|
// The false edges that we currently generate would allow us to only do
|
|
// this on the last Candidate, but it's possible that there might not be
|
|
// so many false edges in the future, so we read for all Candidates for
|
|
// now.
|
|
// Another option would be to make our own block and add our own false
|
|
// edges to it.
|
|
if tcx.emit_read_for_match() {
|
|
for &(pre_binding_block, span) in pre_binding_blocks {
|
|
let pattern_source_info = self.source_info(span);
|
|
for temp in &borrowed_input_temps {
|
|
self.cfg.push(pre_binding_block, Statement {
|
|
source_info: pattern_source_info,
|
|
kind: StatementKind::FakeRead(
|
|
FakeReadCause::ForMatchGuard,
|
|
temp.clone(),
|
|
),
|
|
});
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|