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Use Places for captures in MIR

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- Use closure_min_capture maps to capture precise paths
- PlaceBuilder now searches for ancestors in min_capture list
- Add API to `Ty` to allow access to the n-th element in a
  tuple in O(1) time.

Co-authored-by: Roxane Fruytier <roxane.fruytier@hotmail.com>
This commit is contained in:
Aman Arora 2020-11-26 00:05:18 -05:00
parent d9523622ff
commit 6a1d0699a4
2 changed files with 137 additions and 22 deletions
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9
compiler/rustc_middle/src/ty/sty.rs
View File

@ -2174,6 +2174,15 @@ impl<'tcx> TyS<'tcx> {
}
}
/// Get the `i`-th element of a tuple.
/// Panics when called on anything but a tuple.
pub fn tuple_element_ty(&self, i: usize) -> Option<Ty<'tcx>> {
match self.kind() {
Tuple(substs) => substs.iter().nth(i).map(|field| field.expect_ty()),
_ => bug!("tuple_fields called on non-tuple"),
}
}
/// If the type contains variants, returns the valid range of variant indices.
//
// FIXME: This requires the optimized MIR in the case of generators.

150
compiler/rustc_mir_build/src/build/expr/as_place.rs
View File

@ -7,10 +7,12 @@ use crate::thir::*;
use rustc_hir::def_id::DefId;
use rustc_hir::HirId;
use rustc_middle::middle::region;
use rustc_middle::hir::place::ProjectionKind as HirProjectionKind;
use rustc_middle::mir::AssertKind::BoundsCheck;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt, Variance};
use rustc_span::Span;
use rustc_target::abi::VariantIdx;
use rustc_index::vec::Idx;
@ -70,28 +72,129 @@ struct PlaceBuilder<'tcx> {
projection: Vec<PlaceElem<'tcx>>,
}
fn capture_matching_projections<'a, 'tcx>(
/// Given a list of MIR projections, convert them to list of HIR ProjectionKind.
/// The projections are truncated to represent a path that might be captured by a
/// closure/generator. This implies the vector returned from this function doesn't contain
/// ProjectionElems `Downcast`, `ConstantIndex`, `Index`, or `Subslice` because those will never be
/// part of a path that is captued by a closure. We stop applying projections once we see the first
/// projection that isn't captured by a closure.
fn convert_to_hir_projections_and_truncate_for_capture<'tcx>(
mir_projections: &Vec<PlaceElem<'tcx>>,
) -> Vec<HirProjectionKind> {
let mut hir_projections = Vec::new();
for mir_projection in mir_projections {
let hir_projection = match mir_projection {
ProjectionElem::Deref => HirProjectionKind::Deref,
ProjectionElem::Field(field, _) => {
// We will never encouter this for multivariant enums,
// read the comment for `Downcast`.
HirProjectionKind::Field(field.index() as u32, VariantIdx::new(0))
},
ProjectionElem::Downcast(..) => {
// This projections exist only for enums that have
// multiple variants. Since such enums that are captured
// completely, we can stop here.
break
},
ProjectionElem::Index(..)
| ProjectionElem::ConstantIndex { .. }
| ProjectionElem::Subslice { .. } => {
// We don't capture array-access projections.
// We can stop here as arrays are captured completely.
break
},
};
hir_projections.push(hir_projection);
}
hir_projections
}
/// Return true if the `proj_possible_ancestor` represents an ancestor path
/// to `proj_capture` or `proj_possible_ancestor` is same as `proj_capture`,
/// assuming they both start off of the same root variable.
///
/// **Note:** It's the caller's responsibility to ensure that both lists of projections
/// start off of the same root variable.
///
/// Eg: 1. `foo.x` which is represented using `projections=[Field(x)]` is an ancestor of
/// `foo.x.y` which is represented using `projections=[Field(x), Field(y)]`.
/// Note both `foo.x` and `foo.x.y` start off of the same root variable `foo`.
/// 2. Since we only look at the projections here function will return `bar.x` as an a valid
/// ancestor of `foo.x.y`. It's the caller's responsibility to ensure that both projections
/// list are being applied to the same root variable.
fn is_ancestor_or_same_capture(
proj_possible_ancestor: &Vec<HirProjectionKind>,
proj_capture: &Vec<HirProjectionKind>,
) -> bool {
// We want to make sure `is_ancestor_or_same_capture("x.0.0", "x.0")` to return false.
// Therefore we can't just check if all projections are same in the zipped iterator below.
if proj_possible_ancestor.len() > proj_capture.len() {
return false;
}
proj_possible_ancestor.iter().zip(proj_capture).all(|(a, b)| a == b)
}
/// Computes the index of a capture within the desugared closure provided the closure's
/// `closure_min_captures` and the capture's index of the capture in the
/// `ty::MinCaptureList` of the root variable `var_hir_id`.
fn compute_capture_idx<'tcx>(
closure_min_captures: &ty::RootVariableMinCaptureList<'tcx>,
var_hir_id: HirId,
root_var_idx: usize,
) -> usize {
let mut res = 0;
for (var_id, capture_list) in closure_min_captures {
if *var_id == var_hir_id {
res += root_var_idx;
break;
} else {
res += capture_list.len();
}
}
res
}
/// Given a closure, returns the index of a capture within the desugared closure struct and the
/// `ty::CapturedPlace` which is the ancestor of the Place represented using the `var_hir_id`
/// and `projection`.
///
/// Note there will be at most one ancestor for any given Place.
///
/// Returns None, when the ancestor is not found.
fn find_capture_matching_projections<'a, 'tcx>(
typeck_results: &'a ty::TypeckResults<'tcx>,
var_hir_id: HirId,
closure_def_id: DefId,
_projections: &Vec<PlaceElem<'tcx>>,
) -> Option<(usize, ty::UpvarCapture<'tcx>)> {
typeck_results
.closure_captures
.get(&closure_def_id)
.and_then(|captures| captures.get_full(&var_hir_id))
.and_then(|(capture_index, _, _)|{
let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id.expect_local());
let capture_kind = typeck_results.upvar_capture(upvar_id);
Some((capture_index, capture_kind))
})
projections: &Vec<PlaceElem<'tcx>>,
) -> Option<(usize, &'a ty::CapturedPlace<'tcx>)> {
let closure_min_captures = typeck_results.closure_min_captures.get(&closure_def_id)?;
let root_variable_min_captures = closure_min_captures.get(&var_hir_id)?;
let hir_projections = convert_to_hir_projections_and_truncate_for_capture(projections);
// If an ancestor is found, `idx` is the index within the list of captured places
// for root variable `var_hir_id` and `capture` is the `ty::CapturedPlace` itself.
let (idx, capture) = root_variable_min_captures.iter().enumerate().find(|(_, capture)| {
let possible_ancestor_proj_kinds =
capture.place.projections.iter().map(|proj| proj.kind).collect();
is_ancestor_or_same_capture(&possible_ancestor_proj_kinds, &hir_projections)
})?;
// Convert index to be from the presepective of the entire closure_min_captures map
// instead of just the root variable capture list
Some((compute_capture_idx(closure_min_captures, var_hir_id, idx), capture))
}
/// Takes a PlaceBuilder and resolves the upvar (if any) within it,
/// so that the PlaceBuilder now starts from PlaceBase::Local.
/// Takes a PlaceBuilder and resolves the upvar (if any) within it, so that the
/// `PlaceBuilder` now starts from `PlaceBase::Local`.
///
/// Returns a Result with the error being the HirId of the
/// Upvar that was not found.
/// Returns a Result with the error being the HirId of the Upvar that was not found.
fn to_upvars_resolved_place_builder<'a, 'tcx>(
from_builder: PlaceBuilder<'tcx>,
tcx: TyCtxt<'tcx>,
@ -110,8 +213,8 @@ fn to_upvars_resolved_place_builder<'a, 'tcx>(
ty::ClosureKind::FnOnce => {}
}
let (capture_index, capture_kind) =
if let Some(capture_details) = capture_matching_projections(
let (capture_index, capture) =
if let Some(capture_details) = find_capture_matching_projections(
typeck_results,
var_hir_id,
closure_def_id,
@ -149,21 +252,24 @@ fn to_upvars_resolved_place_builder<'a, 'tcx>(
// Access the capture by accessing the field within the Closure struct.
//
// We must have inferred the capture types since we are building MIR, therefore
// it's safe to call `upvar_tys` and we can unwrap here because
// it's safe to call `tuple_element_ty` and we can unwrap here because
// we know that the capture exists and is the `capture_index`-th capture.
let var_ty = substs.upvar_tys().nth(capture_index).unwrap();
let var_ty = substs.tupled_upvars_ty().tuple_element_ty(capture_index).unwrap();
upvar_resolved_place_builder = upvar_resolved_place_builder.field(Field::new(capture_index), var_ty);
// If the variable is captured via ByRef(Immutable/Mutable) Borrow,
// we need to deref it
upvar_resolved_place_builder = match capture_kind {
upvar_resolved_place_builder = match capture.info.capture_kind {
ty::UpvarCapture::ByRef(_) => upvar_resolved_place_builder.deref(),
ty::UpvarCapture::ByValue(_) => upvar_resolved_place_builder,
};
let next_projection = 0;
let next_projection = capture.place.projections.len();
let mut curr_projections = from_builder.projection;
// We used some of the projections to build the capture itself,
// now we apply the remaining to the upvar resolved place.
upvar_resolved_place_builder.projection.extend(
curr_projections.drain(next_projection..));