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Auto merge of #78801 - sexxi-goose:min_capture, r=nikomatsakis

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RFC-2229: Implement Precise Capture Analysis

### This PR introduces
- Feature gate for RFC-2229 (incomplete) `capture_disjoint_field`
- Rustc Attribute to print out the capture analysis `rustc_capture_analysis`
- Precise capture analysis

### Description of the analysis
1. If the feature gate is not set then all variables that are not local to the closure will be added to the list of captures. (This is for backcompat)
2. The rest of the analysis is based entirely on how the captured `Place`s are used within the closure. Precise information (i.e. projections) about the `Place` is maintained throughout.
3. To reduce the amount of information we need to keep track of, we do a minimization step. In this step, we determine a list such that no Place within this list represents an ancestor path to another entry in the list.  Check rust-lang/project-rfc-2229#9 for more detailed examples.
4. To keep the compiler functional as before we implement a Bridge between the results of this new analysis to existing data structures used for closure captures. Note the new capture analysis results are only part of MaybeTypeckTables that is the information is only available during typeck-ing.

### Known issues
- Statements like `let _ = x` will make the compiler ICE when used within a closure with the feature enabled. More generally speaking the issue is caused by `let` statements that create no bindings and are init'ed using a Place expression.

### Testing
We removed the code that would handle the case where the feature gate is not set, to enable the feature as default and did a bors try and perf run. More information here: #78762

### Thanks
This has been slowly in the works for a while now.
I want to call out `@Azhng` `@ChrisPardy` `@null-sleep` `@jenniferwills` `@logmosier` `@roxelo` for working on this and the previous PRs that led up to this, `@nikomatsakis` for guiding us.

Closes rust-lang/project-rfc-2229#7
Closes rust-lang/project-rfc-2229#9
Closes rust-lang/project-rfc-2229#6
Closes rust-lang/project-rfc-2229#19

r? `@nikomatsakis`
This commit is contained in:
bors 2020-11-17 03:56:03 +00:00
commit b5c37e86ff
37 changed files with 2484 additions and 177 deletions
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69
compiler/rustc_passes/src/liveness.rs
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@ -317,10 +317,11 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
// swap in a new set of IR maps for this body
let mut maps = IrMaps::new(self.tcx);
let hir_id = maps.tcx.hir().body_owner(body.id());
let def_id = maps.tcx.hir().local_def_id(hir_id);
let local_def_id = maps.tcx.hir().local_def_id(hir_id);
let def_id = local_def_id.to_def_id();
// Don't run unused pass for #[derive()]
if let Some(parent) = self.tcx.parent(def_id.to_def_id()) {
if let Some(parent) = self.tcx.parent(def_id) {
if let DefKind::Impl = self.tcx.def_kind(parent.expect_local()) {
if self.tcx.has_attr(parent, sym::automatically_derived) {
return;
@ -328,8 +329,8 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
}
}
if let Some(upvars) = maps.tcx.upvars_mentioned(def_id) {
for (&var_hir_id, _upvar) in upvars {
if let Some(captures) = maps.tcx.typeck(local_def_id).closure_captures.get(&def_id) {
for &var_hir_id in captures.keys() {
let var_name = maps.tcx.hir().name(var_hir_id);
maps.add_variable(Upvar(var_hir_id, var_name));
}
@ -340,7 +341,7 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
intravisit::walk_body(&mut maps, body);
// compute liveness
let mut lsets = Liveness::new(&mut maps, def_id);
let mut lsets = Liveness::new(&mut maps, local_def_id);
let entry_ln = lsets.compute(&body, hir_id);
lsets.log_liveness(entry_ln, body.id().hir_id);
@ -397,10 +398,18 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
// construction site.
let mut call_caps = Vec::new();
let closure_def_id = self.tcx.hir().local_def_id(expr.hir_id);
if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
call_caps.extend(upvars.iter().map(|(&var_id, upvar)| {
if let Some(captures) = self
.tcx
.typeck(closure_def_id)
.closure_captures
.get(&closure_def_id.to_def_id())
{
// If closure captures is Some, upvars_mentioned must also be Some
let upvars = self.tcx.upvars_mentioned(closure_def_id).unwrap();
call_caps.extend(captures.keys().map(|var_id| {
let upvar = upvars[var_id];
let upvar_ln = self.add_live_node(UpvarNode(upvar.span));
CaptureInfo { ln: upvar_ln, var_hid: var_id }
CaptureInfo { ln: upvar_ln, var_hid: *var_id }
}));
}
self.set_captures(expr.hir_id, call_caps);
@ -564,6 +573,7 @@ struct Liveness<'a, 'tcx> {
typeck_results: &'a ty::TypeckResults<'tcx>,
param_env: ty::ParamEnv<'tcx>,
upvars: Option<&'tcx FxIndexMap<hir::HirId, hir::Upvar>>,
closure_captures: Option<&'tcx FxIndexMap<hir::HirId, ty::UpvarId>>,
successors: IndexVec<LiveNode, Option<LiveNode>>,
rwu_table: RWUTable,
@ -587,6 +597,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
let typeck_results = ir.tcx.typeck(body_owner);
let param_env = ir.tcx.param_env(body_owner);
let upvars = ir.tcx.upvars_mentioned(body_owner);
let closure_captures = typeck_results.closure_captures.get(&body_owner.to_def_id());
let closure_ln = ir.add_live_node(ClosureNode);
let exit_ln = ir.add_live_node(ExitNode);
@ -600,6 +611,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
typeck_results,
param_env,
upvars,
closure_captures,
successors: IndexVec::from_elem_n(None, num_live_nodes),
rwu_table: RWUTable::new(num_live_nodes * num_vars),
closure_ln,
@ -850,14 +862,13 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
// if they are live on the entry to the closure, since only the closure
// itself can access them on subsequent calls.
if let Some(upvars) = self.upvars {
if let Some(closure_captures) = self.closure_captures {
// Mark upvars captured by reference as used after closure exits.
for (&var_hir_id, upvar) in upvars.iter().rev() {
let upvar_id = ty::UpvarId {
var_path: ty::UpvarPath { hir_id: var_hir_id },
closure_expr_id: self.body_owner,
};
match self.typeck_results.upvar_capture(upvar_id) {
// Since closure_captures is Some, upvars must exists too.
let upvars = self.upvars.unwrap();
for (&var_hir_id, upvar_id) in closure_captures {
let upvar = upvars[&var_hir_id];
match self.typeck_results.upvar_capture(*upvar_id) {
ty::UpvarCapture::ByRef(_) => {
let var = self.variable(var_hir_id, upvar.span);
self.acc(self.exit_ln, var, ACC_READ | ACC_USE);
@ -869,7 +880,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
let succ = self.propagate_through_expr(&body.value, self.exit_ln);
if self.upvars.is_none() {
if self.closure_captures.is_none() {
// Either not a closure, or closure without any captured variables.
// No need to determine liveness of captured variables, since there
// are none.
@ -1341,7 +1352,21 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
acc: u32,
) -> LiveNode {
match path.res {
Res::Local(hid) => self.access_var(hir_id, hid, succ, acc, path.span),
Res::Local(hid) => {
let in_upvars = self.upvars.map_or(false, |u| u.contains_key(&hid));
let in_captures = self.closure_captures.map_or(false, |c| c.contains_key(&hid));
match (in_upvars, in_captures) {
(false, _) | (true, true) => self.access_var(hir_id, hid, succ, acc, path.span),
(true, false) => {
// This case is possible when with RFC-2229, a wild pattern
// is used within a closure.
// eg: `let _ = x`. The closure doesn't capture x here,
// even though it's mentioned in the closure.
succ
}
}
}
_ => succ,
}
}
@ -1531,11 +1556,15 @@ impl<'tcx> Liveness<'_, 'tcx> {
}
fn warn_about_unused_upvars(&self, entry_ln: LiveNode) {
let upvars = match self.upvars {
let closure_captures = match self.closure_captures {
None => return,
Some(upvars) => upvars,
Some(closure_captures) => closure_captures,
};
for (&var_hir_id, upvar) in upvars.iter() {
// If closure_captures is Some(), upvars must be Some() too.
let upvars = self.upvars.unwrap();
for &var_hir_id in closure_captures.keys() {
let upvar = upvars[&var_hir_id];
let var = self.variable(var_hir_id, upvar.span);
let upvar_id = ty::UpvarId {
var_path: ty::UpvarPath { hir_id: var_hir_id },