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Split DepKindStruct in two.
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@cjgillot
cjgillot committed Feb 19, 2021
1 parent 1ac21e4 commit cdc0b19
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108 changes: 7 additions & 101 deletions compiler/rustc_middle/src/dep_graph/dep_node.rs
View file
Expand Up @@ -55,15 +55,13 @@
//!
//! [dependency graph]: https://rustc-dev-guide.rust-lang.org/query.html

use crate::ty::query::QueryCtxt;
use crate::ty::TyCtxt;

use rustc_data_structures::fingerprint::Fingerprint;
use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_INDEX};
use rustc_hir::definitions::DefPathHash;
use rustc_hir::HirId;
use rustc_span::symbol::Symbol;
use rustc_span::DUMMY_SP;
use std::hash::Hash;

pub use rustc_query_system::dep_graph::{DepContext, DepNodeParams};
Expand Down Expand Up @@ -92,53 +90,6 @@ pub struct DepKindStruct {
// FIXME: Make this a simple boolean once DepNodeParams::can_reconstruct_query_key
// can be made a specialized associated const.
can_reconstruct_query_key: fn() -> bool,

/// The red/green evaluation system will try to mark a specific DepNode in the
/// dependency graph as green by recursively trying to mark the dependencies of
/// that `DepNode` as green. While doing so, it will sometimes encounter a `DepNode`
/// where we don't know if it is red or green and we therefore actually have
/// to recompute its value in order to find out. Since the only piece of
/// information that we have at that point is the `DepNode` we are trying to
/// re-evaluate, we need some way to re-run a query from just that. This is what
/// `force_from_dep_node()` implements.
///
/// In the general case, a `DepNode` consists of a `DepKind` and an opaque
/// GUID/fingerprint that will uniquely identify the node. This GUID/fingerprint
/// is usually constructed by computing a stable hash of the query-key that the
/// `DepNode` corresponds to. Consequently, it is not in general possible to go
/// back from hash to query-key (since hash functions are not reversible). For
/// this reason `force_from_dep_node()` is expected to fail from time to time
/// because we just cannot find out, from the `DepNode` alone, what the
/// corresponding query-key is and therefore cannot re-run the query.
///
/// The system deals with this case letting `try_mark_green` fail which forces
/// the root query to be re-evaluated.
///
/// Now, if `force_from_dep_node()` would always fail, it would be pretty useless.
/// Fortunately, we can use some contextual information that will allow us to
/// reconstruct query-keys for certain kinds of `DepNode`s. In particular, we
/// enforce by construction that the GUID/fingerprint of certain `DepNode`s is a
/// valid `DefPathHash`. Since we also always build a huge table that maps every
/// `DefPathHash` in the current codebase to the corresponding `DefId`, we have
/// everything we need to re-run the query.
///
/// Take the `mir_promoted` query as an example. Like many other queries, it
/// just has a single parameter: the `DefId` of the item it will compute the
/// validated MIR for. Now, when we call `force_from_dep_node()` on a `DepNode`
/// with kind `MirValidated`, we know that the GUID/fingerprint of the `DepNode`
/// is actually a `DefPathHash`, and can therefore just look up the corresponding
/// `DefId` in `tcx.def_path_hash_to_def_id`.
///
/// When you implement a new query, it will likely have a corresponding new
/// `DepKind`, and you'll have to support it here in `force_from_dep_node()`. As
/// a rule of thumb, if your query takes a `DefId` or `LocalDefId` as sole parameter,
/// then `force_from_dep_node()` should not fail for it. Otherwise, you can just
/// add it to the "We don't have enough information to reconstruct..." group in
/// the match below.
pub(crate) force_from_dep_node: fn(tcx: QueryCtxt<'_>, dep_node: &DepNode) -> bool,

/// Invoke a query to put the on-disk cached value in memory.
pub(crate) try_load_from_on_disk_cache: fn(QueryCtxt<'_>, &DepNode),
}

impl std::ops::Deref for DepKind {
Expand Down Expand Up @@ -197,8 +148,7 @@ macro_rules! contains_eval_always_attr {
#[allow(non_upper_case_globals)]
pub mod dep_kind {
use super::*;
use crate::ty::query::{queries, query_keys};
use rustc_query_system::query::{force_query, QueryDescription};
use crate::ty::query::query_keys;

// We use this for most things when incr. comp. is turned off.
pub const Null: DepKindStruct = DepKindStruct {
Expand All @@ -207,8 +157,6 @@ pub mod dep_kind {
is_eval_always: false,

can_reconstruct_query_key: || true,
force_from_dep_node: |_, dep_node| bug!("force_from_dep_node: encountered {:?}", dep_node),
try_load_from_on_disk_cache: |_, _| {},
};

pub const TraitSelect: DepKindStruct = DepKindStruct {
Expand All @@ -217,8 +165,6 @@ pub mod dep_kind {
is_eval_always: false,

can_reconstruct_query_key: || true,
force_from_dep_node: |_, _| false,
try_load_from_on_disk_cache: |_, _| {},
};

pub const CompileCodegenUnit: DepKindStruct = DepKindStruct {
Expand All @@ -227,8 +173,6 @@ pub mod dep_kind {
is_eval_always: false,

can_reconstruct_query_key: || false,
force_from_dep_node: |_, _| false,
try_load_from_on_disk_cache: |_, _| {},
};

macro_rules! define_query_dep_kinds {
Expand All @@ -247,54 +191,11 @@ pub mod dep_kind {
::can_reconstruct_query_key()
}

fn recover<'tcx>(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<query_keys::$variant<'tcx>> {
<query_keys::$variant<'_> as DepNodeParams<TyCtxt<'_>>>::recover(tcx, dep_node)
}

fn force_from_dep_node(tcx: QueryCtxt<'_>, dep_node: &DepNode) -> bool {
if is_anon {
return false;
}

if !can_reconstruct_query_key() {
return false;
}

if let Some(key) = recover(*tcx, dep_node) {
force_query::<queries::$variant<'_>, _>(tcx, key, DUMMY_SP, *dep_node);
return true;
}

false
}

fn try_load_from_on_disk_cache(tcx: QueryCtxt<'_>, dep_node: &DepNode) {
if is_anon {
return
}

if !can_reconstruct_query_key() {
return
}

debug_assert!(tcx.dep_graph
.node_color(dep_node)
.map(|c| c.is_green())
.unwrap_or(false));

let key = recover(*tcx, dep_node).unwrap_or_else(|| panic!("Failed to recover key for {:?} with hash {}", dep_node, dep_node.hash));
if queries::$variant::cache_on_disk(tcx, &key, None) {
let _ = tcx.$variant(key);
}
}

DepKindStruct {
has_params,
is_anon,
is_eval_always,
can_reconstruct_query_key,
force_from_dep_node,
try_load_from_on_disk_cache,
}
};)*
);
Expand All @@ -310,7 +211,12 @@ macro_rules! define_dep_nodes {
$variant:ident $(( $tuple_arg_ty:ty $(,)? ))*
,)*
) => (
static DEP_KINDS: &[DepKindStruct] = &[ $(dep_kind::$variant),* ];
#[macro_export]
macro_rules! make_dep_kind_array {
($mod:ident) => {[ $(($mod::$variant),)* ]};
}

static DEP_KINDS: &[DepKindStruct] = &make_dep_kind_array!(dep_kind);

/// This enum serves as an index into the `DEP_KINDS` array.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_middle/src/dep_graph/mod.rs
View file
Expand Up @@ -3,6 +3,7 @@ use crate::ty::{self, TyCtxt};
use rustc_data_structures::profiling::SelfProfilerRef;
use rustc_data_structures::sync::Lock;

#[macro_use]
mod dep_node;

pub use rustc_query_system::dep_graph::{
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_middle/src/lib.rs
View file
Expand Up @@ -76,6 +76,7 @@ pub mod query;

#[macro_use]
pub mod arena;
#[macro_use]
pub mod dep_graph;
pub mod hir;
pub mod ich;
Expand Down
1 change: 1 addition & 0 deletions compiler/rustc_middle/src/ty/query/mod.rs
View file
Expand Up @@ -62,6 +62,7 @@ use std::sync::Arc;
#[macro_use]
mod plumbing;
pub use plumbing::QueryCtxt;
use plumbing::QueryStruct;
pub(crate) use rustc_query_system::query::CycleError;
use rustc_query_system::query::*;

Expand Down
143 changes: 141 additions & 2 deletions compiler/rustc_middle/src/ty/query/plumbing.rs
View file
Expand Up @@ -69,7 +69,8 @@ impl QueryContext for QueryCtxt<'tcx> {
}

fn try_load_from_on_disk_cache(&self, dep_node: &DepNode) {
(dep_node.kind.try_load_from_on_disk_cache)(*self, dep_node)
let cb = &super::QUERY_CALLBACKS[dep_node.kind as usize];
(cb.try_load_from_on_disk_cache)(*self, dep_node)
}

fn try_force_from_dep_node(&self, dep_node: &DepNode) -> bool {
Expand Down Expand Up @@ -126,7 +127,8 @@ impl QueryContext for QueryCtxt<'tcx> {
"calling force_from_dep_node() on DepKind::codegen_unit"
);

(dep_node.kind.force_from_dep_node)(*self, dep_node)
let cb = &super::QUERY_CALLBACKS[dep_node.kind as usize];
(cb.force_from_dep_node)(*self, dep_node)
}

fn has_errors_or_delayed_span_bugs(&self) -> bool {
Expand Down Expand Up @@ -307,6 +309,60 @@ impl<'tcx> Queries<'tcx> {
}
}

/// This struct stores metadata about each Query.
///
/// Information is retrieved by indexing the `QUERIES` array using the integer value
/// of the `DepKind`. Overall, this allows to implement `QueryContext` using this manual
/// jump table instead of large matches.
pub struct QueryStruct {
/// The red/green evaluation system will try to mark a specific DepNode in the
/// dependency graph as green by recursively trying to mark the dependencies of
/// that `DepNode` as green. While doing so, it will sometimes encounter a `DepNode`
/// where we don't know if it is red or green and we therefore actually have
/// to recompute its value in order to find out. Since the only piece of
/// information that we have at that point is the `DepNode` we are trying to
/// re-evaluate, we need some way to re-run a query from just that. This is what
/// `force_from_dep_node()` implements.
///
/// In the general case, a `DepNode` consists of a `DepKind` and an opaque
/// GUID/fingerprint that will uniquely identify the node. This GUID/fingerprint
/// is usually constructed by computing a stable hash of the query-key that the
/// `DepNode` corresponds to. Consequently, it is not in general possible to go
/// back from hash to query-key (since hash functions are not reversible). For
/// this reason `force_from_dep_node()` is expected to fail from time to time
/// because we just cannot find out, from the `DepNode` alone, what the
/// corresponding query-key is and therefore cannot re-run the query.
///
/// The system deals with this case letting `try_mark_green` fail which forces
/// the root query to be re-evaluated.
///
/// Now, if `force_from_dep_node()` would always fail, it would be pretty useless.
/// Fortunately, we can use some contextual information that will allow us to
/// reconstruct query-keys for certain kinds of `DepNode`s. In particular, we
/// enforce by construction that the GUID/fingerprint of certain `DepNode`s is a
/// valid `DefPathHash`. Since we also always build a huge table that maps every
/// `DefPathHash` in the current codebase to the corresponding `DefId`, we have
/// everything we need to re-run the query.
///
/// Take the `mir_promoted` query as an example. Like many other queries, it
/// just has a single parameter: the `DefId` of the item it will compute the
/// validated MIR for. Now, when we call `force_from_dep_node()` on a `DepNode`
/// with kind `MirValidated`, we know that the GUID/fingerprint of the `DepNode`
/// is actually a `DefPathHash`, and can therefore just look up the corresponding
/// `DefId` in `tcx.def_path_hash_to_def_id`.
///
/// When you implement a new query, it will likely have a corresponding new
/// `DepKind`, and you'll have to support it here in `force_from_dep_node()`. As
/// a rule of thumb, if your query takes a `DefId` or `LocalDefId` as sole parameter,
/// then `force_from_dep_node()` should not fail for it. Otherwise, you can just
/// add it to the "We don't have enough information to reconstruct..." group in
/// the match below.
pub(crate) force_from_dep_node: fn(tcx: QueryCtxt<'_>, dep_node: &DepNode) -> bool,

/// Invoke a query to put the on-disk cached value in memory.
pub(crate) try_load_from_on_disk_cache: fn(QueryCtxt<'_>, &DepNode),
}

macro_rules! handle_cycle_error {
([][$tcx: expr, $error:expr]) => {{
$tcx.report_cycle($error).emit();
Expand Down Expand Up @@ -545,6 +601,89 @@ macro_rules! define_queries {
}
})*

#[allow(non_upper_case_globals)]
pub mod query_callbacks {
use super::*;
use crate::dep_graph::DepNode;
use crate::ty::query::{queries, query_keys};
use rustc_query_system::dep_graph::DepNodeParams;
use rustc_query_system::query::{force_query, QueryDescription};

// We use this for most things when incr. comp. is turned off.
pub const Null: QueryStruct = QueryStruct {
force_from_dep_node: |_, dep_node| bug!("force_from_dep_node: encountered {:?}", dep_node),
try_load_from_on_disk_cache: |_, _| {},
};

pub const TraitSelect: QueryStruct = QueryStruct {
force_from_dep_node: |_, _| false,
try_load_from_on_disk_cache: |_, _| {},
};

pub const CompileCodegenUnit: QueryStruct = QueryStruct {
force_from_dep_node: |_, _| false,
try_load_from_on_disk_cache: |_, _| {},
};

$(pub const $name: QueryStruct = {
const is_anon: bool = is_anon!([$($modifiers)*]);

#[inline(always)]
fn can_reconstruct_query_key() -> bool {
<query_keys::$name<'_> as DepNodeParams<TyCtxt<'_>>>
::can_reconstruct_query_key()
}

fn recover<'tcx>(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<query_keys::$name<'tcx>> {
<query_keys::$name<'_> as DepNodeParams<TyCtxt<'_>>>::recover(tcx, dep_node)
}

fn force_from_dep_node(tcx: QueryCtxt<'_>, dep_node: &DepNode) -> bool {
if is_anon {
return false;
}

if !can_reconstruct_query_key() {
return false;
}

if let Some(key) = recover(*tcx, dep_node) {
force_query::<queries::$name<'_>, _>(tcx, key, DUMMY_SP, *dep_node);
return true;
}

false
}

fn try_load_from_on_disk_cache(tcx: QueryCtxt<'_>, dep_node: &DepNode) {
if is_anon {
return
}

if !can_reconstruct_query_key() {
return
}

debug_assert!(tcx.dep_graph
.node_color(dep_node)
.map(|c| c.is_green())
.unwrap_or(false));

let key = recover(*tcx, dep_node).unwrap_or_else(|| panic!("Failed to recover key for {:?} with hash {}", dep_node, dep_node.hash));
if queries::$name::cache_on_disk(tcx, &key, None) {
let _ = tcx.$name(key);
}
}

QueryStruct {
force_from_dep_node,
try_load_from_on_disk_cache,
}
};)*
}

static QUERY_CALLBACKS: &[QueryStruct] = &make_dep_kind_array!(query_callbacks);

define_provider_struct! {
tcx: $tcx,
input: ($(([$($modifiers)*] [$name] [$($K)*] [$V]))*)
Expand Down

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