Auto merge of #131422 - GnomedDev:smallvec-predicate-obligations, r=c…

…ompiler-errors Use `ThinVec` for PredicateObligation storage ~~I noticed while profiling clippy on a project that a large amount of time is being spent allocating `Vec`s for `PredicateObligation`, and the `Vec`s are often quite small. This is an attempt to optimise this by using SmallVec to avoid heap allocations for these common small Vecs.~~ This PR turns all the `Vec<PredicateObligation>` into a single type alias while avoiding referring to `Vec` around it, then swaps the type over to `ThinVec<PredicateObligation>` and fixes the fallout. This also contains an implementation of `ThinVec::extract_if`, copied from `Vec::extract_if` and currently being upstreamed to Gankra/thin-vec#66. This leads to a small (0.2-0.7%) performance gain in the latest perf run.
rust-lang · Oct 14, 2024 · 2bc47d2 · 2bc47d2
2 parents 17a19e6 + 8de8f46
commit 2bc47d2
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diff --git a/Cargo.lock b/Cargo.lock
@@ -1,6 +1,6 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "addr2line"
@@ -3857,6 +3857,7 @@ dependencies = [
  "rustc_target",
  "rustc_type_ir",
  "smallvec",
+ "thin-vec",
  "tracing",
 ]
 
@@ -4490,6 +4491,7 @@ dependencies = [
  "rustc_transmute",
  "rustc_type_ir",
  "smallvec",
+ "thin-vec",
  "tracing",
 ]
 
@@ -4561,6 +4563,7 @@ dependencies = [
  "rustc_span",
  "rustc_type_ir_macros",
  "smallvec",
+ "thin-vec",
  "tracing",
 ]
 

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -18,6 +18,7 @@ use rustc_infer::infer::region_constraints::RegionConstraintData;
 use rustc_infer::infer::{
     BoundRegion, BoundRegionConversionTime, InferCtxt, NllRegionVariableOrigin,
 };
+use rustc_infer::traits::PredicateObligations;
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::visit::{NonMutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
@@ -40,7 +41,6 @@ use rustc_span::source_map::Spanned;
 use rustc_span::symbol::sym;
 use rustc_span::{DUMMY_SP, Span};
 use rustc_target::abi::{FIRST_VARIANT, FieldIdx};
-use rustc_trait_selection::traits::PredicateObligation;
 use rustc_trait_selection::traits::query::type_op::custom::{
     CustomTypeOp, scrape_region_constraints,
 };
@@ -2940,7 +2940,7 @@ impl NormalizeLocation for Location {
 pub(super) struct InstantiateOpaqueType<'tcx> {
     pub base_universe: Option<ty::UniverseIndex>,
     pub region_constraints: Option<RegionConstraintData<'tcx>>,
-    pub obligations: Vec<PredicateObligation<'tcx>>,
+    pub obligations: PredicateObligations<'tcx>,
 }
 
 impl<'tcx> TypeOp<'tcx> for InstantiateOpaqueType<'tcx> {

diff --git a/compiler/rustc_data_structures/src/lib.rs b/compiler/rustc_data_structures/src/lib.rs
@@ -76,6 +76,7 @@ pub mod svh;
 pub mod sync;
 pub mod tagged_ptr;
 pub mod temp_dir;
+pub mod thinvec;
 pub mod transitive_relation;
 pub mod unhash;
 pub mod unord;

diff --git a/compiler/rustc_data_structures/src/obligation_forest/mod.rs b/compiler/rustc_data_structures/src/obligation_forest/mod.rs
@@ -75,6 +75,7 @@ use std::fmt::Debug;
 use std::hash;
 use std::marker::PhantomData;
 
+use thin_vec::ThinVec;
 use tracing::debug;
 
 use crate::fx::{FxHashMap, FxHashSet};
@@ -141,7 +142,7 @@ pub trait ObligationProcessor {
 #[derive(Debug)]
 pub enum ProcessResult<O, E> {
     Unchanged,
-    Changed(Vec<O>),
+    Changed(ThinVec<O>),
     Error(E),
 }
 
@@ -402,9 +403,10 @@ impl<O: ForestObligation> ObligationForest<O> {
     }
 
     /// Returns the set of obligations that are in a pending state.
-    pub fn map_pending_obligations<P, F>(&self, f: F) -> Vec<P>
+    pub fn map_pending_obligations<P, F, R>(&self, f: F) -> R
     where
         F: Fn(&O) -> P,
+        R: FromIterator<P>,
     {
         self.nodes
             .iter()

diff --git a/compiler/rustc_data_structures/src/obligation_forest/tests.rs b/compiler/rustc_data_structures/src/obligation_forest/tests.rs
@@ -1,5 +1,7 @@
 use std::fmt;
 
+use thin_vec::thin_vec;
+
 use super::*;
 
 impl<'a> super::ForestObligation for &'a str {
@@ -101,9 +103,9 @@ fn push_pop() {
     //        |-> A.3
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A" => ProcessResult::Changed(vec!["A.1", "A.2", "A.3"]),
+            "A" => ProcessResult::Changed(thin_vec!["A.1", "A.2", "A.3"]),
             "B" => ProcessResult::Error("B is for broken"),
-            "C" => ProcessResult::Changed(vec![]),
+            "C" => ProcessResult::Changed(thin_vec![]),
             "A.1" | "A.2" | "A.3" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -123,8 +125,8 @@ fn push_pop() {
         |obligation| match *obligation {
             "A.1" => ProcessResult::Unchanged,
             "A.2" => ProcessResult::Unchanged,
-            "A.3" => ProcessResult::Changed(vec!["A.3.i"]),
-            "D" => ProcessResult::Changed(vec!["D.1", "D.2"]),
+            "A.3" => ProcessResult::Changed(thin_vec!["A.3.i"]),
+            "D" => ProcessResult::Changed(thin_vec!["D.1", "D.2"]),
             "A.3.i" | "D.1" | "D.2" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -139,11 +141,11 @@ fn push_pop() {
     //        |-> D.2 |-> D.2.i
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A.1" => ProcessResult::Changed(vec![]),
+            "A.1" => ProcessResult::Changed(thin_vec![]),
             "A.2" => ProcessResult::Error("A is for apple"),
-            "A.3.i" => ProcessResult::Changed(vec![]),
-            "D.1" => ProcessResult::Changed(vec!["D.1.i"]),
-            "D.2" => ProcessResult::Changed(vec!["D.2.i"]),
+            "A.3.i" => ProcessResult::Changed(thin_vec![]),
+            "D.1" => ProcessResult::Changed(thin_vec!["D.1.i"]),
+            "D.2" => ProcessResult::Changed(thin_vec!["D.2.i"]),
             "D.1.i" | "D.2.i" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -158,7 +160,7 @@ fn push_pop() {
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
             "D.1.i" => ProcessResult::Error("D is for dumb"),
-            "D.2.i" => ProcessResult::Changed(vec![]),
+            "D.2.i" => ProcessResult::Changed(thin_vec![]),
             _ => panic!("unexpected obligation {:?}", obligation),
         },
         |_| {},
@@ -184,10 +186,10 @@ fn success_in_grandchildren() {
 
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A" => ProcessResult::Changed(vec!["A.1", "A.2", "A.3"]),
-            "A.1" => ProcessResult::Changed(vec![]),
-            "A.2" => ProcessResult::Changed(vec!["A.2.i", "A.2.ii"]),
-            "A.3" => ProcessResult::Changed(vec![]),
+            "A" => ProcessResult::Changed(thin_vec!["A.1", "A.2", "A.3"]),
+            "A.1" => ProcessResult::Changed(thin_vec![]),
+            "A.2" => ProcessResult::Changed(thin_vec!["A.2.i", "A.2.ii"]),
+            "A.3" => ProcessResult::Changed(thin_vec![]),
             "A.2.i" | "A.2.ii" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -201,7 +203,7 @@ fn success_in_grandchildren() {
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
             "A.2.i" => ProcessResult::Unchanged,
-            "A.2.ii" => ProcessResult::Changed(vec![]),
+            "A.2.ii" => ProcessResult::Changed(thin_vec![]),
             _ => unreachable!(),
         },
         |_| {},
@@ -211,7 +213,7 @@ fn success_in_grandchildren() {
 
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A.2.i" => ProcessResult::Changed(vec!["A.2.i.a"]),
+            "A.2.i" => ProcessResult::Changed(thin_vec!["A.2.i.a"]),
             "A.2.i.a" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -222,7 +224,7 @@ fn success_in_grandchildren() {
 
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A.2.i.a" => ProcessResult::Changed(vec![]),
+            "A.2.i.a" => ProcessResult::Changed(thin_vec![]),
             _ => unreachable!(),
         },
         |_| {},
@@ -247,7 +249,7 @@ fn to_errors_no_throw() {
     forest.register_obligation("A");
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A" => ProcessResult::Changed(vec!["A.1", "A.2", "A.3"]),
+            "A" => ProcessResult::Changed(thin_vec!["A.1", "A.2", "A.3"]),
             "A.1" | "A.2" | "A.3" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -269,7 +271,7 @@ fn diamond() {
     forest.register_obligation("A");
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A" => ProcessResult::Changed(vec!["A.1", "A.2"]),
+            "A" => ProcessResult::Changed(thin_vec!["A.1", "A.2"]),
             "A.1" | "A.2" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -280,8 +282,8 @@ fn diamond() {
 
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A.1" => ProcessResult::Changed(vec!["D"]),
-            "A.2" => ProcessResult::Changed(vec!["D"]),
+            "A.1" => ProcessResult::Changed(thin_vec!["D"]),
+            "A.2" => ProcessResult::Changed(thin_vec!["D"]),
             "D" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -295,7 +297,7 @@ fn diamond() {
         |obligation| match *obligation {
             "D" => {
                 d_count += 1;
-                ProcessResult::Changed(vec![])
+                ProcessResult::Changed(thin_vec![])
             }
             _ => unreachable!(),
         },
@@ -313,7 +315,7 @@ fn diamond() {
     forest.register_obligation("A'");
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A'" => ProcessResult::Changed(vec!["A'.1", "A'.2"]),
+            "A'" => ProcessResult::Changed(thin_vec!["A'.1", "A'.2"]),
             "A'.1" | "A'.2" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -324,8 +326,8 @@ fn diamond() {
 
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A'.1" => ProcessResult::Changed(vec!["D'", "A'"]),
-            "A'.2" => ProcessResult::Changed(vec!["D'"]),
+            "A'.1" => ProcessResult::Changed(thin_vec!["D'", "A'"]),
+            "A'.2" => ProcessResult::Changed(thin_vec!["D'"]),
             "D'" | "A'" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -366,7 +368,7 @@ fn done_dependency() {
 
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A: Sized" | "B: Sized" | "C: Sized" => ProcessResult::Changed(vec![]),
+            "A: Sized" | "B: Sized" | "C: Sized" => ProcessResult::Changed(thin_vec![]),
             _ => unreachable!(),
         },
         |_| {},
@@ -379,7 +381,9 @@ fn done_dependency() {
     forest.register_obligation("(A,B,C): Sized");
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "(A,B,C): Sized" => ProcessResult::Changed(vec!["A: Sized", "B: Sized", "C: Sized"]),
+            "(A,B,C): Sized" => {
+                ProcessResult::Changed(thin_vec!["A: Sized", "B: Sized", "C: Sized"])
+            }
             _ => unreachable!(),
         },
         |_| {},
@@ -399,10 +403,10 @@ fn orphan() {
 
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
-            "A" => ProcessResult::Changed(vec!["D", "E"]),
+            "A" => ProcessResult::Changed(thin_vec!["D", "E"]),
             "B" => ProcessResult::Unchanged,
-            "C1" => ProcessResult::Changed(vec![]),
-            "C2" => ProcessResult::Changed(vec![]),
+            "C1" => ProcessResult::Changed(thin_vec![]),
+            "C2" => ProcessResult::Changed(thin_vec![]),
             "D" | "E" => ProcessResult::Unchanged,
             _ => unreachable!(),
         },
@@ -416,7 +420,7 @@ fn orphan() {
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
             "D" | "E" => ProcessResult::Unchanged,
-            "B" => ProcessResult::Changed(vec!["D"]),
+            "B" => ProcessResult::Changed(thin_vec!["D"]),
             _ => unreachable!(),
         },
         |_| {},
@@ -459,7 +463,7 @@ fn simultaneous_register_and_error() {
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
             "A" => ProcessResult::Error("An error"),
-            "B" => ProcessResult::Changed(vec!["A"]),
+            "B" => ProcessResult::Changed(thin_vec!["A"]),
             _ => unreachable!(),
         },
         |_| {},
@@ -474,7 +478,7 @@ fn simultaneous_register_and_error() {
     let TestOutcome { completed: ok, errors: err, .. } = forest.process_obligations(&mut C(
         |obligation| match *obligation {
             "A" => ProcessResult::Error("An error"),
-            "B" => ProcessResult::Changed(vec!["A"]),
+            "B" => ProcessResult::Changed(thin_vec!["A"]),
             _ => unreachable!(),
         },
         |_| {},