From 41a9cbeb64f486a27f5b22a6b1dafa9d693c0fb6 Mon Sep 17 00:00:00 2001
From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
Date: Sun, 30 Apr 2023 22:00:16 +0200
Subject: [PATCH 1/2] Shrink `SelectionError` a lot
`SelectionError` used to be 80 bytes (on 64 bit). That's quite big.
Especially because the selection cache contained `Result<_,
SelectionError>. The Ok type is only 32 bytes, so the 80 bytes
significantly inflate the size of the cache.
Most variants of the `SelectionError` seem to be hard errors, only
`Unimplemented` shows up in practice (for cranelift-codegen, it occupies
23.4% of all cache entries). We can just box away the biggest variant,
`OutputTypeParameterMismatch`, to get the size down to 16 bytes, well
within the size of the Ok type inside the cache.
---
.../src/fn_ctxt/adjust_fulfillment_errors.rs | 6 ++++--
compiler/rustc_hir_typeck/src/lib.rs | 1 +
compiler/rustc_middle/src/traits/mod.rs | 13 ++++++++-----
.../src/traits/error_reporting/mod.rs | 13 +++++++++----
.../src/traits/select/confirmation.rs | 9 ++++++++-
5 files changed, 30 insertions(+), 12 deletions(-)
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs
index 05e5d850bf958..3efdab534384b 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs
@@ -278,9 +278,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
span: Span,
) -> bool {
if let traits::FulfillmentErrorCode::CodeSelectionError(
- traits::SelectionError::OutputTypeParameterMismatch(_, expected, _),
+ traits::SelectionError::OutputTypeParameterMismatch(box traits::SelectionOutputTypeParameterMismatch{
+ expected_trait_ref, ..
+ }),
) = error.code
- && let ty::Closure(def_id, _) | ty::Generator(def_id, ..) = expected.skip_binder().self_ty().kind()
+ && let ty::Closure(def_id, _) | ty::Generator(def_id, ..) = expected_trait_ref.skip_binder().self_ty().kind()
&& span.overlaps(self.tcx.def_span(*def_id))
{
true
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
index a2a4362e2f518..dcc323493f479 100644
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@@ -2,6 +2,7 @@
#![feature(let_chains)]
#![feature(try_blocks)]
#![feature(never_type)]
+#![feature(box_patterns)]
#![feature(min_specialization)]
#![feature(control_flow_enum)]
#![feature(drain_filter)]
diff --git a/compiler/rustc_middle/src/traits/mod.rs b/compiler/rustc_middle/src/traits/mod.rs
index 8366567c2c364..449c453555e9e 100644
--- a/compiler/rustc_middle/src/traits/mod.rs
+++ b/compiler/rustc_middle/src/traits/mod.rs
@@ -580,11 +580,7 @@ pub enum SelectionError<'tcx> {
/// After a closure impl has selected, its "outputs" were evaluated
/// (which for closures includes the "input" type params) and they
/// didn't resolve. See `confirm_poly_trait_refs` for more.
- OutputTypeParameterMismatch(
- ty::PolyTraitRef<'tcx>,
- ty::PolyTraitRef<'tcx>,
- ty::error::TypeError<'tcx>,
- ),
+ OutputTypeParameterMismatch(Box<SelectionOutputTypeParameterMismatch<'tcx>>),
/// The trait pointed by `DefId` is not object safe.
TraitNotObjectSafe(DefId),
/// A given constant couldn't be evaluated.
@@ -596,6 +592,13 @@ pub enum SelectionError<'tcx> {
ErrorReporting,
}
+#[derive(Clone, Debug, TypeVisitable, Lift)]
+pub struct SelectionOutputTypeParameterMismatch<'tcx> {
+ pub found_trait_ref: ty::PolyTraitRef<'tcx>,
+ pub expected_trait_ref: ty::PolyTraitRef<'tcx>,
+ pub terr: ty::error::TypeError<'tcx>,
+}
+
/// When performing resolution, it is typically the case that there
/// can be one of three outcomes:
///
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index c9e2ed092d160..9836522392373 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -28,6 +28,7 @@ use rustc_hir::{GenericParam, Item, Node};
use rustc_infer::infer::error_reporting::TypeErrCtxt;
use rustc_infer::infer::{InferOk, TypeTrace};
use rustc_middle::traits::select::OverflowError;
+use rustc_middle::traits::SelectionOutputTypeParameterMismatch;
use rustc_middle::ty::abstract_const::NotConstEvaluatable;
use rustc_middle::ty::error::{ExpectedFound, TypeError};
use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
@@ -1087,17 +1088,21 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
}
}
- OutputTypeParameterMismatch(
+ OutputTypeParameterMismatch(box SelectionOutputTypeParameterMismatch {
found_trait_ref,
expected_trait_ref,
- terr @ TypeError::CyclicTy(_),
- ) => self.report_type_parameter_mismatch_cyclic_type_error(
+ terr: terr @ TypeError::CyclicTy(_),
+ }) => self.report_type_parameter_mismatch_cyclic_type_error(
&obligation,
found_trait_ref,
expected_trait_ref,
terr,
),
- OutputTypeParameterMismatch(found_trait_ref, expected_trait_ref, _) => {
+ OutputTypeParameterMismatch(box SelectionOutputTypeParameterMismatch {
+ found_trait_ref,
+ expected_trait_ref,
+ terr: _,
+ }) => {
match self.report_type_parameter_mismatch_error(
&obligation,
span,
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 616187b69dde4..cf9c8b8fa23f0 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -10,6 +10,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_hir::lang_items::LangItem;
use rustc_infer::infer::LateBoundRegionConversionTime::HigherRankedType;
use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
+use rustc_middle::traits::SelectionOutputTypeParameterMismatch;
use rustc_middle::ty::{
self, Binder, GenericParamDefKind, InternalSubsts, SubstsRef, ToPolyTraitRef, ToPredicate,
TraitRef, Ty, TyCtxt, TypeVisitableExt,
@@ -834,7 +835,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
obligations.extend(nested);
obligations
})
- .map_err(|e| OutputTypeParameterMismatch(expected_trait_ref, obligation_trait_ref, e))
+ .map_err(|terr| {
+ OutputTypeParameterMismatch(Box::new(SelectionOutputTypeParameterMismatch {
+ expected_trait_ref: obligation_trait_ref,
+ found_trait_ref: expected_trait_ref,
+ terr,
+ }))
+ })
}
fn confirm_trait_upcasting_unsize_candidate(
From e8ab6489027098dbf4a407ddd0cedd0fbe40e3a4 Mon Sep 17 00:00:00 2001
From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
Date: Tue, 9 May 2023 07:16:59 +0000
Subject: [PATCH 2/2] Rename `expected_trait_ref` to `self_ty_trait_ref`
This trait ref is derived from the self type and then equated to the
trait ref from the obligation.
For example, for `fn(): Fn(u32)`, `self_ty_trait_ref` is `Fn()`, which
is then equated to `Fn(u32)` (which will fail, causing the obligation to
fail).
---
.../rustc_trait_selection/src/traits/select/confirmation.rs | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index cf9c8b8fa23f0..4dc84e0ad10b1 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -812,7 +812,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
fn confirm_poly_trait_refs(
&mut self,
obligation: &TraitObligation<'tcx>,
- expected_trait_ref: ty::PolyTraitRef<'tcx>,
+ self_ty_trait_ref: ty::PolyTraitRef<'tcx>,
) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
let obligation_trait_ref = obligation.predicate.to_poly_trait_ref();
// Normalize the obligation and expected trait refs together, because why not
@@ -823,7 +823,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
- (obligation_trait_ref, expected_trait_ref),
+ (obligation_trait_ref, self_ty_trait_ref),
)
});