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Auto merge of #117749 - aliemjay:perf-canon-cache, r=lcnr

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cache param env canonicalization

Canonicalize ParamEnv only once and store it. Then whenever we try to canonicalize `ParamEnvAnd<'tcx, T>` we only have to canonicalize `T` and then merge the results.

Prelimiary results show ~3-4% savings in diesel and serde benchmarks.

Best to review commits individually. Some commits have a short description.

Initial implementation had a soundness bug (https://github.com/rust-lang/rust/pull/117749#issuecomment-1840453387) due to cache invalidation:
- When canonicalizing `Ty<'?0>` we first try to resolve region variables in the current InferCtxt which may have a constraint `?0 == 'static`. This means that we register `Ty<'?0> => Canonical<Ty<'static>>` in the cache, which is obviously incorrect in another inference context.
- This is fixed by not doing region resolution when canonicalizing the query *input* (vs. response), which is the only place where ParamEnv is used, and then in a later commit we *statically* guard against any form of inference variable resolution of the cached canonical ParamEnv's.

r? `@ghost`
This commit is contained in:
bors 2023-12-14 04:04:10 +00:00
commit d23e1a6894
8 changed files with 199 additions and 125 deletions
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8
compiler/rustc_trait_selection/src/traits/misc.rs
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@ -9,7 +9,7 @@ use rustc_infer::infer::canonical::Canonical;
use rustc_infer::infer::{RegionResolutionError, TyCtxtInferExt};
use rustc_infer::traits::query::NoSolution;
use rustc_infer::{infer::outlives::env::OutlivesEnvironment, traits::FulfillmentError};
use rustc_middle::ty::{self, AdtDef, GenericArg, List, ParamEnv, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{self, AdtDef, GenericArg, List, Ty, TyCtxt, TypeVisitableExt};
use rustc_span::DUMMY_SP;
use super::outlives_bounds::InferCtxtExt;
@ -209,10 +209,10 @@ pub fn all_fields_implement_trait<'tcx>(
pub fn check_tys_might_be_eq<'tcx>(
tcx: TyCtxt<'tcx>,
canonical: Canonical<'tcx, (ParamEnv<'tcx>, Ty<'tcx>, Ty<'tcx>)>,
canonical: Canonical<'tcx, ty::ParamEnvAnd<'tcx, (Ty<'tcx>, Ty<'tcx>)>>,
) -> Result<(), NoSolution> {
let (infcx, (param_env, ty_a, ty_b), _) =
tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &canonical);
let (infcx, key, _) = tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &canonical);
let (param_env, (ty_a, ty_b)) = key.into_parts();
let ocx = ObligationCtxt::new(&infcx);
let result = ocx.eq(&ObligationCause::dummy(), param_env, ty_a, ty_b);