bjoernager/rust
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Ensure that Fingerprint caching respects hashing configuration

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Fixes #92266

In some `HashStable` impls, we use a cache to avoid re-computing
the same `Fingerprint` from the same structure (e.g. an `AdtDef`).
However, the `StableHashingContext` used can be configured to
perform hashing in different ways (e.g. skipping `Span`s). This
configuration information is not included in the cache key,
which will cause an incorrect `Fingerprint` to be used if
we hash the same structure with different `StableHashingContext`
settings.

To fix this, the configuration settings of `StableHashingContext`
are split out into a separate `HashingControls` struct. This
struct is used as part of the cache key, ensuring that our caches
always produce the correct result for the given settings.

With this in place, we now turn off `Span` hashing during the
entire process of computing the hash included in legacy symbols.
This current has no effect, but will matter when a future PR
starts hashing more `Span`s that we currently skip.
This commit is contained in:
Aaron Hill 2021-12-24 16:36:33 -05:00
parent 936ce3dab7
commit 5580e5e1dd
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GPG key ID: B4087E510E98B164
9 changed files with 101 additions and 48 deletions
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5
compiler/rustc_middle/src/ty/impls_ty.rs
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@ -6,6 +6,7 @@ use crate::mir;
use crate::ty;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::stable_hasher::HashingControls;
use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
use rustc_query_system::ich::StableHashingContext;
use std::cell::RefCell;
@ -17,12 +18,12 @@ where
{
fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
thread_local! {
static CACHE: RefCell<FxHashMap<(usize, usize), Fingerprint>> =
static CACHE: RefCell<FxHashMap<(usize, usize, HashingControls), Fingerprint>> =
RefCell::new(Default::default());
}
let hash = CACHE.with(|cache| {
let key = (self.as_ptr() as usize, self.len());
let key = (self.as_ptr() as usize, self.len(), hcx.hashing_controls());
if let Some(&hash) = cache.borrow().get(&key) {
return hash;
}