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[WIP] Always verify incremental hash #84227

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[WIP] Always verify incremental hash #84227

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15 changes: 14 additions & 1 deletion compiler/rustc_query_system/src/query/plumbing.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -520,7 +520,20 @@ where
if let Some(result) = result {
// If `-Zincremental-verify-ich` is specified, re-hash results from
// the cache and make sure that they have the expected fingerprint.
if unlikely!(tcx.dep_context().sess().opts.debugging_opts.incremental_verify_ich) {
let prev_fingerprint = tcx
.dep_context()
.dep_graph()
.prev_fingerprint_of(dep_node)
.unwrap_or(Fingerprint::ZERO);
// A fingerprint is 128 bits, and this checks if 5 of those bits are
// zero. If the fingerprint is fully random (as we hope for), this
// should limit us to checking every `2^5`th hash. This reduces the
// number of hashes we check low enough that the overhead of
// verification is acceptable to always enable.
let try_verify = prev_fingerprint.as_value().1 & 0x1f == 0;
if try_verify
|| unlikely!(tcx.dep_context().sess().opts.debugging_opts.incremental_verify_ich)
{
incremental_verify_ich(*tcx.dep_context(), &result, dep_node, query);
}

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