Auto merge of #93466 - cjgillot:query-dead, r=nagisa

Make dead code check a query.

Dead code check is run for each invocation of the compiler, even if no modifications were involved.
This PR makes dead code check a query keyed on the module. This allows to skip the check when a module has not changed.
To perform this, a query `live_symbols_and_ignored_derived_traits` is introduced to encapsulate the global analysis of finding live symbols. The second query `check_mod_deathness` outputs diagnostics for each module based on this first query's results.

1 files changed, 16 insertions, 0 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 12ece9e6afb..8e87a262192 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -758,6 +758,22 @@ rustc_queries! {
         desc { |tcx| "checking liveness of variables in {}", describe_as_module(key, tcx) }
     }
 
+    /// Return the live symbols in the crate for dead code check.
+    ///
+    /// The second return value maps from ADTs to ignored derived traits (e.g. Debug and Clone) and
+    /// their respective impl (i.e., part of the derive macro)
+    query live_symbols_and_ignored_derived_traits(_: ()) -> (
+        FxHashSet<LocalDefId>,
+        FxHashMap<LocalDefId, Vec<(DefId, DefId)>>
+    ) {
+        storage(ArenaCacheSelector<'tcx>)
+        desc { "find live symbols in crate" }
+    }
+
+    query check_mod_deathness(key: LocalDefId) -> () {
+        desc { |tcx| "checking deathness of variables in {}", describe_as_module(key, tcx) }
+    }
+
     query check_mod_impl_wf(key: LocalDefId) -> () {
         desc { |tcx| "checking that impls are well-formed in {}", describe_as_module(key, tcx) }
     }