Auto merge of #164217 - tehforsch:fix-160621, r=<try>

Prepare to make `rustc_trivial_field_reads` usable in user code

Author: bors

compiler/rustc_attr_ir/src/data_structures.rs

@@ -1432,7 +1432,7 @@ pub enum AttributeKind {
     RustcThenThisWouldNeed(ThinVec<Ident>),
 
     /// Represents `#[rustc_trivial_field_reads]`
-    RustcTrivialFieldReads,
+    RustcTrivialFieldReads(Span),
 
     /// Represents `#[sanitize]`
     ///

compiler/rustc_attr_ir/src/encode_cross_crate.rs

@@ -194,7 +194,7 @@ impl AttributeKind {
             RustcStrictCoherence(..) => Yes,
             RustcTestMarker(..) => No,
             RustcThenThisWouldNeed(..) => No,
-            RustcTrivialFieldReads => Yes,
+            RustcTrivialFieldReads(..) => Yes,
             Sanitize { .. } => No,
             ShouldPanic { .. } => No,
             Splat(..) => Yes,
@@ -408,7 +408,7 @@ impl AttributeKind {
             RustcStrictCoherence(..) => false,
             RustcTestMarker(..) => false,
             RustcThenThisWouldNeed(..) => false,
-            RustcTrivialFieldReads => false,
+            RustcTrivialFieldReads(..) => false,
             Sanitize { .. } => false,
             ShouldPanic { .. } => false,
             Splat(..) => false,

compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

@@ -440,9 +440,13 @@ pub(crate) struct RustcTrivialFieldReadsParser;
 
 impl NoArgsAttributeParser for RustcTrivialFieldReadsParser {
     const PATH: &[Symbol] = &[sym::rustc_trivial_field_reads];
-    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
+    const ALLOWED_TARGETS: AllowedTargets<'_> = AllowedTargets::AllowList(&[
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Fn),
+    ]);
     const STABILITY: AttributeStability = unstable!(rustc_attrs);
-    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcTrivialFieldReads;
+    const CREATE: fn(Span) -> AttributeKind = |span| AttributeKind::RustcTrivialFieldReads(span);
 }
 
 pub(crate) struct RustcNoMirInlineParser;

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -91,7 +91,10 @@ pub(crate) fn expand_deriving_clone(
             nonself_args: SmallVec::new(),
             has_other_selflike_arg: false,
             ret_ty: cx.ty_self(span),
-            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            attributes: thin_vec![
+                cx.attr_word(sym::inline, span),
+                cx.attr_word(sym::rustc_trivial_field_reads, span)
+            ],
             fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
             combine_substructure: substructure,
         }],

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -36,7 +36,10 @@ pub(crate) fn expand_deriving_debug(
             nonself_args: smallvec![(fmtr, sym::character('f'))],
             has_other_selflike_arg: false,
             ret_ty: cx.ty_path(path_std!(cx, span, fmt::Result)),
-            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            attributes: thin_vec![
+                cx.attr_word(sym::inline, span),
+                cx.attr_word(sym::rustc_trivial_field_reads, span)
+            ],
             fieldless_variants_strategy:
                 FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless,
             combine_substructure: combine_substructure(|cx, span, substr| show_substructure(

compiler/rustc_middle/src/middle/dead_code.rs

@@ -1,14 +1,59 @@
-use rustc_data_structures::fx::FxIndexSet;
-use rustc_hir::def_id::{DefId, LocalDefIdMap, LocalDefIdSet};
+use rustc_hir::HirId;
+use rustc_hir::def_id::{LocalDefId, LocalDefIdMap, LocalDefIdSet};
 use rustc_macros::StableHash;
+use rustc_span::Span;
+
+#[derive(Clone, Debug, StableHash, PartialEq, Eq, Hash)]
+pub enum LiveKind {
+    Trivial,
+    NonTrivial,
+}
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash, StableHash, PartialOrd, Ord)]
+pub struct TrivialUsageSiteId(usize);
+
+#[derive(Debug, Clone, StableHash)]
+pub struct TrivialUsageSite {
+    pub attr_span: Span,
+    pub hir_id: HirId,
+}
+
+#[derive(Clone, Debug, StableHash, Default)]
+pub struct TrivialUsageSites(Vec<TrivialUsageSite>);
 
 /// A single snapshot of dead-code liveness analysis state.
 #[derive(Clone, Debug, StableHash)]
 pub struct DeadCodeLivenessSnapshot {
-    pub live_symbols: LocalDefIdSet,
-    /// Maps each ADT to derived traits (for example `Debug` and `Clone`) that should be ignored
-    /// when checking for dead code diagnostics.
-    pub ignored_derived_traits: LocalDefIdMap<FxIndexSet<DefId>>,
+    pub live: LocalDefIdSet,
+    /// This maps defs that were only used from items annotated with
+    /// `#[rustc_trivial_field_reads]` to those items
+    pub sites_by_defid: LocalDefIdMap<Vec<TrivialUsageSiteId>>,
+    /// List of all items annotated with `#[rustc_trivial_field_reads]`
+    pub sites: TrivialUsageSites,
+}
+
+impl TrivialUsageSites {
+    pub fn add_trivial_usage_site(&mut self, site: TrivialUsageSite) -> TrivialUsageSiteId {
+        self.0.push(site);
+        TrivialUsageSiteId(self.0.len() - 1)
+    }
+}
+
+impl DeadCodeLivenessSnapshot {
+    pub fn is_live(&self, id: &LocalDefId) -> bool {
+        self.live.contains(id)
+    }
+
+    pub fn trivial_usage_sites(
+        &self,
+        def_id: &LocalDefId,
+    ) -> impl Iterator<Item = &TrivialUsageSite> {
+        self.sites_by_defid
+            .get(def_id)
+            .into_iter()
+            .flatten()
+            .map(|site_id| &self.sites.0[site_id.0])
+    }
 }
 
 /// Dead-code liveness data for both analysis phases.

compiler/rustc_middle/src/queries.rs

@@ -1229,7 +1229,7 @@ rustc_queries! {
     }
 
     /// Return dead-code liveness summary for the crate.
-    query live_symbols_and_ignored_derived_traits(_: ()) -> Result<&'tcx DeadCodeLivenessSummary, ErrorGuaranteed> {
+    query live_symbols_and_trivial_usage_sites(_: ()) -> Result<&'tcx DeadCodeLivenessSummary, ErrorGuaranteed> {
         arena_cache
         desc { "finding live symbols in crate" }
     }

compiler/rustc_passes/src/check_attr.rs

@@ -391,7 +391,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             AttributeKind::RustcStrictCoherence(..) => (),
             AttributeKind::RustcTestMarker(..) => (),
             AttributeKind::RustcThenThisWouldNeed(..) => (),
-            AttributeKind::RustcTrivialFieldReads => (),
+            AttributeKind::RustcTrivialFieldReads(..) => (),
             AttributeKind::Sanitize { .. } => {}
             AttributeKind::ShouldPanic { .. } => (),
             AttributeKind::Splat(..) => (),