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Auto merge of #89454 - erikdesjardins:perfattrcheck, r=nikomatsakis

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perf: only check for `rustc_trivial_field_reads` attribute on traits, not items, impls, etc.

The checks that are removed in this PR (originally added in #85200) caused a small perf regression: https://github.com/rust-lang/rust/pull/88824#issuecomment-932664761

Since the attribute is currently only applied to traits, I don't think it's worth keeping the additional checks for now.
If/when we decide to apply the attribute somewhere else, we can (partially) revert this and reevaluate the perf impact.

r? `@nikomatsakis` cc `@FabianWolff`
This commit is contained in:
bors 2021-10-07 03:42:05 +00:00
commit d3e6770efb
1 changed files with 4 additions and 38 deletions
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42
compiler/rustc_passes/src/dead.rs
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@ -243,46 +243,15 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
/// will be ignored for the purposes of dead code analysis (see PR #85200
/// for discussion).
fn should_ignore_item(&self, def_id: DefId) -> bool {
if !self.tcx.has_attr(def_id, sym::automatically_derived)
&& !self
.tcx
.impl_of_method(def_id)
.map_or(false, |impl_id| self.tcx.has_attr(impl_id, sym::automatically_derived))
{
return false;
}
let has_attr = |def_id| self.tcx.has_attr(def_id, sym::rustc_trivial_field_reads);
if has_attr(def_id) {
return true;
}
if let Some(impl_of) = self.tcx.impl_of_method(def_id) {
if has_attr(impl_of) {
return true;
if !self.tcx.has_attr(impl_of, sym::automatically_derived) {
return false;
}
if let Some(trait_of) = self.tcx.trait_id_of_impl(impl_of) {
if has_attr(trait_of) {
if self.tcx.has_attr(trait_of, sym::rustc_trivial_field_reads) {
return true;
}
if let Some(method_ident) = self.tcx.opt_item_name(def_id) {
if let Some(trait_method) = self
.tcx
.associated_items(trait_of)
.find_by_name_and_kind(self.tcx, method_ident, ty::AssocKind::Fn, trait_of)
{
if has_attr(trait_method.def_id) {
return true;
}
}
}
}
} else if let Some(trait_of) = self.tcx.trait_of_item(def_id) {
if has_attr(trait_of) {
return true;
}
}
@ -291,10 +260,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
fn visit_node(&mut self, node: Node<'tcx>) {
if let Some(item_def_id) = match node {
Node::Item(hir::Item { def_id, .. })
| Node::ForeignItem(hir::ForeignItem { def_id, .. })
| Node::TraitItem(hir::TraitItem { def_id, .. })
| Node::ImplItem(hir::ImplItem { def_id, .. }) => Some(def_id.to_def_id()),
Node::ImplItem(hir::ImplItem { def_id, .. }) => Some(def_id.to_def_id()),
_ => None,
} {
if self.should_ignore_item(item_def_id) {