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Don't codegen dead code #104860

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7 changes: 7 additions & 0 deletions compiler/rustc_monomorphize/src/collector.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1186,6 +1186,13 @@ struct RootCollector<'a, 'tcx> {

impl<'v> RootCollector<'_, 'v> {
fn process_item(&mut self, id: hir::ItemId) {
let def_id = id.owner_id.def_id;
let (live_symbols, _) = self.tcx.live_symbols_and_ignored_derived_traits(());
if !live_symbols.contains(&def_id) && !self.tcx.sess.link_dead_code() {
// This is dead code; ignore it.
return;
}
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@bjorn3 bjorn3 Nov 25, 2022 •
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Why would this condition even be true when not compiling in incr comp mode? Also won't this remove all global_asm!() usages?

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@jyn514 jyn514 Nov 25, 2022 •
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Why would this condition even happen when not compiling in incr comp mode?

I've observed this to happen with every unreachable item.

rust/compiler/rustc_monomorphize/src/collector.rs

Lines 376 to 379 in d64517d

let crate_items = tcx.hir_crate_items(());
for id in crate_items.items() {
collector.process_item(id);
looks at every item in the crate regardless of whether it's reachable.

I hadn't considered global_asm, I can special-case it here if you think it's necessary.

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Global_asm mut never be removed. Also please make this early exit conditional on the lazy collection mode. The eager collection mode doesn't omit anything on purpose to improve incr comp object file reuse.


match self.tcx.def_kind(id.owner_id) {
DefKind::Enum | DefKind::Struct | DefKind::Union => {
let item = self.tcx.hir().item(id);
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5 changes: 5 additions & 0 deletions compiler/rustc_passes/src/dead.rs
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Expand Up @@ -623,6 +623,11 @@ fn create_and_seed_worklist<'tcx>(
check_foreign_item(tcx, &mut worklist, id);
}

if let Some(static_) = tcx.proc_macro_decls_static(()) {
// We assume this is always used if present.
worklist.push(static_);
}

(worklist, struct_constructors)
}

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