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Auto merge of #118770 - saethlin:fix-inline-never-uses, r=nnethercote
Fix cases where std accidentally relied on inline(never) This PR increases the power of `-Zcross-crate-inline-threshold=always` so that it applies through `#[inline(never)]`. Note that though this is called "cross-crate-inlining" in this case especially it is _just_ lazy per-CGU codegen. The MIR inliner and LLVM still respect the attribute as much as they ever have. Trying to bootstrap with the new `-Zcross-crate-inline-threshold=always` change revealed two bugs: We have special intrinsics `assert_inhabited`, `assert_zero_valid`, and `assert_mem_uniniitalized_valid` which codegen backends will lower to nothing or a call to `panic_nounwind`. Since we may not have any call to `panic_nounwind` in MIR but emit one anyway, we need to specially tell `MirUsedCollector` about this situation. `#[lang = "start"]` is special-cased already so that `MirUsedCollector` will collect it, but then when we make it cross-crate-inlinable it is only assigned to a CGU based on whether `MirUsedCollector` saw a call to it, which of course we didn't. --- I started looking into this because https://github.com/rust-lang/rust/pull/118683 revealed a case where we were accidentally relying on a function being `#[inline(never)]`, and cranking up cross-crate-inlinability seems like a way to find other situations like that. r? `@nnethercote` because I don't like what I'm doing to the CGU partitioning code here but I can't come up with something much better
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1559dd2dbf
@ -22,6 +22,18 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
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return false;
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}
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// This just reproduces the logic from Instance::requires_inline.
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match tcx.def_kind(def_id) {
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DefKind::Ctor(..) | DefKind::Closure => return true,
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DefKind::Fn | DefKind::AssocFn => {}
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_ => return false,
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}
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// From this point on, it is valid to return true or false.
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if tcx.sess.opts.unstable_opts.cross_crate_inline_threshold == InliningThreshold::Always {
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return true;
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}
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// Obey source annotations first; this is important because it means we can use
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// #[inline(never)] to force code generation.
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match codegen_fn_attrs.inline {
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@ -30,13 +42,6 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
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_ => {}
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}
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// This just reproduces the logic from Instance::requires_inline.
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match tcx.def_kind(def_id) {
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DefKind::Ctor(..) | DefKind::Closure => return true,
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DefKind::Fn | DefKind::AssocFn => {}
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_ => return false,
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}
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// Don't do any inference when incremental compilation is enabled; the additional inlining that
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// inference permits also creates more work for small edits.
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if tcx.sess.opts.incremental.is_some() {
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@ -176,6 +176,7 @@ use rustc_middle::mir::visit::Visitor as MirVisitor;
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use rustc_middle::mir::{self, Location};
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use rustc_middle::query::TyCtxtAt;
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use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCoercion};
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use rustc_middle::ty::layout::ValidityRequirement;
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use rustc_middle::ty::print::with_no_trimmed_paths;
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use rustc_middle::ty::{
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self, AssocKind, GenericParamDefKind, Instance, InstanceDef, Ty, TyCtxt, TypeFoldable,
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@ -923,6 +924,21 @@ fn visit_instance_use<'tcx>(
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return;
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}
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// The intrinsics assert_inhabited, assert_zero_valid, and assert_mem_uninitialized_valid will
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// be lowered in codegen to nothing or a call to panic_nounwind. So if we encounter any
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// of those intrinsics, we need to include a mono item for panic_nounwind, else we may try to
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// codegen a call to that function without generating code for the function itself.
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if let ty::InstanceDef::Intrinsic(def_id) = instance.def {
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let name = tcx.item_name(def_id);
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if let Some(_requirement) = ValidityRequirement::from_intrinsic(name) {
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let def_id = tcx.lang_items().get(LangItem::PanicNounwind).unwrap();
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let panic_instance = Instance::mono(tcx, def_id);
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if should_codegen_locally(tcx, &panic_instance) {
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output.push(create_fn_mono_item(tcx, panic_instance, source));
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}
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}
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}
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match instance.def {
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ty::InstanceDef::Virtual(..) | ty::InstanceDef::Intrinsic(_) => {
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if !is_direct_call {
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@ -212,11 +212,17 @@ where
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let cgu_name_cache = &mut FxHashMap::default();
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for mono_item in mono_items {
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// Handle only root items directly here. Inlined items are handled at
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// the bottom of the loop based on reachability.
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// Handle only root (GloballyShared) items directly here. Inlined (LocalCopy) items
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// are handled at the bottom of the loop based on reachability, with one exception.
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// The #[lang = "start"] item is the program entrypoint, so there are no calls to it in MIR.
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// So even if its mode is LocalCopy, we need to treat it like a root.
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match mono_item.instantiation_mode(cx.tcx) {
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InstantiationMode::GloballyShared { .. } => {}
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InstantiationMode::LocalCopy => continue,
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InstantiationMode::LocalCopy => {
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if Some(mono_item.def_id()) != cx.tcx.lang_items().start_fn() {
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continue;
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}
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}
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}
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let characteristic_def_id = characteristic_def_id_of_mono_item(cx.tcx, mono_item);
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@ -155,7 +155,6 @@ fn lang_start_internal(
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}
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#[cfg(not(test))]
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#[inline(never)]
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#[lang = "start"]
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fn lang_start<T: crate::process::Termination + 'static>(
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main: fn() -> T,
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