diff options
Diffstat (limited to 'compiler/rustc_middle/src/mir/mono.rs')
| -rw-r--r-- | compiler/rustc_middle/src/mir/mono.rs | 138 |
1 files changed, 88 insertions, 50 deletions
diff --git a/compiler/rustc_middle/src/mir/mono.rs b/compiler/rustc_middle/src/mir/mono.rs index 111c3b6956a..d4a9aac3733 100644 --- a/compiler/rustc_middle/src/mir/mono.rs +++ b/compiler/rustc_middle/src/mir/mono.rs @@ -1,6 +1,7 @@ use std::fmt; use std::hash::Hash; +use rustc_ast::expand::autodiff_attrs::AutoDiffItem; use rustc_attr_parsing::InlineAttr; use rustc_data_structures::base_n::{BaseNString, CASE_INSENSITIVE, ToBaseN}; use rustc_data_structures::fingerprint::Fingerprint; @@ -8,7 +9,7 @@ use rustc_data_structures::fx::FxIndexMap; use rustc_data_structures::stable_hasher::{Hash128, HashStable, StableHasher, ToStableHashKey}; use rustc_data_structures::unord::UnordMap; use rustc_hir::ItemId; -use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE}; +use rustc_hir::def_id::{CrateNum, DefId, DefIdSet, LOCAL_CRATE}; use rustc_index::Idx; use rustc_macros::{HashStable, TyDecodable, TyEncodable}; use rustc_query_system::ich::StableHashingContext; @@ -91,57 +92,89 @@ impl<'tcx> MonoItem<'tcx> { } pub fn instantiation_mode(&self, tcx: TyCtxt<'tcx>) -> InstantiationMode { - let generate_cgu_internal_copies = tcx - .sess - .opts - .unstable_opts - .inline_in_all_cgus - .unwrap_or_else(|| tcx.sess.opts.optimize != OptLevel::No) - && !tcx.sess.link_dead_code(); + // The case handling here is written in the same style as cross_crate_inlinable, we first + // handle the cases where we must use a particular instantiation mode, then cascade down + // through a sequence of heuristics. - match *self { - MonoItem::Fn(ref instance) => { - let entry_def_id = tcx.entry_fn(()).map(|(id, _)| id); - // If this function isn't inlined or otherwise has an extern - // indicator, then we'll be creating a globally shared version. - let codegen_fn_attrs = tcx.codegen_fn_attrs(instance.def_id()); - if codegen_fn_attrs.contains_extern_indicator() - || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) - || !instance.def.generates_cgu_internal_copy(tcx) - || Some(instance.def_id()) == entry_def_id - { - return InstantiationMode::GloballyShared { may_conflict: false }; - } - - if let InlineAttr::Never = tcx.codegen_fn_attrs(instance.def_id()).inline - && self.is_generic_fn() - { - // Upgrade inline(never) to a globally shared instance. - return InstantiationMode::GloballyShared { may_conflict: true }; - } - - // At this point we don't have explicit linkage and we're an - // inlined function. If we're inlining into all CGUs then we'll - // be creating a local copy per CGU. - if generate_cgu_internal_copies { - return InstantiationMode::LocalCopy; - } - - // Finally, if this is `#[inline(always)]` we're sure to respect - // that with an inline copy per CGU, but otherwise we'll be - // creating one copy of this `#[inline]` function which may - // conflict with upstream crates as it could be an exported - // symbol. - if tcx.codegen_fn_attrs(instance.def_id()).inline.always() { - InstantiationMode::LocalCopy - } else { - InstantiationMode::GloballyShared { may_conflict: true } - } - } + // The first thing we do is detect MonoItems which we must instantiate exactly once in the + // whole program. + + // Statics and global_asm! must be instantiated exactly once. + let instance = match *self { + MonoItem::Fn(instance) => instance, MonoItem::Static(..) | MonoItem::GlobalAsm(..) => { - InstantiationMode::GloballyShared { may_conflict: false } + return InstantiationMode::GloballyShared { may_conflict: false }; + } + }; + + // Similarly, the executable entrypoint must be instantiated exactly once. + if let Some((entry_def_id, _)) = tcx.entry_fn(()) { + if instance.def_id() == entry_def_id { + return InstantiationMode::GloballyShared { may_conflict: false }; } } + + // If the function is #[naked] or contains any other attribute that requires exactly-once + // instantiation: + let codegen_fn_attrs = tcx.codegen_fn_attrs(instance.def_id()); + if codegen_fn_attrs.contains_extern_indicator() + || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) + { + return InstantiationMode::GloballyShared { may_conflict: false }; + } + + // FIXME: The logic for which functions are permitted to get LocalCopy is actually spread + // across 4 functions: + // * cross_crate_inlinable(def_id) + // * InstanceKind::requires_inline + // * InstanceKind::generate_cgu_internal_copy + // * MonoItem::instantiation_mode + // Since reachable_non_generics calls InstanceKind::generates_cgu_internal_copy to decide + // which symbols this crate exports, we are obligated to only generate LocalCopy when + // generates_cgu_internal_copy returns true. + if !instance.def.generates_cgu_internal_copy(tcx) { + return InstantiationMode::GloballyShared { may_conflict: false }; + } + + // Beginning of heuristics. The handling of link-dead-code and inline(always) are QoL only, + // the compiler should not crash and linkage should work, but codegen may be undesirable. + + // -Clink-dead-code was given an unfortunate name; the point of the flag is to assist + // coverage tools which rely on having every function in the program appear in the + // generated code. If we select LocalCopy, functions which are not used because they are + // missing test coverage will disappear from such coverage reports, defeating the point. + // Note that -Cinstrument-coverage does not require such assistance from us, only coverage + // tools implemented without compiler support ironically require a special compiler flag. + if tcx.sess.link_dead_code() { + return InstantiationMode::GloballyShared { may_conflict: true }; + } + + // To ensure that #[inline(always)] can be inlined as much as possible, especially in unoptimized + // builds, we always select LocalCopy. + if codegen_fn_attrs.inline.always() { + return InstantiationMode::LocalCopy; + } + + // #[inline(never)] functions in general are poor candidates for inlining and thus since + // LocalCopy generally increases code size for the benefit of optimizations from inlining, + // we want to give them GloballyShared codegen. + // The slight problem is that generic functions need to always support cross-crate + // compilation, so all previous stages of the compiler are obligated to treat generic + // functions the same as those that unconditionally get LocalCopy codegen. It's only when + // we get here that we can at least not codegen a #[inline(never)] generic function in all + // of our CGUs. + if let InlineAttr::Never = tcx.codegen_fn_attrs(instance.def_id()).inline + && self.is_generic_fn() + { + return InstantiationMode::GloballyShared { may_conflict: true }; + } + + // The fallthrough case is to generate LocalCopy for all optimized builds, and + // GloballyShared with conflict prevention when optimizations are disabled. + match tcx.sess.opts.optimize { + OptLevel::No => InstantiationMode::GloballyShared { may_conflict: true }, + _ => InstantiationMode::LocalCopy, + } } pub fn explicit_linkage(&self, tcx: TyCtxt<'tcx>) -> Option<Linkage> { @@ -247,6 +280,13 @@ impl ToStableHashKey<StableHashingContext<'_>> for MonoItem<'_> { } } +#[derive(Debug, HashStable, Copy, Clone)] +pub struct MonoItemPartitions<'tcx> { + pub codegen_units: &'tcx [CodegenUnit<'tcx>], + pub all_mono_items: &'tcx DefIdSet, + pub autodiff_items: &'tcx [AutoDiffItem], +} + #[derive(Debug, HashStable)] pub struct CodegenUnit<'tcx> { /// A name for this CGU. Incremental compilation requires that @@ -287,9 +327,7 @@ pub enum Linkage { LinkOnceODR, WeakAny, WeakODR, - Appending, Internal, - Private, ExternalWeak, Common, } |