Auto merge of #36524 - michaelwoerister:trans-inline-only-on-demand, r=nikomatsakis

trans: Only instantiate #[inline] functions in codegen units referencing them

This PR changes how `#[inline]` functions are translated. Before, there was one "master instance" of the function with `external` linkage and a number of on-demand instances with `available_externally` linkage in each codegen unit that referenced the function. This had two downsides:

* Public functions marked with `#[inline]` would be present in machine code of libraries unnecessarily (see #36280 for an example)
* LLVM would crash on `i686-pc-windows-msvc` due to what I suspect to be a bug in LLVM's Win32 exception handling code, because it doesn't like `available_externally` there (#36309).

This PR changes the behavior, so that there is no master instance and only on-demand instances with `internal` linkage. The downside of this is potential code-bloat if LLVM does not completely inline away the `internal` instances because then there'd be N instances of the function instead of 1. However, this can only become a problem when using more than one codegen unit per crate.

cc @rust-lang/compiler

Author: bors

src/librustc_trans/base.rs

@@ -1421,21 +1421,7 @@ fn internalize_symbols<'a, 'tcx>(sess: &Session,
             .iter()
             .cloned()
             .filter(|trans_item|{
-                let def_id = match *trans_item {
-                    TransItem::DropGlue(..) => {
-                        return false
-                    },
-                    TransItem::Fn(ref instance) => {
-                        instance.def
-                    }
-                    TransItem::Static(node_id) => {
-                        tcx.map.local_def_id(node_id)
-                    }
-                };
-
-                trans_item.explicit_linkage(tcx).is_some() ||
-                attr::contains_extern_indicator(tcx.sess.diagnostic(),
-                                                &tcx.get_attrs(def_id))
+                trans_item.explicit_linkage(tcx).is_some()
             })
             .map(|trans_item| symbol_map.get_or_compute(scx, trans_item))
             .collect();
@@ -1591,7 +1577,11 @@ pub fn filter_reachable_ids(tcx: TyCtxt, reachable: NodeSet) -> NodeSet {
                 node: hir::ImplItemKind::Method(..), .. }) => {
                 let def_id = tcx.map.local_def_id(id);
                 let generics = tcx.lookup_generics(def_id);
-                generics.parent_types == 0 && generics.types.is_empty()
+                let attributes = tcx.get_attrs(def_id);
+                (generics.parent_types == 0 && generics.types.is_empty()) &&
+                // Functions marked with #[inline] are only ever translated
+                // with "internal" linkage and are never exported.
+                !attr::requests_inline(&attributes[..])
             }
 
             _ => false
@@ -1896,8 +1886,7 @@ fn collect_and_partition_translation_items<'a, 'tcx>(scx: &SharedCrateContext<'a
         partitioning::partition(scx,
                                 items.iter().cloned(),
                                 strategy,
-                                &inlining_map,
-                                scx.reachable())
+                                &inlining_map)
     });
 
     assert!(scx.tcx().sess.opts.cg.codegen_units == codegen_units.len() ||

src/librustc_trans/collector.rs

@@ -401,7 +401,7 @@ fn record_inlining_canditates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                         callees: &[TransItem<'tcx>],
                                         inlining_map: &mut InliningMap<'tcx>) {
     let is_inlining_candidate = |trans_item: &TransItem<'tcx>| {
-        trans_item.is_from_extern_crate() || trans_item.requests_inline(tcx)
+        trans_item.needs_local_copy(tcx)
     };
 
     let inlining_candidates = callees.into_iter()

src/librustc_trans/partitioning.rs

@@ -133,7 +133,7 @@ use symbol_map::SymbolMap;
 use syntax::ast::NodeId;
 use syntax::parse::token::{self, InternedString};
 use trans_item::TransItem;
-use util::nodemap::{FnvHashMap, FnvHashSet, NodeSet};
+use util::nodemap::{FnvHashMap, FnvHashSet};
 
 pub enum PartitioningStrategy {
     /// Generate one codegen unit per source-level module.
@@ -254,25 +254,17 @@ const FALLBACK_CODEGEN_UNIT: &'static str = "__rustc_fallback_codegen_unit";
 pub fn partition<'a, 'tcx, I>(scx: &SharedCrateContext<'a, 'tcx>,
                               trans_items: I,
                               strategy: PartitioningStrategy,
-                              inlining_map: &InliningMap<'tcx>,
-                              reachable: &NodeSet)
+                              inlining_map: &InliningMap<'tcx>)
                               -> Vec<CodegenUnit<'tcx>>
     where I: Iterator<Item = TransItem<'tcx>>
 {
     let tcx = scx.tcx();
 
-    if let PartitioningStrategy::FixedUnitCount(1) = strategy {
-        // If there is only a single codegen-unit, we can use a very simple
-        // scheme and don't have to bother with doing much analysis.
-        return vec![single_codegen_unit(tcx, trans_items, reachable)];
-    }
-
     // In the first step, we place all regular translation items into their
     // respective 'home' codegen unit. Regular translation items are all
     // functions and statics defined in the local crate.
     let mut initial_partitioning = place_root_translation_items(scx,
-                                                                trans_items,
-                                                                reachable);
+                                                                trans_items);
 
     debug_dump(tcx, "INITIAL PARTITONING:", initial_partitioning.codegen_units.iter());
 
@@ -310,8 +302,7 @@ struct PreInliningPartitioning<'tcx> {
 struct PostInliningPartitioning<'tcx>(Vec<CodegenUnit<'tcx>>);
 
 fn place_root_translation_items<'a, 'tcx, I>(scx: &SharedCrateContext<'a, 'tcx>,
-                                             trans_items: I,
-                                             _reachable: &NodeSet)
+                                             trans_items: I)
                                              -> PreInliningPartitioning<'tcx>
     where I: Iterator<Item = TransItem<'tcx>>
 {
@@ -320,7 +311,7 @@ fn place_root_translation_items<'a, 'tcx, I>(scx: &SharedCrateContext<'a, 'tcx>,
     let mut codegen_units = FnvHashMap();
 
     for trans_item in trans_items {
-        let is_root = !trans_item.is_instantiated_only_on_demand();
+        let is_root = !trans_item.is_instantiated_only_on_demand(tcx);
 
         if is_root {
             let characteristic_def_id = characteristic_def_id_of_trans_item(scx, trans_item);
@@ -350,6 +341,10 @@ fn place_root_translation_items<'a, 'tcx, I>(scx: &SharedCrateContext<'a, 'tcx>,
                                 // This is a non-generic functions, we always
                                 // make it visible externally on the chance that
                                 // it might be used in another codegen unit.
+                                // Later on base::internalize_symbols() will
+                                // assign "internal" linkage to those symbols
+                                // that are not referenced from other codegen
+                                // units (and are not publicly visible).
                                 llvm::ExternalLinkage
                             } else {
                                 // In the current setup, generic functions cannot
@@ -454,7 +449,6 @@ fn place_inlined_translation_items<'tcx>(initial_partitioning: PreInliningPartit
                 // reliably in that case.
                 new_codegen_unit.items.insert(trans_item, llvm::InternalLinkage);
             } else {
-                assert!(trans_item.is_instantiated_only_on_demand());
                 // We can't be sure if this will also be instantiated
                 // somewhere else, so we add an instance here with
                 // InternalLinkage so we don't get any conflicts.
@@ -550,68 +544,6 @@ fn compute_codegen_unit_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     return token::intern_and_get_ident(&mod_path[..]);
 }
 
-fn single_codegen_unit<'a, 'tcx, I>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
-                                    trans_items: I,
-                                    reachable: &NodeSet)
-                                    -> CodegenUnit<'tcx>
-    where I: Iterator<Item = TransItem<'tcx>>
-{
-    let mut items = FnvHashMap();
-
-    for trans_item in trans_items {
-        let linkage = trans_item.explicit_linkage(tcx).unwrap_or_else(|| {
-            match trans_item {
-                TransItem::Static(node_id) => {
-                    if reachable.contains(&node_id) {
-                        llvm::ExternalLinkage
-                    } else {
-                        llvm::PrivateLinkage
-                    }
-                }
-                TransItem::DropGlue(_) => {
-                    llvm::InternalLinkage
-                }
-                TransItem::Fn(instance) => {
-                    if trans_item.is_generic_fn() {
-                        // FIXME(mw): Assigning internal linkage to all
-                        // monomorphizations is potentially a waste of space
-                        // since monomorphizations could be shared between
-                        // crates. The main reason for making them internal is
-                        // a limitation in MingW's binutils that cannot deal
-                        // with COFF object that have more than 2^15 sections,
-                        // which is something that can happen for large programs
-                        // when every function gets put into its own COMDAT
-                        // section.
-                        llvm::InternalLinkage
-                    } else if trans_item.is_from_extern_crate() {
-                        // FIXME(mw): It would be nice if we could mark these as
-                        // `AvailableExternallyLinkage`, since they should have
-                        // been instantiated in the extern crate. But this
-                        // sometimes leads to crashes on Windows because LLVM
-                        // does not handle exception handling table instantiation
-                        // reliably in that case.
-                        llvm::InternalLinkage
-                    } else if reachable.contains(&tcx.map
-                                                     .as_local_node_id(instance.def)
-                                                     .unwrap()) {
-                        llvm::ExternalLinkage
-                    } else {
-                        // Functions that are not visible outside this crate can
-                        // be marked as internal.
-                        llvm::InternalLinkage
-                    }
-                }
-            }
-        });
-
-        items.insert(trans_item, linkage);
-    }
-
-    CodegenUnit::new(
-        numbered_codegen_unit_name(&tcx.crate_name[..], 0),
-        items)
-}
-
 fn numbered_codegen_unit_name(crate_name: &str, index: usize) -> InternedString {
     token::intern_and_get_ident(&format!("{}{}{}",
         crate_name,

src/librustc_trans/trans_item.rs

@@ -241,19 +241,6 @@ impl<'a, 'tcx> TransItem<'tcx> {
         }
     }
 
-    pub fn requests_inline(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> bool {
-        match *self {
-            TransItem::Fn(ref instance) => {
-                instance.substs.types().next().is_some() || {
-                    let attributes = tcx.get_attrs(instance.def);
-                    attr::requests_inline(&attributes[..])
-                }
-            }
-            TransItem::DropGlue(..) => true,
-            TransItem::Static(..)   => false,
-        }
-    }
-
     pub fn is_from_extern_crate(&self) -> bool {
         match *self {
             TransItem::Fn(ref instance) => !instance.def.is_local(),
@@ -262,10 +249,18 @@ impl<'a, 'tcx> TransItem<'tcx> {
         }
     }
 
-    pub fn is_instantiated_only_on_demand(&self) -> bool {
+    /// True if the translation item should only be translated to LLVM IR if
+    /// it is referenced somewhere (like inline functions, for example).
+    pub fn is_instantiated_only_on_demand(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> bool {
+        if self.explicit_linkage(tcx).is_some() {
+            return false;
+        }
+
         match *self {
             TransItem::Fn(ref instance) => {
-                !instance.def.is_local() || instance.substs.types().next().is_some()
+                !instance.def.is_local() ||
+                instance.substs.types().next().is_some() ||
+                attr::requests_inline(&tcx.get_attrs(instance.def)[..])
             }
             TransItem::DropGlue(..) => true,
             TransItem::Static(..)   => false,
@@ -282,6 +277,18 @@ impl<'a, 'tcx> TransItem<'tcx> {
         }
     }
 
+    /// Returns true if there has to be a local copy of this TransItem in every
+    /// codegen unit that references it (as with inlined functions, for example)
+    pub fn needs_local_copy(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> bool {
+        // Currently everything that is instantiated only on demand is done so
+        // with "internal" linkage, so we need a copy to be present in every
+        // codegen unit.
+        // This is coincidental: We could also instantiate something only if it
+        // is referenced (e.g. a regular, private function) but place it in its
+        // own codegen unit with "external" linkage.
+        self.is_instantiated_only_on_demand(tcx)
+    }
+
     pub fn explicit_linkage(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Option<llvm::Linkage> {
         let def_id = match *self {
             TransItem::Fn(ref instance) => instance.def,

src/test/codegen-units/partitioning/local-inlining.rs

@@ -19,7 +19,7 @@
 mod inline {
 
     // Important: This function should show up in all codegen units where it is inlined
-    //~ TRANS_ITEM fn local_inlining::inline[0]::inlined_function[0] @@ local_inlining-inline[External] local_inlining-user1[Available] local_inlining-user2[Available]
+    //~ TRANS_ITEM fn local_inlining::inline[0]::inlined_function[0] @@ local_inlining-user1[Internal] local_inlining-user2[Internal]
     #[inline(always)]
     pub fn inlined_function()
     {

src/test/codegen-units/partitioning/local-transitive-inlining.rs

@@ -18,7 +18,7 @@
 
 mod inline {
 
-    //~ TRANS_ITEM fn local_transitive_inlining::inline[0]::inlined_function[0] @@ local_transitive_inlining-inline[External] local_transitive_inlining-direct_user[Available] local_transitive_inlining-indirect_user[Available]
+    //~ TRANS_ITEM fn local_transitive_inlining::inline[0]::inlined_function[0] @@ local_transitive_inlining-indirect_user[Internal]
     #[inline(always)]
     pub fn inlined_function()
     {
@@ -29,7 +29,7 @@ mod inline {
 mod direct_user {
     use super::inline;
 
-    //~ TRANS_ITEM fn local_transitive_inlining::direct_user[0]::foo[0] @@ local_transitive_inlining-direct_user[External] local_transitive_inlining-indirect_user[Available]
+    //~ TRANS_ITEM fn local_transitive_inlining::direct_user[0]::foo[0] @@ local_transitive_inlining-indirect_user[Internal]
     #[inline(always)]
     pub fn foo() {
         inline::inlined_function();

src/test/run-make/sepcomp-inlining/Makefile

@@ -1,13 +1,14 @@
 -include ../tools.mk
 
-# Test that #[inline(always)] functions still get inlined across compilation
-# unit boundaries.  Compilation should produce three IR files, with each one
-# containing a definition of the inlined function.  Also, the non-#[inline]
-# function should be defined in only one compilation unit.
+# Test that #[inline] functions still get inlined across compilation unit
+# boundaries. Compilation should produce three IR files, but only the two
+# compilation units that have a usage of the #[inline] function should
+# contain a definition. Also, the non-#[inline] function should be defined
+# in only one compilation unit.
 
 all:
 	$(RUSTC) foo.rs --emit=llvm-ir -C codegen-units=3
-	[ "$$(cat "$(TMPDIR)"/foo.?.ll | grep -c define\ i32\ .*inlined)" -eq "1" ]
-	[ "$$(cat "$(TMPDIR)"/foo.?.ll | grep -c define\ available_externally\ i32\ .*inlined)" -eq "2" ]
+	[ "$$(cat "$(TMPDIR)"/foo.?.ll | grep -c define\ i32\ .*inlined)" -eq "0" ]
+	[ "$$(cat "$(TMPDIR)"/foo.?.ll | grep -c define\ internal\ i32\ .*inlined)" -eq "2" ]
 	[ "$$(cat "$(TMPDIR)"/foo.?.ll | grep -c define\ i32\ .*normal)" -eq "1" ]
 	[ "$$(cat "$(TMPDIR)"/foo.?.ll | grep -c declare\ i32\ .*normal)" -eq "2" ]