Auto merge of #45575 - michaelwoerister:tweak-inline-trans-items, r=nikomatsakis

Only instantiate inline- and const-fns if they are referenced (again).

It seems that we have regressed on not translating `#[inline]` functions unless they are actually used. This should bring back this optimization. I also added a regression test this time so it doesn't happen again accidentally.

Fixes #40392.

r? @alexcrichton

UPDATE & PSA
---------------------
This patch **makes translation very lazy** -- in general this is a good thing (we don't want the compiler to do unnecessary work) but it has two consequences:
1. Some error messages are only generated when an item is actually translated. Consequently, this patch will lead to more cases where the compiler will only start emitting errors when the erroneous function is actually used. This has always been true to some extend (e.g. when passing generic values to an intrinsic) but since this is something user-facing it's worth mentioning.
2. When writing tests, one has to make sure that the functions in question are actually generated. In other words, it must not be dead code. This can usually  be achieved by either
    1. making sure the function is exported from the resulting binary or
    2. by making sure the function is called from something that is exported (or `main()`).

Note that it depends on the crate type what functions are exported:
   1. For rlibs and dylibs everything that is reachable from the outside is exported.
   2. For executables, cdylibs, and staticlibs, items are only exported if they are additionally `#[no_mangle]` or have an `#[export_name]`.

The commits in this PR contain many examples of how tests can be updated to comply to the new requirements.

Author: bors

src/librustc/dep_graph/graph.rs

@@ -328,7 +328,12 @@ impl DepGraph {
     }
 
     pub fn fingerprint_of(&self, dep_node: &DepNode) -> Fingerprint {
-        self.fingerprints.borrow()[dep_node]
+        match self.fingerprints.borrow().get(dep_node) {
+            Some(&fingerprint) => fingerprint,
+            None => {
+                bug!("Could not find current fingerprint for {:?}", dep_node)
+            }
+        }
     }
 
     pub fn prev_fingerprint_of(&self, dep_node: &DepNode) -> Option<Fingerprint> {

src/librustc_trans_utils/collector.rs

@@ -211,6 +211,8 @@ use trans_item::{TransItemExt, DefPathBasedNames, InstantiationMode};
 
 use rustc_data_structures::bitvec::BitVector;
 
+use syntax::attr;
+
 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
 pub enum TransItemCollectionMode {
     Eager,
@@ -324,9 +326,14 @@ fn collect_roots<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let mut roots = Vec::new();
 
     {
+        let entry_fn = tcx.sess.entry_fn.borrow().map(|(node_id, _)| {
+            tcx.hir.local_def_id(node_id)
+        });
+
         let mut visitor = RootCollector {
             tcx,
             mode,
+            entry_fn,
             output: &mut roots,
         };
 
@@ -875,6 +882,7 @@ struct RootCollector<'b, 'a: 'b, 'tcx: 'a + 'b> {
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     mode: TransItemCollectionMode,
     output: &'b mut Vec<TransItem<'tcx>>,
+    entry_fn: Option<DefId>,
 }
 
 impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
@@ -932,10 +940,7 @@ impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
                 let tcx = self.tcx;
                 let def_id = tcx.hir.local_def_id(item.id);
 
-                if (self.mode == TransItemCollectionMode::Eager ||
-                    !tcx.is_const_fn(def_id) || tcx.is_exported_symbol(def_id)) &&
-                   !item_has_type_parameters(tcx, def_id) {
-
+                if self.is_root(def_id) {
                     debug!("RootCollector: ItemFn({})",
                            def_id_to_string(tcx, def_id));
 
@@ -957,10 +962,7 @@ impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
                 let tcx = self.tcx;
                 let def_id = tcx.hir.local_def_id(ii.id);
 
-                if (self.mode == TransItemCollectionMode::Eager ||
-                    !tcx.is_const_fn(def_id) ||
-                    tcx.is_exported_symbol(def_id)) &&
-                   !item_has_type_parameters(tcx, def_id) {
+                if self.is_root(def_id) {
                     debug!("RootCollector: MethodImplItem({})",
                            def_id_to_string(tcx, def_id));
 
@@ -973,6 +975,22 @@ impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
     }
 }
 
+impl<'b, 'a, 'v> RootCollector<'b, 'a, 'v> {
+    fn is_root(&self, def_id: DefId) -> bool {
+        !item_has_type_parameters(self.tcx, def_id) && match self.mode {
+            TransItemCollectionMode::Eager => {
+                true
+            }
+            TransItemCollectionMode::Lazy => {
+                self.entry_fn == Some(def_id) ||
+                self.tcx.is_exported_symbol(def_id) ||
+                attr::contains_name(&self.tcx.get_attrs(def_id),
+                                    "rustc_std_internal_symbol")
+            }
+        }
+    }
+}
+
 fn item_has_type_parameters<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
     let generics = tcx.generics_of(def_id);
     generics.parent_types as usize + generics.types.len() > 0

src/librustc_trans_utils/common.rs

@@ -51,7 +51,8 @@ pub fn requests_inline<'a, 'tcx>(
         // available to normal end-users.
         return true
     }
-    attr::requests_inline(&instance.def.attrs(tcx)[..])
+    attr::requests_inline(&instance.def.attrs(tcx)[..]) ||
+        tcx.is_const_fn(instance.def.def_id())
 }
 
 pub fn is_inline_instance<'a, 'tcx>(

src/librustc_trans_utils/lib.rs

@@ -40,14 +40,12 @@ extern crate rustc_data_structures;
 extern crate syntax;
 extern crate syntax_pos;
 
-use rustc::ty::TyCtxt;
+use rustc::ty::{TyCtxt, Instance};
 use rustc::hir;
 use rustc::hir::def_id::LOCAL_CRATE;
 use rustc::hir::map as hir_map;
 use rustc::util::nodemap::NodeSet;
 
-use syntax::attr;
-
 pub mod common;
 pub mod link;
 pub mod collector;
@@ -77,7 +75,7 @@ pub fn check_for_rustc_errors_attr(tcx: TyCtxt) {
 ///
 /// This list is later used by linkers to determine the set of symbols needed to
 /// be exposed from a dynamic library and it's also encoded into the metadata.
-pub fn find_exported_symbols(tcx: TyCtxt) -> NodeSet {
+pub fn find_exported_symbols<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> NodeSet {
     tcx.reachable_set(LOCAL_CRATE).0.iter().cloned().filter(|&id| {
         // Next, we want to ignore some FFI functions that are not exposed from
         // this crate. Reachable FFI functions can be lumped into two
@@ -107,11 +105,10 @@ pub fn find_exported_symbols(tcx: TyCtxt) -> NodeSet {
                 node: hir::ImplItemKind::Method(..), .. }) => {
                 let def_id = tcx.hir.local_def_id(id);
                 let generics = tcx.generics_of(def_id);
-                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)
+                !common::requests_inline(tcx, &Instance::mono(tcx, def_id))
             }
 
             _ => false

src/test/codegen-units/item-collection/unreferenced-const-fn.rs

@@ -0,0 +1,22 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-tidy-linelength
+// compile-flags:-Zprint-trans-items=lazy
+
+// NB: We do not expect *any* translation item to be generated here.
+
+#![feature(const_fn)]
+#![deny(dead_code)]
+#![crate_type = "rlib"]
+
+pub const fn foo(x: u32) -> u32 {
+    x + 0xf00
+}

src/test/codegen-units/item-collection/unreferenced-inline-function.rs

@@ -0,0 +1,23 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// ignore-tidy-linelength
+// compile-flags:-Zprint-trans-items=lazy
+
+// NB: We do not expect *any* translation item to be generated here.
+
+#![deny(dead_code)]
+#![crate_type = "rlib"]
+
+#[inline]
+pub fn foo() -> bool {
+    [1, 2] == [3, 4]
+}
+

src/test/codegen-units/partitioning/extern-drop-glue.rs

@@ -16,7 +16,7 @@
 // compile-flags:-Zinline-in-all-cgus
 
 #![allow(dead_code)]
-#![crate_type="lib"]
+#![crate_type="rlib"]
 
 // aux-build:cgu_extern_drop_glue.rs
 extern crate cgu_extern_drop_glue;
@@ -25,20 +25,20 @@ extern crate cgu_extern_drop_glue;
 
 struct LocalStruct(cgu_extern_drop_glue::Struct);
 
-//~ TRANS_ITEM fn extern_drop_glue::user[0] @@ extern_drop_glue[Internal]
-fn user()
+//~ TRANS_ITEM fn extern_drop_glue::user[0] @@ extern_drop_glue[External]
+pub fn user()
 {
     //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<extern_drop_glue::LocalStruct[0]> @@ extern_drop_glue[Internal]
     let _ = LocalStruct(cgu_extern_drop_glue::Struct(0));
 }
 
-mod mod1 {
+pub mod mod1 {
     use cgu_extern_drop_glue;
 
     struct LocalStruct(cgu_extern_drop_glue::Struct);
 
-    //~ TRANS_ITEM fn extern_drop_glue::mod1[0]::user[0] @@ extern_drop_glue-mod1[Internal]
-    fn user()
+    //~ TRANS_ITEM fn extern_drop_glue::mod1[0]::user[0] @@ extern_drop_glue-mod1[External]
+    pub fn user()
     {
         //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<extern_drop_glue::mod1[0]::LocalStruct[0]> @@ extern_drop_glue-mod1[Internal]
         let _ = LocalStruct(cgu_extern_drop_glue::Struct(0));

src/test/codegen-units/partitioning/inlining-from-extern-crate.rs

@@ -35,10 +35,10 @@ pub fn user()
     cgu_explicit_inlining::never_inlined();
 }
 
-mod mod1 {
+pub mod mod1 {
     use cgu_explicit_inlining;
 
-    //~ TRANS_ITEM fn inlining_from_extern_crate::mod1[0]::user[0] @@ inlining_from_extern_crate-mod1[Internal]
+    //~ TRANS_ITEM fn inlining_from_extern_crate::mod1[0]::user[0] @@ inlining_from_extern_crate-mod1[External]
     pub fn user()
     {
         cgu_explicit_inlining::inlined();
@@ -48,10 +48,10 @@ mod mod1 {
     }
 }
 
-mod mod2 {
+pub mod mod2 {
     use cgu_explicit_inlining;
 
-    //~ TRANS_ITEM fn inlining_from_extern_crate::mod2[0]::user[0] @@ inlining_from_extern_crate-mod2[Internal]
+    //~ TRANS_ITEM fn inlining_from_extern_crate::mod2[0]::user[0] @@ inlining_from_extern_crate-mod2[External]
     pub fn user()
     {
         cgu_explicit_inlining::always_inlined();

src/test/codegen-units/partitioning/local-drop-glue.rs

@@ -15,7 +15,7 @@
 // compile-flags:-Zinline-in-all-cgus
 
 #![allow(dead_code)]
-#![crate_type="lib"]
+#![crate_type="rlib"]
 
 //~ TRANS_ITEM fn core::ptr[0]::drop_in_place[0]<local_drop_glue::Struct[0]> @@ local_drop_glue[Internal] local_drop_glue-mod1[Internal]
 struct Struct {
@@ -32,8 +32,8 @@ struct Outer {
     _a: Struct
 }
 
-//~ TRANS_ITEM fn local_drop_glue::user[0] @@ local_drop_glue[Internal]
-fn user()
+//~ TRANS_ITEM fn local_drop_glue::user[0] @@ local_drop_glue[External]
+pub fn user()
 {
     let _ = Outer {
         _a: Struct {
@@ -42,7 +42,7 @@ fn user()
     };
 }
 
-mod mod1
+pub mod mod1
 {
     use super::Struct;
 
@@ -53,8 +53,8 @@ mod mod1
         _b: (u32, Struct),
     }
 
-    //~ TRANS_ITEM fn local_drop_glue::mod1[0]::user[0] @@ local_drop_glue-mod1[Internal]
-    fn user()
+    //~ TRANS_ITEM fn local_drop_glue::mod1[0]::user[0] @@ local_drop_glue-mod1[External]
+    pub fn user()
     {
         let _ = Struct2 {
             _a: Struct { _a: 0 },

src/test/codegen-units/partitioning/local-inlining-but-not-all.rs

@@ -27,28 +27,28 @@ mod inline {
     }
 }
 
-mod user1 {
+pub mod user1 {
     use super::inline;
 
-    //~ TRANS_ITEM fn local_inlining_but_not_all::user1[0]::foo[0] @@ local_inlining_but_not_all-user1[Internal]
-    fn foo() {
+    //~ TRANS_ITEM fn local_inlining_but_not_all::user1[0]::foo[0] @@ local_inlining_but_not_all-user1[External]
+    pub fn foo() {
         inline::inlined_function();
     }
 }
 
-mod user2 {
+pub mod user2 {
     use super::inline;
 
-    //~ TRANS_ITEM fn local_inlining_but_not_all::user2[0]::bar[0] @@ local_inlining_but_not_all-user2[Internal]
-    fn bar() {
+    //~ TRANS_ITEM fn local_inlining_but_not_all::user2[0]::bar[0] @@ local_inlining_but_not_all-user2[External]
+    pub fn bar() {
         inline::inlined_function();
     }
 }
 
-mod non_user {
+pub mod non_user {
 
-    //~ TRANS_ITEM fn local_inlining_but_not_all::non_user[0]::baz[0] @@ local_inlining_but_not_all-non_user[Internal]
-    fn baz() {
+    //~ TRANS_ITEM fn local_inlining_but_not_all::non_user[0]::baz[0] @@ local_inlining_but_not_all-non_user[External]
+    pub fn baz() {
 
     }
 }

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

@@ -28,28 +28,28 @@ mod inline {
     }
 }
 
-mod user1 {
+pub mod user1 {
     use super::inline;
 
-    //~ TRANS_ITEM fn local_inlining::user1[0]::foo[0] @@ local_inlining-user1[Internal]
-    fn foo() {
+    //~ TRANS_ITEM fn local_inlining::user1[0]::foo[0] @@ local_inlining-user1[External]
+    pub fn foo() {
         inline::inlined_function();
     }
 }
 
-mod user2 {
+pub mod user2 {
     use super::inline;
 
-    //~ TRANS_ITEM fn local_inlining::user2[0]::bar[0] @@ local_inlining-user2[Internal]
-    fn bar() {
+    //~ TRANS_ITEM fn local_inlining::user2[0]::bar[0] @@ local_inlining-user2[External]
+    pub fn bar() {
         inline::inlined_function();
     }
 }
 
-mod non_user {
+pub mod non_user {
 
-    //~ TRANS_ITEM fn local_inlining::non_user[0]::baz[0] @@ local_inlining-non_user[Internal]
-    fn baz() {
+    //~ TRANS_ITEM fn local_inlining::non_user[0]::baz[0] @@ local_inlining-non_user[External]
+    pub fn baz() {
 
     }
 }

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

@@ -15,7 +15,7 @@
 // compile-flags:-Zinline-in-all-cgus
 
 #![allow(dead_code)]
-#![crate_type="lib"]
+#![crate_type="rlib"]
 
 mod inline {
 
@@ -37,19 +37,19 @@ mod direct_user {
     }
 }
 
-mod indirect_user {
+pub mod indirect_user {
     use super::direct_user;
 
-    //~ TRANS_ITEM fn local_transitive_inlining::indirect_user[0]::bar[0] @@ local_transitive_inlining-indirect_user[Internal]
-    fn bar() {
+    //~ TRANS_ITEM fn local_transitive_inlining::indirect_user[0]::bar[0] @@ local_transitive_inlining-indirect_user[External]
+    pub fn bar() {
         direct_user::foo();
     }
 }
 
-mod non_user {
+pub mod non_user {
 
-    //~ TRANS_ITEM fn local_transitive_inlining::non_user[0]::baz[0] @@ local_transitive_inlining-non_user[Internal]
-    fn baz() {
+    //~ TRANS_ITEM fn local_transitive_inlining::non_user[0]::baz[0] @@ local_transitive_inlining-non_user[External]
+    pub fn baz() {
 
     }
 }