Auto merge of #42899 - alexcrichton:compiler-builtins, r=nikomatsakis

Switch to rust-lang-nursery/compiler-builtins

This commit migrates the in-tree `libcompiler_builtins` to the upstream version
at https://github.com/rust-lang-nursery/compiler-builtins. The upstream version
has a number of intrinsics written in Rust and serves as an in-progress rewrite
of compiler-rt into Rust. Additionally it also contains all the existing
intrinsics defined in `libcompiler_builtins` for 128-bit integers.

It's been the intention since the beginning to make this transition but
previously it just lacked the manpower to get done. As this PR likely shows it
wasn't a trivial integration! Some highlight changes are:

* The PR rust-lang-nursery/compiler-builtins#166 contains a number of fixes
  across platforms and also some refactorings to make the intrinsics easier to
  read. The additional testing added there also fixed a number of integration
  issues when pulling the repository into this tree.

* LTO with the compiler-builtins crate was fixed to link in the entire crate
  after the LTO process as these intrinsics are excluded from LTO.

* Treatment of hidden symbols was updated as previously the
  `#![compiler_builtins]` crate would mark all symbol *imports* as hidden
  whereas it was only intended to mark *exports* as hidden.

.gitmodules

@@ -2,9 +2,6 @@
 	path = src/llvm
 	url = https://github.com/rust-lang/llvm.git
 	branch = master
-[submodule "src/compiler-rt"]
-	path = src/compiler-rt
-	url = https://github.com/rust-lang/compiler-rt.git
 [submodule "src/rt/hoedown"]
 	path = src/rt/hoedown
 	url = https://github.com/rust-lang/hoedown.git
@@ -33,3 +30,6 @@
 [submodule "src/tools/rls"]
 	path = src/tools/rls
 	url = https://github.com/rust-lang-nursery/rls.git
+[submodule "src/libcompiler_builtins"]
+	path = src/libcompiler_builtins
+	url = https://github.com/rust-lang-nursery/compiler-builtins

src/Cargo.lock

@@ -276,7 +276,6 @@ dependencies = [
 name = "compiler_builtins"
 version = "0.0.0"
 dependencies = [
- "build_helper 0.1.0",
  "core 0.0.0",
  "gcc 0.3.51 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

src/bootstrap/bin/rustc.rs

@@ -137,6 +137,11 @@ fn main() {
             }
         }
 
+        let crate_name = args.windows(2)
+            .find(|a| &*a[0] == "--crate-name")
+            .unwrap();
+        let crate_name = &*crate_name[1];
+
         // If we're compiling specifically the `panic_abort` crate then we pass
         // the `-C panic=abort` option. Note that we do not do this for any
         // other crate intentionally as this is the only crate for now that we
@@ -145,9 +150,7 @@ fn main() {
         // This... is a bit of a hack how we detect this. Ideally this
         // information should be encoded in the crate I guess? Would likely
         // require an RFC amendment to RFC 1513, however.
-        let is_panic_abort = args.windows(2)
-            .any(|a| &*a[0] == "--crate-name" && &*a[1] == "panic_abort");
-        if is_panic_abort {
+        if crate_name == "panic_abort" {
             cmd.arg("-C").arg("panic=abort");
         }
 
@@ -162,7 +165,15 @@ fn main() {
             Ok(s) => if s == "true" { "y" } else { "n" },
             Err(..) => "n",
         };
+
+        // The compiler builtins are pretty sensitive to symbols referenced in
+        // libcore and such, so we never compile them with debug assertions.
+        if crate_name == "compiler_builtins" {
+            cmd.arg("-C").arg("debug-assertions=no");
+        } else {
             cmd.arg("-C").arg(format!("debug-assertions={}", debug_assertions));
+        }
+
         if let Ok(s) = env::var("RUSTC_CODEGEN_UNITS") {
             cmd.arg("-C").arg(format!("codegen-units={}", s));
         }

src/bootstrap/bootstrap.py

@@ -583,7 +583,7 @@ class RustBuild(object):
                                (self.get_toml('jemalloc') or
                                 self.get_mk('CFG_JEMALLOC_ROOT'))))]
         run(["git", "submodule", "update",
-             "--init"] + submodules,
+             "--init", "--recursive"] + submodules,
             cwd=self.rust_root, verbose=self.verbose)
         run(["git", "submodule", "-q", "foreach", "git",
              "reset", "-q", "--hard"],

src/bootstrap/dist.rs

@@ -553,10 +553,10 @@ pub fn rust_src(build: &Build) {
         "src/libstd",
         "src/libstd_unicode",
         "src/libunwind",
+        "src/rustc/compiler_builtins_shim",
         "src/rustc/libc_shim",
         "src/libtest",
         "src/libterm",
-        "src/compiler-rt",
         "src/jemalloc",
         "src/libprofiler_builtins",
     ];

src/build_helper/lib.rs

@@ -239,7 +239,10 @@ pub fn sanitizer_lib_boilerplate(sanitizer_name: &str) -> Result<NativeLibBoiler
         ),
         _ => return Err(()),
     };
-    native_lib_boilerplate("compiler-rt", sanitizer_name, &link_name, search_path)
+    native_lib_boilerplate("libcompiler_builtins/compiler-rt",
+                           sanitizer_name,
+                           &link_name,
+                           search_path)
 }
 
 fn dir_up_to_date(src: &Path, threshold: &FileTime) -> bool {

src/ci/init_repo.sh

@@ -67,13 +67,14 @@ for module in $modules; do
         mv "src/llvm-$commit" src/llvm
         continue
     fi
-    if [ ! -d "$cache_src_dir/$module" ]; then
+    if [ ! -e "$cache_src_dir/$module/.git" ]; then
         echo "WARNING: $module not found in pristine repo"
-        retry sh -c "git submodule deinit -f $module && git submodule update --init $module"
+        retry sh -c "git submodule deinit -f $module && \
+            git submodule update --init --recursive $module"
         continue
     fi
     retry sh -c "git submodule deinit -f $module && \
-        git submodule update --init --reference $cache_src_dir/$module $module"
+        git submodule update --init --recursive --reference $cache_src_dir/$module $module"
 done
 
 travis_fold end update_submodules

compiler-rt @ c8a8767c

-Subproject commit c8a8767c56ad3d3f4eb45c87b95026936fb9aa35

src/doc/unstable-book/src/library-features/compiler-builtins-lib.md

-# `compiler_builtins_lib`
-
-The tracking issue for this feature is: None.
-
-------------------------
-
-This feature is required to link to the `compiler_builtins` crate which contains
-"compiler intrinsics". Compiler intrinsics are software implementations of basic
-operations like multiplication of `u64`s. These intrinsics are only required on
-platforms where these operations don't directly map to a hardware instruction.
-
-You should never need to explicitly link to the `compiler_builtins` crate when
-building "std" programs as `compiler_builtins` is already in the dependency
-graph of `std`. But you may need it when building `no_std` **binary** crates. If
-you get a *linker* error like:
-
-``` text
-$PWD/src/main.rs:11: undefined reference to `__aeabi_lmul'
-$PWD/src/main.rs:11: undefined reference to `__aeabi_uldivmod'
-```
-
-That means that you need to link to this crate.
-
-When you link to this crate, make sure it only appears once in your crate
-dependency graph. Also, it doesn't matter where in the dependency graph, you
-place the `compiler_builtins` crate.
-
-<!-- NOTE(ignore) doctests don't support `no_std` binaries -->
-
-``` rust,ignore
-#![feature(compiler_builtins_lib)]
-#![no_std]
-
-extern crate compiler_builtins;
-```

libcompiler_builtins @ 238647af

+Subproject commit 238647af806470dc73e585c03682083931d29cd5

src/libcompiler_builtins/build.rs

-// Copyright 2016 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.
-
-//! Compiles the `compiler-rt` library, or at least the builtins part of it.
-//!
-//! Note that while compiler-rt has a build system associated with it, we
-//! specifically don't use it here. The compiler-rt build system, written in
-//! CMake, is actually *very* difficult to work with in terms of getting it to
-//! compile on all the relevant platforms we want it to compile on. In the end
-//! it became so much pain to work with local patches, work around the oddities
-//! of the build system, etc, that we're just building everything by hand now.
-//!
-//! In general compiler-rt is just a bunch of intrinsics that are in practice
-//! *very* stable. We just need to make sure that all the relevant functions and
-//! such are compiled somewhere and placed in an object file somewhere.
-//! Eventually, these should all be written in Rust!
-//!
-//! So below you'll find a listing of every single file in the compiler-rt repo
-//! that we're compiling. We just reach in and compile with the `gcc` crate
-//! which should have all the relevant flags and such already configured.
-//!
-//! The risk here is that if we update compiler-rt we may need to compile some
-//! new intrinsics, but to be honest we surely don't use all of the intrinsics
-//! listed below today so the likelihood of us actually needing a new intrinsic
-//! is quite low. The failure case is also just that someone reports a link
-//! error (if any) and then we just add it to the list. Overall, that cost is
-//! far far less than working with compiler-rt's build system over time.
-
-extern crate build_helper;
-extern crate gcc;
-
-use std::collections::BTreeMap;
-use std::env;
-use std::path::Path;
-use build_helper::native_lib_boilerplate;
-
-struct Sources {
-    // SYMBOL -> PATH TO SOURCE
-    map: BTreeMap<&'static str, &'static str>,
-}
-
-impl Sources {
-    fn new() -> Sources {
-        Sources { map: BTreeMap::new() }
-    }
-
-    fn extend(&mut self, sources: &[&'static str]) {
-        // NOTE Some intrinsics have both a generic implementation (e.g.
-        // `floatdidf.c`) and an arch optimized implementation
-        // (`x86_64/floatdidf.c`). In those cases, we keep the arch optimized
-        // implementation and discard the generic implementation. If we don't
-        // and keep both implementations, the linker will yell at us about
-        // duplicate symbols!
-        for &src in sources {
-            let symbol = Path::new(src).file_stem().unwrap().to_str().unwrap();
-            if src.contains("/") {
-                // Arch-optimized implementation (preferred)
-                self.map.insert(symbol, src);
-            } else {
-                // Generic implementation
-                if !self.map.contains_key(symbol) {
-                    self.map.insert(symbol, src);
-                }
-            }
-        }
-    }
-}
-
-fn main() {
-    let target = env::var("TARGET").expect("TARGET was not set");
-
-    // Emscripten's runtime includes all the builtins
-    if target.contains("emscripten") {
-        return;
-    }
-
-    // Can't reuse `sources` list for the freshness check becuse it doesn't contain header files.
-    let native = match native_lib_boilerplate("compiler-rt", "compiler-rt", "compiler-rt", ".") {
-        Ok(native) => native,
-        _ => return,
-    };
-
-    let cfg = &mut gcc::Config::new();
-    cfg.out_dir(&native.out_dir);
-
-    if target.contains("msvc") {
-        // Don't pull in extra libraries on MSVC
-        cfg.flag("/Zl");
-
-        // Emulate C99 and C++11's __func__ for MSVC prior to 2013 CTP
-        cfg.define("__func__", Some("__FUNCTION__"));
-    } else {
-        // Turn off various features of gcc and such, mostly copying
-        // compiler-rt's build system already
-        cfg.flag("-fno-builtin");
-        cfg.flag("-fvisibility=hidden");
-        // Accepted practice on Solaris is to never omit frame pointer so that
-        // system observability tools work as expected.  In addition, at least
-        // on Solaris, -fomit-frame-pointer on sparcv9 appears to generate
-        // references to data outside of the current stack frame.  A search of
-        // the gcc bug database provides a variety of issues surrounding
-        // -fomit-frame-pointer on non-x86 platforms.
-        if !target.contains("solaris") && !target.contains("sparc") {
-            cfg.flag("-fomit-frame-pointer");
-        }
-        cfg.flag("-ffreestanding");
-        cfg.define("VISIBILITY_HIDDEN", None);
-    }
-
-    let mut sources = Sources::new();
-    sources.extend(&["absvdi2.c",
-                     "absvsi2.c",
-                     "adddf3.c",
-                     "addsf3.c",
-                     "addvdi3.c",
-                     "addvsi3.c",
-                     "apple_versioning.c",
-                     "ashldi3.c",
-                     "ashrdi3.c",
-                     "clzdi2.c",
-                     "clzsi2.c",
-                     "cmpdi2.c",
-                     "comparedf2.c",
-                     "comparesf2.c",
-                     "ctzdi2.c",
-                     "ctzsi2.c",
-                     "divdc3.c",
-                     "divdf3.c",
-                     "divdi3.c",
-                     "divmoddi4.c",
-                     "divmodsi4.c",
-                     "divsc3.c",
-                     "divsf3.c",
-                     "divsi3.c",
-                     "divxc3.c",
-                     "extendsfdf2.c",
-                     "extendhfsf2.c",
-                     "ffsdi2.c",
-                     "fixdfdi.c",
-                     "fixdfsi.c",
-                     "fixsfdi.c",
-                     "fixsfsi.c",
-                     "fixunsdfdi.c",
-                     "fixunsdfsi.c",
-                     "fixunssfdi.c",
-                     "fixunssfsi.c",
-                     "fixunsxfdi.c",
-                     "fixunsxfsi.c",
-                     "fixxfdi.c",
-                     "floatdidf.c",
-                     "floatdisf.c",
-                     "floatdixf.c",
-                     "floatsidf.c",
-                     "floatsisf.c",
-                     "floatundidf.c",
-                     "floatundisf.c",
-                     "floatundixf.c",
-                     "floatunsidf.c",
-                     "floatunsisf.c",
-                     "int_util.c",
-                     "lshrdi3.c",
-                     "moddi3.c",
-                     "modsi3.c",
-                     "muldc3.c",
-                     "muldf3.c",
-                     "muldi3.c",
-                     "mulodi4.c",
-                     "mulosi4.c",
-                     "muloti4.c",
-                     "mulsc3.c",
-                     "mulsf3.c",
-                     "mulvdi3.c",
-                     "mulvsi3.c",
-                     "mulxc3.c",
-                     "negdf2.c",
-                     "negdi2.c",
-                     "negsf2.c",
-                     "negvdi2.c",
-                     "negvsi2.c",
-                     "paritydi2.c",
-                     "paritysi2.c",
-                     "popcountdi2.c",
-                     "popcountsi2.c",
-                     "powidf2.c",
-                     "powisf2.c",
-                     "powixf2.c",
-                     "subdf3.c",
-                     "subsf3.c",
-                     "subvdi3.c",
-                     "subvsi3.c",
-                     "truncdfhf2.c",
-                     "truncdfsf2.c",
-                     "truncsfhf2.c",
-                     "ucmpdi2.c",
-                     "udivdi3.c",
-                     "udivmoddi4.c",
-                     "udivmodsi4.c",
-                     "udivsi3.c",
-                     "umoddi3.c",
-                     "umodsi3.c"]);
-
-    if !target.contains("ios") {
-        sources.extend(&["absvti2.c",
-                         "addvti3.c",
-                         "ashlti3.c",
-                         "ashrti3.c",
-                         "clzti2.c",
-                         "cmpti2.c",
-                         "ctzti2.c",
-                         "divti3.c",
-                         "ffsti2.c",
-                         "fixdfti.c",
-                         "fixsfti.c",
-                         "fixunsdfti.c",
-                         "fixunssfti.c",
-                         "fixunsxfti.c",
-                         "fixxfti.c",
-                         "floattidf.c",
-                         "floattisf.c",
-                         "floattixf.c",
-                         "floatuntidf.c",
-                         "floatuntisf.c",
-                         "floatuntixf.c",
-                         "lshrti3.c",
-                         "modti3.c",
-                         "multi3.c",
-                         "mulvti3.c",
-                         "negti2.c",
-                         "negvti2.c",
-                         "parityti2.c",
-                         "popcountti2.c",
-                         "subvti3.c",
-                         "ucmpti2.c",
-                         "udivmodti4.c",
-                         "udivti3.c",
-                         "umodti3.c"]);
-    }
-
-    if target.contains("apple") {
-        sources.extend(&["atomic_flag_clear.c",
-                         "atomic_flag_clear_explicit.c",
-                         "atomic_flag_test_and_set.c",
-                         "atomic_flag_test_and_set_explicit.c",
-                         "atomic_signal_fence.c",
-                         "atomic_thread_fence.c"]);
-    }
-
-    if target.contains("msvc") {
-        if target.contains("x86_64") {
-            sources.extend(&["x86_64/floatdidf.c", "x86_64/floatdisf.c", "x86_64/floatdixf.c"]);
-        }
-    } else {
-        if !target.contains("freebsd") && !target.contains("netbsd") {
-            sources.extend(&["gcc_personality_v0.c"]);
-        }
-
-        if target.contains("x86_64") {
-            sources.extend(&["x86_64/chkstk.S",
-                             "x86_64/chkstk2.S",
-                             "x86_64/floatdidf.c",
-                             "x86_64/floatdisf.c",
-                             "x86_64/floatdixf.c",
-                             "x86_64/floatundidf.S",
-                             "x86_64/floatundisf.S",
-                             "x86_64/floatundixf.S"]);
-        }
-
-        if target.contains("i386") || target.contains("i586") || target.contains("i686") {
-            sources.extend(&["i386/ashldi3.S",
-                             "i386/ashrdi3.S",
-                             "i386/chkstk.S",
-                             "i386/chkstk2.S",
-                             "i386/divdi3.S",
-                             "i386/floatdidf.S",
-                             "i386/floatdisf.S",
-                             "i386/floatdixf.S",
-                             "i386/floatundidf.S",
-                             "i386/floatundisf.S",
-                             "i386/floatundixf.S",
-                             "i386/lshrdi3.S",
-                             "i386/moddi3.S",
-                             "i386/muldi3.S",
-                             "i386/udivdi3.S",
-                             "i386/umoddi3.S"]);
-        }
-    }
-
-    if target.contains("arm") && !target.contains("ios") {
-        // (At least) udivsi3.S is broken for Thumb 1 which our gcc uses by
-        // default, we don't want Thumb 2 since it isn't supported on some
-        // devices, so disable thumb entirely.
-        // Upstream bug: https://bugs.llvm.org/show_bug.cgi?id=32492
-        cfg.define("__ARM_ARCH_ISA_THUMB", Some("0"));
-
-        sources.extend(&["arm/aeabi_cdcmp.S",
-                         "arm/aeabi_cdcmpeq_check_nan.c",
-                         "arm/aeabi_cfcmp.S",
-                         "arm/aeabi_cfcmpeq_check_nan.c",
-                         "arm/aeabi_dcmp.S",
-                         "arm/aeabi_div0.c",
-                         "arm/aeabi_drsub.c",
-                         "arm/aeabi_fcmp.S",
-                         "arm/aeabi_frsub.c",
-                         "arm/aeabi_idivmod.S",
-                         "arm/aeabi_ldivmod.S",
-                         "arm/aeabi_memcmp.S",
-                         "arm/aeabi_memcpy.S",
-                         "arm/aeabi_memmove.S",
-                         "arm/aeabi_memset.S",
-                         "arm/aeabi_uidivmod.S",
-                         "arm/aeabi_uldivmod.S",
-                         "arm/bswapdi2.S",
-                         "arm/bswapsi2.S",
-                         "arm/clzdi2.S",
-                         "arm/clzsi2.S",
-                         "arm/comparesf2.S",
-                         "arm/divmodsi4.S",
-                         "arm/divsi3.S",
-                         "arm/modsi3.S",
-                         "arm/switch16.S",
-                         "arm/switch32.S",
-                         "arm/switch8.S",
-                         "arm/switchu8.S",
-                         "arm/sync_synchronize.S",
-                         "arm/udivmodsi4.S",
-                         "arm/udivsi3.S",
-                         "arm/umodsi3.S"]);
-    }
-
-    if target.contains("armv7") {
-        sources.extend(&["arm/sync_fetch_and_add_4.S",
-                         "arm/sync_fetch_and_add_8.S",
-                         "arm/sync_fetch_and_and_4.S",
-                         "arm/sync_fetch_and_and_8.S",
-                         "arm/sync_fetch_and_max_4.S",
-                         "arm/sync_fetch_and_max_8.S",
-                         "arm/sync_fetch_and_min_4.S",
-                         "arm/sync_fetch_and_min_8.S",
-                         "arm/sync_fetch_and_nand_4.S",
-                         "arm/sync_fetch_and_nand_8.S",
-                         "arm/sync_fetch_and_or_4.S",
-                         "arm/sync_fetch_and_or_8.S",
-                         "arm/sync_fetch_and_sub_4.S",
-                         "arm/sync_fetch_and_sub_8.S",
-                         "arm/sync_fetch_and_umax_4.S",
-                         "arm/sync_fetch_and_umax_8.S",
-                         "arm/sync_fetch_and_umin_4.S",
-                         "arm/sync_fetch_and_umin_8.S",
-                         "arm/sync_fetch_and_xor_4.S",
-                         "arm/sync_fetch_and_xor_8.S"]);
-    }
-
-    if target.contains("eabihf") {
-        sources.extend(&["arm/adddf3vfp.S",
-                         "arm/addsf3vfp.S",
-                         "arm/divdf3vfp.S",
-                         "arm/divsf3vfp.S",
-                         "arm/eqdf2vfp.S",
-                         "arm/eqsf2vfp.S",
-                         "arm/extendsfdf2vfp.S",
-                         "arm/fixdfsivfp.S",
-                         "arm/fixsfsivfp.S",
-                         "arm/fixunsdfsivfp.S",
-                         "arm/fixunssfsivfp.S",
-                         "arm/floatsidfvfp.S",
-                         "arm/floatsisfvfp.S",
-                         "arm/floatunssidfvfp.S",
-                         "arm/floatunssisfvfp.S",
-                         "arm/gedf2vfp.S",
-                         "arm/gesf2vfp.S",
-                         "arm/gtdf2vfp.S",
-                         "arm/gtsf2vfp.S",
-                         "arm/ledf2vfp.S",
-                         "arm/lesf2vfp.S",
-                         "arm/ltdf2vfp.S",
-                         "arm/ltsf2vfp.S",
-                         "arm/muldf3vfp.S",
-                         "arm/mulsf3vfp.S",
-                         "arm/negdf2vfp.S",
-                         "arm/negsf2vfp.S",
-                         "arm/nedf2vfp.S",
-                         "arm/nesf2vfp.S",
-                         "arm/restore_vfp_d8_d15_regs.S",
-                         "arm/save_vfp_d8_d15_regs.S",
-                         "arm/subdf3vfp.S",
-                         "arm/subsf3vfp.S",
-                         "arm/truncdfsf2vfp.S",
-                         "arm/unorddf2vfp.S",
-                         "arm/unordsf2vfp.S"]);
-    }
-
-    if target.contains("aarch64") {
-        sources.extend(&["comparetf2.c",
-                         "extenddftf2.c",
-                         "extendsftf2.c",
-                         "fixtfdi.c",
-                         "fixtfsi.c",
-                         "fixtfti.c",
-                         "fixunstfdi.c",
-                         "fixunstfsi.c",
-                         "fixunstfti.c",
-                         "floatditf.c",
-                         "floatsitf.c",
-                         "floatunditf.c",
-                         "floatunsitf.c",
-                         "multc3.c",
-                         "trunctfdf2.c",
-                         "trunctfsf2.c"]);
-    }
-
-    for src in sources.map.values() {
-        cfg.file(Path::new("../compiler-rt/lib/builtins").join(src));
-    }
-
-    cfg.compile("libcompiler-rt.a");
-}

src/libprofiler_builtins/build.rs

@@ -53,7 +53,7 @@ fn main() {
     }
 
     for src in profile_sources {
-        cfg.file(Path::new("../compiler-rt/lib/profile").join(src));
+        cfg.file(Path::new("../libcompiler_builtins/compiler-rt/lib/profile").join(src));
     }
 
     cfg.compile("libprofiler-rt.a");

src/librustc_trans/attributes.rs

@@ -13,7 +13,7 @@
 
 use llvm::{self, Attribute, ValueRef};
 use llvm::AttributePlace::Function;
-pub use syntax::attr::InlineAttr;
+pub use syntax::attr::{self, InlineAttr};
 use syntax::ast;
 use context::CrateContext;
 

src/librustc_trans/back/link.rs

@@ -370,6 +370,24 @@ pub fn each_linked_rlib(sess: &Session,
     Ok(())
 }
 
+/// Returns a boolean indicating whether the specified crate should be ignored
+/// during LTO.
+///
+/// Crates ignored during LTO are not lumped together in the "massive object
+/// file" that we create and are linked in their normal rlib states. See
+/// comments below for what crates do not participate in LTO.
+///
+/// It's unusual for a crate to not participate in LTO. Typically only
+/// compiler-specific and unstable crates have a reason to not participate in
+/// LTO.
+pub fn ignored_for_lto(sess: &Session, cnum: CrateNum) -> bool {
+    // `#![no_builtins]` crates don't participate in LTO because the state
+    // of builtins gets messed up (our crate isn't tagged with no builtins).
+    // Similarly `#![compiler_builtins]` doesn't participate because we want
+    // those builtins!
+    sess.cstore.is_no_builtins(cnum) || sess.cstore.is_compiler_builtins(cnum)
+}
+
 fn out_filename(sess: &Session,
                 crate_type: config::CrateType,
                 outputs: &OutputFilenames,
@@ -736,7 +754,10 @@ fn link_staticlib(sess: &Session,
         let skip_object_files = native_libs.iter().any(|lib| {
             lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib)
         });
-        ab.add_rlib(path, &name.as_str(), sess.lto(), skip_object_files).unwrap();
+        ab.add_rlib(path,
+                    &name.as_str(),
+                    sess.lto() && !ignored_for_lto(sess, cnum),
+                    skip_object_files).unwrap();
 
         all_native_libs.extend(sess.cstore.native_libraries(cnum));
     });
@@ -1289,7 +1310,9 @@ fn add_static_crate(cmd: &mut Linker,
             lib.kind == NativeLibraryKind::NativeStatic && !relevant_lib(sess, lib)
         });
 
-        if !sess.lto() && crate_type != config::CrateTypeDylib && !skip_native {
+        if (!sess.lto() || ignored_for_lto(sess, cnum)) &&
+           crate_type != config::CrateTypeDylib &&
+           !skip_native {
             cmd.link_rlib(&fix_windows_verbatim_for_gcc(cratepath));
             return
         }

src/librustc_trans/back/write.rs

@@ -1220,8 +1220,7 @@ fn spawn_work<'a>(sess: &'a Session,
     let crate_types = sess.crate_types.borrow().clone();
     let mut each_linked_rlib_for_lto = Vec::new();
     drop(link::each_linked_rlib(sess, &mut |cnum, path| {
-        // `#![no_builtins]` crates don't participate in LTO.
-        if sess.cstore.is_no_builtins(cnum) {
+        if link::ignored_for_lto(sess, cnum) {
             return
         }
         each_linked_rlib_for_lto.push((cnum, path.to_path_buf()));

src/librustc_trans/declare.rs

@@ -30,7 +30,6 @@
 use common;
 use type_::Type;
 use value::Value;
-use syntax::attr;
 
 use std::ffi::CString;
 
@@ -88,16 +87,6 @@ fn declare_raw_fn(ccx: &CrateContext, name: &str, callconv: llvm::CallConv, ty:
         }
     }
 
-    // If we're compiling the compiler-builtins crate, e.g. the equivalent of
-    // compiler-rt, then we want to implicitly compile everything with hidden
-    // visibility as we're going to link this object all over the place but
-    // don't want the symbols to get exported.
-    if attr::contains_name(ccx.tcx().hir.krate_attrs(), "compiler_builtins") {
-        unsafe {
-            llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
-        }
-    }
-
     match ccx.tcx().sess.opts.cg.opt_level.as_ref().map(String::as_ref) {
         Some("s") => {
             llvm::Attribute::OptimizeForSize.apply_llfn(Function, llfn);

src/librustc_trans/trans_item.rs

@@ -162,6 +162,18 @@ fn predefine_fn(ccx: &CrateContext<'a, 'tcx>,
             llvm::SetUniqueComdat(ccx.llmod(), lldecl);
         }
 
+        // If we're compiling the compiler-builtins crate, e.g. the equivalent of
+        // compiler-rt, then we want to implicitly compile everything with hidden
+        // visibility as we're going to link this object all over the place but
+        // don't want the symbols to get exported.
+        if linkage != llvm::Linkage::InternalLinkage &&
+           linkage != llvm::Linkage::PrivateLinkage &&
+           attr::contains_name(ccx.tcx().hir.krate_attrs(), "compiler_builtins") {
+            unsafe {
+                llvm::LLVMRustSetVisibility(lldecl, llvm::Visibility::Hidden);
+            }
+        }
+
         debug!("predefine_fn: mono_ty = {:?} instance = {:?}", mono_ty, instance);
         if common::is_inline_instance(ccx.tcx(), &instance) {
             attributes::inline(lldecl, attributes::InlineAttr::Hint);

src/libstd/Cargo.toml

@@ -19,7 +19,7 @@ collections = { path = "../libcollections" }
 core = { path = "../libcore" }
 libc = { path = "../rustc/libc_shim" }
 rand = { path = "../librand" }
-compiler_builtins = { path = "../libcompiler_builtins" }
+compiler_builtins = { path = "../rustc/compiler_builtins_shim" }
 profiler_builtins = { path = "../libprofiler_builtins", optional = true }
 std_unicode = { path = "../libstd_unicode" }
 unwind = { path = "../libunwind" }

src/libcompiler_builtins/Cargo.toml → src/rustc/compiler_builtins_shim/Cargo.toml

+# See libc_shim/Cargo.toml for why this exists
+
 [package]
-authors = ["The Rust Project Developers"]
-build = "build.rs"
 name = "compiler_builtins"
+authors = ["The Rust Project Developers"]
 version = "0.0.0"
+build = "../../libcompiler_builtins/build.rs"
 
 [lib]
-name = "compiler_builtins"
-path = "lib.rs"
+path = "../../libcompiler_builtins/src/lib.rs"
 test = false
-bench = false
-doc = false
+doctest = false
 
 [dependencies]
-core = { path = "../libcore" }
+core = { path = "../../libcore" }
 
 [build-dependencies]
-build_helper = { path = "../build_helper" }
-gcc = "0.3.50"
+gcc = "0.3"
+
+[features]
+c = []
+default = ["c", "rustbuild", "compiler-builtins"]
+rustbuild = []
+compiler-builtins = []

src/test/run-pass/auxiliary/clibrary.rs → src/rustc/compiler_builtins_shim/build.rs

-// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -8,8 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// no-prefer-dynamic
-#![crate_type = "staticlib"]
+#![deny(warnings)]
 
-#[no_mangle]
-pub extern "C" fn foo(x:i32) -> i32 { x }
+// See comments in Cargo.toml for why this exists
+
+fn main() {
+    println!("cargo:rustc-cfg=stdbuild");
+    println!("cargo:rerun-if-changed=build.rs");
+}

src/tools/tidy/src/lib.rs

@@ -54,6 +54,7 @@ fn filter_dirs(path: &Path) -> bool {
         "src/jemalloc",
         "src/llvm",
         "src/libbacktrace",
+        "src/libcompiler_builtins",
         "src/compiler-rt",
         "src/rustllvm",
         "src/liblibc",