Upstream, take 2

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 authors = ["Jorge Aparicio <[email protected]>"]
 build = "build.rs"
-name = "rustc_builtins"
+name = "compiler_builtins"
 version = "0.1.0"
 
 [build-dependencies]

build.rs

@@ -407,8 +407,15 @@ fn main() {
             sources.remove(&["aeabi_cdcmp", "aeabi_cfcmp"]);
         }
 
+        let root = if env::var_os("CARGO_FEATURE_RUSTBUILD").is_some() {
+            Path::new("../../libcompiler_builtins")
+        } else {
+            Path::new(".")
+        };
+
+        let src_dir = root.join("compiler-rt/compiler-rt-cdylib/compiler-rt/lib/builtins");
         for src in sources.map.values() {
-            let src = Path::new("compiler-rt/compiler-rt-cdylib/compiler-rt/lib/builtins").join(src);
+            let src = src_dir.join(src);
             cfg.file(&src);
             println!("cargo:rerun-if-changed={}", src.display());
         }

src/bin/intrinsics.rs

@@ -7,6 +7,7 @@
 #![cfg_attr(thumb, no_main)]
 #![deny(dead_code)]
 #![feature(asm)]
+#![feature(compiler_builtins_lib)]
 #![feature(core_float)]
 #![feature(lang_items)]
 #![feature(libc)]
@@ -15,7 +16,7 @@
 
 #[cfg(not(thumb))]
 extern crate libc;
-extern crate rustc_builtins;
+extern crate compiler_builtins;
 
 // NOTE cfg(not(thumbv6m)) means that the operation is not supported on ARMv6-M at all. Not even
 // compiler-rt provides a C/assembly implementation.

src/int/mul.rs

@@ -1,4 +1,6 @@
-use int::{Int, LargeInt};
+#[cfg(not(all(feature = "c", target_arch = "x86")))]
+use int::LargeInt;
+use int::Int;
 
 macro_rules! mul {
     ($intrinsic:ident: $ty:ty) => {

src/int/sdiv.rs

@@ -43,7 +43,12 @@ macro_rules! divmod {
                 fn $div(a: $ty, b: $ty) -> $ty;
             }
 
-            let r = unsafe { $div(a, b) };
+            let r = match () {
+                #[cfg(not(all(feature = "c", any(target_arch = "x86"))))]
+                () => $div(a, b),
+                #[cfg(all(feature = "c", any(target_arch = "x86")))]
+                () => unsafe { $div(a, b) },
+            };
             *rem = a - (r * b);
             r
         }

src/int/shift.rs

@@ -1,3 +1,4 @@
+#[cfg(not(all(feature = "c", target_arch = "x86")))]
 use int::{Int, LargeInt};
 
 macro_rules! ashl {

src/int/udiv.rs

@@ -1,4 +1,4 @@
-use core::{intrinsics, mem};
+use core::intrinsics;
 use int::{Int, LargeInt};
 
 /// Returns `n / d`
@@ -65,7 +65,14 @@ pub extern "C" fn __umodsi3(n: u32, d: u32) -> u32 {
         fn __udivsi3(n: u32, d: u32) -> u32;
     }
 
-    n - unsafe { __udivsi3(n, d) * d }
+    let q = match () {
+        #[cfg(all(feature = "c", target_arch = "arm", not(target_os = "ios")))]
+        () => unsafe { __udivsi3(n, d) },
+        #[cfg(not(all(feature = "c", target_arch = "arm", not(target_os = "ios"))))]
+        () => __udivsi3(n, d),
+    };
+
+    n - q * d
 }
 
 /// Returns `n / d` and sets `*rem = n % d`
@@ -77,7 +84,12 @@ pub extern "C" fn __udivmodsi4(n: u32, d: u32, rem: Option<&mut u32>) -> u32 {
         fn __udivsi3(n: u32, d: u32) -> u32;
     }
 
-    let q = unsafe { __udivsi3(n, d) };
+    let q = match () {
+        #[cfg(all(feature = "c", target_arch = "arm", not(target_os = "ios")))]
+        () => unsafe { __udivsi3(n, d) },
+        #[cfg(not(all(feature = "c", target_arch = "arm", not(target_os = "ios"))))]
+        () => __udivsi3(n, d),
+    };
     if let Some(rem) = rem {
         *rem = n - (q * d);
     }
@@ -95,6 +107,8 @@ pub extern "C" fn __udivdi3(n: u64, d: u64) -> u64 {
 #[cfg(not(all(feature = "c", target_arch = "x86")))]
 #[cfg_attr(not(test), no_mangle)]
 pub extern "C" fn __umoddi3(a: u64, b: u64) -> u64 {
+    use core::mem;
+
     let mut rem = unsafe { mem::uninitialized() };
     __udivmoddi4(a, b, Some(&mut rem));
     rem

src/lib.rs

@@ -1,11 +1,23 @@
+#![cfg_attr(not(stage0), deny(warnings))]
+#![cfg_attr(not(test), no_std)]
+#![cfg_attr(rustbuild, compiler_builtins)]
+#![crate_name = "compiler_builtins"]
+#![crate_type = "rlib"]
+#![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
+       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       html_playground_url = "https://play.rust-lang.org/",
+       test(attr(deny(warnings))))]
 #![feature(asm)]
+#![feature(compiler_builtins)]
 #![feature(core_intrinsics)]
 #![feature(linkage)]
 #![feature(naked_functions)]
-#![cfg_attr(not(test), no_std)]
+#![feature(staged_api)]
 #![no_builtins]
-// TODO(rust-lang/rust#35021) uncomment when that PR lands
-// #![feature(rustc_builtins)]
+#![unstable(feature = "compiler_builtins_lib",
+            reason = "Compiler builtins. Will never become stable.",
+            issue = "0")]
 
 // We disable #[no_mangle] for tests so that we can verify the test results
 // against the native compiler-rt implementations of the builtins.