From 138c956a054c26ea816574bb0e70c63ad55fa512 Mon Sep 17 00:00:00 2001
From: Taiki Endo <te316e89@gmail.com>
Date: Sun, 23 May 2021 13:55:53 +0900
Subject: [PATCH] Allow AtomicConsume to be used on targets that do not support
 atomic

---
 .github/workflows/ci.yml              |  4 +--
 build.rs                              | 32 ---------------------
 ci/check-features.sh                  | 15 ++++++----
 ci/no_atomic.sh                       | 40 +++++++++++++++++++++++++++
 ci/no_atomic_cas.sh                   | 27 ------------------
 crossbeam-epoch/build.rs              |  4 +--
 crossbeam-epoch/no_atomic.rs          |  1 +
 crossbeam-epoch/no_atomic_cas.rs      |  1 -
 crossbeam-epoch/src/lib.rs            |  6 ++--
 crossbeam-queue/build.rs              |  4 +--
 crossbeam-queue/no_atomic.rs          |  1 +
 crossbeam-queue/no_atomic_cas.rs      |  1 -
 crossbeam-skiplist/build.rs           |  4 +--
 crossbeam-skiplist/no_atomic.rs       |  1 +
 crossbeam-skiplist/no_atomic_cas.rs   |  1 -
 crossbeam-utils/build.rs              |  7 ++++-
 crossbeam-utils/no_atomic.rs          |  1 +
 crossbeam-utils/no_atomic_cas.rs      |  1 -
 crossbeam-utils/src/atomic/consume.rs | 14 ++++++----
 crossbeam-utils/src/atomic/mod.rs     |  8 +++---
 crossbeam-utils/src/lib.rs            | 14 ++++------
 no_atomic_cas.rs => no_atomic.rs      |  9 +++++-
 src/lib.rs                            |  1 -
 23 files changed, 97 insertions(+), 100 deletions(-)
 delete mode 100644 build.rs
 create mode 100755 ci/no_atomic.sh
 delete mode 100755 ci/no_atomic_cas.sh
 create mode 120000 crossbeam-epoch/no_atomic.rs
 delete mode 120000 crossbeam-epoch/no_atomic_cas.rs
 create mode 120000 crossbeam-queue/no_atomic.rs
 delete mode 120000 crossbeam-queue/no_atomic_cas.rs
 create mode 120000 crossbeam-skiplist/no_atomic.rs
 delete mode 120000 crossbeam-skiplist/no_atomic_cas.rs
 create mode 120000 crossbeam-utils/no_atomic.rs
 delete mode 120000 crossbeam-utils/no_atomic_cas.rs
 rename no_atomic_cas.rs => no_atomic.rs (53%)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0051f5f5e..0a1c1960c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -86,7 +86,7 @@ jobs:
       - name: dependency tree check
         run: ./ci/dependencies.sh
 
-  # When this job failed, run ci/no_atomic_cas.sh and commit result changes.
+  # When this job failed, run ci/no_atomic.sh and commit result changes.
   # TODO(taiki-e): Ideally, this should be automated using a bot that creates
   #                PR when failed, but there is no bandwidth to implement it
   #                right now...
@@ -96,7 +96,7 @@ jobs:
       - uses: actions/checkout@v2
       - name: Install Rust
         run: rustup update nightly && rustup default nightly
-      - run: ci/no_atomic_cas.sh
+      - run: ci/no_atomic.sh
       - run: git diff --exit-code
 
   # Check formatting.
diff --git a/build.rs b/build.rs
deleted file mode 100644
index ac41a83da..000000000
--- a/build.rs
+++ /dev/null
@@ -1,32 +0,0 @@
-#![warn(rust_2018_idioms)]
-
-use std::env;
-
-include!("no_atomic_cas.rs");
-
-// The rustc-cfg strings below are *not* public API. Please let us know by
-// opening a GitHub issue if your build environment requires some way to enable
-// these cfgs other than by executing our build script.
-fn main() {
-    let target = match env::var("TARGET") {
-        Ok(target) => target,
-        Err(e) => {
-            println!(
-                "cargo:warning={}: unable to get TARGET environment variable: {}",
-                env!("CARGO_PKG_NAME"),
-                e
-            );
-            return;
-        }
-    };
-
-    // Note that this is `no_*`, not `has_*`. This allows treating
-    // `cfg(target_has_atomic = "ptr")` as true when the build script doesn't
-    // run. This is needed for compatibility with non-cargo build systems that
-    // don't run the build script.
-    if NO_ATOMIC_CAS.contains(&&*target) {
-        println!("cargo:rustc-cfg=crossbeam_no_atomic_cas");
-    }
-
-    println!("cargo:rerun-if-changed=no_atomic_cas.rs");
-}
diff --git a/ci/check-features.sh b/ci/check-features.sh
index c6901d0b7..17fc1a8c1 100755
--- a/ci/check-features.sh
+++ b/ci/check-features.sh
@@ -13,14 +13,19 @@ if [[ "$RUST_VERSION" != "nightly"* ]]; then
     # * `--no-dev-deps` - build without dev-dependencies to avoid https://github.com/rust-lang/cargo/issues/4866
     # * `--exclude benchmarks` - benchmarks doesn't published.
     # * `--skip nightly` - skip `nightly` feature as requires nightly compilers.
-    cargo hack check --all --feature-powerset --no-dev-deps --exclude benchmarks --skip nightly
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks --skip nightly
 else
     # On nightly, all feature　combinations should work.
-    cargo hack check --all --feature-powerset --no-dev-deps --exclude benchmarks
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks
 
-    # Check for no_std environment.
+    # Build for no_std environment.
+    # thumbv7m-none-eabi supports atomic CAS.
+    # thumbv6m-none-eabi supports atomic, but not atomic CAS.
+    # riscv32i-unknown-none-elf does not support atomic at all.
     rustup target add thumbv7m-none-eabi
     rustup target add thumbv6m-none-eabi
-    cargo hack check --all --feature-powerset --no-dev-deps --exclude benchmarks --target thumbv7m-none-eabi --skip std,default
-    cargo hack check --all --feature-powerset --no-dev-deps --exclude benchmarks --target thumbv6m-none-eabi --skip std,default
+    rustup target add riscv32i-unknown-none-elf
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks --target thumbv7m-none-eabi --skip std,default
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks --target thumbv6m-none-eabi --skip std,default
+    cargo hack build --all --feature-powerset --no-dev-deps --exclude benchmarks --target riscv32i-unknown-none-elf --skip std,default
 fi
diff --git a/ci/no_atomic.sh b/ci/no_atomic.sh
new file mode 100755
index 000000000..b589dbb17
--- /dev/null
+++ b/ci/no_atomic.sh
@@ -0,0 +1,40 @@
+#!/bin/bash
+
+# Update the list of targets that do not support atomic/CAS operations.
+#
+# Usage:
+#    ./ci/no_atomic.sh
+
+set -euo pipefail
+IFS=$'\n\t'
+
+cd "$(cd "$(dirname "$0")" && pwd)"/..
+
+file="no_atomic.rs"
+
+{
+    echo "// This file is @generated by $(basename "$0")."
+    echo "// It is not intended for manual editing."
+    echo ""
+} >"$file"
+
+echo "const NO_ATOMIC_CAS: &[&str] = &[" >>"$file"
+for target in $(rustc --print target-list); do
+    res=$(rustc --print target-spec-json -Z unstable-options --target "$target" \
+        | jq -r "select(.\"atomic-cas\" == false)")
+    [[ -z "$res" ]] || echo "    \"$target\"," >>"$file"
+done
+echo "];" >>"$file"
+
+# `"max-atomic-width" == 0` means that atomic is not supported at all.
+{
+    # Only crossbeam-utils actually uses this const.
+    echo "#[allow(dead_code)]"
+    echo "const NO_ATOMIC: &[&str] = &["
+} >>"$file"
+for target in $(rustc --print target-list); do
+    res=$(rustc --print target-spec-json -Z unstable-options --target "$target" \
+        | jq -r "select(.\"max-atomic-width\" == 0)")
+    [[ -z "$res" ]] || echo "    \"$target\"," >>"$file"
+done
+echo "];" >>"$file"
diff --git a/ci/no_atomic_cas.sh b/ci/no_atomic_cas.sh
deleted file mode 100755
index bc2e3500f..000000000
--- a/ci/no_atomic_cas.sh
+++ /dev/null
@@ -1,27 +0,0 @@
-#!/bin/bash
-
-# Update the list of targets that do not support atomic CAS operations.
-#
-# Usage:
-#    ./ci/no_atomic_cas.sh
-
-set -euo pipefail
-IFS=$'\n\t'
-
-cd "$(cd "$(dirname "$0")" && pwd)"/..
-
-file="no_atomic_cas.rs"
-
-{
-    echo "// This file is @generated by $(basename "$0")."
-    echo "// It is not intended for manual editing."
-    echo ""
-} >"$file"
-
-echo "const NO_ATOMIC_CAS: &[&str] = &[" >>"$file"
-for target in $(rustc --print target-list); do
-    res=$(rustc --print target-spec-json -Z unstable-options --target "$target" \
-        | jq -r "select(.\"atomic-cas\" == false)")
-    [[ -z "$res" ]] || echo "    \"$target\"," >>"$file"
-done
-echo "];" >>"$file"
diff --git a/crossbeam-epoch/build.rs b/crossbeam-epoch/build.rs
index ac41a83da..4ef1279fc 100644
--- a/crossbeam-epoch/build.rs
+++ b/crossbeam-epoch/build.rs
@@ -2,7 +2,7 @@
 
 use std::env;
 
-include!("no_atomic_cas.rs");
+include!("no_atomic.rs");
 
 // The rustc-cfg strings below are *not* public API. Please let us know by
 // opening a GitHub issue if your build environment requires some way to enable
@@ -28,5 +28,5 @@ fn main() {
         println!("cargo:rustc-cfg=crossbeam_no_atomic_cas");
     }
 
-    println!("cargo:rerun-if-changed=no_atomic_cas.rs");
+    println!("cargo:rerun-if-changed=no_atomic.rs");
 }
diff --git a/crossbeam-epoch/no_atomic.rs b/crossbeam-epoch/no_atomic.rs
new file mode 120000
index 000000000..417886bb7
--- /dev/null
+++ b/crossbeam-epoch/no_atomic.rs
@@ -0,0 +1 @@
+../no_atomic.rs
\ No newline at end of file
diff --git a/crossbeam-epoch/no_atomic_cas.rs b/crossbeam-epoch/no_atomic_cas.rs
deleted file mode 120000
index 3d7380fad..000000000
--- a/crossbeam-epoch/no_atomic_cas.rs
+++ /dev/null
@@ -1 +0,0 @@
-../no_atomic_cas.rs
\ No newline at end of file
diff --git a/crossbeam-epoch/src/lib.rs b/crossbeam-epoch/src/lib.rs
index 8dfd5104a..ba1d3311f 100644
--- a/crossbeam-epoch/src/lib.rs
+++ b/crossbeam-epoch/src/lib.rs
@@ -104,10 +104,11 @@ mod primitive {
     pub(crate) use loom::lazy_static;
     pub(crate) use loom::thread_local;
 }
+#[cfg(not(crossbeam_no_atomic_cas))]
 #[cfg(not(crossbeam_loom))]
 #[allow(unused_imports, dead_code)]
 mod primitive {
-    #[cfg(any(feature = "alloc", feature = "std"))]
+    #[cfg(feature = "alloc")]
     pub(crate) mod cell {
         #[derive(Debug)]
         #[repr(transparent)]
@@ -135,14 +136,13 @@ mod primitive {
             }
         }
     }
-    #[cfg(any(feature = "alloc", feature = "std"))]
+    #[cfg(feature = "alloc")]
     pub(crate) mod sync {
         pub(crate) mod atomic {
             pub(crate) use core::sync::atomic::compiler_fence;
             pub(crate) use core::sync::atomic::fence;
             pub(crate) use core::sync::atomic::AtomicUsize;
         }
-        #[cfg(not(crossbeam_no_atomic_cas))]
         pub(crate) use alloc::sync::Arc;
     }
 
diff --git a/crossbeam-queue/build.rs b/crossbeam-queue/build.rs
index ac41a83da..4ef1279fc 100644
--- a/crossbeam-queue/build.rs
+++ b/crossbeam-queue/build.rs
@@ -2,7 +2,7 @@
 
 use std::env;
 
-include!("no_atomic_cas.rs");
+include!("no_atomic.rs");
 
 // The rustc-cfg strings below are *not* public API. Please let us know by
 // opening a GitHub issue if your build environment requires some way to enable
@@ -28,5 +28,5 @@ fn main() {
         println!("cargo:rustc-cfg=crossbeam_no_atomic_cas");
     }
 
-    println!("cargo:rerun-if-changed=no_atomic_cas.rs");
+    println!("cargo:rerun-if-changed=no_atomic.rs");
 }
diff --git a/crossbeam-queue/no_atomic.rs b/crossbeam-queue/no_atomic.rs
new file mode 120000
index 000000000..417886bb7
--- /dev/null
+++ b/crossbeam-queue/no_atomic.rs
@@ -0,0 +1 @@
+../no_atomic.rs
\ No newline at end of file
diff --git a/crossbeam-queue/no_atomic_cas.rs b/crossbeam-queue/no_atomic_cas.rs
deleted file mode 120000
index 3d7380fad..000000000
--- a/crossbeam-queue/no_atomic_cas.rs
+++ /dev/null
@@ -1 +0,0 @@
-../no_atomic_cas.rs
\ No newline at end of file
diff --git a/crossbeam-skiplist/build.rs b/crossbeam-skiplist/build.rs
index ac41a83da..4ef1279fc 100644
--- a/crossbeam-skiplist/build.rs
+++ b/crossbeam-skiplist/build.rs
@@ -2,7 +2,7 @@
 
 use std::env;
 
-include!("no_atomic_cas.rs");
+include!("no_atomic.rs");
 
 // The rustc-cfg strings below are *not* public API. Please let us know by
 // opening a GitHub issue if your build environment requires some way to enable
@@ -28,5 +28,5 @@ fn main() {
         println!("cargo:rustc-cfg=crossbeam_no_atomic_cas");
     }
 
-    println!("cargo:rerun-if-changed=no_atomic_cas.rs");
+    println!("cargo:rerun-if-changed=no_atomic.rs");
 }
diff --git a/crossbeam-skiplist/no_atomic.rs b/crossbeam-skiplist/no_atomic.rs
new file mode 120000
index 000000000..417886bb7
--- /dev/null
+++ b/crossbeam-skiplist/no_atomic.rs
@@ -0,0 +1 @@
+../no_atomic.rs
\ No newline at end of file
diff --git a/crossbeam-skiplist/no_atomic_cas.rs b/crossbeam-skiplist/no_atomic_cas.rs
deleted file mode 120000
index 3d7380fad..000000000
--- a/crossbeam-skiplist/no_atomic_cas.rs
+++ /dev/null
@@ -1 +0,0 @@
-../no_atomic_cas.rs
\ No newline at end of file
diff --git a/crossbeam-utils/build.rs b/crossbeam-utils/build.rs
index 2e7846fea..e7fabbd0c 100644
--- a/crossbeam-utils/build.rs
+++ b/crossbeam-utils/build.rs
@@ -4,7 +4,7 @@ use std::env;
 
 use autocfg::AutoCfg;
 
-include!("no_atomic_cas.rs");
+include!("no_atomic.rs");
 
 // The rustc-cfg strings below are *not* public API. Please let us know by
 // opening a GitHub issue if your build environment requires some way to enable
@@ -29,6 +29,9 @@ fn main() {
     if NO_ATOMIC_CAS.contains(&&*target) {
         println!("cargo:rustc-cfg=crossbeam_no_atomic_cas");
     }
+    if NO_ATOMIC.contains(&&*target) {
+        println!("cargo:rustc-cfg=crossbeam_no_atomic");
+    }
 
     let cfg = match AutoCfg::new() {
         Ok(cfg) => cfg,
@@ -47,4 +50,6 @@ fn main() {
     cfg.emit_type_cfg("core::sync::atomic::AtomicU32", "has_atomic_u32");
     cfg.emit_type_cfg("core::sync::atomic::AtomicU64", "has_atomic_u64");
     cfg.emit_type_cfg("core::sync::atomic::AtomicU128", "has_atomic_u128");
+
+    println!("cargo:rerun-if-changed=no_atomic.rs");
 }
diff --git a/crossbeam-utils/no_atomic.rs b/crossbeam-utils/no_atomic.rs
new file mode 120000
index 000000000..417886bb7
--- /dev/null
+++ b/crossbeam-utils/no_atomic.rs
@@ -0,0 +1 @@
+../no_atomic.rs
\ No newline at end of file
diff --git a/crossbeam-utils/no_atomic_cas.rs b/crossbeam-utils/no_atomic_cas.rs
deleted file mode 120000
index 3d7380fad..000000000
--- a/crossbeam-utils/no_atomic_cas.rs
+++ /dev/null
@@ -1 +0,0 @@
-../no_atomic_cas.rs
\ No newline at end of file
diff --git a/crossbeam-utils/src/atomic/consume.rs b/crossbeam-utils/src/atomic/consume.rs
index 0fbd93e9f..f28e32bbf 100644
--- a/crossbeam-utils/src/atomic/consume.rs
+++ b/crossbeam-utils/src/atomic/consume.rs
@@ -1,5 +1,6 @@
 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
 use crate::primitive::sync::atomic::compiler_fence;
+#[cfg(not(crossbeam_no_atomic))]
 use core::sync::atomic::Ordering;
 
 /// Trait which allows reading from primitive atomic types with "consume" ordering.
@@ -25,6 +26,7 @@ pub trait AtomicConsume {
     fn load_consume(&self) -> Self::Val;
 }
 
+#[cfg(not(crossbeam_no_atomic))]
 #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
 macro_rules! impl_consume {
     () => {
@@ -37,6 +39,7 @@ macro_rules! impl_consume {
     };
 }
 
+#[cfg(not(crossbeam_no_atomic))]
 #[cfg(not(any(target_arch = "arm", target_arch = "aarch64")))]
 macro_rules! impl_consume {
     () => {
@@ -49,12 +52,13 @@ macro_rules! impl_consume {
 
 macro_rules! impl_atomic {
     ($atomic:ident, $val:ty) => {
-        impl AtomicConsume for ::core::sync::atomic::$atomic {
+        #[cfg(not(crossbeam_no_atomic))]
+        impl AtomicConsume for core::sync::atomic::$atomic {
             type Val = $val;
             impl_consume!();
         }
         #[cfg(crossbeam_loom)]
-        impl AtomicConsume for ::loom::sync::atomic::$atomic {
+        impl AtomicConsume for loom::sync::atomic::$atomic {
             type Val = $val;
             impl_consume!();
         }
@@ -63,7 +67,6 @@ macro_rules! impl_atomic {
 
 impl_atomic!(AtomicBool, bool);
 impl_atomic!(AtomicUsize, usize);
-#[cfg(not(crossbeam_loom))]
 impl_atomic!(AtomicIsize, isize);
 #[cfg(has_atomic_u8)]
 impl_atomic!(AtomicU8, u8);
@@ -82,13 +85,14 @@ impl_atomic!(AtomicU64, u64);
 #[cfg(has_atomic_u64)]
 impl_atomic!(AtomicI64, i64);
 
-impl<T> AtomicConsume for ::core::sync::atomic::AtomicPtr<T> {
+#[cfg(not(crossbeam_no_atomic))]
+impl<T> AtomicConsume for core::sync::atomic::AtomicPtr<T> {
     type Val = *mut T;
     impl_consume!();
 }
 
 #[cfg(crossbeam_loom)]
-impl<T> AtomicConsume for ::loom::sync::atomic::AtomicPtr<T> {
+impl<T> AtomicConsume for loom::sync::atomic::AtomicPtr<T> {
     type Val = *mut T;
     impl_consume!();
 }
diff --git a/crossbeam-utils/src/atomic/mod.rs b/crossbeam-utils/src/atomic/mod.rs
index 874eaf216..fc713fcac 100644
--- a/crossbeam-utils/src/atomic/mod.rs
+++ b/crossbeam-utils/src/atomic/mod.rs
@@ -3,11 +3,9 @@
 //! * [`AtomicCell`], a thread-safe mutable memory location.
 //! * [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.
 
+#[cfg(not(crossbeam_no_atomic_cas))]
 #[cfg(not(crossbeam_loom))]
-use cfg_if::cfg_if;
-
-#[cfg(not(crossbeam_loom))]
-cfg_if! {
+cfg_if::cfg_if! {
     // Use "wide" sequence lock if the pointer width <= 32 for preventing its counter against wrap
     // around.
     //
@@ -25,8 +23,10 @@ cfg_if! {
     }
 }
 
+#[cfg(not(crossbeam_no_atomic_cas))]
 mod atomic_cell;
 mod consume;
 
+#[cfg(not(crossbeam_no_atomic_cas))]
 pub use self::atomic_cell::AtomicCell;
 pub use self::consume::AtomicConsume;
diff --git a/crossbeam-utils/src/lib.rs b/crossbeam-utils/src/lib.rs
index a533af257..6f9df04ae 100644
--- a/crossbeam-utils/src/lib.rs
+++ b/crossbeam-utils/src/lib.rs
@@ -69,13 +69,18 @@ mod primitive {
             // use [`core::hint::spin_loop`] instead.
             #[allow(deprecated)]
             pub(crate) use core::sync::atomic::spin_loop_hint;
+            #[cfg(not(crossbeam_no_atomic))]
             pub(crate) use core::sync::atomic::{AtomicBool, AtomicIsize, AtomicUsize};
+            #[cfg(not(crossbeam_no_atomic))]
             #[cfg(has_atomic_u16)]
             pub(crate) use core::sync::atomic::{AtomicI16, AtomicU16};
+            #[cfg(not(crossbeam_no_atomic))]
             #[cfg(has_atomic_u32)]
             pub(crate) use core::sync::atomic::{AtomicI32, AtomicU32};
+            #[cfg(not(crossbeam_no_atomic))]
             #[cfg(has_atomic_u64)]
             pub(crate) use core::sync::atomic::{AtomicI64, AtomicU64};
+            #[cfg(not(crossbeam_no_atomic))]
             #[cfg(has_atomic_u8)]
             pub(crate) use core::sync::atomic::{AtomicI8, AtomicU8};
         }
@@ -85,15 +90,6 @@ mod primitive {
     }
 }
 
-cfg_if! {
-    if #[cfg(feature = "alloc")] {
-        extern crate alloc;
-    } else if #[cfg(feature = "std")] {
-        extern crate std as alloc;
-    }
-}
-
-#[cfg(not(crossbeam_no_atomic_cas))]
 pub mod atomic;
 
 mod cache_padded;
diff --git a/no_atomic_cas.rs b/no_atomic.rs
similarity index 53%
rename from no_atomic_cas.rs
rename to no_atomic.rs
index 9e8fb4094..015a115ed 100644
--- a/no_atomic_cas.rs
+++ b/no_atomic.rs
@@ -1,4 +1,4 @@
-// This file is @generated by no_atomic_cas.sh.
+// This file is @generated by no_atomic.sh.
 // It is not intended for manual editing.
 
 const NO_ATOMIC_CAS: &[&str] = &[
@@ -9,3 +9,10 @@ const NO_ATOMIC_CAS: &[&str] = &[
     "thumbv4t-none-eabi",
     "thumbv6m-none-eabi",
 ];
+#[allow(dead_code)]
+const NO_ATOMIC: &[&str] = &[
+    "avr-unknown-gnu-atmega328",
+    "msp430-none-elf",
+    "riscv32i-unknown-none-elf",
+    "riscv32imc-unknown-none-elf",
+];
diff --git a/src/lib.rs b/src/lib.rs
index 6fbf4a051..9bc3ec111 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -53,7 +53,6 @@
 )]
 #![cfg_attr(not(feature = "std"), no_std)]
 
-#[cfg(not(crossbeam_no_atomic_cas))]
 pub use crossbeam_utils::atomic;
 
 pub mod utils {