Support non-atomic targets

Refs: rust-lang/rust#51953

.travis.yml

@@ -41,6 +41,7 @@ matrix:
     script: ./ci/crossbeam.sh
     install:
       - rustup target add thumbv7m-none-eabi
+      - rustup target add thumbv6m-none-eabi
   - rust: nightly
     name: "crossbeam-channel on nightly"
     script: ./ci/crossbeam-channel.sh
@@ -52,6 +53,7 @@ matrix:
     script: ./ci/crossbeam-epoch.sh
     install:
       - rustup target add thumbv7m-none-eabi
+      - rustup target add thumbv6m-none-eabi
     addons:
       apt:
         sources:
@@ -71,11 +73,13 @@ matrix:
     script: ./ci/crossbeam-skiplist.sh
     install:
       - rustup target add thumbv7m-none-eabi
+      - rustup target add thumbv6m-none-eabi
   - rust: nightly
     name: "crossbeam-utils on nightly"
     script: ./ci/crossbeam-utils.sh
     install:
       - rustup target add thumbv7m-none-eabi
+      - rustup target add thumbv6m-none-eabi
 
   # Check for duplicate dependencies.
   - rust: nightly

ci/crossbeam-epoch.sh

@@ -25,4 +25,6 @@ if [[ "$TRAVIS_RUST_VERSION" == "nightly" ]]; then
     cargo check --target thumbv7m-none-eabi --no-default-features
     cargo check --target thumbv7m-none-eabi --no-default-features --features alloc
     cargo check --target thumbv7m-none-eabi --no-default-features --features alloc,nightly
+    cargo check --target thumbv6m-none-eabi --no-default-features --features nightly
+    cargo check --target thumbv6m-none-eabi --no-default-features --features alloc,nightly
 fi

ci/crossbeam-skiplist.sh

@@ -17,4 +17,6 @@ if [[ "$TRAVIS_RUST_VERSION" == "nightly" ]]; then
     cargo check --target thumbv7m-none-eabi --no-default-features
     cargo check --target thumbv7m-none-eabi --no-default-features --features alloc
     cargo check --target thumbv7m-none-eabi --no-default-features --features alloc,nightly
+    cargo check --target thumbv6m-none-eabi --no-default-features --features nightly
+    cargo check --target thumbv6m-none-eabi --no-default-features --features alloc,nightly
 fi

ci/crossbeam-utils.sh

@@ -17,4 +17,6 @@ if [[ "$TRAVIS_RUST_VERSION" == "nightly" ]]; then
     cargo check --target thumbv7m-none-eabi --no-default-features
     cargo check --target thumbv7m-none-eabi --no-default-features --features alloc
     cargo check --target thumbv7m-none-eabi --no-default-features --features alloc,nightly
+    cargo check --target thumbv6m-none-eabi --no-default-features --features nightly
+    cargo check --target thumbv6m-none-eabi --no-default-features --features alloc,nightly
 fi

ci/crossbeam.sh

@@ -17,4 +17,6 @@ if [[ "$TRAVIS_RUST_VERSION" == "nightly" ]]; then
     cargo check --target thumbv7m-none-eabi --no-default-features
     cargo check --target thumbv7m-none-eabi --no-default-features --features alloc
     cargo check --target thumbv7m-none-eabi --no-default-features --features alloc,nightly
+    cargo check --target thumbv6m-none-eabi --no-default-features --features nightly
+    cargo check --target thumbv6m-none-eabi --no-default-features --features alloc,nightly
 fi

crossbeam-epoch/src/lib.rs

@@ -58,6 +58,7 @@
 #![warn(missing_debug_implementations)]
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(feature = "nightly", feature(const_fn))]
+#![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
 
 #[macro_use]
 extern crate cfg_if;
@@ -72,6 +73,10 @@ cfg_if! {
     }
 }
 
+#[cfg_attr(
+    feature = "nightly",
+    cfg(all(target_has_atomic = "cas", target_has_atomic = "ptr"))
+)]
 cfg_if! {
     if #[cfg(any(feature = "alloc", feature = "std"))] {
         extern crate arrayvec;

crossbeam-skiplist/src/lib.rs

@@ -3,6 +3,7 @@
 #![warn(missing_docs)]
 #![warn(missing_debug_implementations)]
 #![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
 
 #[macro_use]
 extern crate cfg_if;
@@ -17,6 +18,10 @@ cfg_if! {
     }
 }
 
+#[cfg_attr(
+    feature = "nightly",
+    cfg(all(target_has_atomic = "cas", target_has_atomic = "ptr"))
+)]
 cfg_if! {
     if #[cfg(any(feature = "alloc", feature = "std"))] {
         extern crate crossbeam_epoch as epoch;

crossbeam-utils/src/lib.rs

@@ -44,6 +44,10 @@ cfg_if! {
     }
 }
 
+#[cfg_attr(
+    feature = "nightly",
+    cfg(all(target_has_atomic = "cas", target_has_atomic = "ptr"))
+)]
 pub mod atomic;
 
 mod cache_padded;

src/lib.rs

@@ -68,6 +68,10 @@ pub use _epoch::crossbeam_epoch as epoch;
 
 extern crate crossbeam_utils;
 
+#[cfg_attr(
+    feature = "nightly",
+    cfg(all(target_has_atomic = "cas", target_has_atomic = "ptr"))
+)]
 pub use crossbeam_utils::atomic;
 
 /// Miscellaneous utilities.