Add a min_atomic_width target option, like max_atomic_width

src/librustc/session/config.rs

@@ -943,6 +943,7 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
  let os = &sess.target.target.target_os;
  let env = &sess.target.target.target_env;
  let vendor = &sess.target.target.target_vendor;
+ let min_atomic_width = sess.target.target.min_atomic_width();
  let max_atomic_width = sess.target.target.max_atomic_width();
 
  let mut ret = HashSet::new();
@@ -963,7 +964,7 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
  ret.insert((Symbol::intern("target_thread_local"), None));
  }
  for &i in &[8, 16, 32, 64, 128] {
- if i <= max_atomic_width {
+ if i >= min_atomic_width && i <= max_atomic_width {
  let s = i.to_string();
  ret.insert((Symbol::intern("target_has_atomic"), Some(Symbol::intern(&s))));
  if &s == wordsz {

src/librustc_back/target/mod.rs

@@ -376,6 +376,9 @@ pub struct TargetOptions {
  // file
  pub no_integrated_as: bool,
 
+ /// Don't use this field; instead use the `.min_atomic_width()` method.
+ pub min_atomic_width: Option<u64>,
+
  /// Don't use this field; instead use the `.max_atomic_width()` method.
  pub max_atomic_width: Option<u64>,
 
@@ -439,6 +442,7 @@ impl Default for TargetOptions {
  has_elf_tls: false,
  obj_is_bitcode: false,
  no_integrated_as: false,
+ min_atomic_width: None,
  max_atomic_width: None,
  panic_strategy: PanicStrategy::Unwind,
  abi_blacklist: vec![],
@@ -462,6 +466,12 @@ impl Target {
  }
  }
 
+ /// Minimum integer size in bits that this target can perform atomic
+ /// operations on.
+ pub fn min_atomic_width(&self) -> u64 {
+ self.options.min_atomic_width.unwrap_or(8)
+ }
+
  /// Maximum integer size in bits that this target can perform atomic
  /// operations on.
  pub fn max_atomic_width(&self) -> u64 {
@@ -604,6 +614,7 @@ impl Target {
  key!(obj_is_bitcode, bool);
  key!(no_integrated_as, bool);
  key!(max_atomic_width, Option<u64>);
+ key!(min_atomic_width, Option<u64>);
  try!(key!(panic_strategy, PanicStrategy));
  key!(crt_static_default, bool);
 
@@ -766,6 +777,7 @@ impl ToJson for Target {
  target_option_val!(has_elf_tls);
  target_option_val!(obj_is_bitcode);
  target_option_val!(no_integrated_as);
+ target_option_val!(min_atomic_width);
  target_option_val!(max_atomic_width);
  target_option_val!(panic_strategy);
  target_option_val!(crt_static_default);