Add new test directive needs-atomic to support rust-lang#87377

Author: kei519

src/tools/compiletest/src/common.rs

@@ -477,6 +477,16 @@ impl Config {
         ASM_SUPPORTED_ARCHS.contains(&self.target_cfg().arch.as_str())
     }
 
+    pub fn has_atomic(&self, size: Option<u64>) -> bool {
+        if let Some(size) = size {
+            (self.target_cfg().min_atomic_width()..=self.target_cfg().max_atomic_width())
+                .contains(&size)
+                && self.target_cfg().atomic_cas
+        } else {
+            self.target_cfg().atomic_cas
+        }
+    }
+
     pub fn git_config(&self) -> GitConfig<'_> {
         GitConfig {
             git_repository: &self.git_repository,
@@ -645,12 +655,26 @@ pub struct TargetCfg {
     pub(crate) xray: bool,
     #[serde(default = "default_reloc_model")]
     pub(crate) relocation_model: String,
+    #[serde(default)]
+    max_atomic_width: Option<u64>,
+    #[serde(default)]
+    min_atomic_width: Option<u64>,
+    #[serde(default = "default_atomic_cas")]
+    atomic_cas: bool,
 }
 
 impl TargetCfg {
     pub(crate) fn os_and_env(&self) -> String {
         format!("{}-{}", self.os, self.env)
     }
+
+    fn max_atomic_width(&self) -> u64 {
+        self.max_atomic_width.unwrap_or(self.pointer_width as _)
+    }
+
+    fn min_atomic_width(&self) -> u64 {
+        self.min_atomic_width.unwrap_or(8)
+    }
 }
 
 fn default_os() -> String {
@@ -661,6 +685,10 @@ fn default_reloc_model() -> String {
     "pic".into()
 }
 
+fn default_atomic_cas() -> bool {
+    true
+}
+
 #[derive(Eq, PartialEq, Clone, Debug, Default, serde::Deserialize)]
 #[serde(rename_all = "kebab-case")]
 pub enum Endian {

src/tools/compiletest/src/directive-list.rs

@@ -127,6 +127,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "min-llvm-version",
     "min-system-llvm-version",
     "needs-asm-support",
+    "needs-atomic",
     "needs-deterministic-layouts",
     "needs-dlltool",
     "needs-dynamic-linking",

src/tools/compiletest/src/header/needs.rs

@@ -171,9 +171,12 @@ pub(super) fn handle_needs(
         },
     ];
 
-    let (name, comment) = match ln.split_once([':', ' ']) {
-        Some((name, comment)) => (name, Some(comment)),
-        None => (ln, None),
+    // Because `needs-atomic` accepts one argument after colon to specify data size, we check whther
+    // comment starts with colon.
+    let (name, comment, comment_starts_with_colon) = if let Some(index) = ln.find([':', ' ']) {
+        (&ln[..index], Some(&ln[index + 1..]), ln.as_bytes()[index] == b':')
+    } else {
+        (ln, None, false)
     };
 
     if !name.starts_with("needs-") {
@@ -185,6 +188,69 @@ pub(super) fn handle_needs(
         return IgnoreDecision::Continue;
     }
 
+    // Check here because `needs-atomic` requires parsing comments.
+    if name == "needs-atomic" {
+        let mut comment = comment;
+
+        // Parse the comment to specify data size.
+        // Just comments not arguments are also accepted.
+        // No arguments are handled as (none).
+        let size = if !comment_starts_with_colon {
+            // Comments starting with spaces are not arguments.
+            None
+        } else {
+            if let Some(comment_content) = comment {
+                if comment_content.trim().is_empty() {
+                    None
+                } else {
+                    let (size, rest) = match comment_content.trim_start().split_once([':', ' ']) {
+                        Some((size, rest)) => (size, Some(rest)),
+                        None => (comment_content.trim(), None),
+                    };
+
+                    if size == "ptr" {
+                        comment = rest;
+                        Some(config.target_cfg().pointer_width as _)
+                    } else if let Ok(size) = size.parse() {
+                        if ![128, 64, 32, 16, 8].contains(&size) {
+                            // Numeric literals but non data size are disallowed.
+                            return IgnoreDecision::Error {
+                                message: "expected values for `needs-atomic` are: (none), `128`,\
+                                    `16`, `32`, `64`, `8`, and `ptr"
+                                    .into(),
+                            };
+                        } else {
+                            comment = rest;
+                            Some(size)
+                        }
+                    } else {
+                        // Comments starting with non-numeric literals are not arguments.
+                        None
+                    }
+                }
+            } else {
+                None
+            }
+        };
+
+        return if config.has_atomic(size) {
+            IgnoreDecision::Continue
+        } else {
+            let base = if let Some(size) = size {
+                format!("ignored on targets without {size}-bit atomic operations")
+            } else {
+                format!("ignored on targets without atomic operations")
+            };
+            IgnoreDecision::Ignore {
+                reason: if let Some(comment) = comment {
+                    format!("{base}: ({})", comment.trim())
+                } else {
+                    base
+                },
+            }
+        };
+    }
+
     let mut found_valid = false;
     for need in needs {
         if need.name == name {