support target specific optimized-compiler-builtins

config.example.toml

@@ -922,6 +922,15 @@
 # argument as the test binary.
 #runner = <none> (string)
 
+# Use the optimized LLVM C intrinsics for `compiler_builtins`, rather than Rust intrinsics
+# on this target.
+# Requires the LLVM submodule to be managed by bootstrap (i.e. not external) so that `compiler-rt`
+# sources are available.
+#
+# Setting this to `false` generates slower code, but removes the requirement for a C toolchain in
+# order to run `x check`.
+#optimized-compiler-builtins = build.optimized-compiler-builtins (bool)
+
 # =============================================================================
 # Distribution options
 #

src/bootstrap/src/core/build_steps/compile.rs

@@ -469,7 +469,7 @@ pub fn std_cargo(builder: &Builder<'_>, target: TargetSelection, stage: u32, car
     // If `compiler-rt` is available ensure that the `c` feature of the
     // `compiler-builtins` crate is enabled and it's configured to learn where
     // `compiler-rt` is located.
-    let compiler_builtins_c_feature = if builder.config.optimized_compiler_builtins {
+    let compiler_builtins_c_feature = if builder.config.optimized_compiler_builtins(target) {
         // NOTE: this interacts strangely with `llvm-has-rust-patches`. In that case, we enforce `submodules = false`, so this is a no-op.
         // But, the user could still decide to manually use an in-tree submodule.
         //

src/bootstrap/src/core/config/config.rs

@@ -634,6 +634,7 @@ pub struct Target {
     pub runner: Option<String>,
     pub no_std: bool,
     pub codegen_backends: Option<Vec<String>>,
+    pub optimized_compiler_builtins: Option<bool>,
 }
 
 impl Target {
@@ -1219,6 +1220,7 @@ define_config! {
         no_std: Option<bool> = "no-std",
         codegen_backends: Option<Vec<String>> = "codegen-backends",
         runner: Option<String> = "runner",
+        optimized_compiler_builtins: Option<bool> = "optimized-compiler-builtins",
     }
 }
 
@@ -2096,6 +2098,7 @@ impl Config {
                 target.sanitizers = cfg.sanitizers;
                 target.profiler = cfg.profiler;
                 target.rpath = cfg.rpath;
+                target.optimized_compiler_builtins = cfg.optimized_compiler_builtins;
 
                 if let Some(ref backends) = cfg.codegen_backends {
                     let available_backends = ["llvm", "cranelift", "gcc"];
@@ -2609,6 +2612,13 @@ impl Config {
         self.target_config.get(&target).and_then(|t| t.rpath).unwrap_or(self.rust_rpath)
     }
 
+    pub fn optimized_compiler_builtins(&self, target: TargetSelection) -> bool {
+        self.target_config
+            .get(&target)
+            .and_then(|t| t.optimized_compiler_builtins)
+            .unwrap_or(self.optimized_compiler_builtins)
+    }
+
     pub fn llvm_enabled(&self, target: TargetSelection) -> bool {
         self.codegen_backends(target).contains(&"llvm".to_owned())
     }
@@ -3162,6 +3172,9 @@ fn check_incompatible_options_for_ci_rustc(
 
             let profiler = &ci_cfg.profiler;
             err!(current_cfg.profiler, profiler, "build");
+
+            let optimized_compiler_builtins = &ci_cfg.optimized_compiler_builtins;
+            err!(current_cfg.optimized_compiler_builtins, optimized_compiler_builtins, "build");
         }
     }
 

src/bootstrap/src/core/config/tests.rs

@@ -120,13 +120,15 @@ fn override_toml() {
             "--set=change-id=1".to_owned(),
             "--set=rust.lto=fat".to_owned(),
             "--set=rust.deny-warnings=false".to_owned(),
+            "--set=build.optimized-compiler-builtins=true".to_owned(),
             "--set=build.gdb=\"bar\"".to_owned(),
             "--set=build.tools=[\"cargo\"]".to_owned(),
             "--set=llvm.build-config={\"foo\" = \"bar\"}".to_owned(),
             "--set=target.x86_64-unknown-linux-gnu.runner=bar".to_owned(),
             "--set=target.x86_64-unknown-linux-gnu.rpath=false".to_owned(),
             "--set=target.aarch64-unknown-linux-gnu.sanitizers=false".to_owned(),
             "--set=target.aarch64-apple-darwin.runner=apple".to_owned(),
+            "--set=target.aarch64-apple-darwin.optimized-compiler-builtins=false".to_owned(),
         ]),
         |&_| {
             toml::from_str(
@@ -167,6 +169,7 @@ runner = "x86_64-runner"
     );
     assert_eq!(config.gdb, Some("bar".into()), "setting string value with quotes");
     assert!(!config.deny_warnings, "setting boolean value");
+    assert!(config.optimized_compiler_builtins, "setting boolean value");
     assert_eq!(
         config.tools,
         Some(["cargo".to_string()].into_iter().collect()),
@@ -193,7 +196,11 @@ runner = "x86_64-runner"
         ..Default::default()
     };
     let darwin = TargetSelection::from_user("aarch64-apple-darwin");
-    let darwin_values = Target { runner: Some("apple".into()), ..Default::default() };
+    let darwin_values = Target {
+        runner: Some("apple".into()),
+        optimized_compiler_builtins: Some(false),
+        ..Default::default()
+    };
     assert_eq!(
         config.target_config,
         [(x86_64, x86_64_values), (aarch64, aarch64_values), (darwin, darwin_values)]

src/bootstrap/src/utils/change_tracker.rs

@@ -325,4 +325,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Warning,
         summary: "Removed `rust.parallel-compiler` as it was deprecated in #132282 long time ago.",
     },
+    ChangeInfo {
+        change_id: 135326,
+        severity: ChangeSeverity::Warning,
+        summary: "It is now possible to configure `optimized-compiler-builtins` for per target.",
+    },
 ];