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-rw-r--r--config.toml.example4
-rw-r--r--src/bootstrap/compile.rs15
-rw-r--r--src/bootstrap/config.rs4
-rw-r--r--src/bootstrap/dist.rs32
-rw-r--r--src/ci/docker/host-x86_64/disabled/dist-x86_64-haiku/Dockerfile2
-rw-r--r--src/ci/docker/host-x86_64/dist-various-2/Dockerfile2
-rw-r--r--src/ci/docker/host-x86_64/x86_64-gnu-llvm-13-stage1/Dockerfile1
-rw-r--r--src/ci/docker/host-x86_64/x86_64-gnu-llvm-13/Dockerfile1
-rwxr-xr-xsrc/ci/run.sh5
9 files changed, 44 insertions, 22 deletions
diff --git a/config.toml.example b/config.toml.example
index a967d881b02..ff08dfc553d 100644
--- a/config.toml.example
+++ b/config.toml.example
@@ -291,6 +291,10 @@ changelog-seen = 2
 # on this runtime, such as `-C profile-generate` or `-C instrument-coverage`).
 #profiler = false
 
+# Use the optimized LLVM C intrinsics for `compiler_builtins`, rather than Rust intrinsics.
+# Requires the LLVM submodule to be managed by bootstrap (i.e. not external).
+#optimized-compiler-builtins = false
+
 # Indicates whether the native libraries linked into Cargo will be statically
 # linked or not.
 #cargo-native-static = false
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index c13e83f6c86..58cf3edc317 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -299,9 +299,7 @@ pub fn std_cargo(builder: &Builder<'_>, target: TargetSelection, stage: u32, car
 
     // Determine if we're going to compile in optimized C intrinsics to
     // the `compiler-builtins` crate. These intrinsics live in LLVM's
-    // `compiler-rt` repository, but our `src/llvm-project` submodule isn't
-    // always checked out, so we need to conditionally look for this. (e.g. if
-    // an external LLVM is used we skip the LLVM submodule checkout).
+    // `compiler-rt` repository.
     //
     // Note that this shouldn't affect the correctness of `compiler-builtins`,
     // but only its speed. Some intrinsics in C haven't been translated to Rust
@@ -312,8 +310,15 @@ 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_root = builder.src.join("src/llvm-project/compiler-rt");
-    let compiler_builtins_c_feature = if compiler_builtins_root.exists() {
+    let compiler_builtins_c_feature = if builder.config.optimized_compiler_builtins {
+        if !builder.is_rust_llvm(target) {
+            panic!(
+                "need a managed LLVM submodule for optimized intrinsics support; unset `llvm-config` or `optimized-compiler-builtins`"
+            );
+        }
+
+        builder.update_submodule(&Path::new("src").join("llvm-project"));
+        let compiler_builtins_root = builder.src.join("src/llvm-project/compiler-rt");
         // Note that `libprofiler_builtins/build.rs` also computes this so if
         // you're changing something here please also change that.
         cargo.env("RUST_COMPILER_RT_ROOT", &compiler_builtins_root);
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 74530dec97b..f29b5170ea5 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -73,6 +73,8 @@ pub struct Config {
     pub color: Color,
     pub patch_binaries_for_nix: bool,
     pub stage0_metadata: Stage0Metadata,
+    /// Whether to use the `c` feature of the `compiler_builtins` crate.
+    pub optimized_compiler_builtins: bool,
 
     pub on_fail: Option<String>,
     pub stage: u32,
@@ -597,6 +599,7 @@ define_config! {
         bench_stage: Option<u32> = "bench-stage",
         patch_binaries_for_nix: Option<bool> = "patch-binaries-for-nix",
         metrics: Option<bool> = "metrics",
+        optimized_compiler_builtins: Option<bool> = "optimized-compiler-builtins",
     }
 }
 
@@ -966,6 +969,7 @@ impl Config {
         set(&mut config.print_step_timings, build.print_step_timings);
         set(&mut config.print_step_rusage, build.print_step_rusage);
         set(&mut config.patch_binaries_for_nix, build.patch_binaries_for_nix);
+        set(&mut config.optimized_compiler_builtins, build.optimized_compiler_builtins);
 
         config.verbose = cmp::max(config.verbose, flags.verbose);
 
diff --git a/src/bootstrap/dist.rs b/src/bootstrap/dist.rs
index f387496883b..42352285182 100644
--- a/src/bootstrap/dist.rs
+++ b/src/bootstrap/dist.rs
@@ -1844,23 +1844,21 @@ fn add_env(builder: &Builder<'_>, cmd: &mut Command, target: TargetSelection) {
 ///
 /// Returns whether the files were actually copied.
 fn maybe_install_llvm(builder: &Builder<'_>, target: TargetSelection, dst_libdir: &Path) -> bool {
-    if let Some(config) = builder.config.target_config.get(&target) {
-        if config.llvm_config.is_some() && !builder.config.llvm_from_ci {
-            // If the LLVM was externally provided, then we don't currently copy
-            // artifacts into the sysroot. This is not necessarily the right
-            // choice (in particular, it will require the LLVM dylib to be in
-            // the linker's load path at runtime), but the common use case for
-            // external LLVMs is distribution provided LLVMs, and in that case
-            // they're usually in the standard search path (e.g., /usr/lib) and
-            // copying them here is going to cause problems as we may end up
-            // with the wrong files and isn't what distributions want.
-            //
-            // This behavior may be revisited in the future though.
-            //
-            // If the LLVM is coming from ourselves (just from CI) though, we
-            // still want to install it, as it otherwise won't be available.
-            return false;
-        }
+    if !builder.is_rust_llvm(target) {
+        // If the LLVM was externally provided, then we don't currently copy
+        // artifacts into the sysroot. This is not necessarily the right
+        // choice (in particular, it will require the LLVM dylib to be in
+        // the linker's load path at runtime), but the common use case for
+        // external LLVMs is distribution provided LLVMs, and in that case
+        // they're usually in the standard search path (e.g., /usr/lib) and
+        // copying them here is going to cause problems as we may end up
+        // with the wrong files and isn't what distributions want.
+        //
+        // This behavior may be revisited in the future though.
+        //
+        // If the LLVM is coming from ourselves (just from CI) though, we
+        // still want to install it, as it otherwise won't be available.
+        return false;
     }
 
     // On macOS, rustc (and LLVM tools) link to an unversioned libLLVM.dylib
diff --git a/src/ci/docker/host-x86_64/disabled/dist-x86_64-haiku/Dockerfile b/src/ci/docker/host-x86_64/disabled/dist-x86_64-haiku/Dockerfile
index 5ddd3f18039..637b5fa22f9 100644
--- a/src/ci/docker/host-x86_64/disabled/dist-x86_64-haiku/Dockerfile
+++ b/src/ci/docker/host-x86_64/disabled/dist-x86_64-haiku/Dockerfile
@@ -47,4 +47,6 @@ ENV RUST_CONFIGURE_ARGS --disable-jemalloc \
   --set=$TARGET.cc=x86_64-unknown-haiku-gcc \
   --set=$TARGET.cxx=x86_64-unknown-haiku-g++ \
   --set=$TARGET.llvm-config=/bin/llvm-config-haiku
+ENV EXTERNAL_LLVM 1
+
 ENV SCRIPT python3 ../x.py dist --host=$HOST --target=$HOST
diff --git a/src/ci/docker/host-x86_64/dist-various-2/Dockerfile b/src/ci/docker/host-x86_64/dist-various-2/Dockerfile
index 126c292b38e..8250ec0c311 100644
--- a/src/ci/docker/host-x86_64/dist-various-2/Dockerfile
+++ b/src/ci/docker/host-x86_64/dist-various-2/Dockerfile
@@ -129,4 +129,6 @@ ENV RUST_CONFIGURE_ARGS --enable-extended --enable-lld --disable-docs \
   --set target.wasm32-wasi.wasi-root=/wasm32-wasi \
   --musl-root-armv7=/musl-armv7
 
+ENV EXTERNAL_LLVM 1
+
 ENV SCRIPT python3 ../x.py dist --host='' --target $TARGETS
diff --git a/src/ci/docker/host-x86_64/x86_64-gnu-llvm-13-stage1/Dockerfile b/src/ci/docker/host-x86_64/x86_64-gnu-llvm-13-stage1/Dockerfile
index 23f2215c2d9..1289f116fe9 100644
--- a/src/ci/docker/host-x86_64/x86_64-gnu-llvm-13-stage1/Dockerfile
+++ b/src/ci/docker/host-x86_64/x86_64-gnu-llvm-13-stage1/Dockerfile
@@ -29,6 +29,7 @@ RUN sh /scripts/sccache.sh
 # We are disabling CI LLVM since this builder is intentionally using a host
 # LLVM, rather than the typical src/llvm-project LLVM.
 ENV NO_DOWNLOAD_CI_LLVM 1
+ENV EXTERNAL_LLVM 1
 
 # Using llvm-link-shared due to libffi issues -- see #34486
 ENV RUST_CONFIGURE_ARGS \
diff --git a/src/ci/docker/host-x86_64/x86_64-gnu-llvm-13/Dockerfile b/src/ci/docker/host-x86_64/x86_64-gnu-llvm-13/Dockerfile
index 8f6831bc54e..4b89a72baa1 100644
--- a/src/ci/docker/host-x86_64/x86_64-gnu-llvm-13/Dockerfile
+++ b/src/ci/docker/host-x86_64/x86_64-gnu-llvm-13/Dockerfile
@@ -40,6 +40,7 @@ RUN sh /scripts/sccache.sh
 # We are disabling CI LLVM since this builder is intentionally using a host
 # LLVM, rather than the typical src/llvm-project LLVM.
 ENV NO_DOWNLOAD_CI_LLVM 1
+ENV EXTERNAL_LLVM 1
 
 # Using llvm-link-shared due to libffi issues -- see #34486
 ENV RUST_CONFIGURE_ARGS \
diff --git a/src/ci/run.sh b/src/ci/run.sh
index 9a247fb60a8..9d98ce22498 100755
--- a/src/ci/run.sh
+++ b/src/ci/run.sh
@@ -69,6 +69,11 @@ RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.codegen-units-std=1"
 # space required for CI artifacts.
 RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --dist-compression-formats=xz"
 
+# Enable the `c` feature for compiler_builtins, but only when the `compiler-rt` source is available.
+if [ "$EXTERNAL_LLVM" = "" ]; then
+  RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set build.optimized-compiler-builtins"
+fi
+
 if [ "$DIST_SRC" = "" ]; then
   RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --disable-dist-src"
 fi
generated by cgit-pink 1.4.1-3-g733a5 (git 2.37.1) at 2026-04-27 11:03:47 +0000