Revert "Make the c feature for compiler-builtins opt-in instead of inferred"

This reverts commit 3acb505
(PR rust-lang#101833).

The changes in this commit caused several bugs or at least
incompatibilies. For now we're reverting this commit and will re-land it
alongside fixes for those bugs.

Author: Mark-Simulacrum

config.toml.example

@@ -291,10 +291,6 @@ 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

src/bootstrap/compile.rs

@@ -299,7 +299,9 @@ 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.
+    // `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).
     //
     // 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
@@ -310,15 +312,8 @@ 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 {
-        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");
+    let compiler_builtins_root = builder.src.join("src/llvm-project/compiler-rt");
+    let compiler_builtins_c_feature = if compiler_builtins_root.exists() {
         // 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);

src/bootstrap/config.rs

@@ -73,8 +73,6 @@ 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,
@@ -624,7 +622,6 @@ 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",
     }
 }
 
@@ -1013,7 +1010,6 @@ 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);
 

src/bootstrap/dist.rs

@@ -1847,21 +1847,23 @@ 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 !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;
+    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;
+        }
     }
 
     // On macOS, rustc (and LLVM tools) link to an unversioned libLLVM.dylib

src/ci/docker/host-x86_64/disabled/dist-x86_64-haiku/Dockerfile

@@ -47,6 +47,4 @@ 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

src/ci/docker/host-x86_64/dist-various-2/Dockerfile

@@ -129,6 +129,4 @@ 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

src/ci/docker/host-x86_64/x86_64-gnu-llvm-13-stage1/Dockerfile

@@ -29,7 +29,6 @@ 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 \

src/ci/docker/host-x86_64/x86_64-gnu-llvm-13/Dockerfile

@@ -40,7 +40,6 @@ 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 \

src/ci/run.sh

@@ -69,11 +69,6 @@ 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