Ensure lld is supported with download-ci-llvm

src/bootstrap/dist.rs

@@ -2067,6 +2067,9 @@ impl Step for RustDev {
 
         builder.ensure(crate::native::Llvm { target });
 
+        // We want to package `lld` to use it with `download-ci-llvm`.
+        builder.ensure(crate::native::Lld { target });
+
         let src_bindir = builder.llvm_out(target).join("bin");
         // If updating this list, you likely want to change
         // src/bootstrap/download-ci-llvm-stamp as well, otherwise local users

src/bootstrap/download-ci-llvm-stamp

@@ -1,4 +1,4 @@
 Change this file to make users of the `download-ci-llvm` configuration download
 a new version of LLVM from CI, even if the LLVM submodule hasn’t changed.
 
-Last change is for: https://github.com/rust-lang/rust/pull/102790
+Last change is for: https://github.com/rust-lang/rust/pull/104748

src/bootstrap/native.rs

@@ -63,13 +63,13 @@ impl LdFlags {
     }
 }
 
-// This returns whether we've already previously built LLVM.
-//
-// It's used to avoid busting caches during x.py check -- if we've already built
-// LLVM, it's fine for us to not try to avoid doing so.
-//
-// This will return the llvm-config if it can get it (but it will not build it
-// if not).
+/// This returns whether we've already previously built LLVM.
+///
+/// It's used to avoid busting caches during x.py check -- if we've already built
+/// LLVM, it's fine for us to not try to avoid doing so.
+///
+/// This will return the llvm-config if it can get it (but it will not build it
+/// if not).
 pub fn prebuilt_llvm_config(
     builder: &Builder<'_>,
     target: TargetSelection,
@@ -823,8 +823,21 @@ impl Step for Lld {
         }
         let target = self.target;
 
-        let LlvmResult { llvm_config, llvm_cmake_dir } =
-            builder.ensure(Llvm { target: self.target });
+        let LlvmResult { llvm_config, llvm_cmake_dir } = builder.ensure(Llvm { target });
+
+        // The `dist` step packages LLD next to LLVM's binaries for download-ci-llvm. The root path
+        // we usually expect here is `./build/$triple/ci-llvm/`, with the binaries in its `bin`
+        // subfolder. We check if that's the case, and if LLD's binary already exists there next to
+        // `llvm-config`: if so, we can use it instead of building LLVM/LLD from source.
+        let ci_llvm_bin = llvm_config.parent().unwrap();
+        if ci_llvm_bin.is_dir() && ci_llvm_bin.file_name().unwrap() == "bin" {
+            let lld_path = ci_llvm_bin.join(exe("lld", target));
+            if lld_path.exists() {
+                // The following steps copying `lld` as `rust-lld` to the sysroot, expect it in the
+                // `bin` subfolder of this step's out dir.
+                return ci_llvm_bin.parent().unwrap().to_path_buf();
+            }
+        }
 
         let out_dir = builder.lld_out(target);
         let done_stamp = out_dir.join("lld-finished-building");