Offload: Build offload as a single Step

bootstrap.example.toml

@@ -106,6 +106,9 @@
 # Whether to build LLVM with support for it's gpu offload runtime.
 #llvm.offload = false
 
+# Absolute path to the directory containing ClangConfig.cmake
+#llvm.offload-clang-dir = ""
+
 # When true, link libstdc++ statically into the rustc_llvm.
 # This is useful if you don't want to use the dynamic version of that
 # library provided by LLVM.

src/bootstrap/configure.py

@@ -120,6 +120,11 @@ def v(*args):
 o("llvm-assertions", "llvm.assertions", "build LLVM with assertions")
 o("llvm-enzyme", "llvm.enzyme", "build LLVM with enzyme")
 o("llvm-offload", "llvm.offload", "build LLVM with gpu offload support")
+o(
+    "llvm-offload-clang-dir",
+    "llvm.offload-clang-dir",
+    "pass the absolute directory of ClangConfig.cmake",
+)
 o("llvm-plugins", "llvm.plugins", "build LLVM with plugin interface")
 o("debug-assertions", "rust.debug-assertions", "build with debugging assertions")
 o(

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

@@ -1427,10 +1427,12 @@ fn rustc_llvm_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelect
     if builder.config.llvm_enzyme {
         cargo.env("LLVM_ENZYME", "1");
     }
+    let llvm::LlvmResult { host_llvm_config, .. } = builder.ensure(llvm::Llvm { target });
     if builder.config.llvm_offload {
+        builder.ensure(llvm::OmpOffload { target });
         cargo.env("LLVM_OFFLOAD", "1");
     }
-    let llvm::LlvmResult { host_llvm_config, .. } = builder.ensure(llvm::Llvm { target });
+
     cargo.env("LLVM_CONFIG", &host_llvm_config);
 
     // Some LLVM linker flags (-L and -l) may be needed to link `rustc_llvm`. Its build script
@@ -2293,6 +2295,24 @@ impl Step for Assemble {
             }
         }
 
+        if builder.config.llvm_offload && !builder.config.dry_run() {
+            debug!("`llvm_offload` requested");
+            let offload_install = builder.ensure(llvm::OmpOffload { target: build_compiler.host });
+            if let Some(_llvm_config) = builder.llvm_config(builder.config.host_target) {
+                let target_libdir =
+                    builder.sysroot_target_libdir(target_compiler, target_compiler.host);
+                for p in offload_install.offload_paths() {
+                    let libname = p.file_name().unwrap();
+                    let dst_lib = target_libdir.join(libname);
+                    builder.resolve_symlink_and_copy(&p, &dst_lib);
+                }
+                // FIXME(offload): Add amdgcn-amd-amdhsa and nvptx64-nvidia-cuda folder
+                // This one is slightly more tricky, since we have the same file twice, in two
+                // subfolders for amdgcn and nvptx64. We'll likely find two more in the future, once
+                // Intel and Spir-V support lands in offload.
+            }
+        }
+
         // Build the libraries for this compiler to link to (i.e., the libraries
         // it uses at runtime).
         debug!(