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Update openmp/offload to new LLVM-22 build setup #152011

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Update openmp/offload to new LLVM-22 build setup #152011

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2a50b05
update openmp/offload builds to LLVM 22
ZuseZ4 Feb 6, 2026
a85f0aa
Update the build, blocked on LLVM rc3
ZuseZ4 Feb 6, 2026
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105 changes: 65 additions & 40 deletions src/bootstrap/src/core/build_steps/llvm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1008,30 +1008,6 @@ impl Step for OmpOffload {
t!(fs::create_dir_all(&out_dir));

builder.config.update_submodule("src/llvm-project");
let mut cfg = cmake::Config::new(builder.src.join("src/llvm-project/runtimes/"));

// If we use an external clang as opposed to building our own llvm_clang, than that clang will
// come with it's own set of default include directories, which are based on a potentially older
// LLVM. This can cause issues, so we overwrite it to include headers based on our
// `src/llvm-project` submodule instead.
// FIXME(offload): With LLVM-22 we hopefully won't need an external clang anymore.
let mut cflags = CcFlags::default();
if !builder.config.llvm_clang {
let base = builder.llvm_out(target).join("include");
let inc_dir = base.display();
cflags.push_all(format!(" -I {inc_dir}"));
}

configure_cmake(builder, target, &mut cfg, true, LdFlags::default(), cflags, &[]);

// Re-use the same flags as llvm to control the level of debug information
// generated for offload.
let profile = match (builder.config.llvm_optimize, builder.config.llvm_release_debuginfo) {
(false, _) => "Debug",
(true, false) => "Release",
(true, true) => "RelWithDebInfo",
};
trace!(?profile);

// OpenMP/Offload builds currently (LLVM-21) still depend on Clang, although there are
// intentions to loosen this requirement for LLVM-22. If we were to
Expand All @@ -1044,23 +1020,72 @@ impl Step for OmpOffload {
None
};

// FIXME(offload): Once we move from OMP to Offload (Ol) APIs, we should drop the openmp
// runtime to simplify our build. We should also re-evaluate the LLVM_Root and try to get
// rid of the Clang_DIR, once we upgrade to LLVM-22.
cfg.out_dir(&out_dir)
.profile(profile)
.env("LLVM_CONFIG_REAL", &host_llvm_config)
.define("LLVM_ENABLE_ASSERTIONS", "ON")
.define("LLVM_ENABLE_RUNTIMES", "openmp;offload")
.define("LLVM_INCLUDE_TESTS", "OFF")
.define("OFFLOAD_INCLUDE_TESTS", "OFF")
.define("OPENMP_STANDALONE_BUILD", "ON")
.define("LLVM_ROOT", builder.llvm_out(target).join("build"))
.define("LLVM_DIR", llvm_cmake_dir);
if let Some(p) = clang_dir {
cfg.define("Clang_DIR", p);
let omp_targets = vec![target.triple.as_ref(), "amdgcn-amd-amdhsa", "nvptx64-nvidia-cuda"];
for omp_target in omp_targets {
let mut cfg = cmake::Config::new(builder.src.join("src/llvm-project/runtimes/"));

// If we use an external clang as opposed to building our own llvm_clang, than that clang will
// come with it's own set of default include directories, which are based on a potentially older
// LLVM. This can cause issues, so we overwrite it to include headers based on our
// `src/llvm-project` submodule instead.
// FIXME(offload): With LLVM-22 we hopefully won't need an external clang anymore.
let mut cflags = CcFlags::default();
if !builder.config.llvm_clang {
let base = builder.llvm_out(target).join("include");
let inc_dir = base.display();
cflags.push_all(format!(" -I {inc_dir}"));
}

configure_cmake(builder, target, &mut cfg, true, LdFlags::default(), cflags, &[]);

// Re-use the same flags as llvm to control the level of debug information
// generated for offload.
let profile =
match (builder.config.llvm_optimize, builder.config.llvm_release_debuginfo) {
(false, _) => "Debug",
(true, false) => "Release",
(true, true) => "RelWithDebInfo",
};
trace!(?profile);

// FIXME(offload): Once we move from OMP to Offload (Ol) APIs, we should drop the openmp
// runtime to simplify our build. So far, these are still under development.
cfg.out_dir(&out_dir)
.profile(profile)
.env("LLVM_CONFIG_REAL", &host_llvm_config)
.define("LLVM_ENABLE_ASSERTIONS", "ON")
.define("LLVM_INCLUDE_TESTS", "OFF")
.define("OFFLOAD_INCLUDE_TESTS", "OFF")
.define("LLVM_ROOT", builder.llvm_out(target).join("build"))
.define("LLVM_DIR", llvm_cmake_dir.clone())
// Verify whether per-target-runtime-dir is needed
.define("LLVM_ENABLE_PER_TARGET_RUNTIME_DIR", "ON")
// Verify whether this one is needed.
.define("OPENMP_STANDALONE_BUILD", "ON")
.define("CMAKE_CXX_COMPILER_WORKS", "TRUE")
.define("CMAKE_C_COMPILER_WORKS", "TRUE")
.define("LLVM_DEFAULT_TARGET_TRIPLE", omp_target);
if let Some(p) = clang_dir.clone() {
cfg.define("Clang_DIR", p);
}

// We don't perform a full cross-compilation of rustc, therefore our target.triple
// will still be a CPU target.
if *omp_target == *target.triple {
// The offload library provides functionality which only makes sense on the host.
// Verify whether libc is needed on the host
cfg.define("LLVM_ENABLE_RUNTIMES", "openmp;offload;libc");
} else {
// OpenMP provides some device libraries, so we also compile it for all gpu targets.
cfg.define("LIBC_TARGET_TRIPLE", omp_target);
cfg.define("LLVM_USE_LINKER", "lld");
cfg.define("LLVM_LIBC_FULL_BUILD", "ON");
cfg.define("LLVM_ENABLE_RUNTIMES", "openmp;libc");
cfg.define("CMAKE_C_COMPILER_TARGET", omp_target);
cfg.define("CMAKE_CXX_COMPILER_TARGET", omp_target);
}
cfg.build();
}
cfg.build();

t!(stamp.write());

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