[SYCL][NewOffloadModel] Enable -fno-sycl-rdc in Clang Driver for New Offload Model

[srividya-sundaram]

Summary

This patch adds -fno-sycl-rdc support to the new SYCL offload model in the Clang driver. It is based on the work by @maksimsab in #21973, with review fixes applied.

What this patch does

By default (-fsycl-rdc), all device code across translation units is linked together into one module at link time before post-link processing. With -fno-sycl-rdc, each object file's device code is processed independently — skipping the llvm-link step — which can significantly reduce peak memory and compile time.

Changes:

• clang/lib/Driver/ToolChains/Clang.cpp: In LinkerWrapper::ConstructJob, propagate --no-sycl-rdc to clang-linker-wrapper when -fno-sycl-rdc is passed at link time.
• sycl/doc/design/OffloadDesign.md: Document NoRDC mode for the new offload model.
• sycl/doc/design/NonRelocatableDeviceCode.md: Add a note clarifying that document covers the old offload model only.
• sycl/test-e2e/AOT/early_aot.cpp: Un-XFAIL the test for the new offload model; adjust RUN lines to pass -fno-sycl-rdc at the correct step per model.
• clang/test/Driver/sycl-no-rdc-new-driver.cpp: New driver test verifying --no-sycl-rdc is propagated to clang-linker-wrapper correctly.

Key behavioral difference from the old offload model

Model	Where to pass -fno-sycl-rdc
Old (--no-offload-new-driver)	At each compile step (-c)
New (--offload-new-driver)	At the link step

This inversion exists because in the new model all SYCL offload processing (post-link, AOT, wrapping) lives in clang-linker-wrapper at link time.

Follow-up work

Supporting -fno-sycl-rdc -c in the new model (matching the old model's compile-step ergonomics) will be addressed in a follow-up patch. The plan is to invoke clang-linker-wrapper --sycl-device-link --no-sycl-rdc per translation unit at compile time, embedding the finalized device image directly into the host object.

Supporting -fno-sycl-rdc -c in the new model (matching old model compile-step ergonomics) is addressed in #22833.

Fixes: CMPLRLLVM-51875

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR enables -fno-sycl-rdc support for the new SYCL offload model by propagating the flag at link time to clang-linker-wrapper, updates the related design documentation, and adjusts/extends tests to validate the new behavior.

Changes:

• Propagate NoRDC to clang-linker-wrapper from the Clang driver when linking SYCL with the new offload model.
• Document NoRDC behavior and clarify old-vs-new offload model flag placement (compile step vs link step).
• Update/add tests to reflect the new model’s link-step -fno-sycl-rdc usage and verify driver propagation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
sycl/test-e2e/AOT/early_aot.cpp	Un-XFAIL for new offload model and adjust RUN lines to pass -fno-sycl-rdc at the correct step per model.
sycl/doc/design/OffloadDesign.md	Document NoRDC support and explicitly describe the old vs new model usage inversion.
sycl/doc/design/NonRelocatableDeviceCode.md	Clarify the document applies to the old offload model’s NoRDC design.
clang/test/Driver/sycl-no-rdc-new-driver.cpp	Add driver coverage ensuring --no-sycl-rdc is propagated to clang-linker-wrapper for --offload-new-driver.
clang/lib/Driver/ToolChains/Clang.cpp	Driver change to translate -fno-sycl-rdc into --no-sycl-rdc for clang-linker-wrapper in SYCL link jobs.

[srividya-sundaram]

The build_run_native_cpu_e2e_tests failure is unrelated to this PR. SYCL :: KernelParams/has-special-captures.cpp has XFAIL: native_cpu (tracked via #20127) but the underlying issue seems to be fixed, so the test now unexpectedly passes. This needs a separate cleanup PR to remove the stale XFAIL marker and is un-related to the changes in this PR.

[sarnex]

lgtm just some nits

[sarnex]

lgtm thx