Use `llvm-bitcode-linker` as the default linker for `nvptx64-nvidia-cuda`

[kjetilkjeka]

Proposal

The current default linker for the nvptx64-nvidia-cuda target is rust-ptx-linker. However, the upstream rust-ptx-linker project has been broken since 2022 and is effectively unmaintained. In practice, this makes it difficult or impossible to use for most builds.

Since the introduction of the llvm-bitcode-linker it has become the recommended linker for nvptx64-nvidia-cuda in the official Rust documentation. The llvm-bitcode-linker provides a stable and maintainable path forward, and is in real world use for targeting Nvidia GPUs.

Given that:

• rust-ptx-linker is no longer functional or maintained,
• llvm-bitcode-linker is the officially recommended solution and actively maintained,
• and there are no known current users of rust-ptx-linker,

I propose to switch the default linker for the nvptx64-nvidia-cuda target to llvm-bitcode-linker.

This change will:

• Eliminate the need for explicitly passing -C linker-flavor=llbc.
• Simplify the build setup for CUDA targets.
• Lay the groundwork for potentially removing the dedicated “ptx” linker flavor in the future.

Mentors or Reviewers

The actual engineering work is trivial. I will "mentor" and create the MR if accepted

Process

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  • Outstanding concerns will block the Final Comment Period from finishing. Once all concerns are resolved, the 10 day countdown is restarted.
  • If no concerns are raised after 10 days since the resolution of the last outstanding concern, the MCP is considered approved.

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[rustbot]

Important

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cc @rust-lang/compiler

[Noratrieb]

@RDambrosio016 as our other maintainer

[davidtwco]

@rustbot second

[rustbot]

The final comment period is now complete, this major change is now accepted.

As the automated representative, I would like to thank the author for their work and everyone else who contributed to this major change proposal.

If you think this major change shouldn't have been accepted, feel free to remove the major-change-accepted label and reopen this issue.