[XPU] Automatically detect target platform as XPU in build.

[ccrhx4]

Purpose

Before VLLM_TARGET_DEVICE=xpu is required to build vLLM for XPU, this patch will automatically detect XPU as target platform.

Test Plan

pip install -r requirements/xpu.txt &&
pip install --no-build-isolation .

Test Result

[gemini-code-assist]

Code Review

This pull request adds automatic detection for the XPU platform during the build process. The implementation correctly adds a check for torch.version.xpu. However, the order of platform detection might lead to unexpected behavior. Currently, it prioritizes ROCm, then XPU, and finally CUDA. On a system with both NVIDIA and Intel GPUs, this would default to building for XPU, which might not be the user's intention, especially since CUDA is the primary supported platform for vLLM. I've suggested reordering the checks to prioritize CUDA, which seems more intuitive for most users.

[gemini-code-assist]

The order of device detection prioritizes ROCm and XPU over CUDA. On a system with multiple GPU types (e.g., NVIDIA and Intel), this will cause vLLM to build for XPU by default, even if a more powerful NVIDIA GPU is available. Given that CUDA is the primary and most mature backend for vLLM, it should likely be prioritized in the auto-detection logic to provide a better out-of-the-box experience for users. I suggest reordering to check for CUDA first.

Suggested change

	if torch.version.hip is not None:
	VLLM_TARGET_DEVICE = "rocm"
	logger.info("Auto-detected ROCm")
	elif torch.version.xpu is not None:
	VLLM_TARGET_DEVICE = "xpu"
	logger.info("Auto-detected XPU")
	elif torch.version.cuda is not None:
	VLLM_TARGET_DEVICE = "cuda"
	logger.info("Auto-detected CUDA")
	if torch.version.cuda is not None:
	VLLM_TARGET_DEVICE = "cuda"
	logger.info("Auto-detected CUDA")
	elif torch.version.hip is not None:
	VLLM_TARGET_DEVICE = "rocm"
	logger.info("Auto-detected ROCm")
	elif torch.version.xpu is not None:
	VLLM_TARGET_DEVICE = "xpu"
	logger.info("Auto-detected XPU")

[github-actions]

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[jikunshang]

LGTM. thanks for fixing!