Add test case for compiling multiple graphs

[sarckk]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

In some cases, we might want to compile multiple subgraphs, e.g. if some submodules in the model are not traceable with torch dynamo. See #14913 and #19719 for motivating scenarios.

This PR adds a test case showcasing how this can be supported in vLLM for piecewise compilation. This requires several components:

• Each subgraph in the model being compiled needs to be initialized with set_model_tag(tag) to ensure compile cache is not shared between these subgraphs (initially added in [torch.compile] reorganize the cache directory to support compiling multiple models #19064 to support compiling multiple models)
• Pre-allocate static buffers to be used as arg inputs to each compiled subgraph as CUDA Graph expects static tensor addresses between runs
• Added ignore_torch_compile helper decorator in scenarios where a class inherits a parent module that has support_torch_compile decorator applied but this class does not want to compile its forward(). Added test_ignore_torch_compile_decorator that tests this.

Also disables AOTAutogradCache in StandaloneInductor adaptor which is needed for compilation caching to work. StandaloneInductorAdaptor in PyTorch 2.8+ will fix this problem (thanks @zou3519)

Test Plan

pytest tests/compile/piecewise/test_multiple_graphs.py

Test Result

Both newly added unit tests (test_ignore_torch_compile_decorator and test_multi_graph_piecewise_compile) pass

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.

💬 Join our developer Slack at https://slack.vllm.ai to discuss your PR in #pr-reviews, coordinate on features in #feat- channels, or join special interest groups in #sig- channels.

Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

🚀

[sarckk]

cc: @zou3519 @youkaichao

[gemini-code-assist]

Code Review

This pull request introduces a new ignore_torch_compile decorator and adds test cases for compiling multiple graphs. There is a potential issue with the inheritance of the IGNORE_COMPILE_KEY that needs to be addressed.

[zou3519]

Looks reasonable to me. One minor comment

[zou3519]

cc @BoyuanFeng

[BoyuanFeng]

looks good! a few minor comments

[sarckk]

@houseroad the failing tests don't seem related to this PR, can we merge it? e.g. for model tests (voxtral unrecognized), the test also fails on main

[zou3519]

btw @houseroad @yeqcharlotte this will fix a lot of the compiler cache issues people report