StreamTest no longer needs the HostIrLowering knob.

[wujingyue]

No description provided.

[wujingyue]

!test

[github-actions]

Description

• Removed HostIrLowering configuration from StreamTest class

• Simplified StreamTest to directly inherit from NVFuserTest

• Added explanatory comment about test purpose and location

• StreamTest no longer needs the EnableOption::HostIrLowering setting

Changes walkthrough

	Relevant files
Enhancement	test_stream.cpp Remove HostIrLowering configuration from StreamTest            tests/cpp/test_stream.cpp Removed StreamTest class constructor that set HostIrLowering option Replaced with simple alias: using StreamTest = NVFuserTest Added comment explaining tests verify stream parallelism building blocks Noted end-to-end tests moved to Python API tests +4/-6

PR Reviewer Guide

Here are some key observations to aid the review process:

🧪 PR contains tests

⚡ Recommended focus areas for review

Test Behavior Change The removal of EnableOption::HostIrLowering from StreamTest constructor may change the behavior being tested. While the PR title suggests this knob is no longer needed, the reviewer should verify that all StreamTest tests still pass and produce the expected results without this option enabled. namespace nvfuser { // The tests in this file verify building blocks for stream parallelism, e.g., // sharding propagation and KernelExecutor. End-to-end tests have been moved to // tests/python/direct/test_stream.py because the Python API is sufficient. using StreamTest = NVFuserTest;

Test failures

• (High, 44) NCCL NVLS multicast bind failure in multidevice / nvfuser test suites (dlcluster_viking_ci)

  Test Name	H100 (dist.)	Source
  tests.python.multidevice.test_communication.test_allgather	❌
  tests.python.multidevice.test_communication.test_allgather_expanded_broadcast	❌
  tests.python.multidevice.test_communication.test_allreduce	❌
  tests.python.multidevice.test_communication.test_reduce_scatter	❌
  tests.python.multidevice.test_communication.test_reduce_scatter_noncontiguous	❌
  tests.python.multidevice.test_dtensor.test_column_parallel_linear	❌
  tests.python.multidevice.test_dtensor.test_plus_one	❌
  tests.python.multidevice.test_dtensor.test_row_parallel_linear	❌
  tests.python.multidevice.test_expert_parallel.test_dispatch_and_combine	❌
  tests.python.multidevice.test_matmul.test_column_parallel_grouped_mm	❌
  ... with 34 more test failures omitted. Check internal logs.

• (Medium, 1) NCCL invalid usage errors in multidevice overlap tests (tests/python/multidevice)

  Test Name	H100 (dist.)	Source
  tests.python.multidevice.test_overlap.test_overlap_allgather_matmul_shard_outermost[backend_type=CommunicatorBackend.cuda]	❌

[greptile-apps]

Greptile Summary

This PR simplifies the StreamTest fixture by removing the HostIrLowering knob that is no longer needed. The custom test fixture class that previously enabled HostIrLowering in its constructor has been replaced with a simple type alias to NVFuserTest.

• Replaced custom StreamTest class with type alias: using StreamTest = NVFuserTest
• Removed EnableOptionsGuard::getCurOptions().set(EnableOption::HostIrLowering) from constructor
• Added helpful comment explaining that these tests verify building blocks for stream parallelism, with end-to-end tests moved to Python
• All test cases (AddPerStream, HaveDifferentShardings, ForwardPropagation, etc.) remain unchanged and continue using KernelExecutor directly

The change is consistent with recent work to decouple KernelExecutor from HostIrJit (PR #5616), which made the HostIrLowering flag unnecessary for these tests.

Confidence Score: 5/5

• This PR is safe to merge with no risk
• The change is a straightforward cleanup that removes unnecessary configuration. KernelExecutor no longer requires the HostIrLowering flag after recent refactoring work. All test logic remains identical, only the fixture setup was simplified. Many other tests in the codebase already use KernelExecutor without setting this flag.
• No files require special attention

Important Files Changed

Filename	Overview
tests/cpp/test_stream.cpp	Removed unnecessary HostIrLowering knob from StreamTest fixture, replaced custom test fixture with simple type alias to NVFuserTest

Sequence Diagram

sequenceDiagram
    participant Test as StreamTest
    participant Base as NVFuserTest
    participant Options as EnableOptionsGuard
    participant KE as KernelExecutor

    Note over Test,KE: Before: StreamTest with HostIrLowering
    Test->>Base: Construct (inherits from NVFuserTest)
    Test->>Options: set(EnableOption::HostIrLowering)
    Test->>KE: compile(&fusion, args)
    Test->>KE: run(args, outputs)

    Note over Test,KE: After: StreamTest as alias
    Test->>Base: Use NVFuserTest directly (type alias)
    Note over Options: No HostIrLowering option set
    Test->>KE: compile(&fusion, args)
    Test->>KE: run(args, outputs)
    Note over KE: KernelExecutor works without HostIrLowering flag

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