[2/12] Upgrade cpp_extension and cpp_builder to C++20 by r-barnes · Pull Request #176659 · pytorch/pytorch

r-barnes · 2026-03-05T23:47:13Z

Summary:
Update the default C++ standard from c++17 to c++20 in
torch.utils.cpp_extension and torch._inductor.cpp_builder.
This affects how user C++ extensions and inductor-generated
code are compiled.

Test Plan: Sandcastle

Reviewed By: malfet

cc @jbschlosser @voznesenskym @penguinwu @EikanWang @jgong5 @Guobing-Chen @XiaobingSuper @zhuhaozhe @blzheng @wenzhe-nrv @jiayisunx @ipiszy @kadeng @muchulee8 @amjames @chauhang @aakhundov @coconutruben @jataylo

pytorch-bot · 2026-03-05T23:47:17Z

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/176659

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✅ You can merge normally! (7 Unrelated Failures)

As of commit e2812cd with merge base d87ebee ():

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

trunk / linux-jammy-cuda13.0-py3.10-gcc11 / test (distributed, 3, 3, lf.linux.g4dn.12xlarge.nvidia.gpu) (gh) (similar failure)
distributed/test_distributed_spawn.py::TestDistBackendWithSpawn::test_new_subgroups_by_enumeration_input_rank_exceeds_world_size
trunk / linux-jammy-rocm-py3.10 / test (default, 2, 6, linux.rocm.gpu.gfx950.1) (gh) (similar failure)
test/inductor/test_gpu_cpp_wrapper.py::TestGpuWrapper::test_profiler_mark_wrapper_call_cuda_gpu_wrapper
trunk / macos-py3-arm64 / test (mps, 1, 1, macos-m1-14) (gh) (similar failure)
Build left local git repository checkout dirty
trunk / macos-py3-arm64 / test (openreg, 1, 1, macos-m1-stable) (gh) (similar failure)
Build left local git repository checkout dirty

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

trunk / linux-jammy-rocm-py3.10 / test (distributed, 2, 3, linux.rocm.gpu.gfx950.4) (gh) (trunk failure)
distributed/test_distributed_spawn.py::TestDistBackendWithSpawn::test_new_subgroups_by_enumeration_input_rank_exceeds_world_size
trunk / linux-jammy-rocm-py3.10 / test (distributed, 3, 3, linux.rocm.gpu.gfx950.4) (gh) (trunk failure)
distributed/test_distributed_spawn.py::TestDistBackendWithSpawn::test_new_subgroups_by_enumeration_negative_input_rank

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

inductor / inductor-cpu-test / test (cpu_inductor_torchbench, 1, 2, linux.2xlarge.amx, unstable) (gh) (#174929)
detectron2_maskrcnn_r_50_fpn

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pytorch-bot · 2026-03-05T23:47:20Z

This PR needs a `release notes:` label

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meta-codesync · 2026-03-05T23:47:22Z

@r-barnes has exported this pull request. If you are a Meta employee, you can view the originating Diff in D95103085.

r-barnes · 2026-03-06T17:14:10Z

@pytorchbot rebase

pytorchmergebot · 2026-03-06T17:15:58Z

@pytorchbot started a rebase job onto refs/remotes/origin/viable/strict. Check the current status here

pytorchmergebot · 2026-03-06T17:16:01Z

Tried to rebase and push PR #176659, but it was already up to date. Try rebasing against main by issuing:
@pytorchbot rebase -b main

r-barnes · 2026-03-07T18:04:34Z

@pytorchbot rebase -b main

pytorchmergebot · 2026-03-07T18:06:17Z

@pytorchbot started a rebase job onto refs/remotes/origin/main. Check the current status here

pytorchmergebot · 2026-03-07T18:06:20Z

Successfully rebased export-D95103085 onto refs/remotes/origin/main, please pull locally before adding more changes (for example, via git checkout export-D95103085 && git pull --rebase)

Summary: Update the default C++ standard from c++17 to c++20 in torch.utils.cpp_extension and torch._inductor.cpp_builder. This affects how user C++ extensions and inductor-generated code are compiled. Test Plan: Sandcastle Reviewed By: desertfire, malfet Differential Revision: D95103085

pytorchmergebot · 2026-03-08T16:57:51Z

Merge started

Your change will be merged immediately since you used the force (-f) flag, bypassing any CI checks (ETA: 1-5 minutes). Please use -f as last resort and instead consider -i/--ignore-current to continue the merge ignoring current failures. This will allow currently pending tests to finish and report signal before the merge.

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pytorchmergebot · 2026-03-08T16:57:52Z

Merge failed

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Raised by workflow job

r-barnes · 2026-03-08T17:04:12Z

@pytorchbot merge -f "Failure looks like a flake, internal tests pass, changes to C++ are in Python strings, so skipped C++ format linter shouldn't be problematic"

pytorchmergebot · 2026-03-08T17:06:03Z

Merge started

Your change will be merged immediately since you used the force (-f) flag, bypassing any CI checks (ETA: 1-5 minutes). Please use -f as last resort and instead consider -i/--ignore-current to continue the merge ignoring current failures. This will allow currently pending tests to finish and report signal before the merge.

Learn more about merging in the wiki.

Questions? Feedback? Please reach out to the PyTorch DevX Team

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pytorchmergebot · 2026-03-08T17:06:10Z

Merge failed

Reason: PR #176659 has not been reviewed yet

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Raised by workflow job

Failing merge rule: Core Maintainers

facebook-github-bot · 2026-03-08T19:52:16Z

@pytorchbot merge -i

(Initiating merge automatically since Phabricator Diff has merged, merging with -i because oss signals were bypassed internally)

pytorch-bot · 2026-03-08T19:52:20Z

This PR needs to be approved by an authorized maintainer before merge.

malfet · 2026-03-08T19:55:13Z

@pytorchbot merge -i

pytorchmergebot · 2026-03-08T19:57:16Z

Merge started

Your change will be merged while ignoring the following 1 checks: inductor / inductor-cpu-test / test (cpu_inductor_torchbench, 1, 2, linux.2xlarge.amx, unstable)

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pytorchmergebot · 2026-03-08T20:55:40Z

Merge failed

Reason: 2 jobs have failed, first few of them are: trunk / macos-py3-arm64 / test (mps, 1, 1, macos-m1-14), trunk / macos-py3-arm64 / test (openreg, 1, 1, macos-m1-stable)

Details for Dev Infra team

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wdvr · 2026-03-09T05:12:03Z

@pytorchmergebot merge -i

pytorchmergebot · 2026-03-09T05:14:22Z

Merge started

Your change will be merged while ignoring the following 7 checks: inductor / inductor-cpu-test / test (cpu_inductor_torchbench, 1, 2, linux.2xlarge.amx, unstable), trunk / macos-py3-arm64 / test (mps, 1, 1, macos-m1-14), trunk / macos-py3-arm64 / test (openreg, 1, 1, macos-m1-stable), trunk / linux-jammy-rocm-py3.10 / test (default, 2, 6, linux.rocm.gpu.gfx950.1), trunk / linux-jammy-rocm-py3.10 / test (distributed, 3, 3, linux.rocm.gpu.gfx950.4), trunk / linux-jammy-rocm-py3.10 / test (distributed, 2, 3, linux.rocm.gpu.gfx950.4), trunk / linux-jammy-cuda13.0-py3.10-gcc11 / test (distributed, 3, 3, lf.linux.g4dn.12xlarge.nvidia.gpu)

Learn more about merging in the wiki.

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PyTorch commit ad56ff73b751 ("[2/12] Upgrade cpp_extension and cpp_builder to C++20", pytorch/pytorch#176659) changed the default C++ standard from C++17 to C++20 for extensions built via torch.utils.cpp_extension. Under C++20, std::lerp from <cmath> is visible alongside the custom lerp(float,float,float) defined in this file. When the third argument is c10::BFloat16 (implicitly convertible to float), the compiler finds two equally-valid overload candidates and fails with "more than one instance of overloaded function matches". Rename the custom lerp to _lerp to eliminate the ambiguity. Signed-off-by: Xiao Wang <24860335+xwang233@users.noreply.github.com> Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

PyTorch commit ad56ff73b751 ("[2/12] Upgrade cpp_extension and cpp_builder to C++20", pytorch/pytorch#176659) changed the default C++ standard from C++17 to C++20 for extensions built via torch.utils.cpp_extension. Under C++20, std::lerp from <cmath> is visible alongside the custom lerp(float,float,float) defined in this file. When the third argument is c10::BFloat16 (implicitly convertible to float), the compiler finds two equally-valid overload candidates and fails with "more than one instance of overloaded function matches". Rename the custom lerp to _lerp to eliminate the ambiguity. Signed-off-by: Xiao Wang <24860335+xwang233@users.noreply.github.com> Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Summary: Update the default C++ standard from c++17 to c++20 in torch.utils.cpp_extension and torch._inductor.cpp_builder. This affects how user C++ extensions and inductor-generated code are compiled. Test Plan: Sandcastle Reviewed By: malfet Pull Request resolved: pytorch#176659 Approved by: https://github.com/malfet

r-barnes requested review from ezyang, fmassa and malfet as code owners March 5, 2026 23:47

pytorch-bot bot added ciflow/inductor module: inductor labels Mar 5, 2026

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r-barnes mentioned this pull request Mar 5, 2026

C++20 Rollout Tracking #176662

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r-barnes added module: cpp Related to C++ API topic: improvements topic category release notes: cpp release notes category labels Mar 5, 2026

r-barnes assigned r-barnes and malfet Mar 6, 2026

pytorchmergebot force-pushed the export-D95103085 branch from 35b596b to a22254a Compare March 7, 2026 18:06

r-barnes force-pushed the export-D95103085 branch from a22254a to e2812cd Compare March 7, 2026 20:28

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malfet approved these changes Mar 8, 2026

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xwang233 mentioned this pull request Mar 9, 2026

Fix lerp overload ambiguity with std::lerp under C++20 NVIDIA/apex#1985

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