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Add insertBits edge case regression test#4664

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sudonatalie merged 2 commits into
gpuweb:mainfrom
sudonatalie:metal-insertbits
Jun 13, 2026
Merged

Add insertBits edge case regression test#4664
sudonatalie merged 2 commits into
gpuweb:mainfrom
sudonatalie:metal-insertbits

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@sudonatalie

@sudonatalie sudonatalie commented Jun 12, 2026

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This reproduces a GPU hang on Mac for the Dawn implementation (see crbug.com/506180954).

Requirements for PR author:

  • All missing test coverage is tracked with "TODO" or .unimplemented().
  • New helpers are /** documented */ and new helper files are found in helper_index.txt.
  • Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
  • Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

  • Tests are properly located.
  • Test descriptions are accurate and complete.
  • Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
  • Tests avoid over-parameterization (see case count report).

When landing this PR, be sure to make any necessary issue status updates.

@sudonatalie
Add insertBits edge case regression test
aee4691 
This reproduces a GPU hang on Mac for the Dawn implementation (see
crbug.com/506180954).
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github-actions Bot commented Jun 12, 2026 •
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Results for build job (at e074677):

+webgpu:shader,execution,expression,call,builtin,insertBits:array_index:* - 1 cases, 1 subcases (~1/case)
-TOTAL: 281385 cases, 2323156 subcases
+TOTAL: 281386 cases, 2323157 subcases

@sudonatalie

sudonatalie commented Jun 12, 2026

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Currently fails on my M4 Mac and passes following: https://dawn-review.googlesource.com/c/dawn/+/316515

@sudonatalie sudonatalie requested a review from alan-baker June 12, 2026 19:56
@sudonatalie sudonatalie enabled auto-merge (squash) June 13, 2026 00:50
@sudonatalie sudonatalie merged commit d7791c8 into gpuweb:main Jun 13, 2026
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copybara-service Bot pushed a commit to google/dawn that referenced this pull request Jun 13, 2026
@sudonatalie
[tint][msl] Workaround bug in Metal insert_bits
9533d32 
When MSL's insert_bits builtin is called with an offset of 32 and a
count of 0, it can trigger a GPU hang.

This works around the issue by clamping to 31, which is the greatest
offset in insert_bits that is not a no-op (inserts only 1 bit at most).
If inserting 0 bits, it is a no-op anyways so the clamp has no
functional affect besides preventing the hang.

Since this does not adhere to the MSL spec a feedback has also been
filed to Apple: FB23103184.

Corresponding CTS that passes only after this change:
gpuweb/cts#4664

Bug: 506180954
Change-Id: I6954f22f56340998cb21bcef8f4a2d618298b89a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/316515
Commit-Queue: Natalie Chouinard <chouinard@google.com>
Reviewed-by: James Price <jrprice@google.com>
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@sudonatalie @alan-baker