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[stdlib][simd] Add test for simd construction checks - #6348

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josiahls:fix/simd-assertion-checks
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[stdlib][simd] Add test for simd construction checks#6348
josiahls wants to merge 1 commit into
modular:mainfrom
josiahls:fix/simd-assertion-checks

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@josiahls

@josiahls josiahls commented Apr 3, 2026 •
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Note, currently @always_inline("builtin") basically strips the asserts out of the code.

Summary

SIMD _simd_construction_checks is noop due to @always_inline("builtin")

When you run the test, you will notice that _simd_construction_checks isn't the thing that fails.

def main() raises:
    ^
/home/mojo_user/momanim/third_party/modular/mojo/stdlib/test/builtin/test_simd_compile_fail.mojo:18:49: note: call expansion failed with parameter value(s): (..., "size": 3)
    _simd_construction_checks2[DType.float32, 3]()
                                                ^
mojo/stdlib/std/builtin/simd.mojo:255:5: note: function instantiation failed
mojo/stdlib/std/builtin/simd.mojo:265:5: note: constraint failed: simd width must be power of 2
/home/mojo_user/momanim/.pixi/envs/stdlib-dev/bin/mojo: error: failed to run the pass manager

Testing

I have a compile fail test that demos this.

Checklist

  • PR is small and focused — consider splitting larger changes into a
    sequence of smaller PRs
  • I ran ./bazelw run format to format my changes
  • I added or updated tests to cover my changes

@github-actions github-actions Bot added mojo-stdlib Tag for issues related to standard library waiting-on-review labels Apr 3, 2026
@josiahls
josiahls force-pushed the fix/simd-assertion-checks branch 2 times, most recently from c299114 to 658ae92 Compare April 3, 2026 22:58
@josiahls

josiahls commented Apr 3, 2026 •
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cc @NathanSWard @always_inline("builtin") appears to strip any comptime assertions. _simd_construction_checks is noop as it stands. I can update the test to be smaller, just putting a demo copy of the function without the builtin line.

Basically this pr isn't going to be mergable until an API change or compiler fix.

@josiahls
josiahls force-pushed the fix/simd-assertion-checks branch 2 times, most recently from ce1d83c to 9cd34e3 Compare April 3, 2026 23:11
@josiahls
[stdlib][simd] Add test for simd construction checks
7a0a9a0 
Note, currently @always_inline("builtin") basically strips the
asserts out of the code.

Issue: modular#6349
@josiahls
josiahls force-pushed the fix/simd-assertion-checks branch from 9cd34e3 to 7a0a9a0 Compare April 3, 2026 23:23
@josiahls
josiahls marked this pull request as ready for review April 3, 2026 23:23
@josiahls
josiahls requested a review from a team as a code owner April 3, 2026 23:23
@JoeLoser JoeLoser added the blocked Blocked by another issue that must be resolved first label Apr 8, 2026
@alisterburt

alisterburt commented Oct 1, 2026

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@josiahls sorry this has been sitting a while, the main bug is tracked separately in #6349 and we now reject non-power-of-two SIMD widths so this test no longer shows the no-op check

c.f. e46710e

We're working to better handle OSS contributions in this post 1.0 era and hope to receive many more PRs from you, thank you for your patience here!

@alisterburt alisterburt closed this Oct 1, 2026
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@josiahls @alisterburt @JoeLoser