[all-commits] [llvm/llvm-project] 5cd247: [libc++] Reduce the compilation time required by S...

[Louis Dionne via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 5cd24759c41864215e67c280234b6c745a4cd369
      https://github.com/llvm/llvm-project/commit/5cd24759c41864215e67c280234b6c745a4cd369
  Author: Louis Dionne <ldionne.2 at gmail.com>
  Date:   2023-11-20 (Mon, 20 Nov 2023)

  Changed paths:
    M libcxx/test/std/experimental/simd/simd.reference/reference_assignment.pass.cpp
    M libcxx/test/std/experimental/simd/test_utils.h

  Log Message:
  -----------
  [libc++] Reduce the compilation time required by SIMD tests (#72602)

Testing all the SIMD widths exhaustively is nice in theory, however in
practice it leads to extremely slow tests. Given that
1. our testing resources are finite and actually pretty costly
2. we have thousands of other tests we also need to run
3. the value of executing these SIMD tests for absolutely all supported
SIMD widths is fairly small compared to cherry-picking a few relevant
widths

I think it makes a lot of sense to reduce the exhaustiveness of these
tests. I'm getting a ~4x speedup for the worst offender
(reference_assignment.pass.cpp) after this patch.

I'd also like to make this a reminder to anyone seeing this PR that
tests impact everyone's productivity. Slow unit tests contribute to
making the CI slower as a whole, and that has a direct impact on
everyone's ability to iterate quickly during PRs. Even though we have a
pretty robust CI setup in place, we should remember that it doesn't come
for free and should strive to keep our tests at a good bang for the buck
ratio.