[PATCH] D144638: [lit] Detect Consistent File Access Times

[Sam Elliott via Phabricator via cfe-commits]

lenary created this revision.
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I was seeing flaky tests in my builds due to another process (in my
case, antivirus) modifying the access time of files during the tests,
so those tests using `touch -a` were failing.

This change modifies how we check if a system has consistent atime.
Instead of a list of platforms where we know things might not work, we
instead perform a check similar to the ones used in the tests, but on a
temporary file. If the check is successful, then you get a
`consistent-atime` feature which you can make your test REQUIRE.

This updates all existing tests which mention atime or use `touch -a` to
`REQUIRE: consistent-atime`, fixing their flakiness.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D144638

Files:
  clang/test/Modules/prune.m
  lld/test/COFF/lto-cache.ll
  lld/test/ELF/lto/cache.ll
  lld/test/MachO/lto-cache.ll
  lld/test/wasm/lto/cache.ll
  llvm/test/ThinLTO/X86/cache.ll
  llvm/test/tools/llvm-objcopy/ELF/strip-preserve-atime.test
  llvm/utils/lit/lit/llvm/config.py

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