Even though we have read the times before,
we intentionally forget about it for performance reasons.
But that means we also forget all the times for the tests
that weren't executed this time. This is mildly inconvenient.
So, when recording the new times, first re-read the old times,
and update times for the tests that were executed,
thus preserving all original times, too.
I.e. when you first run lit on a directory, and then on a single test,
the timing knowledge about anything else other than that single test
is lost. This isn't right.
All of these depend on the order of tests, so if one runs them twice,
the tests within them will naturally be reordered
using the previous run times, which breaks them.
The "path" recorded for timing purposes is only used as a key into a dictionary. It is never used as an actual path to a filesystem API, therefore we should use '/' as the canonical separator so that Unix and Windows machines can share timing data. This also ensures that the lit testing works across platforms.
Reviewed By: jhenderson, jmorse
Differential Revision: https://reviews.llvm.org/D98767
The test file has embedded slashes. This is fine for normal users that
are just recording and reordering paths, but not great when the trace
data is committed back to a repository that should work on both Unix and
Windows.
Lit as it exists today has three hacks that allow users to run tests earlier:
1) An entire test suite can set the `is_early` boolean.
2) A very recently introduced "early_tests" feature.
3) The `--incremental` flag forces failing tests to run first.
All of these approaches have problems.
1) The `is_early` feature was until very recently undocumented. Nevertheless it still lacks testing and is a imprecise way of optimizing test starting times.
2) The `early_tests` feature requires manual updates and doesn't scale.
3) `--incremental` is undocumented, untested, and it requires modifying the *source* file system by "touching" the file. This "touch" based approach is arguably a hack because it confuses editors (because it looks like the test was modified behind the back of the editor) and "touching" the test source file doesn't work if the test suite is read only from the perspective of `lit` (via advanced filesystem/build tricks).
This patch attempts to simplify and address all of the above problems.
This patch formalizes, documents, tests, and defaults lit to recording the execution time of tests and then reordering all tests during the next execution. By reordering the tests, high core count machines run faster, sometimes significantly so.
This patch also always runs failing tests first, which is a positive user experience win for those that didn't know about the hidden `--incremental` flag.
Finally, if users want, they can _optionally_ commit the test timing data (or a subset thereof) back to the repository to accelerate bots and first-time runs of the test suite.
Reviewed By: jhenderson, yln
Differential Revision: https://reviews.llvm.org/D98179
Roman Lebedev