[PATCH] D73837: Add minimal test for the ThinLtoJIT example

[Stefan Gränitz via Phabricator via llvm-commits]

sgraenitz created this revision.
sgraenitz added reviewers: lhames, aprantl.
Herald added subscribers: dexonsmith, steven_wu, hiraditya, inglorion, mehdi_amini.
Herald added a project: LLVM.

A lit test for the ThinLtoJIT example from D72486 <https://reviews.llvm.org/D72486>. It will only run in builds configured with `-DLLVM_BUILD_EXAMPLES=ON` (just like the tests for the Kaleidoscope examples).

The ThinLtoJIT example implements "per-module speculation" for lazy loading and compilation of bitcode. Thus, the test is not self-contained in a single module, but comes with a number .ll files in the `Inputs` subfolder. These files are excluded from test discovery via the local lit config file.

The test uses a `workload()` function to simulate CPU load. It's used to give the speculator a chance to submit modules, that will likely be executed soon, asynchronously, before execution reaches them. It's supposed to maximize code coverage and NOT a requirement for the test to succeed. I wanted to use a `sleep` system function first, but I didn't know how to implement it cross-platform in LLVM IR. So, I chose a function that finds the largest prime-factor of the Nth Fibonacci number. It has exponential complexity and can easily be made dependent on the input argc.

The test's call graph looks like this:

               sub1() - workload(3)
             /
  --> main() -- workload(40)
             \
              \           sub21() - workload(4)
               \        /
                 sub2() - sub22() - workload(5)
                        \
                          sub23() - workload(6)

All functions are defined in separate .ll files. The module that contains the `main` entry point is always loaded synchronously (not via the speculator). The same will happen for `sub1`, `workload` and `sub2`, because execution reaches their caller too soon. It will then be blocked for a bit in `workload(40)` and the speculator will likely be faster to discover the `sub2x` modules.

The ThinLtoJIT executable is invoked with `-print-stats`, which dumps the number of synchronously/asynchronously loaded modules on shutdown. Getting these two lines of output is what the test currently checks. The JITed code itself doesn't print anything.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73837

Files:
  llvm/test/Examples/ThinLtoJIT/Inputs/main.ll
  llvm/test/Examples/ThinLtoJIT/Inputs/sub1.ll
  llvm/test/Examples/ThinLtoJIT/Inputs/sub2.ll
  llvm/test/Examples/ThinLtoJIT/Inputs/sub21.ll
  llvm/test/Examples/ThinLtoJIT/Inputs/sub22.ll
  llvm/test/Examples/ThinLtoJIT/Inputs/sub23.ll
  llvm/test/Examples/ThinLtoJIT/Inputs/workload.ll
  llvm/test/Examples/ThinLtoJIT/minimal.test
  llvm/test/Examples/lit.local.cfg

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