Slow test case: tutorial_lesson_15_build_gens

[jayaddison]

This bug report may be low on details while I'm collecting them - I'll provide more information as I learn more about the problem.

While compiling halide v14.0.0 from source on Debian bookworm locally, I've noticed an extremely slow (perhaps infinite loop) unit test behaviour: the tutorial_lesson_15_build_gens test seems to run for minutes, consuming large amounts of CPU time.

I'll try to narrow down the problem by reducing the test's code and build script.

[jayaddison]

The steps to replicate the failure are approximately the following, within a debian:bookworm-based container:

# first, use your favourite EDITOR to add a 'deb-src' entry for 'bookworm main' in /etc/apt/sources.list
# and then:
apt update && apt upgrade -y
apt install -y build-essential devscripts

# retrieve the source package
apt source halide

# install dependencies, and then build and test
mk-build-deps -i
dpkg-buildpackage -b

[jayaddison]

Ok: the test does complete eventually -- it takes a relatively long time, though.

563/569 Test #563: tutorial_lesson_15_build_gens ..............................   Passed  1186.17 sec

(compared to single-digit seconds for other tests)

After attaching strace during a recent run of the test, I saw the UnrollLoops.cpp file being accessed - that seemed strange? Is some of the previously-compiled source code being accessed during a unit test? (perhaps a rebuild of some of the tooling, for some reason?)

[jayaddison]

Ping @alexreinking - sorry to nag directly - it's OK to close this if it's not likely to see much attention. I'm going through a few old issues/pull requests I've opened to do some cleanup, and it seems that you still poke at the build system here from time to time.