Don't build with stdlib assertions on Linux

[drexin]

Apparently we have been building with stdlib assertions enabled on Linux. A recent change (#33390) caused a massive performance regression on Linux, which brought this to light.

[drexin]

@swift-ci smoke test

[drexin]

@swift-ci test centos 7

[drexin]

@swift-ci test centos 7

[drexin]

@swift-ci test centos 7

[drexin]

@swift-ci test centos 7

[drexin]

@swift-ci test centos 7

[drexin]

@swift-ci test centos 7

[drexin]

@swift-ci test amazon linux 2

[swift-ci]

Build failed
Swift Test Amazon Linux 2 Platform
Git Sha - 27102e2

[drexin]

@swift-ci test amazon linux 2

[swift-ci]

Build failed
Swift Test Amazon Linux 2 Platform
Git Sha - 27102e2

[vedantk]

@drexin With this change, it looks like none of the Linux bots test the stdlib with assertions enabled. That disables all the swift reflection tests for ELF. Is there a more targeted option, like disabling stdlib-asserts on a subset of the Linux builders?

cc @augusto2112 @adrian-prantl

[drexin]

@vedantk I think the best option would be to configure the bots in question to enable building with stdlib-asserts. Enabling them by default does not seem like the correct thing to do.

/cc @atrick

[atrick]

@vedantk what really does not make sense here is that build-script --assertions enables runtime verification. Now, on top of that, we have a "lightweight_assertions" mixin that also enables runtime verification. That means that almost every time someone reports benchmark results or performance bugs from their own Swift build, the information is misleading until eventually someone wastes time tracking that down, which is often months later. We've had people working on Swift for up to a year without realizing that all their results were bogus. How long was linux being built incorrectly because of this?

[augusto2112]

@drexin @atrick let me try to explain the problem we're having, and maybe we can come up with a solution together. Basically, we have some runtime functions that return metadata-related information when dealing with Linux (this is due to some constraints in the ELF format). We use these to provide the reflection tests the information they need to run themselves. Because this is used exclusively during testing, and shouldn't do anything on release, these functions have an empty body when assertions are off. So now you see what the problem is from our perspective. Do you have any suggestions on how we can solve this issue?

[atrick]

Yep, the release build obviously should not enable any runtime verification by default. I'm very unhappy with the build-script defaults, but hopefully this PR fixed your specific problem.

[augusto2112]

@atrick the problem is since stdlib's assertions are off, we can't run the reflection tests, since the function functions we added should only run with assertions on.

[atrick]

Reflection testing would need the build with --stdlib-assertions. There are other stdlib unit tests that also require stdlib asserts enabled.