Disable large types irgen pass

[shajrawi]

radar rdar://problem/32064645

Disable large types irgen pass (for now)

Swift 4.0 PR #9447

[shajrawi]

@eeckstein Can you please review?

[eeckstein]

LGTM!

[slavapestov]

Will it be re-enabled again in 4.0 branch? A lot of users are looking forward to this.

[shajrawi]

No.

[jckarter]

Can we keep a flag around so people can try it out, and we can still get bug reports and feedback on it? That's what we did with bridging pch.

[NachoSoto]

😰 Wh.... Why? What's rdar://problem/32064645? What's the point of having a transparent process if you guys keep linking private bugs...? 😕

[shajrawi]

@jckarter I plan to add such a flag in a later commit on master, but, since this is an ABI change anyone whom wants to test their code with that flag enabled will need to rebuild the entire toolchain with it. else they'd crash when calling the standard library..etc

[shajrawi]

@swift-ci Please smoke test

[jckarter]

@NachoSoto Looks like there were some bad interactions between this transform and the rest of the optimizer.

[NachoSoto]

Thanks @jckarter! What's the plan moving forward then? I've been waiting for this change for several years, so I was pretty excited.

[shajrawi]

@NachoSoto we'll get back to this transformation at some point, making sure it is truly great, but it is not going to be re-enabled on the 4.0 branch.

[NachoSoto]

"At some point"?

[NachoSoto]

🤷‍♂️