[SR-13823] Slow compilation involving big C structs

[swift-ci]

Previous ID	SR-13823
Radar	rdar://problem/71040556
Original Reporter	cuscus (JIRA User)
Type	Bug

Attachment: Download

Environment

MacBook Air

macOS 11.0.1

Xcode 12.2

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 08dc0adbec0bf0907d4e82e5325c12f4

Issue Description:

Problems described in this post on Swift Forums

[typesanitizer]

@swift-ci create

[rjmccall]

Can you attach a test case, or anything we can use to reproduce this at all?

[swift-ci]

Comment by Cuscus (JIRA)

Hi, I'm upgrading my machine, will try to reproduce the problem in a test case and upload it as soon as I can.

[swift-ci]

Comment by Cuscus (JIRA)

I managed to reproduce the bug in a small test case, please check the readme for what is what, where, and so on. This is now on macOS 11.0.1, Xcode 12.2. Let me know if there is a problem.

[rjmccall]

Thank you. Seems to be a scaling problem in the definitive-initialization logic; we'll see what we can do. It's related to the large number of subobjects, probably mostly because of the arrays.

The only workaround I can see is to avoid making local variables of these types. As you can see, we don't have a problem simply compiling values of the type as e.g. return values and parameters, although I'm sure there are inefficiencies we could still chase out.

[swift-ci]

Comment by Cuscus (JIRA)

Okay, I see, thanks for the explanation and suggestion. I'll just poke around to avoid this issue for the time being, most of the code is still temporary, just for testing purposes.

[eeckstein]

Will be fixed with #79186