[SR-10587] Release mode optimization causes crash

[swift-ci]

Previous ID	SR-10587
Radar	rdar://problem/50339329
Original Reporter	codezy (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Attachment: Download

Environment

Xcode 10.2.1

swift 5

Additional Detail from JIRA

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

md5: a13145c72556b1a498a55d23d6badc74

Issue Description:

Recently when running a TestFlight build of an app I found that it was crashing in one place. When I went to debug I was unable to replicate. I flipped the configuration to a release configuration and then was able to replicate. Oddly, the code broke on one function but the call stack suggested a much deeper stack which eventually ended in a swift release call. After DAYS of trial and error I finally nailed the code down to one specific area. Then I tried a few different ways of phrasing the code and found a way where it would crash and a way where it would not.

Steps to Reproduce:

1. Unzip the attachment and open the project in Xcode 10.2.1
2. Ensure in edit scheme that the run configuration is set to release.
3. Comment out the two lines in ViewController.swift labeled “B” and run
4. It should crash
5. Comment out the two lines labeled “A” and uncomment “B”
6. Run and witness no crash
7. Flip the configuration to debug and repeat steps 3-6 noting that neither code crashes, not even A which crashes when it is set to release

Expected Results:
That the optimization levels changing does not cause a crash.

Actual Results:
The optimization levels (not sure which) causes a crash

Version/Build:
Xcode 10.2.1

FILED as radar 50339329

[theblixguy]

cc @eeckstein

[swift-ci]

Comment by Paul Thorsteinson (JIRA)

I can confirm that, as per the info from @theblixguy below, this issue no longer occurs in 51. Thank you!

"Your project no longer crashes for me when I use a Swift 5.1 development toolchain. Apparently this was a bug with escape analysis - for now, you can just pass '-Xllvm -sil-disable-pass=stack-promotion' to fix the crash until Swift 5.1 is out."