[Autodiff] Runtime crash when attempting to compute a gradient when the program is built in Release mode.

[fibrechannelscsi]

Description
This appears to affect M1 machines only; I did not see this crash on an x86 Mac.

Steps to reproduce
The following program crashes at runtime when built in Release mode and run. For a command-line build, swift run -c release should be sufficient.

import _Differentiation
func r(a: Float) -> Float {for _ in 0 ..< 1 {}; return a}
func p() {gradient(at: 2, of: r)}
for _ in 0 ..< 2 {p()}

Expected behavior
The program should exit with an exit code of 0.

Environment

• Swift compiler version info: This fails with Toolchains 2022-10-08a up until 2023-05-25a. Toolchains 2022-09-24a don't appear to exhibit this issue (I haven't narrowed down the date range between those two any further at this time).
• Xcode version info: 14.2
• Deployment target: M1. (Note: an x86 Mac does not appear to exhibit this crash, even with the 2023-05-25a toolchain).

Additional context
The for loop in line 2 does not do anything, but is required to replicate this issue.
Running the for loop in line 4 with a range of 0 ..< 1 instead of 0 ..< 2 causes the crash to no longer occur.

[fibrechannelscsi]

We've found some additional information:
Running the program (with swift run -c release) as a single file (outside of a package) does not cause the crash.
If one performs swift package init --type executable, then pastes the above code into the spot where one sees Hello World, then runs swift run -c release, then the program will crash.

[fibrechannelscsi]

This appears to be fixed with the 05-30a toolchain. I'll mark this as closed.