[SR-2339] "Illegal instruction" crash on UInt64 conversions to UInt (armv7 32bit platform)

[swift-ci]

Previous ID	SR-2339
Radar	None
Original Reporter	jmarcelino (JIRA User)
Type	Bug
Status	Resolved
Resolution	Invalid

Environment

Swift version 3.0-dev (LLVM e6ce0a6282, Clang 4ca9e01a7c, Swift b906a25)
Target: armv7--linux-gnueabihf

Additional Detail from JIRA

Votes	0
Component/s	Standard Library
Labels	Bug, RunTimeCrash, arm
Assignee	None
Priority	Medium

md5: 2a13ba44941fd11781b937d55d57c98d

Issue Description:

Code that relies on conversion from UInt64 to UInt or UInt32 is crashing at run-time on 32bit ARM (armv7) with an error of Illegal instruction.

One example where such code is used is the Swift Package Manager.
The code below replicates the issue:

let u64sample: UInt64 = 0x1234567890ABCDEF
print ("UInt64: \(u64sample)")

var i = UInt(u64sample)
print ("UInt: \(i)")

In this case the UInt(u64sample) step causes the run-time crash

[belkadan]

This is correct behavior. The converting (unlabeled) initializer for integers always traps if the value to convert is out of bounds. Use init(truncating:) if you want C-like behavior.

[swift-ci]

Comment by Jose (JIRA)

Thanks Jordan.
I understand that and it's a good idea to throw an error on an attempt at a conversion which leads to loss of data, but perhaps “Illegal instruction” isn’t a good description for it...

For example attempting to initialise the same UInt from a integer literal shows a much better error message

var p = UInt(0x1234567890ABCDEF)

error: integer literal '1311768467294899695' overflows when stored into 'Int'

[belkadan]

Ah, yes, that's definitely true. This is SR-578.