[SR-1647] Compiler hangs on large array of NSLayoutConstraints, with a type annotation

[swift-ci]

Previous ID	SR-1647
Radar	None
Original Reporter	Nowak (JIRA User)
Type	Bug

Environment

Xcode 7.3.1, Xcode 8.0 (8A218a)
iOS 9.3, iOS 10

Additional Detail from JIRA

Votes	5
Component/s	Compiler
Labels	Bug, 2.2Regression, Performance, TypeChecker
Assignee	None
Priority	Medium

md5: 6e1cac7c3070003bafb401696215795b

Issue Description:

I have an project without storyboard.
All Compounds are arrenged by constraints.

On Swift 1 I have set all constraints in one big array an set it, with one addConstraints() call

On Swift 2.2 the Compiler will hang and was killed after 8 hours without any useful error message

As workaround a have found, that I need to set the Constraints on

Here is the function which let the compiler hangs:

func setConstraints()
    {
        
        var constraints:[NSLayoutConstraint] = [
            
            
            NSLayoutConstraint(item: positiveLabel,attribute: NSLayoutAttribute.Top,relatedBy: NSLayoutRelation.Equal,toItem: view,attribute: NSLayoutAttribute.Top,multiplier: 1,constant: 0),
            
            NSLayoutConstraint(item:positiveLabel,attribute: NSLayoutAttribute.Left,relatedBy: NSLayoutRelation.Equal,toItem: view,attribute: NSLayoutAttribute.Left,multiplier: 1,constant: 0),
            
            NSLayoutConstraint(item:positiveLabel,attribute: NSLayoutAttribute.Width,relatedBy: NSLayoutRelation.Equal,toItem: nil,attribute: NSLayoutAttribute.NotAnAttribute,multiplier: 1,constant: 50),
            /*
            ]
        view.addConstraints(constraints)
        constraints = [
 */
            NSLayoutConstraint(item: positiveBox,attribute: NSLayoutAttribute.CenterY,relatedBy: NSLayoutRelation.Equal,toItem: positiveLabel,attribute: NSLayoutAttribute.CenterY,multiplier: 1,constant: 0),
            
            NSLayoutConstraint(item:positiveBox,attribute: NSLayoutAttribute.Left,relatedBy: NSLayoutRelation.Equal,toItem: positiveLabel,attribute: NSLayoutAttribute.Right,multiplier: 1,constant: 10),
            
            NSLayoutConstraint(item:positiveBox,attribute: NSLayoutAttribute.Height,relatedBy: NSLayoutRelation.Equal,toItem: positiveLabel,attribute: NSLayoutAttribute.Height,multiplier: 0.8,constant: 0),
            
            NSLayoutConstraint(item:positiveBox,attribute: NSLayoutAttribute.Width,relatedBy: NSLayoutRelation.Equal,toItem: positiveBox,attribute: NSLayoutAttribute.Height,multiplier: 1,constant: 0),
   /*
        ]
        view.addConstraints(constraints)
        
        
        constraints = [
     */
            NSLayoutConstraint(item:negativeLabel,attribute: NSLayoutAttribute.Top,relatedBy: NSLayoutRelation.Equal,toItem: positiveLabel,attribute: NSLayoutAttribute.Bottom,multiplier: 1,constant: 0),
            NSLayoutConstraint(item:negativeLabel,attribute: NSLayoutAttribute.Left,relatedBy: NSLayoutRelation.Equal,toItem: view,attribute: NSLayoutAttribute.Left,multiplier: 1,constant: 0),
            NSLayoutConstraint(item:negativeLabel,attribute: NSLayoutAttribute.Width,relatedBy: NSLayoutRelation.Equal,toItem: nil,attribute: NSLayoutAttribute.NotAnAttribute,multiplier: 1,constant: 50),
       /*
            ]
        view.addConstraints(constraints)
        constraints = [
 */
            NSLayoutConstraint(item:negativeBox,attribute: NSLayoutAttribute.CenterY,relatedBy: NSLayoutRelation.Equal,toItem: negativeLabel,attribute: NSLayoutAttribute.CenterY,multiplier: 1,constant: 0),
            NSLayoutConstraint(item:negativeBox,attribute: NSLayoutAttribute.Left,relatedBy: NSLayoutRelation.Equal,toItem: negativeLabel,attribute: NSLayoutAttribute.Right,multiplier: 1,constant: 10),
            NSLayoutConstraint(item:negativeBox,attribute: NSLayoutAttribute.Height,relatedBy: NSLayoutRelation.Equal,toItem: negativeLabel,attribute: NSLayoutAttribute.Height,multiplier: 0.8,constant: 0),
            NSLayoutConstraint(item:negativeBox,attribute: NSLayoutAttribute.Width,relatedBy: NSLayoutRelation.Equal,toItem: negativeBox,attribute: NSLayoutAttribute.Height,multiplier: 1,constant: 0),
   /*
        ]
        view.addConstraints(constraints)
        
        
        constraints = [
 */
            NSLayoutConstraint(item:neutralLabel,attribute: NSLayoutAttribute.Top,relatedBy: NSLayoutRelation.Equal,toItem: negativeLabel,attribute: NSLayoutAttribute.Bottom,multiplier: 1,constant: 0),
            NSLayoutConstraint(item:neutralLabel,attribute: NSLayoutAttribute.Left,relatedBy: NSLayoutRelation.Equal,toItem: view,attribute: NSLayoutAttribute.Left,multiplier: 1,constant: 0),
            NSLayoutConstraint(item:neutralLabel,attribute: NSLayoutAttribute.Width,relatedBy: NSLayoutRelation.Equal,toItem: nil,attribute: NSLayoutAttribute.NotAnAttribute,multiplier: 1,constant: 50),
   /*
            ]
        view.addConstraints(constraints)
        constraints = [
 */
            NSLayoutConstraint(item:neutralBox,attribute: NSLayoutAttribute.CenterY,relatedBy: NSLayoutRelation.Equal,toItem: neutralLabel,attribute: NSLayoutAttribute.CenterY,multiplier: 1,constant: 0),
            NSLayoutConstraint(item:neutralBox,attribute: NSLayoutAttribute.Left,relatedBy: NSLayoutRelation.Equal,toItem: neutralLabel,attribute: NSLayoutAttribute.Right,multiplier: 1,constant: 10),
            NSLayoutConstraint(item:neutralBox,attribute: NSLayoutAttribute.Height,relatedBy: NSLayoutRelation.Equal,toItem: neutralLabel,attribute: NSLayoutAttribute.Height,multiplier: 0.8,constant: 0),
            NSLayoutConstraint(item:neutralBox,attribute: NSLayoutAttribute.Width,relatedBy: NSLayoutRelation.Equal,toItem: neutralBox,attribute: NSLayoutAttribute.Height,multiplier: 1,constant: 0),
        ]
        view.addConstraints(constraints)


}

The short project to show the Error can be found here:

https://github.com/tn0/swiftError.git

[swift-ci]

Comment by Ayaka Nonaka (JIRA)

I’ve run into this issue multiple times as well. Happened to me with a view that has only three subviews, and just 12 constraints. My workaround was to split the activation out into multiple calls to activateConstraints, but initially it was not apparently why the compile time got so slow. I deleted derived data, restarted Xcode, restarted computer before I realized that it was the activateConstraints call that was causing the issue.

I’d love to help track down the root issue if anyone with more compiler knowledge could also take a look! 🙂

[swift-ci]

Comment by Ayaka Nonaka (JIRA)

This is still a huge issue in Swift 3.0. It is unfortunate because the alternative is to use isActive = true instead, which is way faster for compiling but slower at runtime and UI performance(1). Let me know how I can help track this issue down, because it’s not ideal to have to trade off between compile time and performance at runtime.

1. from WWDC 2015 Session 219 (http://asciiwwdc.com/2015/sessions/219)

"It turns out that changing a constraint inside update constraints is actually faster than changing a constraint at other times.

The reason for that is because the engine is able to treat all the constraint changes that happen in this pass as a batch.

This is the same kind of performance benefit that you get by calling activate constraints on an entire array of constraints as opposed to activating each of those constraints individually."

[belkadan]

I don't think that's fair. append gets the same behavior without multiple calls to addConstraints.

[swift-ci]

Comment by Ayaka Nonaka (JIRA)

@belkadan Thanks for your reply. Yes we ended up converting almost all of our AL code to `append` after we realized we could do that instead. It would still be nice to be able to pass in an array directly like

`NSLayoutConstraint.activate([NSLayoutConstraint(...), NSLayoutConstraint(...), ...])`

mostly for readability and also to prevent bugs from forgetting to call `NSLayoutConstraint.activate(theArrayWeWereAppendingTo)` because that was I was most afraid of forgetting while refactoring the code to use `append` instead.

[rnapier]

Adding an extra initializer to NSLayoutConstraint fixes this. I believe the problem is the Any? in particular. If you can remove that, things are dramatically faster (basically instant). For example:

extension NSLayoutConstraint {
    public convenience init(item view1: AnyObject, attribute attr1: NSLayoutAttribute, relatedBy relation: NSLayoutRelation, toItem view2: AnyObject?, attribute attr2: NSLayoutAttribute, multiplier: CGFloat, constant c: CGFloat) {
        self.init(item: view1 as Any, attribute: attr1, relatedBy: relation, toItem: view2 as Any?, attribute: attr2, multiplier: multiplier, constant: c)
    }
}

Here I've changed view1 and view2 to be AnyObject and AnyObject? rather than Any and Any? (and use as to make sure I call the original version). Similar improvements occur if you make them UIView and UIView? or even just both Any (so there is no Any?). Basically the entire problem is in the Any?.

(In Swift 2.2, these were AnyObject and it also had a problem. I suspect adding a non-optional version would fix 2.2, but I haven't tested that.)

[swift-ci]

Comment by Rudd T (JIRA)

Confirming that @rnapier's extension fixes this issue nicely, and that this bug still exists as of Xcode Version 8.1 (8T61a)