Open Radar

 
Summary:
Accessing a member of an object cast inside an if {} conditional that checks the object is not of some type crashes the swift compiler when optimizations are enabled.
This only occurs inside an application target, I cannot reproduce it via swiftc or in a playground.

Steps to Reproduce:
Compile the following code in an iOS target with optimizations enabled:

class A { var d = "" }
func t() {
    let o: AnyObject = A()
    if !(o is A) {
        _ = (o as! A).d
    }
}

Expected Results:
The code compiles

Actual Results:
The compiler crashes with the following error:
0  swift                    0x00000001048a1508 llvm::sys::PrintStackTrace(__sFILE*) + 40
1  swift                    0x00000001048a19e4 SignalHandler(int) + 452
2  libsystem_platform.dylib 0x00007fff97c49f1a _sigtramp + 26
3  libsystem_platform.dylib 0x00007fff5ba78650 _sigtramp + 3286427472
4  swift                    0x00000001043e0eda (anonymous namespace)::DCE::markControllingTerminatorsLive(swift::SILBasicBlock*) + 346
5  swift                    0x00000001043e0c69 (anonymous namespace)::DCE::markValueLive(swift::ValueBase*) + 201
6  swift                    0x00000001043e047f (anonymous namespace)::DCE::run() + 1983
7  swift                    0x000000010438814e swift::SILPassManager::runFunctionPasses(llvm::ArrayRef<swift::SILFunctionTransform*>) + 1310
8  swift                    0x0000000104388bd9 swift::SILPassManager::runOneIteration() + 633
9  swift                    0x0000000104387646 swift::runSILOptimizationPasses(swift::SILModule&) + 790
10 swift                    0x000000010418b478 frontend_main(llvm::ArrayRef<char const*>, char const*, void*) + 4584
11 swift                    0x000000010418a0e6 main + 1814
12 libdyld.dylib            0x00007fff8e5a15c9 start + 1
13 libdyld.dylib            0x000000000000003c start + 1906698868


Regression:
This does not occur with Swift 1.1 and Xcode 6.1.1

Notes:
The test given is a meaningless trivial example, but this error happens in less tautological code. Removing either the ! in the if check, or the member access inside the body, causes the crash to go away.