Open Radar

 
Summary:

In the function test of the (arguably useless) Swift program below all code is reachable (depends on the value of the boolean parameter `b`):

--- SNIP ---
import Darwin.C.stdlib

func test(b:Bool) -> ((), ()) {
    return (b ? exit(1) : (), ())
}

print("\(test(true))\n")
--- SNAP ---

However the compiler pretends that `exit(1)` would be unreachable:

$ xcrun -sdk macosx swiftc main.swift 
main.swift:4:17: warning: will never be executed
    return (b ? exit(1) : (), ())
                ^ (this carent points the the "e" of "exit(1)")
main.swift:4:17: note: a call to a noreturn function
    return (b ? exit(1) : (), ())
                ^ (this carent points the the "e" of "exit(1)")

Steps to Reproduce:
1. Download the attached swift program (main.swift) and save as /tmp/main.swift
2. xcrun -sdk macosx swiftc /tmp/main.swift

Expected Results:
swiftc exits successfully and doesn't output anything

Actual Results:
swiftc outputs a warning about unreachable code but still compiles the program

Regression:
not that I'd be aware of