is duplicated by:

• SR-7068 Casting concrete class to protocol with type constraint triggers runtime exception
• SR-7393 Bad access crash surrounding self constraint on protocol
• SR-7955 EXC_BAD_ACCESS while accessing property of a constrained protocol
• SR-8011 The curious case of protocol with class conformance and casting…
• SR-8032 Compiler doesn't recognise constraints defined by where clause
• SR-8098 Compiler segfault on instantiating object from protocol Type that requires base class
• SR-7048 Layout constraint warning or compilation error

relates to:

• SR-7068 Casting concrete class to protocol with type constraint triggers runtime exception

Issue Description:

In Swift 4.0.3, the following crashes with EXC_BAD_ACCESS at runtime (looks like its being mis-compiled):

class Person {}

protocol Parent where Self : Person {
  func speak()
}

class GrandMotherPerson : Person, Parent {
  func speak() {}
}

let parent: Parent = GrandMotherPerson()
parent.speak()

In the latest dev snapshot, it triggers a compiler assertion instead:

TYPE MISMATCH IN ARGUMENT 0 OF APPLY AT expression at [/Users/Hamish/Desktop/main.swift:20:1 - line:20:14] RangeText="parent.speak()"
  argument value:   %27 = open_existential_addr immutable_access %23 : $*Parent to $*@opened("32F07EA8-0071-11E8-AFDA-DCA9047B1400") Parent // user: %28
  parameter type: $@opened("32F07EA8-0071-11E8-AFDA-DCA9047B1400") Parent