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Issue Description:

The attached code crashes during compilation, I tried to reduce it as much as possible.

The full stack trace is attached, but the summary reads

1.  Apple Swift version 5.3.1 (swiftlang-1200.0.41 clang-1200.0.32.8)
2.  While evaluating request SILGenSourceFileRequest(SIL Generation for file "crasher.swift")
3.  While emitting SIL for 'f(_:_:)' (at crasher.swift:17:1)
4.  While silgen emitFunction SIL function "@$s7crasher1fyyx_xtlF".
 for 'f(_:_:)' (at crasher.swift:17:1)
5.  While silgen closureexpr SIL function "@$s7crasher1fyyx_xtlFySRyXeGXEfU_".
 for expression at [crasher.swift:19:46 - line:21:3] RangeText="{ buffer in
    f(array, Array(UnsafeBufferPointer(buffer)))
  "

There are two small changes I discovered which when applied don't lead to a crash:

1.  func f<T>(_ : T, _ : T) {
      let array = Array<Int>()
   -  S2(array).withContiguousStorageIfAvailable { buffer in
   +  S2<[Int]>(array).withContiguousStorageIfAvailable { buffer in
        f(array, Array(UnsafeBufferPointer(buffer)))
      }
    }

2.  func f<T>(_ : T, _ : T) {
      let array = Array<Int>()
      S2(array).withContiguousStorageIfAvailable { buffer in
   -    f(array, Array(UnsafeBufferPointer(buffer)))
   +    f(array, Array(buffer))
      }
    }