swift

7f684b62 - SIL optimizer: Add a new string optimization.

SIL optimizer: Add a new string optimization. Optimizes String operations with constant operands. Specifically: * Replaces x.append(y) with x = y if x is empty. * Removes x.append("") * Replaces x.append(y) with x = x + y if x and y are constant strings. * Replaces _typeName(T.self) with a constant string if T is statically known. With this optimization it's possible to constant fold string interpolations, like "the \(Int.self) type" -> "the Int type" This new pass runs on high-level SIL, where semantic calls are still in place. rdar://problem/65642843