Optimize code like:
puts("\(String.self)")
Optimizing string interpolation and optimizing C-strings are both done in StringOptimization.
A second run of the StringOptimization is needed in the pipeline to optimize such code, because the result of the interpolation-optimization must be cleaned up so that the C-String optimization can kick in.
Also, StringOptimization must handle struct_extract(struct(literal)), where the struct_extract may be in a called function.
To solve a phase ordering problem with inlining String semantics and inlining the `String(stringInterpolation: DefaultStringInterpolation)` constructor, we do a simple analysis of the callee. Doing this simple "interprocedural" analysis avoids relying on inlining that String constructor.
rdar://74941849
Replace a String initializer followed by String.utf8CString with a (UTF8 encoded) string literal.
This code pattern is generated when calling C functions with string literals, e.g.
puts("hello!")
rdar://74941849
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
