def Lean.IR.ensureHasDefault (alts : Array Alt) : Array Alt

partial def Lean.IR.FnBody.simpCase (b : FnBody) : FnBody

def Lean.IR.Decl.simpCase (d : Decl) : Decl

Simplify case

• Remove unreachable branches.
• Remove case if there is only one branch.
• Merge most common branches using Alt.default.