This provides a significant speedup for symbol, true, false, nil, and 0-9, class/module, and a small speedup in most other cases. Speedups (using included benchmarks): :symbol :: 60% 0-9 :: 50% Class/Module :: 50% nil/true/false :: 20% integer :: 10% [] :: 10% "" :: 3% One reason this approach is faster is it reduces the number of VM instructions for each interpolated value. Initial idea, approach, and benchmarks from Eric Wong. I applied the same approach against the master branch, updating it to handle the significant internal changes since this was first proposed 4 years ago (such as CALL_INFO/CALL_CACHE -> CALL_DATA). I also expanded it to optimize true/false/nil/0-9/class/module, and added handling of missing methods, refined methods, and RUBY_DEBUG. This renames the tostring insn to anytostring, and adds an objtostring insn that implements the optimization. This requires making a few functions non-static, and adding some non-static functions. This disables 4 YJIT tests. Those tests should be reenabled after YJIT optimizes the new objtostring insn. Implements [Feature #13715] Co-authored-by: Eric Wong <[email protected]> Co-authored-by: Alan Wu <[email protected]> Co-authored-by: Yusuke Endoh <[email protected]> Co-authored-by: Koichi Sasada <[email protected]>