Issue #21452 has been reported by tekknolagi (Maxwell Bernstein). ---------------------------------------- Bug #21452: ARGS_SPLAT bytecode regression between 3.3 and 3.4 https://bugs.ruby-lang.org/issues/21452 * Author: tekknolagi (Maxwell Bernstein) * Status: Open * ruby -v: ruby 3.4.3 (2025-04-14 revision d0b7e5b6a0) +PRISM [arm64-darwin24] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- On Ruby 3.3, `f(1, 2, *[3, 4])` splats all arguments to the stack and uses `ARGS_SIMPLE`: ``` plum% ruby --version ruby 3.3.2 (2024-05-30 revision e5a195edf6) [arm64-darwin24] plum% ruby --dump=insns -e 'f(1, 2, *[3, 4])' == disasm: #<ISeq:<main>@-e:1 (1,0)-(1,16)> 0000 putself ( 1)[Li] 0001 putobject_INT2FIX_1_ 0002 putobject 2 0004 putobject 3 0006 putobject 4 0008 opt_send_without_block <calldata!mid:f, argc:4, FCALL|ARGS_SIMPLE> 0010 leave plum% ``` On Ruby 3.4, the same expression results in creating a new array and using `ARGS_SPLAT`: ``` plum% ruby --version ruby 3.4.3 (2025-04-14 revision d0b7e5b6a0) +PRISM [arm64-darwin24] plum% ruby --dump=insns -e 'f(1, 2, *[3, 4])' == disasm: #<ISeq:<main>@-e:1 (1,0)-(1,16)> 0000 putself ( 1)[Li] 0001 putobject_INT2FIX_1_ 0002 putobject 2 0004 duparray [3, 4] 0006 opt_send_without_block <calldata!mid:f, argc:3, ARGS_SPLAT|FCALL> 0008 leave plum% ``` I think we should keep the behavior of 3.3. -- https://bugs.ruby-lang.org/