YJIT: Drop bogus checks for ruby2_keywords

These checks don't correspond to anything that ruby2_keywords actually
does, so YJIT was refusing to compile things needlessly. About 16% of
fallback reasons in `lobsters` was due to the ISeq one.

As for the correct logic, we already handle the tagging part with
exit_if_supplying_kw_and_has_no_kw() and have a dynamic guard for the
splat logic.

yjit/src/codegen.rs

@@ -5555,18 +5555,6 @@ fn gen_send_cfunc(
         return None;
     }
 
-    // In order to handle backwards compatibility between ruby 3 and 2
-    // ruby2_keywords was introduced. It is called only on methods
-    // with splat and changes they way they handle them.
-    // We are just going to not compile these.
-    // https://docs.ruby-lang.org/en/3.2/Module.html#method-i-ruby2_keywords
-    if unsafe {
-        get_iseq_flags_ruby2_keywords(jit.iseq) && flags & VM_CALL_ARGS_SPLAT != 0
-    } {
-        gen_counter_incr(asm, Counter::send_args_splat_cfunc_ruby2_keywords);
-        return None;
-    }
-
     let kw_arg = unsafe { vm_ci_kwarg(ci) };
     let kw_arg_num = if kw_arg.is_null() {
         0
@@ -6152,7 +6140,6 @@ fn gen_send_iseq(
     exit_if_has_post(asm, iseq)?;
     exit_if_has_kwrest(asm, iseq)?;
     exit_if_kw_splat(asm, flags)?;
-    exit_if_splat_and_ruby2_keywords(asm, jit, flags)?;
     exit_if_has_rest_and_captured(asm, iseq_has_rest, captured_opnd)?;
     exit_if_has_rest_and_supplying_kws(asm, iseq_has_rest, iseq, supplying_kws)?;
     exit_if_supplying_kw_and_has_no_kw(asm, supplying_kws, iseq)?;
@@ -6968,20 +6955,6 @@ fn exit_if_kw_splat(asm: &mut Assembler, flags: u32) -> Option<()> {
     exit_if(asm, flags & VM_CALL_KW_SPLAT != 0, Counter::send_iseq_kw_splat)
 }
 
-#[must_use]
-fn exit_if_splat_and_ruby2_keywords(asm: &mut Assembler, jit: &mut JITState, flags: u32) -> Option<()> {
-    // In order to handle backwards compatibility between ruby 3 and 2
-    // ruby2_keywords was introduced. It is called only on methods
-    // with splat and changes they way they handle them.
-    // We are just going to not compile these.
-    // https://www.rubydoc.info/stdlib/core/Proc:ruby2_keywords
-    exit_if(
-        asm,
-        unsafe { get_iseq_flags_ruby2_keywords(jit.iseq) } && flags & VM_CALL_ARGS_SPLAT != 0,
-        Counter::send_iseq_ruby2_keywords,
-    )
-}
-
 #[must_use]
 fn exit_if_has_rest_and_captured(asm: &mut Assembler, iseq_has_rest: bool, captured_opnd: Option<Opnd>) -> Option<()> {
     exit_if(asm, iseq_has_rest && captured_opnd.is_some(), Counter::send_iseq_has_rest_and_captured)

yjit/src/stats.rs

@@ -358,10 +358,8 @@ make_counters! {
     send_args_splat_opt_call,
     send_args_splat_cfunc_var_args,
     send_args_splat_cfunc_zuper,
-    send_args_splat_cfunc_ruby2_keywords,
     send_iseq_splat_arity_error,
     send_splat_too_long,
-    send_iseq_ruby2_keywords,
     send_send_not_imm,
     send_send_wrong_args,
     send_send_null_mid,