Optimize send calls

Similar to the bmethod optimization, this avoids using
CALLER_ARG_SPLAT if not necessary.  As long as the method argument
can be shifted off, other arguments are passed through as-is.

This optimizes the following types of calls:

* send(meth, arg) ~5%
* send(meth, *args) ~75% for args.length == 200
* send(meth, *args, **kw) ~50% for args.length == 200
* send(meth, **kw) ~25%
* send(meth, kw: 1) ~115%

Note that empty argument splats do get slower with this approach,
by about 20%.  This is probably because iseq argument setup is
slower for empty argument splats than CALLER_SETUP_ARG is. Other
than non-empty argument splats, other argument splats are faster,
with the speedup depending on the number of arguments.

The following types of calls are not optimized:

* send(*args)
* send(*args, **kw)

This is because the you cannot shift the method argument off
without first splatting the arg.

benchmark/vm_call_send_iseq.yml

@@ -0,0 +1,77 @@
+prelude: |
+  def a0; end
+  def a1(a) a; end
+  def s(*a) a; end
+  def b(kw: 1) kw end
+  def sb(*a, kw: 1) kw end
+
+  t0 = 0.times.to_a
+  t1 = 1.times.to_a
+  t10 = 10.times.to_a
+  t200 = 200.times.to_a
+
+  a0_t0 = [:a0, *t0]
+  a1_t1 = [:a1, *t1]
+  s_t0 = [:s, *t0]
+  s_t1 = [:s, *t1]
+  s_t10 = [:s, *t10]
+  s_t200 = [:s, *t200]
+  sb_t0 = [:sb, *t0]
+  sb_t1 = [:sb, *t1]
+  sb_t10 = [:sb, *t10]
+  sb_t200 = [:sb, *t200]
+  kw = {kw: 2}
+benchmark:
+  send_simple_0: |
+    send(:a0)
+  send_simple_1: |
+    send(:a1, 1)
+  send_simple_0_splat: |
+    send(:a0, *t0)
+  send_simple_1_splat: |
+    send(:a1, *t1)
+  send_simple_0_splat_comb: |
+    send(*a0_t0)
+  send_simple_1_splat_comb: |
+    send(*a1_t1)
+  send_no_splat: |
+    send(:s)
+  send_0_splat: |
+    send(:s, *t0)
+  send_1_splat: |
+    send(:s, *t1)
+  send_10_splat: |
+    send(:s, *t10)
+  send_200_splat: |
+    send(:s, *t200)
+  send_0_splat_comb: |
+    send(*s_t0)
+  send_1_splat_comb: |
+    send(*s_t1)
+  send_10_splat_comb: |
+    send(*s_t10)
+  send_200_splat_comb: |
+    send(*s_t200)
+  send_kw: |
+    send(:b, kw: 1)
+  send_no_kw: |
+    send(:b)
+  send_kw_splat: |
+    send(:b, **kw)
+  send_0_splat_kw: |
+    send(:sb, *t0, **kw)
+  send_1_splat_kw: |
+    send(:sb, *t1, **kw)
+  send_10_splat_kw: |
+    send(:sb, *t10, **kw)
+  send_200_splat_kw: |
+    send(:sb, *t200, **kw)
+  send_0_splat_comb_kw: |
+    send(*sb_t0, **kw)
+  send_1_splat_comb_kw: |
+    send(*sb_t1, **kw)
+  send_10_splat_comb_kw: |
+    send(*sb_t10, **kw)
+  send_200_splat_comb_kw: |
+    send(*sb_t200, **kw)
+loop_count: 3000000

vm_insnhelper.c

@@ -3813,14 +3813,13 @@ vm_call_symbol(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp,
                struct rb_calling_info *calling, const struct rb_callinfo *ci, VALUE symbol, int flags)
 {
     ASSUME(calling->argc >= 0);
-    /* Also assumes CALLER_SETUP_ARG is already done. */
 
     enum method_missing_reason missing_reason = MISSING_NOENTRY;
     int argc = calling->argc;
     VALUE recv = calling->recv;
     VALUE klass = CLASS_OF(recv);
     ID mid = rb_check_id(&symbol);
-    flags |= VM_CALL_OPT_SEND | (calling->kw_splat ? VM_CALL_KW_SPLAT : 0);
+    flags |= VM_CALL_OPT_SEND;
 
     if (UNLIKELY(! mid)) {
         mid = idMethodMissing;
@@ -3910,24 +3909,12 @@ vm_call_symbol(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp,
 }
 
 static VALUE
-vm_call_opt_send(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, struct rb_calling_info *calling)
+vm_call_opt_send0(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, struct rb_calling_info *calling, int flags)
 {
-    RB_DEBUG_COUNTER_INC(ccf_opt_send);
+    const struct rb_callinfo *ci = calling->ci;
+    int i;
+    VALUE sym;
 
-    int i, flags = VM_CALL_FCALL;
-    VALUE sym, argv_ary;
-
-    CALLER_SETUP_ARG(reg_cfp, calling, calling->ci, ALLOW_HEAP_ARGV);
-    if (UNLIKELY(argv_ary = calling->heap_argv)) {
-        sym = rb_ary_shift(argv_ary);
-        flags |= VM_CALL_ARGS_SPLAT;
-        if (calling->kw_splat) {
-            VALUE last_hash = rb_ary_last(0, NULL, argv_ary);
-            ((struct RHash *)last_hash)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
-            calling->kw_splat = 0;
-        }
-    }
-    else {
     i = calling->argc - 1;
 
     if (calling->argc == 0) {
@@ -3954,9 +3941,60 @@ vm_call_opt_send(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, struct
     }
     calling->argc -= 1;
     DEC_SP(1);
+
+    return vm_call_symbol(ec, reg_cfp, calling, ci, sym, flags);
 }
 
-    return vm_call_symbol(ec, reg_cfp, calling, calling->ci, sym, flags);
+static VALUE
+vm_call_opt_send_complex(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, struct rb_calling_info *calling)
+{
+    RB_DEBUG_COUNTER_INC(ccf_opt_send_complex);
+    const struct rb_callinfo *ci = calling->ci;
+    int flags = VM_CALL_FCALL;
+    VALUE sym;
+
+    VALUE argv_ary;
+    CALLER_SETUP_ARG(reg_cfp, calling, ci, ALLOW_HEAP_ARGV);
+    if (UNLIKELY(argv_ary = calling->heap_argv)) {
+        sym = rb_ary_shift(argv_ary);
+        flags |= VM_CALL_ARGS_SPLAT;
+        if (calling->kw_splat) {
+            VALUE last_hash = rb_ary_last(0, NULL, argv_ary);
+            ((struct RHash *)last_hash)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
+            calling->kw_splat = 0;
+        }
+        return vm_call_symbol(ec, reg_cfp, calling, ci, sym, flags);
+    }
+
+    if (calling->kw_splat) flags |= VM_CALL_KW_SPLAT;
+    return vm_call_opt_send0(ec, reg_cfp, calling, flags);
+}
+
+static VALUE
+vm_call_opt_send_simple(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, struct rb_calling_info *calling)
+{
+    RB_DEBUG_COUNTER_INC(ccf_opt_send_simple);
+    return vm_call_opt_send0(ec, reg_cfp, calling, vm_ci_flag(calling->ci) | VM_CALL_FCALL);
+}
+
+static VALUE
+vm_call_opt_send(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, struct rb_calling_info *calling)
+{
+    RB_DEBUG_COUNTER_INC(ccf_opt_send);
+
+    const struct rb_callinfo *ci = calling->ci;
+    int flags = vm_ci_flag(ci);
+
+    if (UNLIKELY(!(flags & VM_CALL_ARGS_SIMPLE) &&
+        ((calling->argc == 1 && (flags & (VM_CALL_ARGS_SPLAT | VM_CALL_KW_SPLAT))) ||
+         (calling->argc == 2 && (flags & VM_CALL_ARGS_SPLAT) && (flags & VM_CALL_KW_SPLAT)) ||
+         ((flags & VM_CALL_KWARG) && (vm_ci_kwarg(ci)->keyword_len == calling->argc))))) {
+        CC_SET_FASTPATH(calling->cc, vm_call_opt_send_complex, TRUE);
+        return vm_call_opt_send_complex(ec, reg_cfp, calling);
+    }
+
+    CC_SET_FASTPATH(calling->cc, vm_call_opt_send_simple, TRUE);
+    return vm_call_opt_send_simple(ec, reg_cfp, calling);
 }
 
 static VALUE
@@ -4819,6 +4857,9 @@ vm_invoke_symbol_block(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp,
         }
         calling->recv = TOPN(--calling->argc);
     }
+    if (calling->kw_splat) {
+        flags |= VM_CALL_KW_SPLAT;
+    }
     return vm_call_symbol(ec, reg_cfp, calling, ci, symbol, flags);
 }