https://git.ruby-lang.org/ruby.git/commit/?id=d0a213b30d

From d0a213b30d04372d1a1b5012246ac7da3236db31 Mon Sep 17 00:00:00 2001
From: Alan Wu <XrXr@u...>
Date: Wed, 22 Sep 2021 16:11:45 -0400
Subject: Remove a memory load in gen_send_iseq

Instead of loading from meory for REG_SP, do a register rename instead.
It's cheaper.
---
 yjit_codegen.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/yjit_codegen.c b/yjit_codegen.c
index ac7f866d9e..e3a23b3bb8 100644
--- a/yjit_codegen.c
+++ b/yjit_codegen.c
@@ -3477,15 +3477,16 @@ gen_send_iseq(jitstate_t *jit, ctx_t *ctx, const struct rb_callinfo *ci, const r https://github.com/ruby/ruby/blob/trunk/yjit_codegen.c#L3477
     //    .block_code = 0,
     //    .__bp__     = sp,
     // };
-    mov(cb, member_opnd(REG_CFP, rb_control_frame_t, block_code), imm_opnd(0));
+    mov(cb, REG1, recv);
+    mov(cb, member_opnd(REG_CFP, rb_control_frame_t, self), REG1);
+    mov(cb, REG_SP, REG0); // Switch to the callee's REG_SP
     mov(cb, member_opnd(REG_CFP, rb_control_frame_t, sp), REG0);
     mov(cb, member_opnd(REG_CFP, rb_control_frame_t, __bp__), REG0);
     sub(cb, REG0, imm_opnd(sizeof(VALUE)));
     mov(cb, member_opnd(REG_CFP, rb_control_frame_t, ep), REG0);
-    mov(cb, REG0, recv);
-    mov(cb, member_opnd(REG_CFP, rb_control_frame_t, self), REG0);
     jit_mov_gc_ptr(jit, cb, REG0, (VALUE)iseq);
     mov(cb, member_opnd(REG_CFP, rb_control_frame_t, iseq), REG0);
+    mov(cb, member_opnd(REG_CFP, rb_control_frame_t, block_code), imm_opnd(0));
 
     // No need to set cfp->pc since the callee sets it whenever calling into routines
     // that could look at it through jit_save_pc().
@@ -3532,9 +3533,6 @@ gen_send_iseq(jitstate_t *jit, ctx_t *ctx, const struct rb_callinfo *ci, const r https://github.com/ruby/ruby/blob/trunk/yjit_codegen.c#L3533
     //print_str(cb, "calling Ruby func:");
     //print_str(cb, rb_id2name(vm_ci_mid(ci)));
 
-    // Load the updated SP from the CFP
-    mov(cb, REG_SP, member_opnd(REG_CFP, rb_control_frame_t, sp));
-
     // Directly jump to the entry point of the callee
     gen_direct_jump(
         jit,
-- 
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