https://git.ruby-lang.org/ruby.git/commit/?id=251531bdf0

From 251531bdf06b03a6531ca6863d19c693fc62631a Mon Sep 17 00:00:00 2001
From: Maxime Chevalier-Boisvert <maxime.chevalierboisvert@s...>
Date: Thu, 10 Sep 2020 11:09:45 -0400
Subject: Reimplement Alan's pop instruction with the new assembler

---
 iseq.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/iseq.c b/iseq.c
index 03f322e514..51d923cf8e 100644
--- a/iseq.c
+++ b/iseq.c
@@ -3178,6 +3178,14 @@ typedef struct insn_data_struct { https://github.com/ruby/ruby/blob/trunk/iseq.c#L3178
 } insn_data_t;
 static insn_data_t insn_data[VM_INSTRUCTION_SIZE/2];
 
+
+
+
+#include "ujit_asm.h"
+
+
+
+
 void
 rb_vm_encoded_insn_data_table_init(void)
 {
@@ -3210,6 +3218,8 @@ rb_vm_encoded_insn_data_table_init(void) https://github.com/ruby/ruby/blob/trunk/iseq.c#L3218
         st_add_direct(encoded_insn_data, key2, (st_data_t)&insn_data[insn]);
     }
 
+
+    /*
     native_pop_code = mmap(0, 4096, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_ANON|MAP_PRIVATE, 0, 0);
     if (native_pop_code == MAP_FAILED) rb_bug("mmap failed");
     uint8_t *head = native_pop_code;
@@ -3225,11 +3235,27 @@ rb_vm_encoded_insn_data_table_init(void) https://github.com/ruby/ruby/blob/trunk/iseq.c#L3235
     head += sizeof(handmade_pop);
     memcpy(head, ujit_post_call_bytes, sizeof(ujit_post_call_bytes));
     // TODO this is small enough to fit in the page we allocated but that can change
+    */
+
+
 
+    // I decided to start by replicating Alan's code above using the new assembler
+    codeblock_t block;
+    codeblock_t* cb = &block;
+    cb_init(cb, 4096);
 
+    // Write the pre call bytes
+    cb_write_prologue(cb);
 
+    sub(cb, mem_opnd(64, RDI, 8), imm_opnd(8)); // decrement SP
+    add(cb, RSI, imm_opnd(8));                  // increment PC
+    mov(cb, mem_opnd(64, RDI, 0), RSI);         // write new PC to EC object, not necessary for pop bytecode?
+    mov(cb, RAX, RSI);                          // return new PC
 
+    // Write the post call bytes
+    cb_write_epilogue(cb);
 
+    native_pop_code = cb_get_ptr(cb, 0);
 
 
 
-- 
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