Rust YJIT

In December 2021, we opened an [issue] to solicit feedback regarding the
porting of the YJIT codebase from C99 to Rust. There were some
reservations, but this project was given the go ahead by Ruby core
developers and Matz. Since then, we have successfully completed the port
of YJIT to Rust.

The new Rust version of YJIT has reached parity with the C version, in
that it passes all the CRuby tests, is able to run all of the YJIT
benchmarks, and performs similarly to the C version (because it works
the same way and largely generates the same machine code). We've even
incorporated some design improvements, such as a more fine-grained
constant invalidation mechanism which we expect will make a big
difference in Ruby on Rails applications.

Because we want to be careful, YJIT is guarded behind a configure
option:

```shell
./configure --enable-yjit # Build YJIT in release mode
./configure --enable-yjit=dev # Build YJIT in dev/debug mode
```

By default, YJIT does not get compiled and cargo/rustc is not required.
If YJIT is built in dev mode, then `cargo` is used to fetch development
dependencies, but when building in release, `cargo` is not required,
only `rustc`. At the moment YJIT requires Rust 1.60.0 or newer.

The YJIT command-line options remain mostly unchanged, and more details
about the build process are documented in `doc/yjit/yjit.md`.

The CI tests have been updated and do not take any more resources than
before.

The development history of the Rust port is available at the following
commit for interested parties:
https://github.com/Shopify/ruby/commit/1fd9573d8b4b65219f1c2407f30a0a60e537f8be

Our hope is that Rust YJIT will be compiled and included as a part of
system packages and compiled binaries of the Ruby 3.2 release. We do not
anticipate any major problems as Rust is well supported on every
platform which YJIT supports, but to make sure that this process works
smoothly, we would like to reach out to those who take care of building
systems packages before the 3.2 release is shipped and resolve any
issues that may come up.

[issue]: https://bugs.ruby-lang.org/issues/18481

Co-authored-by: Maxime Chevalier-Boisvert <maximechevalierb@gmail.com>
Co-authored-by: Noah Gibbs <the.codefolio.guy@gmail.com>
Co-authored-by: Kevin Newton <kddnewton@gmail.com>

1 files changed, 34 insertions, 131 deletions

diff --git a/yjit.rb b/yjit.rb
index 09ed3faaf3..7c5311d79a 100644
--- a/yjit.rb
+++ b/yjit.rb
@@ -9,155 +9,58 @@
 # for which CRuby is built. There is also no API stability guarantee as to in
 # what situations this module is defined.
 module RubyVM::YJIT
-  if defined?(Disasm)
-    def self.disasm(iseq, tty: $stdout && $stdout.tty?)
-      iseq = RubyVM::InstructionSequence.of(iseq)
-
-      blocks = blocks_for(iseq)
-      return if blocks.empty?
-
-      str = String.new
-      str << iseq.disasm
-      str << "\n"
-
-      # Sort the blocks by increasing addresses
-      sorted_blocks = blocks.sort_by(&:address)
-
-      highlight = ->(str) {
-        if tty
-          "\x1b[1m#{str}\x1b[0m"
-        else
-          str
-        end
-      }
-
-      cs = Disasm.new
-      sorted_blocks.each_with_index do |block, i|
-        str << "== BLOCK #{i+1}/#{blocks.length}: #{block.code.length} BYTES, ISEQ RANGE [#{block.iseq_start_index},#{block.iseq_end_index}) ".ljust(80, "=")
-        str << "\n"
-
-        comments = comments_for(block.address, block.address + block.code.length)
-        comment_idx = 0
-        cs.disasm(block.code, block.address).each do |i|
-          while (comment = comments[comment_idx]) && comment.address <= i.address
-            str << "  ; #{highlight.call(comment.comment)}\n"
-            comment_idx += 1
-          end
-
-          str << sprintf(
-            "  %<address>08x:  %<instruction>s\t%<details>s\n",
-            address: i.address,
-            instruction: i.mnemonic,
-            details: i.op_str
-          )
-        end
-      end
-
-      block_sizes = blocks.map { |block| block.code.length }
-      total_bytes = block_sizes.sum
-      str << "\n"
-      str << "Total code size: #{total_bytes} bytes"
-      str << "\n"
-
-      str
-    end
-
-    def self.comments_for(start_address, end_address)
-      Primitive.comments_for(start_address, end_address)
-    end
-
-    def self.graphviz_for(iseq)
-      iseq = RubyVM::InstructionSequence.of(iseq)
-      cs = Disasm.new
-
-      highlight = ->(comment) { "<b>#{comment}</b>" }
-      linebreak = "<br align=\"left\"/>\n"
-
-      buff = +''
-      blocks = blocks_for(iseq).sort_by(&:id)
-      buff << "digraph g {\n"
-
-      # Write the iseq info as a legend
-      buff << "  legend [shape=record fontsize=\"30\" fillcolor=\"lightgrey\" style=\"filled\"];\n"
-      buff << "  legend [label=\"{ Instruction Disassembly For: | {#{iseq.base_label}@#{iseq.absolute_path}:#{iseq.first_lineno}}}\"];\n"
-
-      # Subgraph contains disassembly
-      buff << "  subgraph disasm {\n"
-      buff << "  node [shape=record fontname=\"courier\"];\n"
-      buff << "  edge [fontname=\"courier\" penwidth=3];\n"
-      blocks.each do |block|
-        disasm = disasm_block(cs, block, highlight)
-
-        # convert newlines to breaks that graphviz understands
-        disasm.gsub!(/\n/, linebreak)
-
-        # strip leading whitespace
-        disasm.gsub!(/^\s+/, '')
-
-        buff << "b#{block.id} [label=<#{disasm}>];\n"
-        buff << block.outgoing_ids.map { |id|
-          next_block = blocks.bsearch { |nb| id <=> nb.id }
-          if next_block.address == (block.address + block.code.length)
-            "b#{block.id} -> b#{id}[label=\"Fall\"];"
-          else
-            "b#{block.id} -> b#{id}[label=\"Jump\" style=dashed];"
-          end
-        }.join("\n")
-        buff << "\n"
-      end
-      buff << "  }"
-      buff << "}"
-      buff
-    end
+  # Check if YJIT is enabled
+  def self.enabled?
+    Primitive.cexpr! 'RBOOL(rb_yjit_enabled_p())'
+  end
 
-    def self.disasm_block(cs, block, highlight)
-      comments = comments_for(block.address, block.address + block.code.length)
-      comment_idx = 0
-      str = +''
-      cs.disasm(block.code, block.address).each do |i|
-        while (comment = comments[comment_idx]) && comment.address <= i.address
-          str << "  ; #{highlight.call(comment.comment)}\n"
-          comment_idx += 1
-        end
+  def self.stats_enabled?
+    Primitive.rb_yjit_stats_enabled_p
+  end
 
-        str << sprintf(
-          "  %<address>08x:  %<instruction>s\t%<details>s\n",
-          address: i.address,
-          instruction: i.mnemonic,
-          details: i.op_str
-        )
-      end
-      str
-    end
+  # Discard statistics collected for --yjit-stats.
+  def self.reset_stats!
+    Primitive.rb_yjit_reset_stats_bang
   end
 
   # Return a hash for statistics generated for the --yjit-stats command line option.
   # Return nil when option is not passed or unavailable.
   def self.runtime_stats
-    # defined in yjit_iface.c
-    Primitive.get_yjit_stats
+    Primitive.rb_yjit_get_stats
   end
 
-  # Discard statistics collected for --yjit-stats.
-  def self.reset_stats!
-    # defined in yjit_iface.c
-    Primitive.reset_stats_bang
+  # Produce disassembly for an iseq
+  def self.disasm(iseq)
+    # If a method or proc is passed in, get its iseq
+    iseq = RubyVM::InstructionSequence.of(iseq)
+
+    if self.enabled?
+      # Produce the disassembly string
+      # Include the YARV iseq disasm in the string for additional context
+      iseq.disasm + "\n" + Primitive.rb_yjit_disasm_iseq(iseq)
+    else
+      iseq.disasm
+    end
   end
 
-  def self.stats_enabled?
-    Primitive.yjit_stats_enabled_p
-  end
+  # Produce a list of instructions compiled by YJIT for an iseq
+  def self.insns_compiled(iseq)
+    # If a method or proc is passed in, get its iseq
+    iseq = RubyVM::InstructionSequence.of(iseq)
 
-  def self.enabled?
-    Primitive.cexpr! 'RBOOL(rb_yjit_enabled_p())'
+    if self.enabled?
+      Primitive.rb_yjit_insns_compiled(iseq)
+    else
+      Qnil
+    end
   end
 
   def self.simulate_oom!
-    Primitive.simulate_oom_bang
+    Primitive.rb_yjit_simulate_oom_bang
   end
 
   # Avoid calling a method here to not interfere with compilation tests
-  if Primitive.yjit_stats_enabled_p
+  if Primitive.rb_yjit_stats_enabled_p
     at_exit { _print_stats }
   end