YJIT: Add compilation log (#11818)

* YJIT: Add `--yjit-compilation-log` flag to print out the compilation log at exit.

* YJIT: Add an option to enable the compilation log at runtime.

* YJIT: Fix a typo in the `IseqPayload` docs.

* YJIT: Add stubs for getting the YJIT compilation log in memory.

* YJIT: Add a compilation log based on a circular buffer to cap the log size.

* YJIT: Allow specifying either a file or directory name for the YJIT compilation log.

The compilation log will be populated as compilation events occur. If a directory is supplied, then a filename based on the PID will be used as the write target. If a file name is supplied instead, the log will be written to that file.

* YJIT: Add JIT compilation of C function substitutions to the compilation log.

* YJIT: Add compilation events to the circular buffer even if output is sent to a file.

Previously, the two modes were treated as being exclusive of one another. However, it could be beneficial to log all events to a file while also allowing for direct access of the last N events via `RubyVM::YJIT.compilation_log`.

* YJIT: Make timestamps the first element in the YJIT compilation log tuple.

* YJIT: Stream log to stderr if `--yjit-compilation-log` is supplied without an argument.

* YJIT: Eagerly compute compilation log messages to avoid hanging on to references that may GC.

* YJIT: Log all compiled blocks, not just the method entry points.

* YJIT: Remove all compilation events other than block compilation to slim down the log.

* YJIT: Replace circular buffer iterator with a consuming loop.

* YJIT: Support `--yjit-compilation-log=quiet` as a way to activate the in-memory log without printing it.

Co-authored-by: Randy Stauner <randy.stauner@shopify.com>

* YJIT: Promote the compilation log to being the one YJIT log.

Co-authored-by: Randy Stauner <randy.stauner@shopify.com>

* Update doc/yjit/yjit.md

* Update doc/yjit/yjit.md

---------

Co-authored-by: Randy Stauner <randy.stauner@shopify.com>
Co-authored-by: Maxime Chevalier-Boisvert <maximechevalierb@gmail.com>

yjit.rb

@@ -18,6 +18,11 @@ module RubyVM::YJIT
     Primitive.rb_yjit_stats_enabled_p
   end
 
+  # Check if `--yjit-log` is used.
+  def self.log_enabled?
+    Primitive.rb_yjit_log_enabled_p
+  end
+
   # Check if rb_yjit_trace_exit_locations_enabled_p is enabled.
   def self.trace_exit_locations_enabled? # :nodoc:
     Primitive.rb_yjit_trace_exit_locations_enabled_p
@@ -28,15 +33,22 @@ module RubyVM::YJIT
     Primitive.rb_yjit_reset_stats_bang
   end
 
-  # Enable \YJIT compilation. `stats` option decides whether to enable \YJIT stats or not.
+  # Enable \YJIT compilation. `stats` option decides whether to enable \YJIT stats or not. `compilation_log` decides
+  # whether to enable \YJIT compilation logging or not.
   #
+  # `stats`:
   # * `false`: Disable stats.
   # * `true`: Enable stats. Print stats at exit.
   # * `:quiet`: Enable stats. Do not print stats at exit.
-  def self.enable(stats: false)
+  #
+  # `log`:
+  # * `false`: Don't enable the log.
+  # * `true`: Enable the log. Print log at exit.
+  # * `:quiet`: Enable the log. Do not print log at exit.
+  def self.enable(stats: false, log: false)
     return false if enabled?
     at_exit { print_and_dump_stats } if stats
-    Primitive.rb_yjit_enable(stats, stats != :quiet)
+    Primitive.rb_yjit_enable(stats, stats != :quiet, log, log != :quiet)
   end
 
   # If --yjit-trace-exits is enabled parse the hashes from
@@ -173,6 +185,16 @@ module RubyVM::YJIT
     strio.string
   end
 
+  # Return an array of log entries.
+  # Return `nil` when option is not passed or unavailable.
+  def self.log
+    return nil unless log_enabled?
+
+    Primitive.rb_yjit_get_log.map do |timestamp, path|
+      [Time.at(timestamp), path]
+    end
+  end
+
   # Produce disassembly for an iseq. This requires a `--enable-yjit=dev` build.
   def self.disasm(iseq) # :nodoc:
     # If a method or proc is passed in, get its iseq