Manage AST NODEs out of GC

NODEs in AST are no longer objects managed by GC.  This change will
remove the restriction imposed by the GC.  For example, a NODE can use
more than five words (this is my primary purpose; we want to store the
position data for each NODE, for coverage library), or even a NODE can
have variable length (some kinds of NODEs have unused fields).
To do this, however, we need more work, since Ripper still uses T_NODE
objects managed by the GC.

The life time of NODEs is more obvious than other kinds of objects; they
are created at parsing, and they become disused immediately after
compilation.  This change releases all NODEs by a few `xfree`s after
compilation, so performance will be improved a bit.  In extreme example,
`eval("x=1;" * 10000000)` runs much faster (40 sec. -> 7.8 sec. on my
machine).

The most important part of this change is `ast_t` struct, which has
three contents: (1) NODE buffer (malloc'ed memory), (2) a reference to
the root NODE, and (3) an array that contains objects that must be
marked during parsing (such as literal objects).  Some functions that
had received `NODE*` arguments, must now receive `ast_t*`.

* node.c, node.h: defines `ast_t` struct and related operations.
* gc.c, internal.h: defines `imemo_ast`.
* parse.y: makes `parser_params` struct have a reference to `ast_t`.
  Instead of `rb_node_newnode`, use `rb_ast_newnode` to create a NODE.
* iseq.c, load.c, ruby.c, template/prelude.c.tmpl: modifies some
  functions to handle `ast_t*` instead of `NODE*`.
* test/ruby/test_gc.rb: ad-hoc fix for a failed test.  The test assumes
  GC eden is increased at startup by NODE object creation.  However,
  this change now create no NODE object, so GC eden is not necessarily
  increased.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60485 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 3 insertions, 0 deletions

diff --git a/test/ruby/test_gc.rb b/test/ruby/test_gc.rb
index 67fd40a51e..7a6309b6a3 100644
--- a/test/ruby/test_gc.rb
+++ b/test/ruby/test_gc.rb
@@ -290,6 +290,9 @@ class TestGc < Test::Unit::TestCase
     base_length = GC.stat[:heap_eden_pages]
     (base_length * 500).times{ 'a' }
     GC.start
+    base_length = GC.stat[:heap_eden_pages]
+    (base_length * 500).times{ 'a' }
+    GC.start
     assert_in_epsilon base_length, (v = GC.stat[:heap_eden_pages]), 1/8r,
            "invalid heap expanding (base_length: #{base_length}, GC.stat[:heap_eden_pages]: #{v})"