[Feature #18239] Implement VWA for strings

This commit adds support for embedded strings with variable capacity and
uses Variable Width Allocation to allocate strings.

2 files changed, 32 insertions, 11 deletions

diff --git a/test/-ext-/string/test_capacity.rb b/test/-ext-/string/test_capacity.rb
index df59e76778..583c98fca4 100644
--- a/test/-ext-/string/test_capacity.rb
+++ b/test/-ext-/string/test_capacity.rb
@@ -4,13 +4,10 @@ require '-test-/string'
 require 'rbconfig/sizeof'
 
 class Test_StringCapacity < Test::Unit::TestCase
-  def capa(str)
-    Bug::String.capacity(str)
-  end
-
   def test_capacity_embedded
-    size = RbConfig::SIZEOF['void*'] * 3 - 1
-    assert_equal size, capa('foo')
+    assert_equal GC::INTERNAL_CONSTANTS[:RVALUE_SIZE] - embed_header_size - 1, capa('foo')
+    assert_equal max_embed_len, capa('1' * max_embed_len)
+    assert_equal max_embed_len, capa('1' * (max_embed_len - 1))
   end
 
   def test_capacity_shared
@@ -18,7 +15,8 @@ class Test_StringCapacity < Test::Unit::TestCase
   end
 
   def test_capacity_normal
-    assert_equal 128, capa('1'*128)
+    assert_equal max_embed_len + 1, capa('1' * (max_embed_len + 1))
+    assert_equal max_embed_len + 100, capa('1' * (max_embed_len + 100))
   end
 
   def test_s_new_capacity
@@ -39,7 +37,10 @@ class Test_StringCapacity < Test::Unit::TestCase
   end
 
   def test_literal_capacity
-    s = "I am testing string literal capacity"
+    s = eval(%{
+      # frozen_string_literal: true
+      "#{"a" * (max_embed_len + 1)}"
+    })
     assert_equal(s.length, capa(s))
   end
 
@@ -51,9 +52,27 @@ class Test_StringCapacity < Test::Unit::TestCase
   end
 
   def test_capacity_fstring
-    s = String.new("I am testing", capacity: 1000)
+    s = String.new("a" * max_embed_len, capacity: 1000)
     s << "fstring capacity"
     s = -s
     assert_equal(s.length, capa(s))
   end
+
+  private
+
+  def capa(str)
+    Bug::String.capacity(str)
+  end
+
+  def embed_header_size
+    if GC.using_rvargc?
+      2 * RbConfig::SIZEOF['void*'] + RbConfig::SIZEOF['short']
+    else
+      2 * RbConfig::SIZEOF['void*']
+    end
+  end
+
+  def max_embed_len
+    GC::INTERNAL_CONSTANTS[:RVARGC_MAX_ALLOCATE_SIZE] - embed_header_size - 1
+  end
 end
diff --git a/test/-ext-/string/test_rb_str_dup.rb b/test/-ext-/string/test_rb_str_dup.rb
index 49b6af9598..c76a90252f 100644
--- a/test/-ext-/string/test_rb_str_dup.rb
+++ b/test/-ext-/string/test_rb_str_dup.rb
@@ -3,13 +3,15 @@ require '-test-/string'
 
 class Test_RbStrDup < Test::Unit::TestCase
   def test_nested_shared_non_frozen
-    str = Bug::String.rb_str_dup(Bug::String.rb_str_dup("a" * 50))
+    orig_str = "a" * GC::INTERNAL_CONSTANTS[:RVARGC_MAX_ALLOCATE_SIZE]
+    str = Bug::String.rb_str_dup(Bug::String.rb_str_dup(orig_str))
     assert_send([Bug::String, :shared_string?, str])
     assert_not_send([Bug::String, :sharing_with_shared?, str], '[Bug #15792]')
   end
 
   def test_nested_shared_frozen
-    str = Bug::String.rb_str_dup(Bug::String.rb_str_dup("a" * 50).freeze)
+    orig_str = "a" * GC::INTERNAL_CONSTANTS[:RVARGC_MAX_ALLOCATE_SIZE]
+    str = Bug::String.rb_str_dup(Bug::String.rb_str_dup(orig_str).freeze)
     assert_send([Bug::String, :shared_string?, str])
     assert_not_send([Bug::String, :sharing_with_shared?, str], '[Bug #15792]')
   end