Don't create T_MATCH object if /regexp/.match(string) doesn't match

Fixes [Bug #20104]

re.c

@@ -1747,15 +1747,18 @@ rb_reg_search_set_match(VALUE re, VALUE str, long pos, int reverse, int set_back
         .range = reverse ? 0 : len,
     };
 
-    VALUE match = match_alloc(rb_cMatch);
-    struct re_registers *regs = RMATCH_REGS(match);
+    struct re_registers regs = {0};
 
-    OnigPosition result = rb_reg_onig_match(re, str, reg_onig_search, &args, regs);
+    OnigPosition result = rb_reg_onig_match(re, str, reg_onig_search, &args, &regs);
     if (result == ONIG_MISMATCH) {
         rb_backref_set(Qnil);
         return ONIG_MISMATCH;
     }
 
+    VALUE match = match_alloc(rb_cMatch);
+    rb_matchext_t *rm = RMATCH_EXT(match);
+    rm->regs = regs;
+
     if (set_backref_str) {
         RB_OBJ_WRITE(match, &RMATCH(match)->str, rb_str_new4(str));
     }

test/ruby/test_regexp.rb

@@ -711,6 +711,18 @@ class TestRegexp < Test::Unit::TestCase
     }
   end
 
+  def test_match_no_match_no_matchdata
+    EnvUtil.without_gc do
+      h = {}
+      ObjectSpace.count_objects(h)
+      prev_matches = h[:T_MATCH] || 0
+      md = /[A-Z]/.match('1') # no match
+      ObjectSpace.count_objects(h)
+      new_matches = h[:T_MATCH] || 0
+      assert_equal prev_matches, new_matches, "Bug [#20104]"
+    end
+  end
+
   def test_initialize
     assert_raise(ArgumentError) { Regexp.new }
     assert_equal(/foo/, assert_warning(/ignored/) {Regexp.new(/foo/, Regexp::IGNORECASE)})

tool/lib/envutil.rb

@@ -254,6 +254,14 @@ module EnvUtil
   end
   module_function :under_gc_compact_stress
 
+  def without_gc
+    prev_disabled = GC.disable
+    yield
+  ensure
+    GC.enable unless prev_disabled
+  end
+  module_function :without_gc
+
   def with_default_external(enc)
     suppress_warning { Encoding.default_external = enc }
     yield