Fix Regexp#match for GC compaction

The test fails when RGENGC_CHECK_MODE is turned on:

    TestRegexp#test_match_under_gc_compact_stress:
    NoMethodError: undefined method `match' for nil
        test_regexp.rb:878:in `block in test_match_under_gc_compact_stress'

re.c

@@ -1581,7 +1581,6 @@ rb_reg_prepare_re(VALUE re, VALUE str)
 {
     int r;
     OnigErrorInfo einfo;
-    const char *pattern;
     VALUE unescaped;
     rb_encoding *fixed_enc = 0;
     rb_encoding *enc = rb_reg_prepare_enc(re, str, 1);
@@ -1590,11 +1589,13 @@ rb_reg_prepare_re(VALUE re, VALUE str)
     if (reg->enc == enc) return reg;
 
     rb_reg_check(re);
-    pattern = RREGEXP_SRC_PTR(re);
+
+    VALUE src_str = RREGEXP_SRC(re);
+    const char *pattern = RSTRING_PTR(src_str);
 
     onig_errmsg_buffer err = "";
     unescaped = rb_reg_preprocess(
-        pattern, pattern + RREGEXP_SRC_LEN(re), enc,
+        pattern, pattern + RSTRING_LEN(src_str), enc,
         &fixed_enc, err, 0);
 
     if (NIL_P(unescaped)) {
@@ -1639,6 +1640,7 @@ rb_reg_prepare_re(VALUE re, VALUE str)
     reg->timelimit = timelimit;
 
     RB_GC_GUARD(unescaped);
+    RB_GC_GUARD(src_str);
     return reg;
 }
 

test/ruby/test_regexp.rb

@@ -872,6 +872,13 @@ def test_match
     $_ = nil; assert_nil(~/./)
   end
 
+  def test_match_under_gc_compact_stress
+    EnvUtil.under_gc_compact_stress do
+      m = /(?<foo>.)(?<n>[^aeiou])?(?<bar>.+)/.match("hoge\u3042")
+      assert_equal("h", m.match(:foo))
+    end
+  end
+
   def test_match_p
     /backref/ =~ 'backref'
     # must match here, but not in a separate method, e.g., assert_send,