merge revision(s) a6a26e42b15c46f117f4fce07a2050e9d727355d: [Backport #15906]

compile.c: Partially revert r63870 which caused wrong optimization
	[Bug #15906]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@67757 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

compile.c

@@ -2513,7 +2513,8 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
 	    ELEM_INSERT_NEXT(&iobj->link, &pop->link);
 	    goto again;
 	}
-	else if ((piobj = (INSN *)get_prev_insn(iobj)) != 0 &&
+        else if (IS_INSN(iobj->link.prev) &&
+                 (piobj = (INSN *)iobj->link.prev) &&
 		 (IS_INSN_ID(piobj, branchif) ||
 		  IS_INSN_ID(piobj, branchunless))) {
 	    INSN *pdiobj = (INSN *)get_destination_insn(piobj);

test/ruby/test_optimization.rb

@@ -755,6 +755,21 @@ class TestRubyOptimization < Test::Unit::TestCase
     assert_equal(:ok, x.bug(:ok))
   end
 
+  def test_jump_elimination_with_optimized_out_block_2
+    x = Object.new
+    def x.bug
+      a = "aaa"
+      ok = :NG
+      if a == "bbb" || a == "ccc" then
+        a = a
+      else
+        ok = :ok
+      end
+      ok
+    end
+    assert_equal(:ok, x.bug)
+  end
+
   def test_peephole_jump_after_newarray
     i = 0
     %w(1) || 2 while (i += 1) < 100

version.h

@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.5.6"
 #define RUBY_RELEASE_DATE "2019-08-26"
-#define RUBY_PATCHLEVEL 176
+#define RUBY_PATCHLEVEL 177
 
 #define RUBY_RELEASE_YEAR 2019
 #define RUBY_RELEASE_MONTH 8