nobu	2018-07-06 17:01:58 +0900 (Fri, 06 Jul 2018)

  New Revision: 63870

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=63870

  Log:
    compile.c: remove unreachable jump only
    
    * compile.c (iseq_peephole_optimize): remove unreachable jump
      instruction only.  if it is labeled and referred from other
      instructions, it is reachable and must not be removed.
      [ruby-core:87830] [Bug #14897]

  Modified files:
    trunk/compile.c
    trunk/test/ruby/test_optimization.rb
Index: compile.c
===================================================================
--- compile.c	(revision 63869)
+++ compile.c	(revision 63870)
@@ -2730,12 +2730,13 @@ iseq_peephole_optimize(rb_iseq_t *iseq, https://github.com/ruby/ruby/blob/trunk/compile.c#L2730
 	    ELEM_INSERT_NEXT(&dniobj->link, &pop->link);
 	    goto again;
 	}
-	else if (IS_INSN(iobj->link.prev) &&
-                 (piobj = (INSN *)iobj->link.prev) &&
+	else if ((piobj = (INSN *)get_prev_insn(iobj)) != 0 &&
 		 (IS_INSN_ID(piobj, branchif) ||
 		  IS_INSN_ID(piobj, branchunless))) {
 	    INSN *pdiobj = (INSN *)get_destination_insn(piobj);
 	    if (niobj == pdiobj) {
+		int refcnt = IS_LABEL(piobj->link.next) ?
+		    ((LABEL *)piobj->link.next)->refcnt : 0;
 		/*
 		 * useless jump elimination (if/unless destination):
 		 *   if   L1
@@ -2753,7 +2754,12 @@ iseq_peephole_optimize(rb_iseq_t *iseq, https://github.com/ruby/ruby/blob/trunk/compile.c#L2754
 		piobj->insn_id = (IS_INSN_ID(piobj, branchif))
 		  ? BIN(branchunless) : BIN(branchif);
 		replace_destination(piobj, iobj);
-		ELEM_REMOVE(&iobj->link);
+		if (refcnt <= 1) {
+		    ELEM_REMOVE(&iobj->link);
+		}
+		else {
+		    /* TODO: replace other branch destinations too */
+		}
 		return COMPILE_OK;
 	    }
 	    else if (diobj == pdiobj) {
Index: test/ruby/test_optimization.rb
===================================================================
--- test/ruby/test_optimization.rb	(revision 63869)
+++ test/ruby/test_optimization.rb	(revision 63870)
@@ -771,4 +771,17 @@ class TestRubyOptimization < Test::Unit: https://github.com/ruby/ruby/blob/trunk/test/ruby/test_optimization.rb#L771
       tap {true || tap {}}
     end;
   end
+
+  def test_jump_elimination_with_optimized_out_block
+    x = Object.new
+    def x.bug(obj)
+      if obj || obj
+        obj = obj
+      else
+        raise "[ruby-core:87830] [Bug #14897]"
+      end
+      obj
+    end
+    assert_equal(:ok, x.bug(:ok))
+  end
 end

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