merge revision(s) 63868,63870: [Backport #14897]

	Fix a bug of peephole optimization

	```
	  if   L1
	L0:
	  jump L2
	L1:
	  ...
	L2:
	```

	was wrongly optimized to:

	```
	  unless L2
	L0:
	L1:
	  ...
	L2:
	```

	To make it conservative, this optimization is now disabled when there is
	any label between `if` and `jump` instructions.
	Fixes [Bug #14897].

	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]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@64893 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 8 insertions, 1 deletions

diff --git a/compile.c b/compile.c
index 2f1e46aaa1..95ba803995 100644
--- a/compile.c
+++ b/compile.c
@@ -2469,6 +2469,8 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
 		  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
@@ -2486,7 +2488,12 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
 		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) {