[Bug #19611] Remove never-reachable branch in logical expression

compile.c

@@ -4252,6 +4252,37 @@ compile_flip_flop(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const nod
     return COMPILE_OK;
 }
 
+static int
+compile_branch_condition(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *cond,
+                         LABEL *then_label, LABEL *else_label);
+
+static int
+compile_logical(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *cond,
+                LABEL *then_label, LABEL *else_label)
+{
+    DECL_ANCHOR(seq);
+    INIT_ANCHOR(seq);
+    LABEL *label = NEW_LABEL(nd_line(cond));
+    if (!then_label) then_label = label;
+    else if (!else_label) else_label = label;
+
+    CHECK(compile_branch_condition(iseq, seq, cond, then_label, else_label));
+
+    if (LIST_INSN_SIZE_ONE(seq)) {
+        INSN *insn = (INSN *)ELEM_FIRST_INSN(FIRST_ELEMENT(seq));
+        if (insn->insn_id == BIN(jump) && (LABEL *)(insn->operands[0]) == label)
+            return COMPILE_OK;
+    }
+    if (!label->refcnt) {
+        ADD_INSN(seq, cond, putnil);
+    }
+    else {
+        ADD_LABEL(seq, label);
+    }
+    ADD_SEQ(ret, seq);
+    return COMPILE_OK;
+}
+
 static int
 compile_branch_condition(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *cond,
                          LABEL *then_label, LABEL *else_label)
@@ -4259,31 +4290,13 @@ compile_branch_condition(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *co
   again:
     switch (nd_type(cond)) {
       case NODE_AND:
-        {
-            LABEL *label = NEW_LABEL(nd_line(cond));
-            CHECK(compile_branch_condition(iseq, ret, cond->nd_1st, label,
-                                           else_label));
-            if (!label->refcnt) {
-                ADD_INSN(ret, cond, putnil);
-                break;
-            }
-            ADD_LABEL(ret, label);
-            cond = cond->nd_2nd;
-            goto again;
-        }
+        CHECK(compile_logical(iseq, ret, cond->nd_1st, NULL, else_label));
+        cond = cond->nd_2nd;
+        goto again;
       case NODE_OR:
-        {
-            LABEL *label = NEW_LABEL(nd_line(cond));
-            CHECK(compile_branch_condition(iseq, ret, cond->nd_1st, then_label,
-                                           label));
-            if (!label->refcnt) {
-                ADD_INSN(ret, cond, putnil);
-                break;
-            }
-            ADD_LABEL(ret, label);
-            cond = cond->nd_2nd;
-            goto again;
-        }
+        CHECK(compile_logical(iseq, ret, cond->nd_1st, then_label, NULL));
+        cond = cond->nd_2nd;
+        goto again;
       case NODE_LIT:		/* NODE_LIT is always true */
       case NODE_TRUE:
       case NODE_STR:

test/ruby/test_iseq.rb

@@ -759,4 +759,14 @@ class TestISeq < Test::Unit::TestCase
       assert_equal :new, r.take
     RUBY
   end
+
+  def test_ever_condition_loop
+    assert_ruby_status([], "BEGIN {exit}; while true && true; end")
+  end
+
+  def test_unreachable_syntax_error
+    mesg = /Invalid break/
+    assert_syntax_error("false and break", mesg)
+    assert_syntax_error("if false and break; end", mesg)
+  end
 end