From 6e64d4370456190541705ec4c6cf3af6bf4ac647 Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Wed, 6 Sep 2023 00:44:35 +0900
Subject: [PATCH] [Bug #19862] Skip compiled result of never reachable
 expression

---
 compile.c              | 28 ++++++++++++++++++++--------
 test/ruby/test_iseq.rb | 11 +++++++++++
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/compile.c b/compile.c
index 86797cb793..6144ab4472 100644
--- a/compile.c
+++ b/compile.c
@@ -4154,9 +4154,10 @@ compile_flip_flop(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const nod
 }
 
 static int
-compile_branch_condition(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *cond,
+compile_branch_condition(rb_iseq_t *iseq, LINK_ANCHOR *ret, const NODE *cond,
                          LABEL *then_label, LABEL *else_label);
 
+#define COMPILE_SINGLE 2
 static int
 compile_logical(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *cond,
                 LABEL *then_label, LABEL *else_label)
@@ -4175,28 +4176,39 @@ compile_logical(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *cond,
             return COMPILE_OK;
     }
     if (!label->refcnt) {
-        ADD_INSN(seq, cond, putnil);
-    }
-    else {
-        ADD_LABEL(seq, label);
+        return COMPILE_SINGLE;
     }
+    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,
+compile_branch_condition(rb_iseq_t *iseq, LINK_ANCHOR *ret, const NODE *cond,
                          LABEL *then_label, LABEL *else_label)
 {
+    int ok;
+    DECL_ANCHOR(ignore);
+
   again:
     switch (nd_type(cond)) {
       case NODE_AND:
-        CHECK(compile_logical(iseq, ret, cond->nd_1st, NULL, else_label));
+        CHECK(ok = compile_logical(iseq, ret, cond->nd_1st, NULL, else_label));
         cond = cond->nd_2nd;
+        if (ok == COMPILE_SINGLE) {
+            INIT_ANCHOR(ignore);
+            ret = ignore;
+            then_label = NEW_LABEL(nd_line(cond));
+        }
         goto again;
       case NODE_OR:
-        CHECK(compile_logical(iseq, ret, cond->nd_1st, then_label, NULL));
+        CHECK(ok = compile_logical(iseq, ret, cond->nd_1st, then_label, NULL));
         cond = cond->nd_2nd;
+        if (ok == COMPILE_SINGLE) {
+            INIT_ANCHOR(ignore);
+            ret = ignore;
+            else_label = NEW_LABEL(nd_line(cond));
+        }
         goto again;
       case NODE_LIT:		/* NODE_LIT is always true */
       case NODE_TRUE:
diff --git a/test/ruby/test_iseq.rb b/test/ruby/test_iseq.rb
index 4ff808418f..0af29d9f32 100644
--- a/test/ruby/test_iseq.rb
+++ b/test/ruby/test_iseq.rb
@@ -770,4 +770,15 @@ class TestISeq < Test::Unit::TestCase
     assert_syntax_error("false and break", mesg)
     assert_syntax_error("if false and break; end", mesg)
   end
+
+  def test_unreachable_pattern_matching
+    assert_in_out_err([], "#{<<~"begin;"}\n#{<<~'end;'}", %w[1])
+    begin;
+      if true or {a: 0} in {a:}
+        p 1
+      else
+        p 0
+      end
+    end;
+  end
 end