From 3e95fb90fa6e4d10ca6d0de7fe16ba841939f002 Mon Sep 17 00:00:00 2001
From: katkerem <katkerem@amazon.com>
Date: Fri, 16 Jan 2026 12:33:47 +0000
Subject: [PATCH] 8374903: C2 VectorAPI: assert(vbox->as_Phi()->region() ==
 vect->as_Phi()->region()) failed

---
 src/hotspot/share/opto/vector.cpp             |  4 +-
 .../vectorapi/VectorBoxExpandPhi.java         | 50 +++++++++++++++++++
 2 files changed, 52 insertions(+), 2 deletions(-)
 create mode 100644 test/hotspot/jtreg/compiler/vectorapi/VectorBoxExpandPhi.java

diff --git a/src/hotspot/share/opto/vector.cpp b/src/hotspot/share/opto/vector.cpp
index 54aa1ca3812..f44df7e6da2 100644
--- a/src/hotspot/share/opto/vector.cpp
+++ b/src/hotspot/share/opto/vector.cpp
@@ -332,9 +332,9 @@ Node* PhaseVector::expand_vbox_node_helper(Node* vbox,
   // The vector input may also be a Phi (Phi2 above), or it may have been
   // value-numbered to a single node if all inputs were identical.
   if (vbox->is_Phi()) {
-    assert(!vect->is_Phi() || vbox->as_Phi()->region() == vect->as_Phi()->region(), "");
+    bool same_region = vect->is_Phi() && vbox->as_Phi()->region() == vect->as_Phi()->region();
     for (uint i = 1; i < vbox->req(); i++) {
-      Node* new_box = expand_vbox_node_helper(vbox->in(i), vect->is_Phi() ? vect->in(i) : vect,
+      Node* new_box = expand_vbox_node_helper(vbox->in(i), same_region ? vect->in(i) : vect,
                                               box_type, vect_type, visited);
       if (!new_box->is_Phi()) {
         C->initial_gvn()->hash_delete(vbox);
diff --git a/test/hotspot/jtreg/compiler/vectorapi/VectorBoxExpandPhi.java b/test/hotspot/jtreg/compiler/vectorapi/VectorBoxExpandPhi.java
new file mode 100644
index 00000000000..936d24e4767
--- /dev/null
+++ b/test/hotspot/jtreg/compiler/vectorapi/VectorBoxExpandPhi.java
@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2026, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package compiler.vectorapi;
+
+import jdk.incubator.vector.*;
+
+/*
+ * @test
+ * @bug 8374903
+ * @summary C2 crashes when VectorBox Phi and vector Phi have different regions
+ * @modules jdk.incubator.vector
+ * @library /test/lib
+ *
+ * @run main/othervm -Xbatch -XX:CompileCommand=compileonly,compiler.vectorapi.VectorBoxExpandPhi::test compiler.vectorapi.VectorBoxExpandPhi
+ */
+public class VectorBoxExpandPhi {
+    public static void main(String[] args) {
+        for (int i = 0; i < 10_000; i++) {
+            test();
+        }
+    }
+
+    public static Object test() {
+        var v0 = DoubleVector.broadcast(DoubleVector.SPECIES_128, 1.0);
+        var v1 = (FloatVector)v0.convertShape(VectorOperators.Conversion.ofCast(double.class, float.class), FloatVector.SPECIES_64, 0);
+        var v2 = (FloatVector)v1.convertShape(VectorOperators.Conversion.ofReinterpret(float.class, float.class), FloatVector.SPECIES_64, 0);
+        return v2;
+    }
+}