8371716: C2: Phi node fails Value()'s verification when speculative types clash

src/hotspot/share/opto/cfgnode.cpp

@@ -1351,6 +1351,82 @@ const Type* PhiNode::Value(PhaseGVN* phase) const {
   }
 #endif //ASSERT
 
+
+  // In rare cases, `_type` and `t` have incompatible opinion on speculative type, resulting into a too small intersection
+  // (such as AnyNull), which is removed in cleanup_speculative. From that `ft` has empty speculative type. After the end
+  // of the current `Value` call, `ft` (that is returned) is becoming `_type`. If verification happens then, `t` would be the
+  // same (union of input types), but the new `_type` has now no speculative type, the result of `t->filter_speculative(_type)`
+  // has the speculative type of `t` (if it's not removed because e.g. the resulting type is exact and non null) and not empty
+  // (like the previously returned type). In such a case, doing the filtering one time more allows to reach a fixpoint.
+  if (ft->speculative() == nullptr && t->speculative() != nullptr) {
+    const Type* first_ft = ft;
+    ft = t->filter_speculative(first_ft);
+#ifdef ASSERT
+    // The following logic has been moved into TypeOopPtr::filter.
+    const Type* jt = t->join_speculative(first_ft);
+    if (jt->empty()) {           // Emptied out???
+      // Otherwise it's something stupid like non-overlapping int ranges
+      // found on dying counted loops.
+      assert(ft == Type::TOP, ""); // Canonical empty value
+    }
+
+    else {
+
+      if (jt != ft && jt->base() == ft->base()) {
+        if (jt->isa_int() &&
+            jt->is_int()->_lo == ft->is_int()->_lo &&
+            jt->is_int()->_hi == ft->is_int()->_hi)
+          jt = ft;
+        if (jt->isa_long() &&
+            jt->is_long()->_lo == ft->is_long()->_lo &&
+            jt->is_long()->_hi == ft->is_long()->_hi)
+          jt = ft;
+      }
+      if (jt != ft) {
+        tty->print("merge type:  "); t->dump(); tty->cr();
+        tty->print("kill type:   "); _type->dump(); tty->cr();
+        tty->print("join type:   "); jt->dump(); tty->cr();
+        tty->print("filter type: "); ft->dump(); tty->cr();
+      }
+      assert(jt == ft, "");
+    }
+#endif //ASSERT
+  }
+
+#ifdef ASSERT
+  const Type* ft_ = t->filter_speculative(ft);
+  if (!Type::equals(ft, ft_)) {
+    stringStream ss;
+
+    for (uint i = 1; i < req(); ++i) {
+      ss.print("in(%d): ", i);
+      if (r->in(i) && phase->type(r->in(i)) == Type::CONTROL) {
+        const Type* ti = phase->type(in(i));
+        ti->dump_on(&ss);
+      }
+      ss.print_cr("");
+    }
+
+    ss.print("t: ");
+    t->dump_on(&ss);
+    ss.print_cr("");
+
+    ss.print("_type: ");
+    _type->dump_on(&ss);
+    ss.print_cr("");
+
+    ss.print("Filter once: ");
+    ft->dump_on(&ss);
+    ss.print_cr("");
+    ss.print("Filter twice: ");
+    ft_->dump_on(&ss);
+    ss.print_cr("");
+    tty->print("%s", ss.base());
+    tty->flush();
+    assert(false, "computed type would not pass verification");
+  }
+#endif
+
   // Deal with conversion problems found in data loops.
   ft = phase->saturate_and_maybe_push_to_igvn_worklist(this, ft);
   return ft;

test/hotspot/jtreg/compiler/igvn/ClashingSpeculativeTypePhiNode.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2025, Red Hat, Inc.
+ * Copyright (c) 2025, 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.
+ */
+
+/**
+ * @test
+ * @bug 8371716
+ * @summary Ranges can be proven to be disjoint but not orderable (thanks to unsigned range)
+ *          Comparing such values in such range with != should always be true.
+ * @run main/othervm -XX:-TieredCompilation
+ *                   -XX:-UseOnStackReplacement
+ *                   -XX:-BackgroundCompilation
+ *                   -XX:CompileOnly=compiler.igvn.ClashingSpeculativeTypePhiNode::test1
+ *                   -XX:CompileCommand=quiet
+ *                   -XX:TypeProfileLevel=222
+ *                   -XX:+AlwaysIncrementalInline
+ *                   -XX:VerifyIterativeGVN=10
+ *                   -XX:CompileCommand=dontinline,compiler.igvn.ClashingSpeculativeTypePhiNode::notInlined1
+ *                   compiler.igvn.ClashingSpeculativeTypePhiNode
+ *
+ * @run main compiler.igvn.ClashingSpeculativeTypePhiNode
+ */
+
+package compiler.igvn;
+
+public class ClashingSpeculativeTypePhiNode {
+    public static void main(String[] args) {
+        for (int i = 0; i < 20_000; i++) {
+            test1(false);
+            inlined1(true, true);
+            inlined2(false);
+        }
+    }
+
+    private static Object test1(boolean flag1) {
+        return inlined1(flag1, false);
+    }
+
+    private static Object inlined1(boolean flag1, boolean flag2) {
+        if (flag1) {
+            return inlined2(flag2); // C1
+        }
+        return null;
+    }
+
+    private static Object inlined2(boolean flag2) {
+        if (flag2) {
+            return new C1();
+        }
+        return notInlined1(); // C2
+    }
+
+    private static Object notInlined1() {
+        return new C2();
+    }
+
+    static class C1 {
+
+    }
+
+    static class C2 {
+
+    }
+}