8370200: Crash: assert(outer->outcnt() >= phis + 2 - be_loads && outer->outcnt() <= phis + 2 + stores + 1) failed: only phis

Reviewed-by: rcastanedalo, dlunden, dfenacci

Author: rwestrel

src/hotspot/share/opto/cfgnode.cpp

@@ -1547,18 +1547,9 @@ Node* PhiNode::Identity(PhaseGVN* phase) {
     Node* phi_reg = region();
     for (DUIterator_Fast imax, i = phi_reg->fast_outs(imax); i < imax; i++) {
       Node* u = phi_reg->fast_out(i);
-      if (u->is_Phi() && u->as_Phi()->type() == Type::MEMORY &&
-          u->adr_type() == TypePtr::BOTTOM && u->in(0) == phi_reg &&
-          u->req() == phi_len) {
-        for (uint j = 1; j < phi_len; j++) {
-          if (in(j) != u->in(j)) {
-            u = nullptr;
-            break;
-          }
-        }
-        if (u != nullptr) {
-          return u;
-        }
+      assert(!u->is_Phi() || u->in(0) == phi_reg, "broken Phi/Region subgraph");
+      if (u->is_Phi() && u->req() == phi_len && can_be_replaced_by(u->as_Phi())) {
+        return u;
       }
     }
   }
@@ -2790,6 +2781,25 @@ Node *PhiNode::Ideal(PhaseGVN *phase, bool can_reshape) {
     progress = merge_through_phi(this, phase->is_IterGVN());
   }
 
+  // PhiNode::Identity replaces a non-bottom memory phi with a bottom memory phi with the same inputs, if it exists.
+  // If the bottom memory phi's inputs are changed (so it can now replace the non-bottom memory phi) or if it's created
+  // only after the non-bottom memory phi is processed by igvn, PhiNode::Identity doesn't run and the transformation
+  // doesn't happen.
+  // Look for non-bottom Phis that should be transformed and enqueue them for igvn so that PhiNode::Identity executes for
+  // them.
+  if (can_reshape && type() == Type::MEMORY && adr_type() == TypePtr::BOTTOM) {
+    PhaseIterGVN* igvn = phase->is_IterGVN();
+    uint phi_len = req();
+    Node* phi_reg = region();
+    for (DUIterator_Fast imax, i = phi_reg->fast_outs(imax); i < imax; i++) {
+      Node* u = phi_reg->fast_out(i);
+      assert(!u->is_Phi() || (u->in(0) == phi_reg && u->req() == phi_len), "broken Phi/Region subgraph");
+      if (u->is_Phi() && u->as_Phi()->can_be_replaced_by(this)) {
+        igvn->_worklist.push(u);
+      }
+    }
+  }
+
   return progress;              // Return any progress
 }
 
@@ -2839,6 +2849,11 @@ const TypeTuple* PhiNode::collect_types(PhaseGVN* phase) const {
   return TypeTuple::make(types.length(), flds);
 }
 
+bool PhiNode::can_be_replaced_by(const PhiNode* other) const {
+  return type() == Type::MEMORY && other->type() == Type::MEMORY && adr_type() != TypePtr::BOTTOM &&
+    other->adr_type() == TypePtr::BOTTOM && has_same_inputs_as(other);
+}
+
 Node* PhiNode::clone_through_phi(Node* root_phi, const Type* t, uint c, PhaseIterGVN* igvn) {
   Node_Stack stack(1);
   VectorSet  visited;

src/hotspot/share/opto/cfgnode.hpp

@@ -274,6 +274,7 @@ class PhiNode : public TypeNode {
 #endif //ASSERT
 
   const TypeTuple* collect_types(PhaseGVN* phase) const;
+  bool can_be_replaced_by(const PhiNode* other) const;
 };
 
 //------------------------------GotoNode---------------------------------------

src/hotspot/share/opto/node.cpp

@@ -2879,23 +2879,26 @@ Node* Node::find_similar(int opc) {
         Node* use = def->fast_out(i);
         if (use != this &&
             use->Opcode() == opc &&
-            use->req() == req()) {
-          uint j;
-          for (j = 0; j < use->req(); j++) {
-            if (use->in(j) != in(j)) {
-              break;
-            }
-          }
-          if (j == use->req()) {
-            return use;
-          }
+            use->req() == req() &&
+            has_same_inputs_as(use)) {
+          return use;
         }
       }
     }
   }
   return nullptr;
 }
 
+bool Node::has_same_inputs_as(const Node* other) const {
+  assert(req() == other->req(), "should have same number of inputs");
+  for (uint j = 0; j < other->req(); j++) {
+    if (in(j) != other->in(j)) {
+      return false;
+    }
+  }
+  return true;
+}
+
 Node* Node::unique_multiple_edges_out_or_null() const {
   Node* use = nullptr;
   for (DUIterator_Fast kmax, k = fast_outs(kmax); k < kmax; k++) {

src/hotspot/share/opto/node.hpp

@@ -1179,6 +1179,7 @@ class Node {
   // Return a node with opcode "opc" and same inputs as "this" if one can
   // be found; Otherwise return null;
   Node* find_similar(int opc);
+  bool has_same_inputs_as(const Node* other) const;
 
   // Return the unique control out if only one. Null if none or more than one.
   Node* unique_ctrl_out_or_null() const;

test/hotspot/jtreg/compiler/c2/TestReplaceNarrowPhiWithBottomPhi.java

@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2025 IBM Corporation. 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 8370200
+ * @library /test/lib /
+ * @run driver ${test.main.class}
+ */
+
+package compiler.c2;
+
+import compiler.lib.ir_framework.*;
+import compiler.lib.ir_framework.Test;
+
+public class TestReplaceNarrowPhiWithBottomPhi {
+    private int field1;
+    private volatile int field2;
+
+    static public void main(String[] args) {
+        TestFramework.run();
+    }
+
+    @Test
+    @IR(counts = { IRNode.PHI, "2" })
+    public void test1() {
+        int j;
+        for (j = 0; j < 10; j++) {
+
+        }
+        inlined1(j);
+
+        // Initially, there are 2 memory Phis: one for bottom, one for field1. After loop opts, both
+        // Phis have the same inputs and the narrower Phi should be replaced by the bottom Phi.
+        for (int i = 1; i < 100; i *= 2) {
+            field2 = 42;
+        }
+    }
+
+    private void inlined1(int j) {
+        if (j == 42) {
+            field1 = 42;
+        }
+    }
+
+    @Run(test = "test1")
+    private void test1Runner() {
+        test1();
+        inlined1(42);
+    }
+}

test/hotspot/jtreg/compiler/loopstripmining/TestMismatchedMemoryPhis.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2025 IBM Corporation. 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 8370200
+ * @summary Crash: assert(outer->outcnt() >= phis + 2 - be_loads && outer->outcnt() <= phis + 2 + stores + 1) failed: only phis
+ * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:+UnlockDiagnosticVMOptions -XX:StressSeed=36200582 -XX:CompileCommand=quiet
+ *                   -XX:CompileCommand=compileonly,*TestMismatchedMemoryPhis*::mainTest -XX:-TieredCompilation
+ *                   -Xcomp -XX:+StressIGVN -XX:+StressLoopPeeling -XX:PerMethodTrapLimit=0 ${test.main.class}
+ * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:+UnlockDiagnosticVMOptions -XX:CompileCommand=quiet
+ *                   -XX:CompileCommand=compileonly,*TestMismatchedMemoryPhis*::mainTest -XX:-TieredCompilation
+ *                   -Xcomp -XX:+StressIGVN -XX:+StressLoopPeeling -XX:PerMethodTrapLimit=0 ${test.main.class}
+ * @run main ${test.main.class}
+ */
+
+package compiler.loopstripmining;
+
+public class TestMismatchedMemoryPhis {
+    long l;
+    volatile int iArrFld[];
+
+    void mainTest() {
+        int i, i1, i15 = 4, i16 = 4;
+        for (i = 1; i < 7; ++i) {
+            l = i;
+        }
+        int j = 1;
+        while (++j < 4) {
+            try {
+                i1 = i15 % i16;
+                i16 = i15;
+                i1 = 0 % iArrFld[j];
+            } catch (ArithmeticException a_e) {
+            }
+        }
+    }
+
+    static public void main(String[] args) {
+        try {
+            new TestMismatchedMemoryPhis().mainTest();
+        } catch (NullPointerException npe) {
+            // Expected
+        }
+    }
+}