diff --git a/src/hotspot/share/opto/cfgnode.cpp b/src/hotspot/share/opto/cfgnode.cpp
index 4cf080a2e196a..73c57a1ceb80a 100644
--- a/src/hotspot/share/opto/cfgnode.cpp
+++ b/src/hotspot/share/opto/cfgnode.cpp
@@ -2573,11 +2573,10 @@ Node *PhiNode::Ideal(PhaseGVN *phase, bool can_reshape) {
igvn->replace_node(this, result);
igvn->set_type(result, result->bottom_type());
- // now transform the new nodes, and return the mergemem
- for (MergeMemStream mms(result); mms.next_non_empty(); ) {
- Node* phi = mms.memory();
- mms.set_memory(phase->transform(phi));
- }
+ // We could immediately transform the new Phi nodes here, but that can
+ // result in creating an excessive number of new nodes within a single
+ // IGVN iteration. We have put the Phi nodes on the IGVN worklist, so
+ // they are transformed later on in any case.
hook->destruct(igvn);
// Replace self with the result.
return result;
diff --git a/src/hotspot/share/opto/phaseX.cpp b/src/hotspot/share/opto/phaseX.cpp
index ad6d8b4112f53..28dae5ca41c10 100644
--- a/src/hotspot/share/opto/phaseX.cpp
+++ b/src/hotspot/share/opto/phaseX.cpp
@@ -1024,11 +1024,18 @@ void PhaseIterGVN::optimize() {
shuffle_worklist();
}
+ // The node count check in the loop below (check_node_count) assumes that we
+ // increase the live node count with at most
+ // max_live_nodes_increase_per_iteration in between checks. If this
+ // assumption does not hold, there is a risk that we exceed the max node
+ // limit in between checks and trigger an assert during node creation.
+ const int max_live_nodes_increase_per_iteration = NodeLimitFudgeFactor * 2;
+
uint loop_count = 0;
// Pull from worklist and transform the node. If the node has changed,
// update edge info and put uses on worklist.
while(_worklist.size()) {
- if (C->check_node_count(NodeLimitFudgeFactor * 2, "Out of nodes")) {
+ if (C->check_node_count(max_live_nodes_increase_per_iteration, "Out of nodes")) {
C->print_method(PHASE_AFTER_ITER_GVN, 3);
return;
}
@@ -1043,7 +1050,16 @@ void PhaseIterGVN::optimize() {
if (n->outcnt() != 0) {
NOT_PRODUCT(const Type* oldtype = type_or_null(n));
// Do the transformation
+ DEBUG_ONLY(int live_nodes_before = C->live_nodes();)
Node* nn = transform_old(n);
+ DEBUG_ONLY(int live_nodes_after = C->live_nodes();)
+ // Ensure we did not increase the live node count with more than
+ // max_live_nodes_increase_per_iteration during the call to transform_old
+ DEBUG_ONLY(int increase = live_nodes_after - live_nodes_before;)
+ assert(increase < max_live_nodes_increase_per_iteration,
+ "excessive live node increase in single iteration of IGVN: %d "
+ "(should be at most %d)",
+ increase, max_live_nodes_increase_per_iteration);
NOT_PRODUCT(trace_PhaseIterGVN(n, nn, oldtype);)
} else if (!n->is_top()) {
remove_dead_node(n);
diff --git a/test/hotspot/jtreg/TEST.groups b/test/hotspot/jtreg/TEST.groups
index 71b9e497e25c5..5a4db43d4ec7f 100644
--- a/test/hotspot/jtreg/TEST.groups
+++ b/test/hotspot/jtreg/TEST.groups
@@ -184,6 +184,7 @@ tier1_compiler_2 = \
compiler/integerArithmetic/ \
compiler/interpreter/ \
compiler/jvmci/ \
+ compiler/itergvn/ \
-compiler/classUnloading/methodUnloading/TestOverloadCompileQueues.java \
-compiler/codecache/stress \
-compiler/codegen/aes \
diff --git a/test/hotspot/jtreg/compiler/itergvn/TestSplitPhiThroughMergeMem.java b/test/hotspot/jtreg/compiler/itergvn/TestSplitPhiThroughMergeMem.java
new file mode 100644
index 0000000000000..8930168be0874
--- /dev/null
+++ b/test/hotspot/jtreg/compiler/itergvn/TestSplitPhiThroughMergeMem.java
@@ -0,0 +1,70 @@
+/*
+ * 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 8351833
+ * @summary Splitting Phi memory nodes through MergeMem nodes in PhiNode::Ideal
+ * could sometimes result in a too large number of added nodes within
+ * a single iteration of the main loop in PhaseIterGVN::optimize. This
+ * test, reduced from TestScalarReplacementMaxLiveNodes, triggers an
+ * assert added as part of the fix for the linked bug/issue (the
+ * assert naturally triggers only before the fix). The test's ability
+ * to trigger the issue is quite sensitive to the specific String
+ * constants used. The current set of chosen String constants happened
+ * to work particularly well.
+ * @run main/othervm -Xbatch
+ * -XX:CompileCommand=CompileOnly,compiler.itergvn.TestSplitPhiThroughMergeMem::test
+ * compiler.itergvn.TestSplitPhiThroughMergeMem
+ * @run main compiler.itergvn.TestSplitPhiThroughMergeMem
+ */
+
+package compiler.itergvn;
+
+public class TestSplitPhiThroughMergeMem {
+
+ public static void main(String[] args) {
+ for (int i = 0; i < 10_000; i++) {
+ int val = i % 50;
+ test(val == 0, val % 10, val % 20);
+ }
+ }
+
+ static void test(boolean flag, int param1, int param2) {
+ if (flag) {
+ new String("tenth" + param1);
+ new String("eleventh" + param2);
+ new String("fifteenth" + param2);
+ new String("sixteenth" + param1);
+ new String("seventeenth" + param1);
+ new String("nineteenth" + param2);
+ new String("tweenth" + param1);
+ new String("nineth" + param1);
+ new String("nineth" + param1);
+ new String("eighteenth" + param1);
+ new String("abcdef" + param2);
+ new String("ghijklmn" + param1);
+ new String("ghijklmn" + param1);
+ }
+ }
+}