8322854: Incorrect rematerialization of scalar replaced objects in C2

Reviewed-by: kvn, thartmann

src/hotspot/share/opto/macro.cpp

@@ -167,7 +167,8 @@ void PhaseMacroExpand::eliminate_gc_barrier(Node* p2x) {
 // Search for a memory operation for the specified memory slice.
 static Node *scan_mem_chain(Node *mem, int alias_idx, int offset, Node *start_mem, Node *alloc, PhaseGVN *phase) {
   Node *orig_mem = mem;
-  Node *alloc_mem = alloc->in(TypeFunc::Memory);
+  Node *alloc_mem = alloc->as_Allocate()->proj_out_or_null(TypeFunc::Memory, /*io_use:*/false);
+  assert(alloc_mem != nullptr, "Allocation without a memory projection.");
   const TypeOopPtr *tinst = phase->C->get_adr_type(alias_idx)->isa_oopptr();
   while (true) {
     if (mem == alloc_mem || mem == start_mem ) {
@@ -371,7 +372,8 @@ Node *PhaseMacroExpand::value_from_mem_phi(Node *mem, BasicType ft, const Type *
     return nullptr; // Give up: phi tree too deep
   }
   Node *start_mem = C->start()->proj_out_or_null(TypeFunc::Memory);
-  Node *alloc_mem = alloc->in(TypeFunc::Memory);
+  Node *alloc_mem = alloc->proj_out_or_null(TypeFunc::Memory, /*io_use:*/false);
+  assert(alloc_mem != nullptr, "Allocation without a memory projection.");
 
   uint length = mem->req();
   GrowableArray <Node *> values(length, length, nullptr);
@@ -456,7 +458,8 @@ Node *PhaseMacroExpand::value_from_mem(Node *sfpt_mem, Node *sfpt_ctl, BasicType
   int offset = adr_t->offset();
   Node *start_mem = C->start()->proj_out_or_null(TypeFunc::Memory);
   Node *alloc_ctrl = alloc->in(TypeFunc::Control);
-  Node *alloc_mem = alloc->in(TypeFunc::Memory);
+  Node *alloc_mem = alloc->proj_out_or_null(TypeFunc::Memory, /*io_use:*/false);
+  assert(alloc_mem != nullptr, "Allocation without a memory projection.");
   VectorSet visited;
 
   bool done = sfpt_mem == alloc_mem;

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

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2024, 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 8322854
+ * @summary Check that the RAM optimization works when there is a memory loop.
+ * @library /test/lib /
+ * @requires vm.compiler2.enabled
+ * @run main/othervm -XX:CompileCommand=compileonly,*TestReduceAllocationAndMemoryLoop*::test*
+ *                   -XX:-TieredCompilation -Xbatch
+ *                   compiler.c2.TestReduceAllocationAndMemoryLoop
+ */
+
+package compiler.c2;
+
+public class TestReduceAllocationAndMemoryLoop {
+    public static void main(String[] args) throws Exception {
+        // Warmup
+        for (int i = 0; i < 50_000; ++i) {
+            test(false, 10);
+        }
+
+        // Trigger deoptimization
+        MyClass obj = test(false, 11);
+        if (obj.val != 42) {
+            throw new RuntimeException("Test failed, val = " + obj.val);
+        }
+    }
+
+    static class MyClass {
+        final int val;
+
+        public MyClass(int val) {
+            this.val = val;
+        }
+    }
+
+    public static MyClass test(boolean alwaysFalse, int limit) {
+        for (int i = 0; ; ++i) {
+            MyClass obj = new MyClass(42);
+            if (alwaysFalse || i > 10) {
+                return obj;
+            }
+            if (i == limit) {
+              return null;
+            }
+        }
+    }
+}