8343067: C2: revisit constant-offset AddP chains after successful input idealizations

Reviewed-by: kvn, vlivanov

src/hotspot/share/opto/phaseX.cpp

@@ -27,6 +27,7 @@
 #include "gc/shared/c2/barrierSetC2.hpp"
 #include "memory/allocation.inline.hpp"
 #include "memory/resourceArea.hpp"
+#include "opto/addnode.hpp"
 #include "opto/block.hpp"
 #include "opto/callnode.hpp"
 #include "opto/castnode.hpp"
@@ -1634,12 +1635,19 @@ void PhaseIterGVN::add_users_of_use_to_worklist(Node* n, Node* use, Unique_Node_
       }
     }
   }
-  // If changed AddP inputs, check Stores for loop invariant
-  if( use_op == Op_AddP ) {
+  // If changed AddP inputs:
+  // - check Stores for loop invariant, and
+  // - if the changed input is the offset, check constant-offset AddP users for
+  //   address expression flattening.
+  if (use_op == Op_AddP) {
+    bool offset_changed = n == use->in(AddPNode::Offset);
     for (DUIterator_Fast i2max, i2 = use->fast_outs(i2max); i2 < i2max; i2++) {
       Node* u = use->fast_out(i2);
-      if (u->is_Mem())
+      if (u->is_Mem()) {
         worklist.push(u);
+      } else if (offset_changed && u->is_AddP() && u->in(AddPNode::Offset)->is_Con()) {
+        worklist.push(u);
+      }
     }
   }
   // If changed initialization activity, check dependent Stores

test/hotspot/jtreg/compiler/c2/irTests/igvn/TestCombineAddPWithConstantOffsets.java

@@ -0,0 +1,56 @@
+/*
+ * 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.
+ */
+package compiler.c2.irTests.igvn;
+
+import compiler.lib.ir_framework.*;
+
+/*
+ * @test
+ * @bug 8343067
+ * @requires os.simpleArch == "x64" | os.simpleArch == "aarch64"
+ * @requires vm.compiler2.enabled
+ * @summary Test that chains of AddP nodes with constant offsets are idealized
+ *          when their offset input changes.
+ * @library /test/lib /
+ * @run driver compiler.c2.irTests.igvn.TestCombineAddPWithConstantOffsets
+ */
+public class TestCombineAddPWithConstantOffsets {
+
+    public static void main(String[] args) {
+        TestFramework.run();
+    }
+
+    @Test
+    @IR(applyIfPlatform = {"x64", "true"}, failOn = {IRNode.ADD_P_OF, ".*"})
+    @IR(applyIfPlatform = {"aarch64", "true"}, failOn = {IRNode.ADD_P_OF, "reg_imm"})
+    static void testCombineAddPWithConstantOffsets(int[] arr) {
+        for (long i = 6; i < 14; i++) {
+            arr[(int)i] = 1;
+        }
+    }
+
+    @Run(test = {"testCombineAddPWithConstantOffsets"})
+    public void runTests() {
+        testCombineAddPWithConstantOffsets(new int[14]);
+    }
+}

test/hotspot/jtreg/compiler/lib/ir_framework/IRNode.java

@@ -279,6 +279,12 @@ public class IRNode {
         superWordNodes(ADD_REDUCTION_VL, "AddReductionVL");
     }
 
+    public static final String ADD_P_OF = COMPOSITE_PREFIX + "ADD_P_OF" + POSTFIX;
+    static {
+        String regex = START + "addP_" + IS_REPLACED + MID + ".*" + END;
+        machOnly(ADD_P_OF, regex);
+    }
+
     public static final String ALLOC = PREFIX + "ALLOC" + POSTFIX;
     static {
         String optoRegex = "(.*precise .*\\R((.*(?i:mov|mv|xorl|nop|spill).*|\\s*)\\R)*.*(?i:call,static).*wrapper for: C2 Runtime new_instance" + END;