8348678: [PPC64] C2: unaligned vector load/store is ok

8343906: test2 of compiler/c2/TestCastX2NotProcessedIGVN.java fails on some platforms

Reviewed-by: mdoerr, amitkumar

Author: reinrich

src/hotspot/cpu/ppc/matcher_ppc.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 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
@@ -37,10 +37,12 @@
     return false;
   }
 
-  // PPC implementation uses VSX load/store instructions (if
-  // SuperwordUseVSX) which support 4 byte but not arbitrary alignment
+  // The PPC implementation uses VSX lxvd2x/stxvd2x instructions (if
+  // SuperwordUseVSX). They do not have alignment requirements.
+  // Some VSX storage access instructions cannot encode arbitrary displacements
+  // (e.g. lxv). None of them is currently used.
   static constexpr bool misaligned_vectors_ok() {
-    return false;
+    return true;
   }
 
   // Whether code generation need accurate ConvI2L types.

src/hotspot/cpu/ppc/vm_version_ppc.cpp

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012, 2024 SAP SE. All rights reserved.
+ * Copyright (c) 2012, 2025 SAP SE. 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
@@ -131,6 +131,9 @@ void VM_Version::initialize() {
     }
   }
   MaxVectorSize = SuperwordUseVSX ? 16 : 8;
+  if (FLAG_IS_DEFAULT(AlignVector)) {
+    FLAG_SET_ERGO(AlignVector, false);
+  }
 
   if (PowerArchitecturePPC64 >= 9) {
     if (FLAG_IS_DEFAULT(UseCountTrailingZerosInstructionsPPC64)) {

test/hotspot/jtreg/compiler/c2/TestCastX2NotProcessedIGVN.java

@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2024, Red Hat, Inc. All rights reserved.
- * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2024, 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
@@ -77,7 +77,7 @@ public static void test1Runner() {
     @Test
     @IR(counts = {IRNode.LOAD_VECTOR_I, "> 1"},
         applyIfOr = {"UseCompactObjectHeaders", "false", "AlignVector", "false"},
-        applyIfPlatformOr = {"x64", "true", "aarch64", "true"})
+        applyIfPlatformOr = {"x64", "true", "aarch64", "true", "ppc", "true"})
     public static int test2(int stop, int[] array) {
         int v = 0;
         stop = Math.min(stop, Integer.MAX_VALUE / 4);