From 83cd98426ed97e14aa1521d7253bc0f88aa502e8 Mon Sep 17 00:00:00 2001
From: Xiaolong Peng <xpeng@openjdk.org>
Date: Fri, 8 May 2026 22:06:14 +0000
Subject: [PATCH] 8383861: Shenandoah: Use int[] as filling class for
 compressed oop array allocation

Reviewed-by: shade, kdnilsen
---
 .../gc/shenandoah/shenandoahObjArrayAllocator.cpp   | 13 +++++--------
 .../jtreg/gc/shenandoah/TestLargeArrayInit.java     | 12 ++++++++++++
 .../gc/shenandoah/TestLargeArrayInitGCStress.java   | 12 ++++++++++++
 3 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/src/hotspot/share/gc/shenandoah/shenandoahObjArrayAllocator.cpp b/src/hotspot/share/gc/shenandoah/shenandoahObjArrayAllocator.cpp
index e2215ea58ef..dc9fef16cf6 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahObjArrayAllocator.cpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahObjArrayAllocator.cpp
@@ -71,16 +71,14 @@ oop ShenandoahObjArrayAllocator::initialize(HeapWord* mem) const {
   // Always initialize the mem with primitive array first so GC won't look into the elements in the array.
   // For obj array, the header will be corrected to object array after clearing the memory.
   Klass* filling_klass = _klass;
-  int filling_array_length = _length;
-  const bool is_ref_type = is_reference_type(element_type, true);
+  const bool is_ref_type = is_reference_type(element_type);
 
   if (is_ref_type) {
-    const bool is_narrow_oop = element_type == T_NARROWOOP;
-    size_t filling_element_byte_size = is_narrow_oop ? T_INT_aelem_bytes : T_LONG_aelem_bytes;
-    filling_klass = is_narrow_oop ? Universe::intArrayKlass() : Universe::longArrayKlass();
-    filling_array_length = (int) ((process_size << LogBytesPerWord) / filling_element_byte_size);
+    filling_klass = LP64_ONLY(UseCompressedOops ? Universe::intArrayKlass() : Universe::longArrayKlass()) NOT_LP64(Universe::intArrayKlass());
+    assert(type2aelembytes(ArrayKlass::cast(filling_klass)->element_type()) == type2aelembytes(element_type), "filling element size must match ref size");
   }
-  ObjArrayAllocator filling_array_allocator(filling_klass, _word_size,  filling_array_length , /* do_zero */ false);
+  // Use _length directly: it matches the ref count, and the filling element size equals the ref size.
+  ObjArrayAllocator filling_array_allocator(filling_klass, _word_size, _length, /* do_zero */ false);
   filling_array_allocator.initialize(mem);
 
   // Invisible roots will be scanned and marked at the end of marking.
@@ -106,7 +104,6 @@ oop ShenandoahObjArrayAllocator::initialize(HeapWord* mem) const {
 
   // reference array, header need to be overridden to its own.
   if (is_ref_type) {
-    arrayOopDesc::set_length(mem, _length);
     finish(mem);
     // zap paddings after setting correct klass
     mem_zap_start_padding(mem);
diff --git a/test/hotspot/jtreg/gc/shenandoah/TestLargeArrayInit.java b/test/hotspot/jtreg/gc/shenandoah/TestLargeArrayInit.java
index 9ce254ff845..83c74866a95 100644
--- a/test/hotspot/jtreg/gc/shenandoah/TestLargeArrayInit.java
+++ b/test/hotspot/jtreg/gc/shenandoah/TestLargeArrayInit.java
@@ -68,6 +68,18 @@
  *      TestLargeArrayInit
  */
 
+/*
+ * @test id=compressed-oops-off
+ * @summary Verify zero-initialization completeness for large arrays with compressed oops disabled
+ * @requires vm.gc.Shenandoah
+ * @library /test/lib
+ *
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -Xmx512m -Xms512m
+ *      -XX:+UseShenandoahGC -XX:ShenandoahGCHeuristics=adaptive
+ *      -XX:-UseCompressedOops
+ *      TestLargeArrayInit
+ */
+
 /**
  *
  * Allocates large byte[], int[], long[], and Object[] arrays whose sizes span
diff --git a/test/hotspot/jtreg/gc/shenandoah/TestLargeArrayInitGCStress.java b/test/hotspot/jtreg/gc/shenandoah/TestLargeArrayInitGCStress.java
index 34f3b70197a..6dfd250e3cc 100644
--- a/test/hotspot/jtreg/gc/shenandoah/TestLargeArrayInitGCStress.java
+++ b/test/hotspot/jtreg/gc/shenandoah/TestLargeArrayInitGCStress.java
@@ -69,6 +69,18 @@
  *      TestLargeArrayInitGCStress
  */
 
+/*
+ * @test id=compressed-oops-off
+ * @summary Verify correct object metadata for large arrays with compressed oops disabled under GC stress
+ * @requires vm.gc.Shenandoah
+ * @library /test/lib
+ *
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -Xmx256m -Xms256m
+ *      -XX:+UseShenandoahGC -XX:ShenandoahGCHeuristics=aggressive
+ *      -XX:-UseCompressedOops
+ *      TestLargeArrayInitGCStress
+ */
+
 /**
  *
  * Allocates large arrays of various types under GC stress (aggressive heuristics,