From c7816b0b444019aef047b7f0d8281cbf3b8d17fb Mon Sep 17 00:00:00 2001
From: Chad Rakoczy <crakoczy@openjdk.org>
Date: Tue, 30 Jun 2026 19:44:04 +0000
Subject: [PATCH] 8382135: AArch64: HotCodeCollectorMoveFunction.java fails
 intermittently

Reviewed-by: eastigeevich, aph
---
 src/hotspot/share/runtime/hotCodeSampler.cpp     | 16 +++++++---------
 .../hotcode/HotCodeCollectorMoveFunction.java    | 12 +++++++++++-
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/src/hotspot/share/runtime/hotCodeSampler.cpp b/src/hotspot/share/runtime/hotCodeSampler.cpp
index 94242b718a5..e033765c1f2 100644
--- a/src/hotspot/share/runtime/hotCodeSampler.cpp
+++ b/src/hotspot/share/runtime/hotCodeSampler.cpp
@@ -61,15 +61,13 @@ bool ThreadSampler::sample_all_java_threads() {
       continue;
     }
 
-    if (CodeCache::contains(pc)) {
-      nmethod* nm = CodeCache::find_blob(pc)->as_nmethod_or_null();
-      if (nm != nullptr) {
-        bool created = false;
-        int *count = _samples.put_if_absent(nm, 0, &created);
-        (*count)++;
-        if (created) {
-          _samples.maybe_grow();
-        }
+    CodeBlob* cb = CodeCache::find_blob(pc);
+    if (cb != nullptr && cb->is_nmethod()) {
+      bool created = false;
+      int *count = _samples.put_if_absent(cb->as_nmethod(), 0, &created);
+      (*count)++;
+      if (created) {
+        _samples.maybe_grow();
       }
     }
   }
diff --git a/test/hotspot/jtreg/compiler/hotcode/HotCodeCollectorMoveFunction.java b/test/hotspot/jtreg/compiler/hotcode/HotCodeCollectorMoveFunction.java
index 5677ca88eb2..2b93c24e255 100644
--- a/test/hotspot/jtreg/compiler/hotcode/HotCodeCollectorMoveFunction.java
+++ b/test/hotspot/jtreg/compiler/hotcode/HotCodeCollectorMoveFunction.java
@@ -79,6 +79,8 @@ public class HotCodeCollectorMoveFunction {
         private static final int C2_LEVEL = 4;
         private static final int FUNC_RUN_MILLIS = 60_000;
 
+        private static volatile int blackholeCount = 0;
+
         static {
             try {
                 method = Runner.class.getMethod("func");
@@ -111,7 +113,15 @@ public class HotCodeCollectorMoveFunction {
 
         public static void func() {
             long start = System.currentTimeMillis();
-            while (System.currentTimeMillis() - start < FUNC_RUN_MILLIS) {}
+            while (System.currentTimeMillis() - start < FUNC_RUN_MILLIS) {
+                // Perform multiplicative LCG to ensure the compiler does not optimize away the code.
+                // Integer overflow is used for the modulus so the loop terminates after (2^32)/4 iterations
+                int num = 1;
+                do {
+                    blackholeCount++;
+                    num *= 69069;
+                } while (num != 1);
+            }
         }
     }
 }