8370409: Incorrect computation in Float16 reduction loop

src/hotspot/cpu/x86/x86.ad

@@ -10733,6 +10733,7 @@ instruct reinterpretHF2S(rRegI dst, regF src)
   format %{ "vmovw $dst, $src" %}
   ins_encode %{
     __ vmovw($dst$$Register, $src$$XMMRegister);
+    __ movswl($dst$$Register, $dst$$Register);
   %}
   ins_pipe(pipe_slow);
 %}

test/hotspot/jtreg/compiler/c2/TestFloat16Reduction.java

@@ -0,0 +1,166 @@
+/*
+ * Copyright (c) 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
+ * 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;
+
+/*
+ * @test
+ * @bug 8370409
+ * @summary Incorrect computation in Float16 reduction loop
+ *
+ * @library /test/lib /
+ * @run main/othervm -XX:-TieredCompilation
+ *                   compiler.c2.TestFloat16Reduction
+ */
+
+import compiler.lib.ir_framework.*;
+import compiler.lib.verify.*;
+import compiler.lib.generators.Generator;
+import static compiler.lib.generators.Generators.G;
+import jdk.test.lib.Utils;
+import java.util.Arrays;
+
+public class TestFloat16Reduction {
+
+    public short [] arr;
+    private static Generator<Short> genHF = G.uniformFloat16s();
+
+    public long GOLDEN_ADD;
+    public long GOLDEN_SUB;
+    public long GOLDEN_MUL;
+    public long GOLDEN_DIV;
+    public long GOLDEN_MAX;
+    public long GOLDEN_MIN;
+
+    @Test
+    @IR(counts = {IRNode.ADD_HF, " >0 "}, applyIfCPUFeature = {"avx512_fp16", "true"})
+    @IR(counts = {IRNode.ADD_HF, " >0 "}, applyIfCPUFeatureAnd = {"fphp", "true", "asimdhp", "true"})
+    long ADDReduceLong() {
+        short res = 0;
+        for (int i = 0; i < arr.length; i++) {
+            res = Float.floatToFloat16(Float.float16ToFloat(res) + Float.float16ToFloat(arr[i]));
+        }
+        return (long)res;
+    }
+
+    @Check(test="ADDReduceLong")
+    void checkADDReduceLong(long actual) {
+        Verify.checkEQ(actual, GOLDEN_ADD);
+    }
+
+    @Test
+    @IR(counts = {IRNode.SUB_HF, " >0 "}, applyIfCPUFeature = {"avx512_fp16", "true"})
+    @IR(counts = {IRNode.SUB_HF, " >0 "}, applyIfCPUFeatureAnd = {"fphp", "true", "asimdhp", "true"})
+    long SUBReduceLong() {
+        short res = 0;
+        for (int i = 0; i < arr.length; i++) {
+            res = Float.floatToFloat16(Float.float16ToFloat(res) - Float.float16ToFloat(arr[i]));
+        }
+        return (long)res;
+    }
+
+    @Check(test="SUBReduceLong")
+    void checkSUBReduceLong(long actual) {
+        Verify.checkEQ(actual, GOLDEN_SUB);
+    }
+
+    @Test
+    @IR(counts = {IRNode.MUL_HF, " >0 "}, applyIfCPUFeature = {"avx512_fp16", "true"})
+    @IR(counts = {IRNode.MUL_HF, " >0 "}, applyIfCPUFeatureAnd = {"fphp", "true", "asimdhp", "true"})
+    long MULReduceLong() {
+        short res = 0;
+        for (int i = 0; i < arr.length; i++) {
+            res = Float.floatToFloat16(Float.float16ToFloat(res) * Float.float16ToFloat(arr[i]));
+        }
+        return (long)res;
+    }
+
+    @Check(test="MULReduceLong")
+    void checkMULReduceLong(long actual) {
+        Verify.checkEQ(actual, GOLDEN_MUL);
+    }
+
+    @Test
+    @IR(counts = {IRNode.DIV_HF, " >0 "}, applyIfCPUFeature = {"avx512_fp16", "true"})
+    @IR(counts = {IRNode.DIV_HF, " >0 "}, applyIfCPUFeatureAnd = {"fphp", "true", "asimdhp", "true"})
+    long DIVReduceLong() {
+        short res = 0;
+        for (int i = 0; i < arr.length; i++) {
+            res = Float.floatToFloat16(Float.float16ToFloat(res) / Float.float16ToFloat(arr[i]));
+        }
+        return (long)res;
+    }
+
+    @Check(test="DIVReduceLong")
+    void checkDIVReduceLong(long actual) {
+        Verify.checkEQ(actual, GOLDEN_DIV);
+    }
+
+    @Test
+    @IR(counts = {IRNode.MAX_HF, " >0 "}, applyIfCPUFeature = {"avx512_fp16", "true"})
+    @IR(counts = {IRNode.MAX_HF, " >0 "}, applyIfCPUFeatureAnd = {"fphp", "true", "asimdhp", "true"})
+    long MAXReduceLong() {
+        short res = 0;
+        for (int i = 0; i < arr.length; i++) {
+            res = Float.floatToFloat16(Math.max(Float.float16ToFloat(res), Float.float16ToFloat(arr[i])));
+        }
+        return (long)res;
+    }
+
+    @Check(test="MAXReduceLong")
+    void checkMAXReduceLong(long actual) {
+        Verify.checkEQ(actual, GOLDEN_MAX);
+    }
+
+    @Test
+    @IR(counts = {IRNode.MIN_HF, " >0 "}, applyIfCPUFeature = {"avx512_fp16", "true"})
+    @IR(counts = {IRNode.MIN_HF, " >0 "}, applyIfCPUFeatureAnd = {"fphp", "true", "asimdhp", "true"})
+    long MINReduceLong() {
+        short res = 0;
+        for (int i = 0; i < arr.length; i++) {
+            res = Float.floatToFloat16(Math.min(Float.float16ToFloat(res), Float.float16ToFloat(arr[i])));
+        }
+        return (long)res;
+    }
+
+    @Check(test = "MINReduceLong")
+    void checkMINReduceLong(long actual) {
+        Verify.checkEQ(actual, GOLDEN_MIN);
+    }
+
+    public TestFloat16Reduction() {
+        arr = new short[32];
+        G.fill(genHF, arr);
+
+        GOLDEN_ADD = ADDReduceLong();
+        GOLDEN_SUB = SUBReduceLong();
+        GOLDEN_MUL = MULReduceLong();
+        GOLDEN_DIV = DIVReduceLong();
+        GOLDEN_MAX = MAXReduceLong();
+        GOLDEN_MIN = MINReduceLong();
+    }
+
+    public static void main(String [] args) {
+        TestFramework.run(TestFloat16Reduction.class);
+    }
+}