8265917: Different values computed by C2 and interpreter/C1 for Math.…

…pow(x, 2.0) on x86_32

Reviewed-by: kvn, thartmann

src/hotspot/cpu/x86/macroAssembler_x86_pow.cpp

@@ -2515,6 +2515,8 @@ ATTRIBUTE_ALIGNED(16) juint _static_const_table_pow[] =
 
 };
 
+ATTRIBUTE_ALIGNED(8) double _DOUBLE2 = 2.0;
+
 //registers,
 // input: xmm0, xmm1
 // scratch: xmm1, xmm2, xmm3, xmm4, xmm5, xmm6, xmm7
@@ -2538,17 +2540,28 @@ void MacroAssembler::fast_pow(XMMRegister xmm0, XMMRegister xmm1, XMMRegister xm
   Label L_2TAG_PACKET_48_0_2, L_2TAG_PACKET_49_0_2, L_2TAG_PACKET_50_0_2, L_2TAG_PACKET_51_0_2;
   Label L_2TAG_PACKET_52_0_2, L_2TAG_PACKET_53_0_2, L_2TAG_PACKET_54_0_2, L_2TAG_PACKET_55_0_2;
   Label L_2TAG_PACKET_56_0_2, L_2TAG_PACKET_57_0_2, L_2TAG_PACKET_58_0_2, start;
+  Label L_NOT_DOUBLE2;
 
   assert_different_registers(tmp, eax, ecx, edx);
 
   address static_const_table_pow = (address)_static_const_table_pow;
+  address DOUBLE2 = (address) &_DOUBLE2;
 
   bind(start);
   subl(rsp, 120);
   movl(Address(rsp, 64), tmp);
   lea(tmp, ExternalAddress(static_const_table_pow));
   movsd(xmm0, Address(rsp, 128));
   movsd(xmm1, Address(rsp, 136));
+
+  // Special case: pow(x, 2.0) => x * x
+  ucomisd(xmm1, ExternalAddress(DOUBLE2));
+  jccb(Assembler::notEqual, L_NOT_DOUBLE2);
+  jccb(Assembler::parity, L_NOT_DOUBLE2);
+  mulsd(xmm0, xmm0);
+  jmp(L_2TAG_PACKET_21_0_2);
+
+  bind(L_NOT_DOUBLE2);
   xorpd(xmm2, xmm2);
   movl(eax, 16368);
   pinsrw(xmm2, eax, 3);

test/hotspot/jtreg/compiler/intrinsics/math/TestPow2Opt.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2021 THL A29 Limited, a Tencent company. 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.
+ */
+
+/*
+ * @test
+ * @bug 8265917
+ * @summary test the optimization of pow(x, 2.0)
+ * @run main/othervm TestPow2Opt
+ * @run main/othervm -Xint TestPow2Opt
+ * @run main/othervm -Xbatch -XX:TieredStopAtLevel=1 TestPow2Opt
+ * @run main/othervm -Xbatch -XX:-TieredCompilation  TestPow2Opt
+ */
+
+public class TestPow2Opt {
+
+  static void test(double a) {
+    double r1 = a * a;
+    double r2 = Math.pow(a, 2.0);
+    if (r1 != r2) {
+      throw new RuntimeException("pow(" + a + ", 2.0), expected: " + r1 + ", actual: " + r2);
+    }
+  }
+
+  public static void main(String[] args) throws Exception {
+    for (int i = 0; i < 10; i++) {
+      for (int j = 1; j < 100000; j++) {
+        test(j * 1.0);
+        test(1.0 / j);
+      }
+    }
+  }
+
+}