8379327: 128-bit multiplication uses two multiply instructions on x86_64

src/hotspot/cpu/x86/x86.ad

@@ -11647,6 +11647,58 @@ instruct mulL_mem_imm(rRegL dst, memory src, immL32 imm, rFlagsReg cr)
   ins_pipe(ialu_reg_mem_alu0);
 %}
 
+instruct mulHiLoL_rReg(rax_RegL rax, rdx_RegL rdx, rRegL src, rFlagsReg cr)
+%{
+  match(MulHiLoL src rax);
+  effect(KILL cr);
+
+  ins_cost(300);
+  format %{ "imulq   RDX:RAX, RAX, $src\t# mulhilo" %}
+  ins_encode %{
+    __ imulq($src$$Register);
+  %}
+  ins_pipe(ialu_reg_reg_alu0);
+%}
+
+instruct mulHiLoL_rReg_swap(rax_RegL rax, rdx_RegL rdx, rRegL src, rFlagsReg cr)
+%{
+  match(MulHiLoL rax src);
+  effect(KILL cr);
+
+  ins_cost(300);
+  format %{ "imulq   RDX:RAX, RAX, $src\t# mulhilo" %}
+  ins_encode %{
+    __ imulq($src$$Register);
+  %}
+  ins_pipe(ialu_reg_reg_alu0);
+%}
+
+instruct umulHiLoL_rReg(rax_RegL rax, rdx_RegL rdx, rRegL src, rFlagsReg cr)
+%{
+  match(UMulHiLoL src rax);
+  effect(KILL cr);
+
+  ins_cost(300);
+  format %{ "mulq   RDX:RAX, RAX, $src\t# umulhilo" %}
+  ins_encode %{
+    __ mulq($src$$Register);
+  %}
+  ins_pipe(ialu_reg_reg_alu0);
+%}
+
+instruct umulHiLoL_rReg_swap(rax_RegL rax, rdx_RegL rdx, rRegL src, rFlagsReg cr)
+%{
+  match(UMulHiLoL rax src);
+  effect(KILL cr);
+
+  ins_cost(300);
+  format %{ "mulq   RDX:RAX, RAX, $src\t# umulhilo" %}
+  ins_encode %{
+    __ mulq($src$$Register);
+  %}
+  ins_pipe(ialu_reg_reg_alu0);
+%}
+
 instruct mulHiL_rReg(rdx_RegL dst, rRegL src, rax_RegL rax, rFlagsReg cr)
 %{
   match(Set dst (MulHiL src rax));

src/hotspot/share/opto/classes.hpp

@@ -266,6 +266,8 @@ macro(MulD)
 macro(MulF)
 macro(MulHiL)
 macro(UMulHiL)
+macro(MulHiLoL)
+macro(UMulHiLoL)
 macro(MulI)
 macro(MulL)
 macro(Multi)

src/hotspot/share/opto/compile.cpp

@@ -3259,6 +3259,41 @@ void Compile::handle_div_mod_op(Node* n, BasicType bt, bool is_unsigned) {
   }
 }
 
+void Compile::handle_mulhi_mul_op(Node* n, bool is_unsigned) {
+  const int fused_opcode = is_unsigned ? Op_UMulHiLoL : Op_MulHiLoL;
+  if (!Matcher::has_match_rule(fused_opcode)) {
+    return;
+  }
+
+  Node* mul = n->find_similar(Op_MulL);
+  if (mul == nullptr) {
+    Node* lhs = n->in(1);
+    Node* rhs = n->in(2);
+    if (rhs != nullptr && rhs->outcnt() >= 2) {
+      for (DUIterator_Fast dmax, i = rhs->fast_outs(dmax); i < dmax; i++) {
+        Node* use = rhs->fast_out(i);
+        if (use != n &&
+            use->Opcode() == Op_MulL &&
+            use->req() == n->req() &&
+            use->in(1) == rhs &&
+            use->in(2) == lhs) {
+          mul = use;
+          break;
+        }
+      }
+    }
+  }
+
+  if (mul == nullptr) {
+    return;
+  }
+
+  MulHiLoLNode* mul_hi_lo = is_unsigned ? static_cast<MulHiLoLNode*>(UMulHiLoLNode::make(n))
+                                        : MulHiLoLNode::make(n);
+  mul->subsume_by(mul_hi_lo->lo_proj(), this);
+  n->subsume_by(mul_hi_lo->hi_proj(), this);
+}
+
 void Compile::final_graph_reshaping_main_switch(Node* n, Final_Reshape_Counts& frc, uint nop, Unique_Node_List& dead_nodes) {
   switch( nop ) {
   // Count all float operations that may use FPU
@@ -3730,6 +3765,14 @@ void Compile::final_graph_reshaping_main_switch(Node* n, Final_Reshape_Counts& f
     handle_div_mod_op(n, T_LONG, true);
     break;
 
+  case Op_MulHiL:
+    handle_mulhi_mul_op(n, false);
+    break;
+
+  case Op_UMulHiL:
+    handle_mulhi_mul_op(n, true);
+    break;
+
   case Op_LoadVector:
   case Op_StoreVector:
 #ifdef ASSERT

src/hotspot/share/opto/compile.hpp

@@ -1241,6 +1241,7 @@ public:
   void final_graph_reshaping_main_switch(Node* n, Final_Reshape_Counts& frc, uint nop, Unique_Node_List& dead_nodes);
   void final_graph_reshaping_walk(Node_Stack& nstack, Node* root, Final_Reshape_Counts& frc, Unique_Node_List& dead_nodes);
   void handle_div_mod_op(Node* n, BasicType bt, bool is_unsigned);
+  void handle_mulhi_mul_op(Node* n, bool is_unsigned);
 
   // Logic cone optimization.
   void optimize_logic_cones(PhaseIterGVN &igvn);

src/hotspot/share/opto/mulnode.cpp

@@ -23,6 +23,8 @@
  */
 
 #include "memory/allocation.inline.hpp"
+#include "opto/machnode.hpp"
+#include "opto/matcher.hpp"
 #include "opto/addnode.hpp"
 #include "opto/connode.hpp"
 #include "opto/convertnode.hpp"
@@ -606,6 +608,36 @@ const Type* UMulHiLNode::Value(PhaseGVN* phase) const {
   return MulHiValue(t1, t2, bot);
 }
 
+MulHiLoLNode* MulHiLoLNode::make(Node* mul_hi) {
+  assert(mul_hi->Opcode() == Op_MulHiL, "expected MulHiL");
+
+  MulHiLoLNode* mul_hi_lo = new MulHiLoLNode(mul_hi->in(1), mul_hi->in(2));
+  [[maybe_unused]] Node* lo_proj = new ProjNode(mul_hi_lo, MulHiLoLNode::lo_proj_num);
+  [[maybe_unused]] Node* hi_proj = new ProjNode(mul_hi_lo, MulHiLoLNode::hi_proj_num);
+  return mul_hi_lo;
+}
+
+UMulHiLoLNode* UMulHiLoLNode::make(Node* umul_hi) {
+  assert(umul_hi->Opcode() == Op_UMulHiL, "expected UMulHiL");
+
+  UMulHiLoLNode* umul_hi_lo = new UMulHiLoLNode(umul_hi->in(1), umul_hi->in(2));
+  [[maybe_unused]] Node* lo_proj = new ProjNode(umul_hi_lo, MulHiLoLNode::lo_proj_num);
+  [[maybe_unused]] Node* hi_proj = new ProjNode(umul_hi_lo, MulHiLoLNode::hi_proj_num);
+  return umul_hi_lo;
+}
+
+Node* MulHiLoLNode::match(const ProjNode* proj, const Matcher* match) {
+  uint ideal_reg = proj->ideal_reg();
+  RegMask rm;
+  if (proj->_con == lo_proj_num) {
+    rm.assignFrom(match->divL_proj_mask());
+  } else {
+    assert(proj->_con == hi_proj_num, "must be lo or hi projection");
+    rm.assignFrom(match->modL_proj_mask());
+  }
+  return new MachProjNode(this, proj->_con, rm, ideal_reg);
+}
+
 // A common routine used by UMulHiLNode and MulHiLNode
 const Type* MulHiValue(const Type *t1, const Type *t2, const Type *bot) {
   // Either input is TOP ==> the result is TOP

src/hotspot/share/opto/mulnode.hpp

@@ -25,6 +25,7 @@
 #ifndef SHARE_OPTO_MULNODE_HPP
 #define SHARE_OPTO_MULNODE_HPP
 
+#include "opto/multnode.hpp"
 #include "opto/node.hpp"
 #include "opto/opcodes.hpp"
 #include "opto/type.hpp"
@@ -32,6 +33,7 @@
 // Portions of code courtesy of Clifford Click
 
 class PhaseTransform;
+class Matcher;
 
 //------------------------------MulNode----------------------------------------
 // Classic MULTIPLY functionality.  This covers all the usual 'multiply'
@@ -205,6 +207,52 @@ public:
   friend const Type* MulHiValue(const Type *t1, const Type *t2, const Type *bot);
 };
 
+//------------------------------MulHiLoLNode-----------------------------------
+// Lower and upper 64-bit results of a signed 64x64->128 multiply.
+class MulHiLoLNode : public MultiNode {
+protected:
+  MulHiLoLNode(Node* in1, Node* in2) : MultiNode(3) {
+    init_req(0, nullptr);
+    init_req(1, in1);
+    init_req(2, in2);
+  }
+
+public:
+  enum {
+    lo_proj_num = 0,
+    hi_proj_num = 1
+  };
+
+  virtual int Opcode() const;
+  virtual Node* Identity(PhaseGVN* phase) { return this; }
+  virtual Node* Ideal(PhaseGVN* phase, bool can_reshape) { return nullptr; }
+  virtual const Type* Value(PhaseGVN* phase) const { return bottom_type(); }
+  virtual uint hash() const { return Node::hash(); }
+  virtual bool is_CFG() const { return false; }
+  virtual uint ideal_reg() const { return NotAMachineReg; }
+  virtual const Type* bottom_type() const { return TypeTuple::LONG_PAIR; }
+
+  virtual Node* match(const ProjNode* proj, const Matcher* m);
+
+  static MulHiLoLNode* make(Node* mul_hi);
+
+  ProjNode* lo_proj() { return proj_out_or_null(lo_proj_num); }
+  ProjNode* hi_proj() { return proj_out_or_null(hi_proj_num); }
+
+private:
+  virtual bool depends_only_on_test() const { return false; }
+};
+
+//------------------------------UMulHiLoLNode----------------------------------
+// Lower and upper 64-bit results of an unsigned 64x64->128 multiply.
+class UMulHiLoLNode : public MulHiLoLNode {
+public:
+  UMulHiLoLNode(Node* in1, Node* in2) : MulHiLoLNode(in1, in2) {}
+  virtual int Opcode() const;
+
+  static UMulHiLoLNode* make(Node* umul_hi);
+};
+
 //------------------------------AndINode---------------------------------------
 // Logically AND 2 integers.  Included with the MUL nodes because it inherits
 // all the behavior of multiplication on a ring.

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

@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2026, 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.
+ */
+
+/*
+ * @test
+ * @bug 8379327
+ * @summary Verify correctness for combined low/high 64-bit multiplication patterns.
+ * @run main/othervm -Xbatch -XX:-TieredCompilation -XX:CompileThreshold=100
+ *   -XX:CompileCommand=compileonly,compiler.c2.TestMultiplyHighLowFusion::doMath
+ *   -XX:CompileCommand=compileonly,compiler.c2.TestMultiplyHighLowFusion::doMathSwapped
+ *   -XX:CompileCommand=compileonly,compiler.c2.TestMultiplyHighLowFusion::doUnsignedMath
+ *   -XX:CompileCommand=compileonly,compiler.c2.TestMultiplyHighLowFusion::doUnsignedMathSwapped
+ *   compiler.c2.TestMultiplyHighLowFusion
+ */
+
+package compiler.c2;
+
+import java.math.BigInteger;
+import java.util.Random;
+
+public class TestMultiplyHighLowFusion {
+  private static final BigInteger MASK_64 = BigInteger.ONE.shiftLeft(64).subtract(BigInteger.ONE);
+  private static final long[] CORNER_CASES = {
+      0L,
+      1L,
+      -1L,
+      Long.MIN_VALUE,
+      Long.MAX_VALUE,
+      0x00000000FFFFFFFFL,
+      0xFFFFFFFF00000000L,
+      0x123456789ABCDEFL,
+      0xFEDCBA9876543210L
+  };
+
+  private static long doMath(long a, long b) {
+    long low = a * b;
+    long high = Math.multiplyHigh(a, b);
+    return low + high;
+  }
+
+  private static long doMathSwapped(long a, long b) {
+    long low = b * a;
+    long high = Math.multiplyHigh(b, a);
+    return low + high;
+  }
+
+  private static long doUnsignedMath(long a, long b) {
+    long low = a * b;
+    long high = Math.unsignedMultiplyHigh(a, b);
+    return low + high;
+  }
+
+  private static long doUnsignedMathSwapped(long a, long b) {
+    long low = b * a;
+    long high = Math.unsignedMultiplyHigh(b, a);
+    return low + high;
+  }
+
+  private static long expectedSigned(long a, long b) {
+    BigInteger product = BigInteger.valueOf(a).multiply(BigInteger.valueOf(b));
+    long low = product.longValue();
+    long high = product.shiftRight(64).longValue();
+    return low + high;
+  }
+
+  private static long expectedUnsigned(long a, long b) {
+    BigInteger ua = BigInteger.valueOf(a).and(MASK_64);
+    BigInteger ub = BigInteger.valueOf(b).and(MASK_64);
+    BigInteger product = ua.multiply(ub);
+    long low = product.longValue();
+    long high = product.shiftRight(64).longValue();
+    return low + high;
+  }
+
+  private static void verifyPair(long a, long b) {
+    long expectedSigned = expectedSigned(a, b);
+    long expectedUnsigned = expectedUnsigned(a, b);
+
+    long signed = doMath(a, b);
+    long signedSwapped = doMathSwapped(a, b);
+    long unsigned = doUnsignedMath(a, b);
+    long unsignedSwapped = doUnsignedMathSwapped(a, b);
+
+    if (signed != expectedSigned || signedSwapped != expectedSigned) {
+      throw new RuntimeException("Signed mismatch for a=" + a + ", b=" + b +
+          ": got=" + signed + ", gotSwapped=" + signedSwapped + ", expected=" + expectedSigned);
+    }
+    if (unsigned != expectedUnsigned || unsignedSwapped != expectedUnsigned) {
+      throw new RuntimeException("Unsigned mismatch for a=" + a + ", b=" + b +
+          ": got=" + unsigned + ", gotSwapped=" + unsignedSwapped + ", expected=" + expectedUnsigned);
+    }
+  }
+
+  public static void main(String[] args) {
+    Random random = new Random(0x8379327L);
+
+    for (long a : CORNER_CASES) {
+      for (long b : CORNER_CASES) {
+        verifyPair(a, b);
+      }
+    }
+
+    for (int i = 0; i < 200_000; i++) {
+      verifyPair(random.nextLong(), random.nextLong());
+    }
+  }
+}

test/hotspot/jtreg/compiler/c2/TestMultiplyHighLowFusionX64.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright (c) 2026, 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.
+ */
+
+/*
+ * @test
+ * @bug 8379327
+ * @summary Verify x64 backend emits one multiply for low+high 64-bit multiply pattern.
+ *
+ * @requires vm.compiler2.enabled
+ * @requires os.arch=="amd64" | os.arch=="x86_64"
+ *
+ * @library /test/lib
+ * @run driver compiler.c2.TestMultiplyHighLowFusionX64
+ */
+
+package compiler.c2;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import jdk.test.lib.process.OutputAnalyzer;
+import jdk.test.lib.process.ProcessTools;
+
+public class TestMultiplyHighLowFusionX64 {
+  private static final Pattern MULHILO = Pattern.compile("#\\s*mulhilo\\b");
+  private static final Pattern UMULHILO = Pattern.compile("#\\s*umulhilo\\b");
+
+  public static void main(String[] args) throws Exception {
+    verifyMethod("doMath", true);
+    verifyMethod("doMathSwapped", true);
+    verifyMethod("doUnsignedMath", false);
+    verifyMethod("doUnsignedMathSwapped", false);
+  }
+
+  private static void verifyMethod(String methodName, boolean signed) throws Exception {
+    List<String> command = new ArrayList<>();
+    command.add("-XX:+UnlockDiagnosticVMOptions");
+    command.add("-XX:-TieredCompilation");
+    command.add("-Xbatch");
+    command.add("-XX:CompileCommand=compileonly," + Launcher.class.getName() + "::" + methodName);
+    command.add("-XX:CompileCommand=print," + Launcher.class.getName() + "::" + methodName);
+    command.add(Launcher.class.getName());
+    command.add(methodName);
+
+    OutputAnalyzer output = ProcessTools.executeTestJava(command);
+    output.shouldHaveExitValue(0);
+
+    int mulCount = countMul(output.getOutput(), signed);
+    if (mulCount != 1) {
+      throw new RuntimeException("Expected exactly one multiply in " + methodName + ", found " + mulCount +
+          "\nFull output:\n" + output.getOutput());
+    }
+  }
+
+  private static int countMul(String output, boolean signed) {
+    String lower = output.toLowerCase(Locale.ROOT);
+    Pattern pattern = signed ? MULHILO : UMULHILO;
+    int count = 0;
+    Matcher matcher = pattern.matcher(lower);
+    while (matcher.find()) {
+      count++;
+    }
+    return count;
+  }
+
+  static class Launcher {
+    static long doMath(long a, long b) {
+      long low = a * b;
+      long high = Math.multiplyHigh(a, b);
+      return low + high;
+    }
+
+    static long doMathSwapped(long a, long b) {
+      long low = b * a;
+      long high = Math.multiplyHigh(b, a);
+      return low + high;
+    }
+
+    static long doUnsignedMath(long a, long b) {
+      long low = a * b;
+      long high = Math.unsignedMultiplyHigh(a, b);
+      return low + high;
+    }
+
+    static long doUnsignedMathSwapped(long a, long b) {
+      long low = b * a;
+      long high = Math.unsignedMultiplyHigh(b, a);
+      return low + high;
+    }
+
+    public static void main(String[] args) {
+      String mode = args[0];
+      long acc = 0;
+      long b = 987654321L;
+      for (int i = 0; i < 200_000; i++) {
+        switch (mode) {
+          case "doMath":
+            acc += doMath(i, b);
+            break;
+          case "doMathSwapped":
+            acc += doMathSwapped(i, b);
+            break;
+          case "doUnsignedMath":
+            acc += doUnsignedMath(i, b);
+            break;
+          case "doUnsignedMathSwapped":
+            acc += doUnsignedMathSwapped(i, b);
+            break;
+          default:
+            throw new RuntimeException("Unknown mode: " + mode);
+        }
+      }
+      if (acc == 42) {
+        System.out.println("Impossible");
+      }
+    }
+  }
+}