6800154: Add comments to long_by_long_mulhi() for better understandability

Summary: This patch adds a comment pointing to the Hacker's Delight version of the algorithm plus a verbatim copy of it.  Furthermore it adds inline comments.
Reviewed-by: kvn, jrose

src/share/vm/opto/divnode.cpp

 /*
- * Copyright 1997-2008 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 1997-2009 Sun Microsystems, Inc.  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
@@ -244,42 +244,73 @@ static bool magic_long_divide_constants(jlong d, jlong &M, jint &s) {
 
 //---------------------long_by_long_mulhi--------------------------------------
 // Generate ideal node graph for upper half of a 64 bit x 64 bit multiplication
-static Node *long_by_long_mulhi( PhaseGVN *phase, Node *dividend, jlong magic_const) {
+static Node* long_by_long_mulhi(PhaseGVN* phase, Node* dividend, jlong magic_const) {
   // If the architecture supports a 64x64 mulhi, there is
   // no need to synthesize it in ideal nodes.
   if (Matcher::has_match_rule(Op_MulHiL)) {
-    Node *v = phase->longcon(magic_const);
+    Node* v = phase->longcon(magic_const);
     return new (phase->C, 3) MulHiLNode(dividend, v);
   }
 
+  // Taken from Hacker's Delight, Fig. 8-2. Multiply high signed.
+  // (http://www.hackersdelight.org/HDcode/mulhs.c)
+  //
+  // int mulhs(int u, int v) {
+  //    unsigned u0, v0, w0;
+  //    int u1, v1, w1, w2, t;
+  //
+  //    u0 = u & 0xFFFF;  u1 = u >> 16;
+  //    v0 = v & 0xFFFF;  v1 = v >> 16;
+  //    w0 = u0*v0;
+  //    t  = u1*v0 + (w0 >> 16);
+  //    w1 = t & 0xFFFF;
+  //    w2 = t >> 16;
+  //    w1 = u0*v1 + w1;
+  //    return u1*v1 + w2 + (w1 >> 16);
+  // }
+  //
+  // Note: The version above is for 32x32 multiplications, while the
+  // following inline comments are adapted to 64x64.
+
   const int N = 64;
 
-  Node *u_hi = phase->transform(new (phase->C, 3) RShiftLNode(dividend, phase->intcon(N / 2)));
-  Node *u_lo = phase->transform(new (phase->C, 3) AndLNode(dividend, phase->longcon(0xFFFFFFFF)));
+  // u0 = u & 0xFFFFFFFF;  u1 = u >> 32;
+  Node* u0 = phase->transform(new (phase->C, 3) AndLNode(dividend, phase->longcon(0xFFFFFFFF)));
+  Node* u1 = phase->transform(new (phase->C, 3) RShiftLNode(dividend, phase->intcon(N / 2)));
+
+  // v0 = v & 0xFFFFFFFF;  v1 = v >> 32;
+  Node* v0 = phase->longcon(magic_const & 0xFFFFFFFF);
+  Node* v1 = phase->longcon(magic_const >> (N / 2));
+
+  // w0 = u0*v0;
+  Node* w0 = phase->transform(new (phase->C, 3) MulLNode(u0, v0));
+
+  // t = u1*v0 + (w0 >> 32);
+  Node* u1v0 = phase->transform(new (phase->C, 3) MulLNode(u1, v0));
+  Node* temp = phase->transform(new (phase->C, 3) URShiftLNode(w0, phase->intcon(N / 2)));
+  Node* t    = phase->transform(new (phase->C, 3) AddLNode(u1v0, temp));
 
-  Node *v_hi = phase->longcon(magic_const >> N/2);
-  Node *v_lo = phase->longcon(magic_const & 0XFFFFFFFF);
+  // w1 = t & 0xFFFFFFFF;
+  Node* w1 = new (phase->C, 3) AndLNode(t, phase->longcon(0xFFFFFFFF));
 
-  Node *hihi_product = phase->transform(new (phase->C, 3) MulLNode(u_hi, v_hi));
-  Node *hilo_product = phase->transform(new (phase->C, 3) MulLNode(u_hi, v_lo));
-  Node *lohi_product = phase->transform(new (phase->C, 3) MulLNode(u_lo, v_hi));
-  Node *lolo_product = phase->transform(new (phase->C, 3) MulLNode(u_lo, v_lo));
+  // w2 = t >> 32;
+  Node* w2 = new (phase->C, 3) RShiftLNode(t, phase->intcon(N / 2));
 
-  Node *t1 = phase->transform(new (phase->C, 3) URShiftLNode(lolo_product, phase->intcon(N / 2)));
-  Node *t2 = phase->transform(new (phase->C, 3) AddLNode(hilo_product, t1));
+  // 6732154: Construct both w1 and w2 before transforming, so t
+  // doesn't go dead prematurely.
+  w1 = phase->transform(w1);
+  w2 = phase->transform(w2);
 
-  // Construct both t3 and t4 before transforming so t2 doesn't go dead
-  // prematurely.
-  Node *t3 = new (phase->C, 3) RShiftLNode(t2, phase->intcon(N / 2));
-  Node *t4 = new (phase->C, 3) AndLNode(t2, phase->longcon(0xFFFFFFFF));
-  t3 = phase->transform(t3);
-  t4 = phase->transform(t4);
+  // w1 = u0*v1 + w1;
+  Node* u0v1 = phase->transform(new (phase->C, 3) MulLNode(u0, v1));
+  w1         = phase->transform(new (phase->C, 3) AddLNode(u0v1, w1));
 
-  Node *t5 = phase->transform(new (phase->C, 3) AddLNode(t4, lohi_product));
-  Node *t6 = phase->transform(new (phase->C, 3) RShiftLNode(t5, phase->intcon(N / 2)));
-  Node *t7 = phase->transform(new (phase->C, 3) AddLNode(t3, hihi_product));
+  // return u1*v1 + w2 + (w1 >> 32);
+  Node* u1v1  = phase->transform(new (phase->C, 3) MulLNode(u1, v1));
+  Node* temp1 = phase->transform(new (phase->C, 3) AddLNode(u1v1, w2));
+  Node* temp2 = phase->transform(new (phase->C, 3) RShiftLNode(w1, phase->intcon(N / 2)));
 
-  return new (phase->C, 3) AddLNode(t7, t6);
+  return new (phase->C, 3) AddLNode(temp1, temp2);
 }
 
 

test/compiler/6603011/Test.java

+/*
+ * Copyright 2009 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/**
+ * @test
+ * @bug 6603011
+ * @summary long/int division by constant
+ *
+ * @run main/othervm -Xcomp -Xbatch -XX:-Inline Test
+ */
+
+//
+// -XX:-Inline is essential to this test so that verification functions
+//   divi, modi, divl and modl generate "plain" divides.
+// -Xcomp -Xbatch are also useful to ensure the full range of
+//   dividend and divisor combinations are tested
+//
+
+import java.net.*;
+
+class s {
+  static int  divi(int  dividend, int  divisor) { return dividend / divisor; }
+  static int  modi(int  dividend, int  divisor) { return dividend % divisor; }
+  static long divl(long dividend, long divisor) { return dividend / divisor; }
+  static long modl(long dividend, long divisor) { return dividend % divisor; }
+}
+
+public class Test implements Runnable {
+  // Report verbose messages on failure; turn off to suppress
+  // too much output with gross numbers of failures.
+  static final boolean VERBOSE = true;
+
+  // Initailize DIVISOR so that it is final in this class.
+  static final int DIVISOR;
+  static {
+    int value = 0;
+    try {
+      value = Integer.decode(System.getProperty("divisor"));
+    } catch (Throwable e) {
+    }
+    DIVISOR = value;
+  }
+
+  // The methods of interest. We want the JIT to compile these
+  // and convert the divide into a multiply.
+  public int divbyI (int dividend)   { return dividend / DIVISOR; }
+  public int modbyI (int dividend)   { return dividend % DIVISOR; }
+  public long divbyL (long dividend) { return dividend / DIVISOR; }
+  public long modbyL (long dividend) { return dividend % DIVISOR; }
+
+  public int divisor() { return DIVISOR; }
+
+  public boolean checkI (int dividend) {
+    int quo = divbyI(dividend);
+    int rem = modbyI(dividend);
+    int quo0 = s.divi(dividend, divisor());
+    int rem0 = s.modi(dividend, divisor());
+
+    if (quo != quo0 || rem != rem0) {
+      if (VERBOSE) {
+        System.out.println("Computed: " + dividend + " / " + divisor() + " = " +
+                           quo  + ", " + dividend + " % " + divisor() + " = " + rem );
+        System.out.println("expected: " + dividend + " / " + divisor() + " = " +
+                           quo0 + ", " + dividend + " % " + divisor() + " = " + rem0);
+        // Report sign of rem failure
+        if (rem != 0 && (rem ^ dividend) < 0) {
+          System.out.println("  rem & dividend have different signs");
+        }
+        // Report range of rem failure
+        if (java.lang.Math.abs(rem) >= java.lang.Math.abs(divisor())) {
+          System.out.println("  remainder out of range");
+        }
+        // Report quo/rem identity relationship failure
+        if ((quo * divisor()) + rem != dividend) {
+          System.out.println("  quotien/remainder invariant broken");
+        }
+      }
+      return false;
+    }
+    return true;
+  }
+
+  public boolean checkL (long dividend) {
+    long quo = divbyL(dividend);
+    long rem = modbyL(dividend);
+    long quo0 = s.divl(dividend, divisor());
+    long rem0 = s.modl(dividend, divisor());
+
+    if (quo != quo0 || rem != rem0) {
+      if (VERBOSE) {
+        System.out.println("  " + dividend + " / " + divisor() + " = " +
+                           quo + ", " + dividend + " % " + divisor() + " = " + rem);
+        // Report sign of rem failure
+        if (rem != 0 && (rem ^ dividend) < 0) {
+          System.out.println("  rem & dividend have different signs");
+        }
+        // Report range of rem failure
+        if (java.lang.Math.abs(rem) >= java.lang.Math.abs(divisor())) {
+          System.out.println("  remainder out of range");
+        }
+        // Report quo/rem identity relationship failure
+        if ((quo * divisor()) + rem != dividend) {
+          System.out.println(" (" + quo + " * " + divisor() + ") + " + rem + " != "
+                             + dividend);
+        }
+      }
+      return false;
+    }
+    return true;
+  }
+
+  public void run() {
+    // Don't try to divide by zero
+    if (divisor() == 0) return;
+
+    // Range of dividends to check. Try dividends from start to end
+    // inclusive, as well as variations on those values as shifted
+    // left.
+    int start = -1024;
+    int end = 1024;
+
+    // Test int division using a variety of dividends.
+    int wrong = 0;
+    int total = 0;
+
+    outerloop:
+    for (int i = start; i <= end; i++) {
+      for (int s = 0; s < 32; s += 4) {
+        total++;
+        int dividend = i << s;
+        if (!checkI(dividend)) {
+          wrong++;
+          // Stop on the first failure
+          // break outerloop;
+        }
+      }
+    }
+    if (wrong > 0) {
+      System.out.println("divisor " + divisor() + ": " +
+                         wrong + "/" + total + " wrong int divisions");
+    }
+
+    // Test long division using a variety of dividends.
+    wrong = 0;
+    total = 0;
+
+    outerloop:
+    for (int i = start; i <= end; i++) {
+      for (int s = 0; s < 64; s += 4) {
+        total++;
+        long dividend = i << s;
+        if (!checkL(dividend)) {
+          wrong++;
+          // Stop on the first failure
+          // break outerloop;
+        }
+      }
+    }
+    if (wrong > 0) {
+      System.out.println("divisor " + divisor() + ": " +
+                         wrong + "/" + total + " wrong long divisions");
+    }
+
+  }
+
+  // Reload this class with the "divisor" property set to the input parameter.
+  // This allows the JIT to see q.DIVISOR as a final constant, and change
+  // any divisions or mod operations into multiplies.
+  public static void test_divisor(int divisor,
+                                  URLClassLoader apploader) throws Exception {
+    System.setProperty("divisor", "" + divisor);
+    ClassLoader loader = new URLClassLoader(apploader.getURLs(),
+                                            apploader.getParent());
+    Class c = loader.loadClass("Test");
+    Runnable r = (Runnable)c.newInstance();
+    r.run();
+  }
+
+  public static void main(String[] args) throws Exception {
+    Class cl = Class.forName("Test");
+    URLClassLoader apploader = (URLClassLoader)cl.getClassLoader();
+
+
+    // Test every divisor between -100 and 100.
+    for (int i = -100; i <= 100; i++) {
+      test_divisor(i, apploader);
+    }
+
+    // Try a few divisors outside the typical range.
+    // The values below have been observed in rt.jar.
+    test_divisor(101, apploader);
+    test_divisor(400, apploader);
+    test_divisor(1000, apploader);
+    test_divisor(3600, apploader);
+    test_divisor(9973, apploader);
+    test_divisor(86400, apploader);
+    test_divisor(1000000, apploader);
+  }
+
+}

test/compiler/6800154/Test6800154.java

+/*
+ * Copyright 2009 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/**
+ * @test
+ * @bug 6800154
+ * @summary Add comments to long_by_long_mulhi() for better understandability
+ *
+ * @run main/othervm -Xcomp -XX:CompileOnly=Test6800154.divcomp Test6800154
+ */
+
+import java.net.URLClassLoader;
+
+public class Test6800154 implements Runnable {
+    static final long[] DIVIDENDS = {
+        0,
+        1,
+        2,
+        1423487,
+        4444441,
+        4918923241323L,
+        -1,
+        -24351,
+        0x3333,
+        0x0000000080000000L,
+        0x7fffffffffffffffL,
+        0x8000000000000000L
+    };
+
+    static final long[] DIVISORS = {
+        1,
+        2,
+        17,
+        12342,
+        24123,
+        143444,
+        123444442344L,
+        -1,
+        -2,
+        -4423423234231423L,
+        0x0000000080000000L,
+        0x7fffffffffffffffL,
+        0x8000000000000000L
+    };
+
+    // Initialize DIVISOR so that it is final in this class.
+    static final long DIVISOR;
+
+    static {
+        long value = 0;
+        try {
+            value = Long.decode(System.getProperty("divisor"));
+        } catch (Throwable e) {
+        }
+        DIVISOR = value;
+    }
+
+    public static void main(String[] args) throws Exception
+    {
+        Class cl = Class.forName("Test6800154");
+        URLClassLoader apploader = (URLClassLoader) cl.getClassLoader();
+
+        // Iterate over all divisors.
+        for (int i = 0; i < DIVISORS.length; i++) {
+            System.setProperty("divisor", "" + DIVISORS[i]);
+            ClassLoader loader = new URLClassLoader(apploader.getURLs(), apploader.getParent());
+            Class c = loader.loadClass("Test6800154");
+            Runnable r = (Runnable) c.newInstance();
+            r.run();
+        }
+    }
+
+    public void run()
+    {
+        // Iterate over all dividends.
+        for (int i = 0; i < DIVIDENDS.length; i++) {
+            long dividend = DIVIDENDS[i];
+
+            long expected = divint(dividend);
+            long result = divcomp(dividend);
+
+            if (result != expected)
+                throw new InternalError(dividend + " / " + DIVISOR + " failed: " + result + " != " + expected);
+        }
+    }
+
+    static long divint(long a)  { return a / DIVISOR; }
+    static long divcomp(long a) { return a / DIVISOR; }
+}