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8060249: Backout fix for JDK-8058243

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Reviewed-by: vromero
This commit is contained in:
Paul Govereau 2014-10-13 17:09:12 -04:00
parent ef05cafd6b
commit 8cc03657e9
2 changed files with 11 additions and 96 deletions
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19
langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Gen.java
View File

@ -1220,14 +1220,17 @@ public class Gen extends JCTree.Visitor {
}
// Determine whether to issue a tableswitch or a lookupswitch
// instruction. The difference in computation cost is
// proportional to log(#cases), which is negligable, so we only
// consider the size of the bytecode.
// A discussion of the metric can be found here:
// http://mail.openjdk.java.net/pipermail/compiler-dev/2014-September/008987.html
long table_cost = 4 + ((long)hi - lo + 1); // words
long lookup_cost = 3 + 2 * (long)nlabels;
int opcode = table_cost <= lookup_cost ? tableswitch : lookupswitch;
// instruction.
long table_space_cost = 4 + ((long) hi - lo + 1); // words
long table_time_cost = 3; // comparisons
long lookup_space_cost = 3 + 2 * (long) nlabels;
long lookup_time_cost = nlabels;
int opcode =
nlabels > 0 &&
table_space_cost + 3 * table_time_cost <=
lookup_space_cost + 3 * lookup_time_cost
?
tableswitch : lookupswitch;
int startpc = code.curCP(); // the position of the selector operation
code.emitop0(opcode);

88
langtools/test/tools/javac/SwitchMetricTest.java
View File

@ -1,88 +0,0 @@
/*
* Copyright (c) 2014, 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 8058243
* @summary Reduce size of bytecode for large switch statements
* @library /tools/lib
* @build ToolBox
* @run main SwitchMetricTest
*/
import java.net.URL;
import java.util.List;
public class SwitchMetricTest {
public static void main(String... args) throws Exception {
new SwitchMetricTest().run();
}
// This code should produce a tableswitch
class Test1 {
int m(int x) {
switch (x) {
case 1:
case 2:
case 3:
case 4:
case 5: return 1;
default: return 0;
}
}
}
// This code should produce a lookupswitch
class Test2 {
int m(int x) {
switch (x) {
case 1:
case 2:
case 3:
case 4:
case 50: return 1;
default: return 0;
}
}
}
void check(String classfile, String bytecode) throws Exception {
ToolBox tb = new ToolBox();
URL url = SwitchMetricTest.class.getResource(classfile);
List<String> result = tb.new JavapTask()
.options("-c")
.classes(url.getFile())
.run()
.write(ToolBox.OutputKind.DIRECT)
.getOutputLines(ToolBox.OutputKind.DIRECT);
List<String> matches = tb.grep(bytecode, result);
if (matches.isEmpty())
throw new Exception(bytecode + " not found");
}
void run() throws Exception {
check("SwitchMetricTest$Test1.class", "tableswitch");
check("SwitchMetricTest$Test2.class", "lookupswitch");
}
}