The pattern matching switches are using a bootstrap method
`SwitchBootstrap.typeSwitch` to implement the jumps in the switch. Basically,
for a switch like:
switch (obj) {
case String s when s.isEmpty() -> {}
case String s -> {}
case CharSequence cs -> {}
...
}
this method will produce a MethodHandle that will be analyze the provided
selector value (`obj` in the example), and will return the case index to which
the switch should jump. This method also accepts a (re)start index for the
search, which is used to handle guards. For example, if the `s.isEmpty()` guard
in the above sample returns false, the matching is restarted on the next case.
The current implementation is fairly slow, it basically goes through the labels
in a loop. The proposal here is to replace that with a MethodHandle structure
like this:
obj == null ? -1
: switch (restartIndex) {
case 0 -> obj instanceof String ? 0 : obj instanceof
CharSequence ? 2 : ... ;
case 1 -> obj instanceof String ? 1 : obj instanceof
CharSequence ? 2 : ... ;
case 2 -> obj instanceof CharSequence ? 2 : ... ;
...
default -> <labels-count>;
}
This appear to run faster than the current implementation, using testcase
similar to the one used for https://github.com/openjdk/jdk/pull/9746 , these
are the results
PatternsOptimizationTest.testLegacyIndyLongSwitch thrpt 25 1515989.562 ±
32047.918 ops/s
PatternsOptimizationTest.testHandleIndyLongSwitch thrpt 25 2630707.585 ±
37202.210 ops/s
PatternsOptimizationTest.testLegacyIndyShortSwitch thrpt 25 6789310.900 ±
61921.636 ops/s
PatternsOptimizationTest.testHandleIndyShortSwitch thrpt 25 10771729.464 ±
69607.467 ops/s
The "LegacyIndy" is the current implementation, "HandleIndy" is the one
proposed here. The translation in javac used is the one from #9746 in all cases.
-------------
Commit messages:
- 8291966: SwitchBootstrap.typeSwitch could be faster
Changes: https://git.openjdk.org/jdk/pull/9779/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9779&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8291966
Stats: 74 lines in 1 file changed: 50 ins; 4 del; 20 mod
Patch: https://git.openjdk.org/jdk/pull/9779.diff
Fetch: git fetch https://git.openjdk.org/jdk pull/9779/head:pull/9779
PR: https://git.openjdk.org/jdk/pull/9779
