Hi John,
That was my suspicion and thanks for confirming it.
I wrote a simple benchmark to try to compare the speed of a 'real'
method invocation vs MH.invokeExact
http://cr.openjdk.java.net/~iklam/misc/method_handle_bench/BenchMH.java
Basically
private static void loopMH(int loops, MethodHandle mh) throws
Throwable {
for (int i=0; i<loops; i++) {
mh.invokeExact("yo!");
}
}
-vs-
private static void loopDirect(int loops) {
for (int i=0; i<loops; i++) {
callme("yo!");
}
}
$ java -cp . BenchMH 1000000000
...
MH: loops = 1000000000: elapsed = 10332 ms
direct: loops = 1000000000: elapsed = 7500 ms
So it seems like the JIT still can't handle such a simple case ... :-(
On 4/9/18 1:32 PM, John Rose wrote:
On Apr 9, 2018, at 1:17 PM, Ioi Lam <ioi....@oracle.com
<mailto:ioi....@oracle.com>> wrote:
So why is this first argument not declared as a MethodHandle?
The short answer is to simplify the plumbing of lambda forms.
Method handles are strongly typed but the underlying IR of
lambda forms is weakly typed. This keeps the IR simple.
To make up the difference, casts are inserted where necessary.
Most (not all) uses of MHs are inlined and/or customized,
in which case the JIT simply drops the casts.
— John
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