RFR: 8332528: Generate code in SwitchBootstraps.generateTypeSwitch that require fewer adaptations

[Claes Redestad]

On Tue, 21 May 2024 00:16:51 GMT, Chen Liang <liach at openjdk.org> wrote:

>> We can fold the call to `Objects.checkIndex` into the code generated in generateTypeSwitchSkeleton instead of doing so by filtering the MH argument. This loads 9 less classes (of which 8 generated LFs and Species classes) on a minimal test, while being neutral on a throughput sanity test:
>> 
>> 
>> Name                   Cnt  Base   Error   Test   Error  Unit  Change
>> SwitchSanity.switchSum  15 8,162 ± 0,117  8,152 ± 0,131 ns/op   1,00x (p = 0,800 )
>>   * = significant
>>   ```
>> 
>> A few additional optimizations includes generating the switch method using the precise type (to avoid the need for an explicitCast adaptation), and moving some seldom used `findStatic` calls to a holder. All in all this means a reduction by 33-34M cycles to bootstrap a trivial switch expression on my M1.
>
> src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java line 630:
> 
>> 628:                        .withMethodBody("typeSwitch",
>> 629:                                        MethodTypeDescImpl.ofValidated(ConstantDescs.CD_int,
>> 630:                                             ClassDesc.ofDescriptor(selectorType.descriptorString()),
> 
> `selectorType` can be primitive, therefore verification errors arise at `aload` in the generated code. This is why tests fail on GitHub actions.

Dang. I had focused on making the `java/lang/runtime` tests pass locally, thinking that'd be sufficient. Luckily bf68b1d had only a minor benefit. Backing it out and tidying up a bit gives me these numbers:

Wall clock:    65.0 ms/op
.taskclock:    75.0 ms/op
.cycles:       255323158 average cycles elapsed
.instructions: 626086160 average instructions retired

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PR Review Comment: https://git.openjdk.org/jdk/pull/19307#discussion_r1607874407