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

[Chen Liang]

On Mon, 20 May 2024 10:52:27 GMT, Claes Redestad <redestad 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.

Changes requested by liach (Author).

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.

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PR Review: https://git.openjdk.org/jdk/pull/19307#pullrequestreview-2067245226
PR Review Comment: https://git.openjdk.org/jdk/pull/19307#discussion_r1607425026