RFR: 8266530: HotSpot changes for JEP 306 [v3]

[David Holmes]

On 11/05/2021 5:14 am, Harold Seigel wrote:
> On Fri, 7 May 2021 04:58:22 GMT, Joe Darcy <darcy at openjdk.org> wrote:
> 
>>> Please review these VM changes in support of JEP 306: Restore Always-Strict Floating-Point Semantics.
>>>
>>> JEP 306 is considering the following changes to the JVMS:
>>>
>>> 1) Require "strict" floating-point evaluation in all circumstances.
>>> 2) For class file version 61 and higher, undefine ACC_STRICT, moving that bit position back to undefined for methods. For class file versions, 46 through, ACC_STRICT would remain a defined modifier.
>>>
>>> Since all floating-point evaluation is done strictly, a modifier bit is not needed to indicate this anymore. There are a few mandated modifier checks when ACC_STRICT is defined, such as not allowing an "abstract strictfp" method. These checks in classFileParser are now conditional on the class file version.
>>>
>>> The tests verify  "abstract strictfp" triggers a ClassFormatError  for version 60 and does not trigger an error or exception for version 61. (As an undefined bit in version 61, the VM is supposed to ignore it.)
>>>
>>> FYI, the javac and core libs portions of JEP 306 are out for review under https://github.com/openjdk/jdk/pull/3831.
>>>
>>> The HotSpot and javac/core libs parts of JEP 306 are independent in that neither relies on the other:
>>>   * javac will not output class files which expose the difference in class parsing behavior; the ACC_STRICT modifier will not be set in any version 61 class file emitted by javac.
>>>   *  since HotSpot already does all floating-point evaluation strictly, no changes are needed to support strict evaluation.
>>
>> Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
>>
>>   - Merge branch 'master' into 8266530
>>   - Respond to review feedback.
>>   - 8266530: HotSpot changes for JEP 306
> 
> Hi Joe,
> If the code that calls is_strict() (and other code that looks at ACC_STRICT) is no longer needed then it should be removed.  Otherwise, that code should be changed to also check if ik->major_version() >= 61.

Right - the normal process would be to update the code based on 
is_strict() always returning true thus eliding it, but retaining the 
code it causes to be called.

David
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> 
> PR: https://git.openjdk.java.net/jdk/pull/3891
>