RFR: 8248817: Windows: Improving common cross-platform code

[David Holmes]

Hi Ludovic,

On 9/07/2020 11:55 pm, Ludovic Henry wrote:
> Hello,
> 
> As part of adding support for Windows-AArch64, I've had the opportunity to read through most of the Windows-x86 code. In doing so, I found some code that I think can be simplified and made easier to read and maintain.
> 
> The three areas I have found are:
> - Atomics: Hotspot doesn't make use of existing intrinsics provided by MSVC and Win32, even ones available since Windows XP.
> - Exception handling: there is some code repetition which, even if functional, is subpar.
> - Frames: we can use the existing os::fetch_frame_from_context to simplify the code and reduce frame parsing logic duplication.
> 
> I've split the webrevs along the above lines, making each simpler to review. I'm also hosting these webrevs on Bernhard Urban's CR as I currently do not have authorship. I'll also work with him to update the description of the JBS.

Thanks for doing the split!

As a general comment can you please ensure that the Oracle copyright 
second year is updated to 2020. Thanks.

Overall these cleanups look good. Thanks for providing them.

> JBS: https://bugs.openjdk.java.net/browse/JDK-8248817
> Webrevs:
> http://cr.openjdk.java.net/~burban/luhenry/8248817-atomics/

Love this cleanup! Great to see all the stubroutines go for x86.

src/hotspot/os_cpu/windows_x86/atomic_windows_x86.hpp

Please delete this entire (archaic) comment block.

  42 // The following alternative implementations are needed because
  43 // Windows 95 doesn't support (some of) the corresponding Windows NT
  44 // calls. Furthermore, these versions allow inlining in the caller.
  45 // (More precisely: The documentation for InterlockedExchange says
  46 // it is supported for Windows 95. However, when single-stepping
  47 // through the assembly code we cannot step into the routine and
  48 // when looking at the routine address we see only garbage code.
  49 // Better safe then sorry!). Was bug 7/31/98 (gri).
  50 //
  51 // Performance note: On uniprocessors, the 'lock' prefixes are not
  52 // necessary (and expensive). We should generate separate cases if
  53 // this becomes a performance problem.

In this (and elsewhere):

  80 DEFINE_STUB_ADD(4, long,    InterlockedAdd)
  81 DEFINE_STUB_ADD(8, __int64, InterlockedAdd64)

can we use __int32 for clarity rather than "long"?

> http://cr.openjdk.java.net/~burban/luhenry/8248817-exception-handling/

Looks good!

> http://cr.openjdk.java.net/~burban/luhenry/8248817-frames/

Looks good!

Thanks,
David
-----

> Tests: jtreg:hotspot:tier, jtreg:jdk:tier1, jtreg:jdk:tier2, jtreg:langtools on Windows-x86 and Windows-x86_64, no regressions.
> 
> Thank you,
> 
> --
> Ludovic
>