RFR[M]: 8151779: Some intrinsic flags could be replaced with one general flag
Vladimir Kozlov
vladimir.kozlov at oracle.com
Sat May 2 01:00:37 UTC 2020
Hi
I am CCing to runtime group too. I would like to see comments about these changes. No need to look on compiler's changes.
The latest https://cr.openjdk.java.net/~xliu/8151779/02/webrev/
Good work.
On 4/24/20 1:33 AM, Liu, Xin wrote:
> Hi,
>
> May I get reviewed for this new revision?
> JBS: https://bugs.openjdk.java.net/browse/JDK-8151779
> webrev: https://cr.openjdk.java.net/~xliu/8151779/01/webrev/
>
> I introduce a new option -XX:ControlIntrinsic=+_id1,-id2...
> The id is vmIntrinsics::ID. As prior discussion, ControlIntrinsic is expected to replace DisableIntrinsic.
> I keep DisableIntrinsic in this revision. DisableIntrinsic prevails when an intrinsic appears on both lists.
Yes, you have to keep DisableIntrinsic for now. We will deprecate it later.
>
> I use an array of tribool to mark each intrinsic is enabled or not. In this way, hotspot can avoid expensive string querying among intrinsics.
> A Tribool value has 3 states: Default, true, or false.
> If developers don't explicitly set an intrinsic, it will be available unless is disabled by the corresponding UseXXXIntrinsics.
> Traditional Boolean value can't express fine/coarse-grained control. Ie. We only go through those auxiliary options UseXXXIntrinsics if developers don't control a specific intrinsic.
>
> I also add the support of ControlIntrinsic to CompilerDirectives.
>
> Test:
> I reuse jtreg tests of DisableIntrinsic. Add add more @run annotations to verify ControlIntrinsics.
> I passed hotspot:Tier1 test and all tests on x86_64/linux.
Good. I submitted hotspot tier1-3 testing.
Thanks,
Vladimir
>
> Thanks,
> --lx
>
> On 4/17/20, 7:22 PM, "hotspot-compiler-dev on behalf of Liu, Xin" <hotspot-compiler-dev-bounces at openjdk.java.net on behalf of xxinliu at amazon.com> wrote:
>
> Hi, Vladimir,
>
> Thanks for the clarification.
> Oh, yes, it's theoretically possible, but it's tedious. I am wrong at that point.
> I think I got your point. ControlIntrinsics will make developer's life easier. I will implement it.
>
> Thanks,
> --lx
>
>
> On 4/17/20, 6:46 PM, "Vladimir Kozlov" <vladimir.kozlov at oracle.com> wrote:
>
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
>
>
>
> I withdraw my suggestion about EnableIntrinsic from JDK-8151779 because ControlIntrinsics will provide such
> functionality and will replace existing DisableIntrinsic.
>
> Note, we can start deprecating Use*Intrinsic flags (and DisableIntrinsic) later in other changes. You don't need to do
> everything at once. What we need now a mechanism to replace them.
>
> On 4/16/20 11:58 PM, Liu, Xin wrote:
> > Hi, Corey and Vladimir,
> >
> > I recently go through vmSymbols.hpp/cpp. I think I understand your comments.
> > Each UseXXXIntrinsics does control a bunch of intrinsics (plural). Thanks for the hint.
> >
> > Even though I feel I know intrinsics mechanism of hotspot better, I still need a clarification of JDK- 8151779.
> >
> > There're 321 intrinsics (https://chriswhocodes.com/hotspot_intrinsics_jdk15.html).
> > If there's no any option, they are all available for compilers. That makes sense because intrinsics are always beneficial.
> > But there're reasons we need to disable a subset of them. A specific architecture may miss efficient instructions or fixed functions. Or simply because an intrinsic is buggy.
> >
> > Currently, JDK provides developers 2 ways to control intrinsics. > 1. Some diagnostic options. Eg. InlineMathNatives, UseBase64Intrinsics.
> > Developers can use one option to disable a group of intrinsics. That is to say, it's a coarse-grained approach.
> >
> > 2. DisableIntrinsic="a,b,c"
> > By passing a string list of vmIntrinsics::IDs, it's capable of disabling any specified intrinsic.
> >
> > But even putting above 2 approaches together, we still can't precisely control any intrinsic.
>
> Yes, you are right. We seems are trying to put these 2 different ways into one flag which may be mistake.
>
> -XX:ControlIntrinsic=-_updateBytesCRC32C,-_updateDirectByteBufferCRC32C is a similar to -XX:-UseCRC32CIntrinsics but it
> requires more detailed knowledge about intrinsics ids.
>
> May be we can have 2nd flag, as you suggested -XX:UseIntrinsics=-AESCTR,+CRC32C, for such cases.
>
> > If we want to enable an intrinsic which is under control of InlineMathNatives but keep others disable, it's impossible now. [please correct if I am wrong here].
>
> You can disable all other from 321 intrinsics with DisableIntrinsic flag which is very tedious I agree.
>
> > I think that the motivation JDK-8151779 tried to solve.
>
> The idea is that instead of flags we use to control particular intrinsics depending on CPU we will use vmIntrinsics::IDs
> or other tables as you showed in your changes. It will require changes in vm_version_<cpu> codes.
>
> >
> > If we provide a new option EnableIntrinsic and put it least priority, then we can precisely control any intrinsic.
> > Quote Vladimir Kozlov "DisableIntrinsic list prevails if an intrinsic is specified on both EnableIntrinsic and DisableIntrinsic."
> >
> > "-XX:ControlIntrinsic=+_dabs,-_fabs,-_getClass" looks more elegant, but it will confuse developers with DisableIntrinsic.
> > If we decide to deprecate DisableIntrinsic, I think ControlIntrinsic may be a better option. Now I prefer to provide EnableIntrinsic for simplicity and symmetry.
>
> I prefer to have one ControlIntrinsic flag and deprecate DisableIntrinsic. I don't think it is confusing.
>
> Thanks,
> Vladimir
>
> > What do you think?
> >
> > Thanks,
> > --lx
> >
> >
> > On 4/13/20, 1:47 PM, "hotspot-compiler-dev on behalf of Corey Ashford" <hotspot-compiler-dev-bounces at openjdk.java.net on behalf of cjashfor at linux.ibm.com> wrote:
> >
> > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> >
> >
> >
> > On 4/13/20 10:33 AM, Liu, Xin wrote:
> > > Hi, compiler developers,
> > > I attempt to refactor UseXXXIntrinsics for JDK-8151779. I think we still need to keep UseXXXIntrinsics options because many applications may be using them.
> > >
> > > My change provide 2 new features:
> > > 1) a shorthand to enable/disable intrinsics.
> > > A comma-separated string. Each one is an intrinsic. An optional tailing symbol + or '-' denotes enabling or disabling.
> > > If the tailing symbol is missing, it means enable.
> > > Eg. -XX:UseIntrinsics="AESCTR-,CRC32C+,CRC32-,MathExact"
> > > This jvm option will expand to multiple options -XX:-UseAESCTRIntrinsics, -XX:+UseCRC32CIntrinsics, -XX:-UseCRC32Intrinsics, -XX:UseMathExactIntrinsics
> > >
> > > 2) provide a set of macro to declare intrinsic options
> > > Developers declare once in intrinsics.hpp and macros will take care all other places.
> > > Here are example: https://cr.openjdk.java.net/~xliu/8151779/00/webrev/src/hotspot/share/compiler/intrinsics.hpp.html
> > > Ion Lam is overhauling jvm options. I am thinking how to be consistent with his proposal.
> > >
> >
> > Great idea, though to be consistent with the original syntax, I think
> > the +/- should be in front of the name:
> >
> > -XX:UseIntrinsics=-AESCTR,+CRC32C,...
> >
> >
> > > I handle UseIntrinsics before VM_Version::initialize. It means that platform-specific initialization still has a chance to correct those options.
> > > If we do that after VM_Version::initialize, some intrinsics may cause JVM crash. Eg. +UseBase64Intrinsics on x86_64 Linux.
> > > Even though this behavior is same as -XX:+UseXXXIntrinsics, from user's perspective, it's not straightforward when JVM overrides what users specify implicitly. It's dilemma here, stable jvm or fidelity of cmdline. What do you think?
> > >
> > > Another problem is naming convention. Almost all intrinsics options use UseXXXIntrinsics. One exception is UseVectorizedMismatchIntrinsic.
> > > Personally, I think it should be "UseXXXIntrinsic" because one option is for one intrinsic, right? Is it possible to change this name convention?
> >
> > Some (many?) intrinsic options turn on more than one .ad instruct
> > instrinsic, or library instrinsics at the same time. I think that's why
> > the plural is there. Also, consistently adding the plural allows you to
> > add more capabilities to a flag that initially only had one intrinsic
> > without changing the plurality (and thus backward compatibility).
> >
> > Regards,
> >
> > - Corey
> >
> >
>
>
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