RFR[M]: 8151779: Some intrinsic flags could be replaced with one general flag

[Liu, Xin]

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.   

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. 

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
        >
        >