8374169: too many unsafe intrinsics (simplify unsafe intrinsic processing)

[rose00]

first cut: passes smoke tests in interpreter and C1 (aarch64)

https://bugs.openjdk.org/browse/JDK-8374169
too many intrinsics

Fold getIntAcquire and every other getFooBar into getPrimitiveBitsMO(mo, bt, base, offset).
Do similar moves for put and the various CAS operations.

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 ⚠️ Title mismatch between PR and JBS for issue JDK-8374169

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 ⚠️ Found leading lowercase letter in issue title for 8374169: too many unsafe intrinsics (simplify unsafe intrinsic processing)

Issue

• JDK-8374169: too many unsafe intrinsics (Enhancement - P4) ⚠️ Title mismatch between PR and JBS.

Reviewers without OpenJDK IDs

• @khanbilal732 (no known openjdk.org user name / role) 🔄 Re-review required (review applies to d2f0c35a)

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[openjdk]

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[rose00]

Status:

No testing beyond looking for smoke when I run javac (in the changed VM).

I have not gone looking for inlining failures. I know they are endemic in C2.

I think the interpreter support (native methods) is stable, as are JDK code adjustments.

The vmIntrinsics.hpp declarations define a bunch of “polymorphic intrinsic wrappers” (F_PW).
I think we should eventually remove them all; there’s no value to this classification.
(But we should find a way to ensure that Unsafe wrappers never fail to inline!)

C2 support is not started yet. It should be relatively simple, as with C1.
When C2 is done, I will try to remove the old intrinsic names, and see what breaks.

The C1 support is nearly stable. Smoke test with javac passes.
The IR for CAS should be further simplified, to make it easier to consider cmpxchg.

I added some C1 canonicalization logic for back-to-back conversions.
For example, when you run javac on a small job, C1 simplifies 71 instances of l2i(i2l(x) ⇒ x.
It may be we can avoid adding those canonicalizations, but they do help the poly-intrinsics.

[rose00]

Overall goal is to thin out the current Dark Forest of intrinsics, which has become overgrown.
Besides improving maintainability, my goal here is to prepare for new intrinsics in the future.
Keeping up with the hardware is too difficult, if you have to add a new intrinsic for every single instruction.
That why folding groups of single-instruction intrinsics to single polymorphic intrinsics
will help us keep up with hardware capabilities.

[ExE-Boss]

I think the final modifier should be kept on the Unsafe methods to ease the burden on reviewing the git diff.

[ExE-Boss]

I think it might be better to keep these parametrised memory order implementation methods private without changing the Java API by changing @IntrinsicCandidate to @ForceInline on all the [get/put/compareAnd​[Set/⁠Exchange]]​<Type>​[/Opaque/Acquire/Release/Volatile] methods.

[rose00]

Yes, exporting the primitive type polymorphism is too much, at least for now. (I know about the one public method that is still private.) The BT values can go private as well.

As you can see, I am experimenting with polymorphism of memory ordering, although I think we need to retain the Volatile versions of everything, which I find annoying. But the Plain Acquire Release and Opaque versions are just too niche-y; the power user that wants them needs to just use the new MO constants.

Regarding the final modifier, 1. it has no force since the class as a whole is already final, 2. it has been used inconsistently in the API to date, and 3. there is lots of review friction in this big changeset, which may require breaking it up into a queue of changesets. We’ll probably do that breakup when the time for integration comes closer.

The OP constants will stay public, to reduce the number of names while still providing full functionality. Also, RISC-V has min and max reduction ops (signed and unsigned) and that suggests to me that we are not done adding OP modes, for the get-and-operate API points.

[openjdk]

@rose00 shenandoah has been added to this pull request based on files touched in new commit(s).

[rose00]

One idea behind this new polymorphism of MO and BT and OP: The Unsafe API is not useful as an important arbitration point for what hardware operations are surfaced upward through the JDK. The JITs have a much more fundamental role as arbitration points. Unsafe “gets out of the way” by providing all reasonable combinations of MO and BT and OP, and then the JITs can make the call (following the evolution of hardware) what to expose.

In the previous configuration, get-and-bitop (bitop = and, xor, etc.) are provided by our major platforms, and yet they are inaccessible because Unsafe provides a choke-point that blocks them from the rest of the system.

BTW, get-and-max might be a good way to handle monotonically versioned values. And 128-bit atomics are here today, but not visible yet. Valhalla comes first to open up the possibilities for a 128-bit hyper-long, and then we can consider surfacing the 128-bit hardware primitives. Polymorphism makes it easy to climb the hill of functionality without slipping into a combinatorial swamp.

[rose00]

BTW, I am not asking for anybody to press the Review button, yet. This is a draft review.

If you have a helpful comment, please do make it. (Thanks, ExE-Boss.)

But pressing the Review button, at this point, doesn’t help me with this task.

Also, pressing the review button with no comments is the same as adding a silly comment, identifying the button-presser as a noise source.