8347981: RISC-V: Add Zfa zli imm loads

[robehn]

Hi, please consider!

This patch the Zfa zli floating point immediate load.
As a bonus it adds fmv_?_x(Rd, zr); for loading fp/dp 0x0.
There are some more instruction in Zfa, but this was such a clear use-case so I only did fli as a start.

When using one of the 32 'popular' floats we can now materialze them without a load.
E.g.
float f = f1 * 0.5 + f2 * 2.0;
Only require 2 loads instead of 4: as '0.5' and '2.0' is such popular float values.

As Java is often memory bound we should also investigate doing lui+ssli+fmv for float/doubles instead of a load when materializing.

Note the _fli_s/_fli_d will be proper merged on the 8347794: RISC-V: Add Zfhmin - Float cleanup.

Passes:
./test/jdk/java/lang/Math
./test/hotspot/jtreg/compiler/floatingpoint/
./test/jdk/java/util/Formatter/
./test/jdk/java/lang/Float/
./test/jdk/java/lang/Double/
./test/hotspot/jtreg/compiler/c2/FloatingPointFoldingTest.java
./test/hotspot/jtreg/compiler/eliminateAutobox/
./test/hotspot/jtreg/vmTestbase/jit/

Running tier1

Thanks!

---

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Issue

• JDK-8347981: RISC-V: Add Zfa zli imm loads (Enhancement - P4)

Reviewers

• Fei Yang (@RealFYang - Reviewer)
• Ludovic Henry (@luhenry - Committer)

Reviewing

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[bridgekeeper]

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[openjdk]

@robehn This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8347981: RISC-V: Add Zfa zli imm loads

Reviewed-by: fyang, luhenry

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At the time when this comment was updated there had been 46 new commits pushed to the master branch:

• 4a375e5: 8344232: [PPC64] secondary_super_cache does not scale well: C1 and interpreter
• 0df9dcb: 8346572: Check is_reserved() before using ReservedSpace instances
• a09f06d: 8348265: RMIConnectionImpl: Remove Subject.callAs on MarshalledObject
• 0395593: 8346751: Internal java compiler error with type annotations in constants expression in constant fields
• 2daafe4: 8348283: java.lang.classfile.components.snippets.PackageSnippets shipped in java.base.jmod
• 50ca450: 8340784: Remove PassFailJFrame constructor with screenshots
• 416d469: 8347008: beancontext package spec does not clearly explain why the API is deprecated
• 471d63c: 8343609: Broken links in java.xml
• 7f16a08: 8348240: Remove SystemDictionaryShared::lookup_super_for_unregistered_class()
• 48ece07: 8282862: AwtWindow::SetIconData leaks old icon handles if an exception is detected
• ... and 36 more: https://git.openjdk.org/jdk/compare/fb438492275cd15390d26460cada2d5e1a49c159...master

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[openjdk]

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[mlbridge]

Webrevs

• 02: Full (7e2c9d70)
• 01: Full - Incremental (6b3affe0)
• 00: Full (60491784)

[robehn]

Thanks for havinga look @luhenry !

[robehn]

It's seem you made a non-review comment above, I can't reply.

can_zfa_zli_float() method only checks if we can use a zli for that imm.
can_fp_imm_load() checks if we can do something better than loading the imm.

Right now we have two cases:

• imm == 0-bits sets
• imm == zli Rs pattern

As many application are memory bound and loading may miss L1.
This means we want to do plain materializing if we can't more or less guarantee L1 hit and the load do not stall other loads.

Therefore we should add more cases to above, for exampel:
lui + slli + fmw

The callsite is asking do I need to load from an address using fld/flw or can I materialize.
So I prefer the callsite to be unaware that in one of the cases we map an imm to a bit pattern in Rs.

[RealFYang]

Thanks for the update. Seems fine to me modulo one minor comment.

[RealFYang]

Looks good to me. Thanks.

[robehn]

Looks good to me. Thanks.

Thank you !

[robehn]

@luhenry do you have any futher concerns, or are you happy ? :)

[robehn]

Thank you @luhenry !

[robehn]

/integrate

[openjdk]

Going to push as commit 9c55e25.
Since your change was applied there have been 48 commits pushed to the master branch:

• e20bd01: 8344361: Restore null return for invalid services from legacy providers
• 5a0bdd0: 8346890: AArch64: Type profile counters generate suboptimal code
• 4a375e5: 8344232: [PPC64] secondary_super_cache does not scale well: C1 and interpreter
• 0df9dcb: 8346572: Check is_reserved() before using ReservedSpace instances
• a09f06d: 8348265: RMIConnectionImpl: Remove Subject.callAs on MarshalledObject
• 0395593: 8346751: Internal java compiler error with type annotations in constants expression in constant fields
• 2daafe4: 8348283: java.lang.classfile.components.snippets.PackageSnippets shipped in java.base.jmod
• 50ca450: 8340784: Remove PassFailJFrame constructor with screenshots
• 416d469: 8347008: beancontext package spec does not clearly explain why the API is deprecated
• 471d63c: 8343609: Broken links in java.xml
• ... and 38 more: https://git.openjdk.org/jdk/compare/fb438492275cd15390d26460cada2d5e1a49c159...master

Your commit was automatically rebased without conflicts.

[openjdk]

@robehn Pushed as commit 9c55e25.

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