8331764: C2 SuperWord: refactor _align_to_ref/_mem_ref_for_main_loop_alignment

[eme64]

This PR accomplishes these things:

• Rename _align_to_ref -> _mem_ref_for_main_loop_alignment.
• Move the mem_ref finding for alignment out of SuperWord::find_adjacent_refs. This is too early, and we don't even know if the relevant mem_ref is going to be vectorized. It makes more sense to pick a mem_ref directly in SuperWord::adjust_pre_loop_limit_to_align_main_loop_vectors, where we already know what packs are going to be vectorized.
• For the alignment width (aw), we can use the vector_width of the pack to which the mem_ref belongs, rather than the potentially much larger vector_width_in_bytes. I track this with _aw_for_main_loop_alignment now.

I need this for #18822, and decided to split it out into an independent change.

---

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Issue

• JDK-8331764: C2 SuperWord: refactor _align_to_ref/_mem_ref_for_main_loop_alignment (Enhancement - P4)

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer)
• Christian Hagedorn (@chhagedorn - Reviewer)

Reviewing

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[openjdk]

@eme64 This change now passes all automated pre-integration checks.

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8331764: C2 SuperWord: refactor _align_to_ref/_mem_ref_for_main_loop_alignment

Reviewed-by: kvn, chagedorn

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At the time when this comment was updated there had been 203 new commits pushed to the master branch:

• d654124: 8331932: Startup regressions in 23-b13
• 7db6a3f: 8331905: Fix direct includes of g1_globals.hpp
• f47fc86: 8331908: Simplify log code in vectorintrinsics.cpp
• b9a142a: 8226990: GTK & Nimbus LAF: Tabbed pane's background color is not expected one when change the opaque checkbox.
• d2d37c9: 8331942: On Linux aarch64, CDS archives should be using 64K alignment by default
• a706ca4: 8329418: Replace pointers to tables with offsets in relocation bitmap
• a643d6c: 8331862: Remove split relocation info implementation
• d47a4e9: 8332008: Enable issuestitle check
• 0bf7282: 8331231: containers/docker/TestContainerInfo.java fails
• ffbdfff: 8331999: BasicDirectoryModel/LoaderThreadCount.java frequently fails on Windows in CI
• ... and 193 more: https://git.openjdk.org/jdk/compare/ea3909acd117cab97c6c0b496f98f9a4a3a22be4...master

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[mlbridge]

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• 00: Full (3c149798)

[vnkozlov]

I assume first is verified already and first->memory_size() is reasonable (size of primitive type).

[eme64]

Yes, it is. All of this code is run in SuperWord::output, and at this point we are committed to vectorization - everything is verified.

[eme64]

That is what I tried to say in the PR description:

It makes more sense to pick a mem_ref directly in SuperWord::adjust_pre_loop_limit_to_align_main_loop_vectors, where we already know what packs are going to be vectorized.

[eme64]

Yes, first->memory_size() knows the size in bytes of the load/store. It is used many places in SuperWord.

[vnkozlov]

Good.

[chhagedorn]

Looks good to me, too!

[eme64]

Thanks @vnkozlov @chhagedorn for the reviews!
/integrate

[openjdk]

Going to push as commit d517d2d.
Since your change was applied there have been 223 commits pushed to the master branch:

• 5053b70: 8278255: Add more warning text in ReentrantLock and ReentrantReadWriteLock
• 32c7681: 8332029: Provide access to initial value of stderr via JavaLangAccess
• f9a1d33: 8332020: jwebserver tool prints invalid URL in case of IPv6 address binding
• b87a7e9: 8144100: Incorrect case-sensitive equality in com.sun.net.httpserver.BasicAuthenticator
• 1dac34f: 8331098: [Aarch64] Fix crash in Arrays.equals() intrinsic with -CCP
• 5e8e8ef: 8315431: ArchiveHeapWriter::get_filler_size_at() cannot handle buffer expansion
• 1b476f5: 8293345: SunPKCS11 provider checks on PKCS11 Mechanism are problematic
• 1c5f150: 8331734: Atomic MemorySegment VarHandle operations fails for element layouts
• 65abf24: 8331866: Add warnings for locale data dependence
• d215bc4: 8332066: AArch64: Math test failures since JDK-8331558
• ... and 213 more: https://git.openjdk.org/jdk/compare/ea3909acd117cab97c6c0b496f98f9a4a3a22be4...master

Your commit was automatically rebased without conflicts.

[openjdk]

@eme64 Pushed as commit d517d2d.

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