8325155: C2 SuperWord: remove alignment boundaries

[eme64]

I have tried for a very long time to get rid of all the alignment(n) code that is all over the SuperWord code. With lots of previous work, I am now finally ready to remove it.

I was able to remove lots of VM code, about 300 lines. And the removed code is I think much more complicated than the new code.

This is what I did in this PR:

• Removal of _node_info: used to have many fields, which I refactored out to the VLoopAnalyzer modules. alignment is the last component, which I now remove.
• Changed the implementation of SuperWord::find_adjacent_refs, now SuperWord::find_adjacent_memop_pairs, completely:
  • It used to be an algorithm that would scan over all memops repeatedly, try to find some mem_ref and see which other memops were comparable, and then pack pairs for all of those, by comparing all-vs-all memops. This algorithm is at least quadratic, if not much worse.
  • I now add all memops into a single array, sort them by groups (those that are comparable with each other and could be packed into vectors), and inside the groups by ascending offset. This allows me to split off the groups much more efficiently, and also the sorting by offset allows me finding adjacent pairs much more efficiently. In the most cases this reduces the cost to O(n log n) for sort, and a linear scan for finding adjacent memops.
• I removed the "alignment boundaries" created in SuperWord::memory_alignment by int off_rem = offset % vw;.
  • This used to have the effect that all offsets were computed modulo the vector width. Hence, pairs could not be packed across this boundary (e.g. we have nodes with offsets 31, 32, which are adjacent in theory, but if we have a vw = 32, then the modulo-offsets are 31, 0, and they are not detected as adjacent).
  • These "alignment boundaries" used to be required for correctness about a year ago, before I fixed and relaxed much of the alignment code.
• The alignment used to have another important task: Ensuring compatibility of the input-size of a use node, with the output-size of the def-node.
  • This was done by giving all nodes an alignment, even the non-memop nodes. This alignment was then scaled up and down at type casts (e.g. int 0, 4, 8, 12 -> long 0, 8, 16, 24). If the output-size of the def-node did not match the input-size of the use-node, then the alignment would not match up, and we would not pack.
  • This is why we used to have checks like alignment(s1) + data_size(s1) == alignment(s2) and s2_align == align + data_size(s1), and why we did set_alignment(s2, align + data_size(s1)); inside SuperWord::set_alignment(Node* s1, Node* s2, int align).
  • I decided to NOT check if use/def type sizes match during packing, but only much later in SuperWord::profitable (bad name, it has always been more about checking consistency than profitability, but I will rename that in a Future RFE). The relevant code is in SuperWord::is_velt_basic_type_compatible_use_def.

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Issue

• JDK-8325155: C2 SuperWord: remove alignment boundaries (Enhancement - P4)

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

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8325155: C2 SuperWord: remove alignment boundaries

Reviewed-by: chagedorn, kvn

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At the time when this comment was updated there had been 165 new commits pushed to the master branch:

• 2a37764e7428d579a3080e62681f1c9c9f816c1e: 8333743: Change .jcheck/conf branches property to match valid branches
• 75dc2f8518d0adea30f7065d6732b807c0220756: 8330182: Start of release updates for JDK 24
• 054362abe040938b87eb1a1cab8a0a94540e0667: 8332550: [macos] Voice Over: java.awt.IllegalComponentStateException: component must be showing on the screen to determine its location
• 9b436d048ec92f74ec6812ae20fde21751927d4b: 8333674: Disable CollectorPolicy.young_min_ergo_vm for PPC64
• 487c4771818999749bfd507ab85777795bba0832: 8333647: C2 SuperWord: some additional PopulateIndex tests
• d02cb742f79e88c6438ca58a6357fe432fb286cb: 8333270: HandlersOnComplexResetUpdate and HandlersOnComplexUpdate tests fail with "Unexpected reference" if timeoutFactor is less than 1/3
• 02f240415cbda5f67a91af50d5974fb001104170: 8333560: -Xlint:restricted does not work with --release
• 606df441410a69034b4c113e85ce21937d1a0808: 8332670: C1 clone intrinsic needs memory barriers
• 33fd6ae98638d2a4b33d18cc4acee4f0daaa9b35: 8333622: ubsan: relocInfo_x86.cpp:101:56: runtime error: pointer index expression with base (-1) overflowed
• 8de5d2014a87d58d389eb8400f619d1b1fa3abe7: 8332865: ubsan: os::attempt_reserve_memory_between reports overflow
• ... and 155 more: https://git.openjdk.org/jdk/compare/da6aa2a86c86ba5fce747b36dcb2d6001cfcc44e...master

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[eme64]

Thanks @chhagedorn for the review! I think I addressed all your points. Except for this:

You should mention here that this method finally adds a new pair to the _pairset. On a separate note, find_adjacent_memop_pairs_in_group() suggests that we find something but we actually "find and add" something without returning anything from the method. Should we make this more clear in the method name?

I have not yet found a better name. I think find is ok here. I guess we could have it be find_and_add but this seems unnecessarily long to me.

[eme64]

FYI: I ran performance benchmarking, and there was no significant difference.

[vnkozlov]

Thank you for running performance testing.

[eme64]

@vnkozlov thanks for the review! I will integrate as soon as the JDK24 fork happens ;)

[eme64]

Thanks @chhagedorn @vnkozlov for the reviews! /integrate

[openjdk[bot]]

Going to push as commit 944aeb81b16e3e7a3019cafdefe67b797fa6be96. Since your change was applied there have been 167 commits pushed to the master branch:

• d8af58941b5dedb9774c0971895c4924e57ac28b: 8026127: Deflater/Inflater documentation incomplete/misleading
• 6238bc8da2abe7a1f0cdd98c0af01e9ba1869ec3: 8333456: CompactNumberFormat integer parsing fails when string has no suffix
• 2a37764e7428d579a3080e62681f1c9c9f816c1e: 8333743: Change .jcheck/conf branches property to match valid branches
• 75dc2f8518d0adea30f7065d6732b807c0220756: 8330182: Start of release updates for JDK 24
• 054362abe040938b87eb1a1cab8a0a94540e0667: 8332550: [macos] Voice Over: java.awt.IllegalComponentStateException: component must be showing on the screen to determine its location
• 9b436d048ec92f74ec6812ae20fde21751927d4b: 8333674: Disable CollectorPolicy.young_min_ergo_vm for PPC64
• 487c4771818999749bfd507ab85777795bba0832: 8333647: C2 SuperWord: some additional PopulateIndex tests
• d02cb742f79e88c6438ca58a6357fe432fb286cb: 8333270: HandlersOnComplexResetUpdate and HandlersOnComplexUpdate tests fail with "Unexpected reference" if timeoutFactor is less than 1/3
• 02f240415cbda5f67a91af50d5974fb001104170: 8333560: -Xlint:restricted does not work with --release
• 606df441410a69034b4c113e85ce21937d1a0808: 8332670: C1 clone intrinsic needs memory barriers
• ... and 157 more: https://git.openjdk.org/jdk/compare/da6aa2a86c86ba5fce747b36dcb2d6001cfcc44e...master

Your commit was automatically rebased without conflicts.

[openjdk[bot]]

@eme64 Pushed as commit 944aeb81b16e3e7a3019cafdefe67b797fa6be96.

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