RFR: 8354242: VectorAPI: combine vector not operation with compare [v9]

[Emanuel Peter]

On Wed, 25 Jun 2025 10:08:23 GMT, erifan <duke at openjdk.org> wrote:

>> This patch optimizes the following patterns:
>> For integer types:
>> 
>> (XorV (VectorMaskCmp src1 src2 cond) (Replicate -1))
>>     => (VectorMaskCmp src1 src2 ncond)
>> (XorVMask (VectorMaskCmp src1 src2 cond) (MaskAll m1))
>>     => (VectorMaskCmp src1 src2 ncond)
>> 
>> cond can be eq, ne, le, ge, lt, gt, ule, uge, ult and ugt, ncond is the negative comparison of cond.
>> 
>> For float and double types:
>> 
>> (XorV (VectorMaskCast (VectorMaskCmp src1 src2 cond)) (Replicate -1))
>>     => (VectorMaskCast (VectorMaskCmp src1 src2 ncond))
>> (XorVMask (VectorMaskCast (VectorMaskCmp src1 src2 cond)) (MaskAll m1))
>>     => (VectorMaskCast (VectorMaskCmp src1 src2 ncond))
>> 
>> cond can be eq or ne.
>> 
>> Benchmarks on Nvidia Grace machine with 128-bit SVE2: With option `-XX:UseSVE=2`:
>> 
>> Benchmark			Unit	Before		Score Error	After		Score Error	Uplift
>> testCompareEQMaskNotByte	ops/s	7912127.225	2677.289518	10266136.26	8955.008548	1.29
>> testCompareEQMaskNotDouble	ops/s	884737.6799	446.963779	1179760.772	448.031844	1.33
>> testCompareEQMaskNotFloat	ops/s	1765045.787	682.332214	2359520.803	896.305743	1.33
>> testCompareEQMaskNotInt		ops/s	1787221.411	977.743935	2353952.519	960.069976	1.31
>> testCompareEQMaskNotLong	ops/s	895297.1974	673.44808	1178449.02	323.804205	1.31
>> testCompareEQMaskNotShort	ops/s	3339987.002	3415.2226	4712761.965	2110.862053	1.41
>> testCompareGEMaskNotByte	ops/s	7907615.16	4094.243652	10251646.9	9486.699831	1.29
>> testCompareGEMaskNotInt		ops/s	1683738.958	4233.813092	2352855.205	1251.952546	1.39
>> testCompareGEMaskNotLong	ops/s	854496.1561	8594.598885	1177811.493	521.1229	1.37
>> testCompareGEMaskNotShort	ops/s	3341860.309	1578.975338	4714008.434	1681.10365	1.41
>> testCompareGTMaskNotByte	ops/s	7910823.674	2993.367032	10245063.58	9774.75138	1.29
>> testCompareGTMaskNotInt		ops/s	1673393.928	3153.099431	2353654.521	1190.848583	1.4
>> testCompareGTMaskNotLong	ops/s	849405.9159	2432.858159	1177952.041	359.96413	1.38
>> testCompareGTMaskNotShort	ops/s	3339509.141	3339.976585	4711442.496	2673.364893	1.41
>> testCompareLEMaskNotByte	ops/s	7911340.004	3114.69191	10231626.5	27134.20035	1.29
>> testCompareLEMaskNotInt		ops/s	1675812.113	1340.969885	2353255.341	1452.4522	1.4
>> testCompareLEMaskNotLong	ops/s	848862.8036	6564.841731	1177763.623	539.290106	1.38
>> testCompareLEMaskNotShort	ops/s	3324951.54	2380.29473	4712116.251	1544.559684	1.41
>> testCompareLTMaskNotByte	ops/s	7910390.844	2630.861436	10239567.69	6487.441672	1.29
>> testCompareLTMaskNotInt		ops/s	16721...
>
> erifan has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 15 additional commits since the last revision:
> 
>  - Address more comments
>    
>    ATT.
>  - Merge branch 'master' into JDK-8354242
>  - Support negating unsigned comparison for BoolTest::mask
>    
>    Added a static method `negate_mask(mask btm)` into BoolTest class to
>    negate both signed and unsigned comparison.
>  - Addressed some review comments
>  - Merge branch 'master' into JDK-8354242
>  - Refactor the JTReg tests for compare.xor(maskAll)
>    
>    Also made a bit change to support pattern `VectorMask.fromLong()`.
>  - Merge branch 'master' into JDK-8354242
>  - Refactor code
>    
>    Add a new function XorVNode::Ideal_XorV_VectorMaskCmp to do this
>    optimization, making the code more modular.
>  - Merge branch 'master' into JDK-8354242
>  - Update the jtreg test
>  - ... and 5 more: https://git.openjdk.org/jdk/compare/78e42324...5ebdc572

src/hotspot/share/opto/vectornode.cpp line 2243:

> 2241:       !VectorNode::is_all_ones_vector(in2)) {
> 2242:     return nullptr;
> 2243:   }

Suggestion:

  if (in1->Opcode() != Op_VectorMaskCmp ||
      in1->outcnt() != 1 ||
      !(in1->as_VectorMaskCmp())->predicate_can_be_negated() ||
        !VectorNode::is_all_ones_vector(in2)) {
    return nullptr;
  }

Indentation for clarity.

Currently, you exiting if one of these is the case:
1. Not `MaskCmp`
2. More than one use
3. predicate cannot be negated AND the vector is all ones. Can you explain this condition? Do you have tests for cases:
   - predicate negatable and vector not all ones
   - predircate not negatable and vector not all ones
   - predicate negatable and vector all ones
   - predicate not negatable and vectors all ones
 
Why do you guard against `VectorNode::is_all_ones_vector(in2)` at all?

The condition for 3. is easy to get wrong, so good testing is important here :)

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/24674#discussion_r2189075462