8384571: C2: Add some basic IGVN optimization for VectorBlendNode

[erifan]

This PR introduces the basic Ideal/Identity transformations for VectorBlendNode.

The semantic of VectorBlend(X, Y, M) is: M ? Y : X.

Identity:

  (VectorBlend X Y (Replicate -1)) => Y
  (VectorBlend X Y (MaskAll   -1)) => Y
  (VectorBlend X Y (Replicate  0)) => X
  (VectorBlend X Y (MaskAll    0)) => X

Ideal:

  (VectorBlend (VectorBlend X A M) B M)  => (VectorBlend X B M)
  (VectorBlend A (VectorBlend B X M) M)  => (VectorBlend A X M)
  (VectorBlend A B (XorV/XorVMask M -1)) => (VectorBlend B A M)

Also corrects the VectorBlendNode header comment: across all backends (X86 SSE/AVX, AArch64 NEON/SVE, RISC-V V) the active mask lane selects vec2 (in(2)), and the inactive lane selects vec1 (in(1)).

JTReg and JMH tests are also added for each optimization pattern. All tests (tier1, tier2, and tier3) passed on AArch64 and X86 platforms.

JMH benchmark test results:

On a Nvidia Grace (Neoverse-V2) machine with 128-bit SVE2:

Benchmark		        Unit	Before	Error	After		Error	Uplift
blendNegatedMaskInt	    ops/ms	7990.6	2.8	    10215.2		11.0	1.3
identityAllOnesInt	    ops/ms	3574.8	2.6	    7967.1		0.3	    2.2
identityAllZerosLong	ops/ms	3575.6	1.0	    7966.0		3.6	    2.2
nestedBlendInnerLong	ops/ms	3533.8	2.8	    478573.0	3178.5	135.4
nestedBlendOuterInt	    ops/ms	3537.6	3.4	    472242.2	3034.2	133.5

On an AWS Graviton3 (Neoverse-V1) machine with 256-bit SVE1:

Benchmark		        Unit	Before	Error	After		Error	Uplift
blendNegatedMaskInt	    ops/ms	5171.9	5.2	    8129.0		17.3	1.6
identityAllOnesInt	    ops/ms	2722.0	0.1	    5891.3		0.1	    2.2
identityAllZerosLong	ops/ms	2722.4	0.1	    5891.1		0.3	    2.2
nestedBlendInnerLong	ops/ms	2697.6	0.0	    312148.7	2366.4	115.7
nestedBlendOuterInt	    ops/ms	2702.7	0.1	    308686.0	2709.8	114.2

On a Nvidia Grace (Neoverse-V2) machine with -XX:UseSVE=0:

Benchmark		        Unit	Before	Error	After		Error	Uplift
blendNegatedMaskInt	    ops/ms	7718.1	1.9	    9515.9		54.0	1.2
identityAllOnesInt	    ops/ms	3581.9	0.6	    8062.5		0.5	    2.3
identityAllZerosLong	ops/ms	3582.7	0.6	    8058.5		11.9	2.2
nestedBlendInnerLong	ops/ms	3529.6	1.4	    476029.8	5190.2	134.9
nestedBlendOuterInt	    ops/ms	3536.9	2.1	    486060.0	3442.1	137.4

On an AMD EPYC 9124 16-Core Processor with option -XX:UseAVX=3:

Benchmark		        Unit	Before	Error	After		Error	Uplift
blendNegatedMaskInt	    ops/ms	36773.6	541.7	46467.4		499.4	1.3
identityAllOnesInt	    ops/ms	5262.7	3.7	    13644.7		12.1	2.6
identityAllZerosLong	ops/ms	5272.4	3.4	    13665.3		8.4	    2.6
nestedBlendInnerLong	ops/ms	5256.6	4.9	    436643.3	14778.8	83.1
nestedBlendOuterInt	    ops/ms	5253.2	1.5	    223851.3	106003	42.6

On an AMD EPYC 9124 16-Core Processor with option -XX:UseAVX=2:

Benchmark		        Unit	Before	Error	After		Error	Uplift
blendNegatedMaskInt	    ops/ms	24335.3	32.1	30412.3		28.1	1.2
identityAllOnesInt	    ops/ms	5248.8	5.0	    13677.5		18.4	2.6
identityAllZerosLong	ops/ms	5248.8	2.2	    13655.8		2.9	    2.6
nestedBlendInnerLong	ops/ms	5146.2	4.6	    649242.6	1174.4	126.2
nestedBlendOuterInt	    ops/ms	5141.8	6.2	    646255.2	10654.1	125.7

The microbenchmark shows a significant speedup. This is mainly because this PR eliminates redundant computations inside the loop by hoisting them out of the loop. At the same time, it reduces the number of IR uses, which can in turn enable further optimizations.

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Issue

• JDK-8384571: C2: Add some basic IGVN optimization for VectorBlendNode (Enhancement - P4)

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