8380424: C2: Fix missing identity optimization for vector nodes

[erifan]

Ideal and Identity optimizations require all input nodes of the IR pattern to be ready for the optimization to take effect. However, node generation in the incremental inlining phase is unordered, so sometimes downstream nodes in the IR pattern are generated before upstream nodes, causing Ideal or Identity optimizations to miss. If no subsequent process triggers the optimization again, the optimization misses forever.

Vector nodes (especially generated by VectorAPI) are often wrapped using VectorBoxNode during generation, and the existence of these box nodes and unbox nodes further hinders the matching of IR optimization patterns. The -XX:VerifyIterativeGVN option allows us to check which IGVN optimizations are missed; however, currently, the verification for Vector nodes is skipped. Enabling the Identity optimization check for vector nodes shows that many tests fail, as shown below.

jdk/incubator/vector/ByteVector128LoadStoreTests.java
jdk/incubator/vector/ByteVector256LoadStoreTests.java
jdk/incubator/vector/ByteVector512LoadStoreTests.java
jdk/incubator/vector/ByteVector64LoadStoreTests.java
jdk/incubator/vector/ByteVectorMaxLoadStoreTests.java
jdk/incubator/vector/ShortVector128LoadStoreTests.java
jdk/incubator/vector/ShortVector256LoadStoreTests.java
jdk/incubator/vector/ShortVector512LoadStoreTests.java
jdk/incubator/vector/ShortVector64LoadStoreTests.java
jdk/incubator/vector/ShortVectorMaxLoadStoreTests.java
jdk/incubator/vector/Vector512ConversionTests.java
jdk/incubator/vector/Vector64ConversionTests.java#id0
jdk/incubator/vector/VectorMaxConversionTests.java#id0

They are caused by the missed optimizations of AndVNode::Identity() and ShiftVNode::Identity(). And from JDK-8370863, we know that VectorStoreMaskNode::Identity() may miss as well.

To recover these potential missed optimizations, we need to trigger them again at appropriate points. Currently, a GVN optimization runs once during node generation, and if no subsequent changes are made, the node will not be added to the IGVN worklist to trigger IGVN optimization again. Therefore, the corresponding nodes need to be added to the IGVN worklist at appropriate points.

Many phases affect the shape of the node tree, but inlining and boxing have a particularly significant impact on vector nodes. After PhaseVector, inlining is complete, and vector boxing/unboxing has been eliminated. At this point, the node tree is fully materialized, with no additional interfering nodes. Therefore, this PR adds all nodes to the IGVN worklist at this point to recover potentially missed GVN optimizations.

However, this modification still cannot handle the situation after PhaseVector, so this PR also enhances the notification of multi-hop IR optimization patterns in add_users_of_use_to_worklist.

With this PR, the above test failures passed in 100 tests, so this PR enables identity optimization verification for vector nodes. We expect that with this PR, there will be very few cases of Vector identity optimization misses; if they do occur, we should fix them rather than skip them.

This PR does not enable Ideal optimization verification for vector nodes because the inputs of some commutative nodes may be swapped in Ideal, causing changes in the hash value, which could lead to verification failure.

We also found many test failures caused by the missing of ShenandoahLoadReferenceBarrierNode::Identity(). This PR skipped the identity verification of the ShenandoahLoadReferenceBarrierNode because it was not investigated in this PR.

This PR tested all tier1 to tier3 jtreg tests on aarch64 (sve, neon) and x64 (avx3, avx2) platforms using options -ea -esa -XX:-TieredCompilation -XX:CompileThreshold=100 -XX:VerifyIterativeGVN=1110, and repeated the test 100 times for the aforementioned error cases. All tests passed.

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 ⚠️ Dependency #28313 must be integrated first

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• JDK-8380424: C2: Fix missing identity optimization for vector nodes (Enhancement - P4)

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