8266528: Optimize C2 VerifyIterativeGVN execution time

[huishi-hs]

Optimization for VerifyIterativeGVN, motiviation is running with -XX:+VerifyIterativeGVN is extremly slow.

In simple test "-Xcomp -XX:+VerifyIterativeGVN -XX:-TieredCompilation -version", time reduced from 8.67s to 2.4s.
In extreme case hotspot/test/jtreg/compiler/escapeAnalysis/Test6689060.java, time reduced from 20000s to 92s.
Detail data in JBS description.

Optimizations includes:

1. Optimize redundant verfications in PhaseIterGVN::verify_step. Nodes might verified multiple times.
   Redundant verifications between full pass and _verify_window single node process.
   Redundant verifications between different nodes in _verify_window

2. Optimize def-use edge checking:
   Skip multiple checks for same x->n input edges.
   Skip redundant check in inner loop when counting how many x in n's input edges, skip current index.

3. Optimize field access
   Replace "n->in(j)" with "n->_in[j]", skipping unuseful assert when invoking Node::in(int index).

Optimization#2/#3 decrease execution time and no other overhead.
optimization#1 adds 3 fields in class Node in debug build, they can be squeezed into an "int/long" if needed.

  jint _igvn_verify_depth_cur;
  jint _igvn_verify_depth_prev;
  julong _igvn_verify_epoch;

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Issue

• JDK-8266528: Optimize C2 VerifyIterativeGVN execution time

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[openjdk]

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[huishi-hs]

Not sure if adding fields in Node class debug builds in acceptable for verification purpose. Would appreciate for any comments.

[mlbridge]

Webrevs

• 00: Full (11842903)

[huishi-hs]

close this. optimize VerifyIterativeGVN with better solution