RFR: 8274328: C2: Redundant CFG edges fixup in block ordering [v2]

[Yi Yang]

> I think Trace::fixup_blocks is redundant because PhaseCFG::fixup_flow will nevertheless fix up the CFG flow(i.e. flip successor blocks of IfNode) right after PhaseBlockLayout pass, we can remove this step when doing PhaseBlockLayout pass.(Testing: jtreg/compiler/c2, presubmit test)
> 
> https://github.com/openjdk/jdk/blob/5ec1cdcaf39229a7d2457313600b0dc2bf8c6453/src/hotspot/share/opto/compile.cpp#L2765
> 
> https://github.com/openjdk/jdk/blob/5ec1cdcaf39229a7d2457313600b0dc2bf8c6453/src/hotspot/share/opto/block.cpp#L1679
> 
> https://github.com/openjdk/jdk/blob/5ec1cdcaf39229a7d2457313600b0dc2bf8c6453/src/hotspot/share/opto/block.cpp#L908-L916

Yi Yang 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 three additional commits since the last revision:

 - use swap(ref,ref)
 - Merge branch 'master' into blockordering
 - 8274328: C2: Redundant CFG edges fixup in block ordering

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5705/files
  - new: https://git.openjdk.java.net/jdk/pull/5705/files/46381c61..7d58a18f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5705&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5705&range=00-01

  Stats: 51547 lines in 1497 files changed: 35427 ins; 10271 del; 5849 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5705.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5705/head:pull/5705

PR: https://git.openjdk.java.net/jdk/pull/5705