RFR: 8305324: C2: Wrong execution of vectorizing Interger.reverseBytes [v3]

[Daohan Qu]

> This patch should fix [JDK-8305324](https://bugs.openjdk.org/browse/JDK-8305324).
> 
> `SuperWord::compute_vector_element_type()` implemented in `jdk/src/hotspot/share/opto/superword.cpp` propagates backward a narrower integer type when the upper bits of the value are not needed. However, `Integer.reverseBytes()` depends on higher-order bits of an integer and should be prevented from being narrowed and vectorized. Instead, it needs to be treated like `Math.abs()` (which is represented by `Op_AbsI` in the following code).
> 
> https://github.com/openjdk/jdk/blob/0243da2e4adc1b7ab6fcd5b10778532101158dce/src/hotspot/share/opto/superword.cpp#L3935-L3945
> 
> I have tested this patch for tier 1-3 on x86-64.

Daohan Qu has updated the pull request incrementally with one additional commit since the last revision:

  Use a function in branch condition as suggested

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13406/files
  - new: https://git.openjdk.org/jdk/pull/13406/files/cafec83b..7d90bfaa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13406&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13406&range=01-02

  Stats: 24 lines in 3 files changed: 17 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/13406.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13406/head:pull/13406

PR: https://git.openjdk.org/jdk/pull/13406