RFR: 8258946: Fix optimization-unstable code involving signed integer overflow [v2]

[Hao Sun]

> Optimization-unstable code refers to code that is unexpectedly discarded
> by compiler optimizations due to undefined behavior in the program.
> 
> We applied a static checker called STACK (prototype from SOSP'13 paper
> [1]) to OpenJDK source code and found the following six sites of
> potential unstable code involving signed integer overflow.
> 
> Removing undefined behaviors would make the code stable.
> 
> [1] https://css.csail.mit.edu/stack/
> 
> -----
> Note that we tested locally Jtreg tests ( tier1 and jdk::tier3) were passed on Linux x86-64/aarch64 machines after apply this patch.

Hao Sun has updated the pull request incrementally with one additional commit since the last revision:

  Update the copyright year to 2021
  
  Update the copyright year to 2021.
  
  Change-Id: If1c44ff5e88accb96367bec64aa58449a97a36e5
  CustomizedGitHooks: yes

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1900/files
  - new: https://git.openjdk.java.net/jdk/pull/1900/files/1df6f7cd..c3ceef68

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1900&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1900&range=00-01

  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1900.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1900/head:pull/1900

PR: https://git.openjdk.java.net/jdk/pull/1900