RFR: 8283232: x86: Improve vector broadcast operations

[Quan Anh Mai]

Hi,

This patch improves the generation of broadcasting a scalar in several ways:

- Avoid potential data bypass delay which can be observed on some platforms by using the correct type of instruction if it does not require extra instructions.
- As it has been pointed out, dumping the whole vector into the constant table is costly in terms of code size, this patch minimises this overhead for vector replicate of constants. Also, options are available for constants to be generated with more alignment so that vector load can be made efficiently without crossing cache lines.
- Vector broadcasting should prefer rematerialising to spilling when register pressure is high.

This patch also removes some redundant code paths and rename some incorrectly named instructions.

Thank you very much.

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Commit messages:
 - fix
 - fix
 - minor changes
 - rematerialize
 - improve
 - fix
 - initial commit

Changes: https://git.openjdk.java.net/jdk/pull/7832/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7832&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283232
  Stats: 400 lines in 12 files changed: 237 ins; 79 del; 84 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7832.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7832/head:pull/7832

PR: https://git.openjdk.java.net/jdk/pull/7832