RFR: 8254146: Avoid unnecessary volatile write on new AtomicBoolean(false)

[Christoph Dreis]

Hi,

the following PR optimizes `new AtomicBoolean(boolean)` by avoiding the volatile write in case `false` is passed.
Essentially, it changes the ternary operator to a simple `if` without the `else` that would cause the volatile write.

The resulting bytecode seems to also benefit from the change:
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: aload_0
       5: iload_1
       6: ifeq          13
       9: iconst_1
      10: goto          14
      13: iconst_0
      14: putfield      #7                  // Field value:I
      17: return

After:
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: iload_1
       5: ifeq          13
       8: aload_0
       9: iconst_1
      10: putfield      #7                  // Field value:I
      13: return

A simple benchmark that returns `new AtomicBoolean(false)` shows the following results, that brings it on par to `new
AtomicBoolean()`: MyBenchmark.empty                                         avgt   10     3,103 ±   0,246   ns/op
MyBenchmark.explicitNew                                   avgt   10     2,966 ±   0,071   ns/op
MyBenchmark.explicitOld                                   avgt   10     7,738 ±   0,321   ns/op

In case you think this is worthwhile I'd be happy if this is sponsored.
Cheers,
Christoph

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

Commit messages:
 - Avoid unnecessary volatile write on new AtomicBoolean(false)

Changes: https://git.openjdk.java.net/jdk/pull/510/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=510&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254146
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/510.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/510/head:pull/510

PR: https://git.openjdk.java.net/jdk/pull/510