On 23/07/2017 14:37, Claes Redestad wrote:
Hi,
java.lang.CharacterDataLatin1 and others are generated at build time
by the GenerateCharacter tool, which has a -string mode to generate
lookup tables as Strings literals rather than arrays directly. This
serves multiple purposes:
1. it reduces the size of the generated bytecode, which is necessary
to keep code below method bytecode limits if the arrays generated are
very large
2. it may under certain circumstances (large enough arrays, JITed
code) be a performance optimization
While having other performance benefits, the compact strings feature
that went into 9 made String::toCharArray less friendly to startup,
and since the same feature means we're now always loading
CharacterDataLatin1 on bootstrap in all locales it seemed reasonable
to re-examine whether this class in particular really gains from
generating its lookup tables via String literals.
Turns out it doesn't. By generating CharacterDataLatin1 tables as
arrays explicitly:
- executed bytecode drop from 21,782 to 2,077 when initializing this
class (approximately 2% of executed bytecode; 1.5% of total instructions)
- slight reduction (~1Kb) in the minimum retained heap usage
- the size of CharacterDataLatin1.class only grows from 6458 to 7385
bytes
Proposed patch is to drop passing -string to GenerateCharacter for the
latin1 case:
Webrev: http://cr.openjdk.java.net/~redestad/8185104/jdk.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8185104
This is a good sleuthing. I can't see of any reason why the tables in
CharacterDataLatin1 need to be generated as Strings now I think this
change is good.
-Alan
