RFR: 8215380: Backout accidental change to String::length

[Stuart Marks]

Hi Claes,

Thank for catching this. Looks good.

Note that the original changeset (JDK-8215281) went into JDK 12 before the RDP1 
fork, so this fix should also go into JDK 12. That's a different repo now. It 
will then be auto-propagated to the JDK mainline ("JDK 13").

Since JDK-8215380 is a P3 bug, it's eligible to go into JDK 12 after RDP1 
without any further approval.

s'marks


On 12/13/18 3:20 PM, Claes Redestad wrote:
> Hi,
> 
> I need to revert an accidental change to String.length
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8215380
> Patch inlined below
> 
> Running the accidentally pushed version in naive microbenchmarks showed
> that avoiding the shift operation can improve throughput of str.length()
> by a small measure (~1.06x) for latin1-only inputs, neutral for mixed
> or utf16-only inputs, but also adds a branch (visible in profiling)
> which could blow up in more real cases. Regardless, it should be
> reviewed and discussed on it's own merits. Sorry!
> 
> /Claes
> 
> diff -r 8bf9268df0e2 src/java.base/share/classes/java/lang/String.java
> --- a/src/java.base/share/classes/java/lang/String.java    Thu Dec 13 15:31:05 
> 2018 +0100
> +++ b/src/java.base/share/classes/java/lang/String.java    Thu Dec 13 23:59:43 
> 2018 +0100
> @@ -664,7 +664,7 @@
>        *          object.
>        */
>       public int length() {
> -        return isLatin1() ? value.length : value.length >> UTF16;
> +        return value.length >> coder();
>       }
> 
>       /**