review (M) for 4809552: Optimize Arrays.fill(...)

[Osvaldo Doederlein]

2010/8/20 Ulf Zibis <Ulf.Zibis at gmx.de>:
> A comment aside:
> Having:
>     int[] ia = new int[SIZE];
>     Arrays.fill(ia, 1234);
>
> The 1st line causes the array to be first filled with zeroes according the
> JLS.
> The 2nd line causes the array to be *again* filled with 1234's.
>
> This situation could be optimized by the JIT in skipping the zero-filling.
> Maybe this is just done by HotSpot, then forget my 2 cents.

I think the zero-filling is already performed as part of memory
management & GC, so new[] never needs to zero-fill?

A+
Osvaldo

> 1 cent more:
> To give programmer better control of that and to enhance the interpreter in
> the same way, we would need to have an additional syntax, something like:
> int [] ia = new int[SIZE](1234); // Project Coin candidate!
>
> -Ulf
>
>
> Am 20.08.2010 00:11, schrieb Tom Rodriguez:
>
> 4809552: Optimize Arrays.fill(...)
> Reviewed-by:
>
> This adds new logic to recognize fill idioms and convert them into a
> call to an optimized fill routine.  Loop predication creates easily
> matched loops that are simply replaced with calls to the new assembly
> stubs.  Currently only 1,2 and 4 byte primitive types are supported.
> Objects and longs/double will be supported in a later putback.  Tested
> with runthese, nsk and ctw plus jbb2005.
>
> http://cr.openjdk.java.net/~never/4809552
>
>
>