On Wed, 12 Jan 2022 15:48:20 GMT, Maurizio Cimadamore <[email protected]>
wrote:
> When looking at larger benchmarks, I noted a discrepancy between the
> performance of off-heap segments and on-heap segments. Looking at the
> assembly for the `MemorySegment::asSlice` method I could see some additional
> barriers in the off-heap case, but could not initially make sense of them.
> Vlad pointed me at G1 (in fact no such barrier was emitted when using a
> different GC, such as the serial GC, or ZGC), and later Erik narrowed the
> problem down to a failure in a C2 optimization to remove barriers around
> initializing stores. This problem was caused by a synthetic cast added by
> javac to a value (the base object) that initialized the newly created memory
> segment slice. Because of that case, C2 missed the store as an "initializing"
> one, and inserted additional barriers. This patch should make performance of
> on-heap segments a lot more reliable, especially when slicing is involved.
src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/HeapMemorySegmentImpl.java
line 89:
> 87: public static class OfByte extends HeapMemorySegmentImpl {
> 88:
> 89: OfByte(long offset, Object base, long length, int mask) {
Is it possible to retain the array type for the constructor?
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PR: https://git.openjdk.java.net/jdk18/pull/97
