RFR: 8221647: [lworld] Performance regression due to the fact that check if array is array of values is not hoisted out of the loop.
sergey.kuksenko at oracle.com
Wed May 29 20:16:14 UTC 2019
Quick check have shown that the fix solves the issue. Looks very
promising. More details will be available tomorrow.
On 5/29/19 6:51 AM, Roland Westrelin wrote:
> This patch includes:
> - an implementation of null free array checks using the storage
> properties encoded on the class pointer. This uses a new node type
> GetNullFreePropertyNode that takes a LoadKlass or LoadNKlass as
> input. Masking out the property bits, extracting the null free bit is
> done at final graph reshaping time. Checking whether an array is
> flattened is not implemented with storage properties yet.
> - to guarantee known accesses to flattened arrays are not incorrectly
> reordered with flattened accesses hidden behind Object arrays, at
> parse time, all flattened array accesses are now on a unique new slice
> (for type TypeAryPtr::VALUES). When the access is on an Object
> array, membars on the TypeAryPtr::VALUES slice are added around the
> runtime call that performs the unknown value load/store. Once parse
> time is over and the compiler is aware of all accesses to flattened
> arrays in the compile unit, a pass is performed to move each field
> access for each flattened array to their own slice (the way the IR
> graph is currently built at parse time). The membars for Object
> arrays are duplicated, one per slice so proper orderin between
> accesses is still guaranteed. This should help performance because
> there's no wide membar that prevents c2 from optimizing memory
> - loading the layout helper from the klass structure is now performed
> on immutable memory so it can be hoisted.
> - loop unswitching is extended so rather than clone loops for each
> flattened array check (and produce 2^n loops for n accesses), it
> produces 2 copies of the loop: one loop with no flattened array check
> for legacy array accesses and another for flattened array accesses
> that still contain flattened array check if the loop has more than 1
> array access.
> - The control for array loads is also now always set to the null check
> or array bound check for the access so after unswitching, the body of
> the reference access loops is identical to the loop we would get when
> running with -EnableValhalla.
> - Not using a newly allocated value buffer for an unknown flattened load
> before it's fully initialized is now guaranteed with a StoreStore
> membar on raw memory and a CastPP that flagged as carrying a
> - MonomorphicArrayCheck is also improved so the casted array's type is
> propagated during parsing.
> - a fix for replay compilation
> Upstream 8173196 that's being reviewed hotspot-compiler-dev is also
> needed to recover performance.
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