RFR: 8352415: x86: Tighten up template interpreter method entry code

[Coleen Phillimore]

On Wed, 19 Mar 2025 13:44:40 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Interpreter performance is the still important for faster startup, since it would carry application until compilers kick in. After looking at Leyden scenarios in Xint mode, I believe incremental improvements are possible in template interpreter to make it faster.
> 
> One of those improvements is tightening up method entry code. Profiling shows the hottest path in the whole ordeal for non-native methods is resolving the Java mirror to store the GC root for currently executing Method*. It involves 4-5 chained memory accesses, which incurs significant latency.
> 
> We can massage the code to reuse some memory accesses and also spread them out to allow more latency-hiding hardware mechanisms to kick in.
> 
> Additional testing:
>  - [x] Ad-hoc `-Xint` benchmarks
>  - [x] Linux x86_64 server fastdebug, `all`

Sorry I was away and didn't see this.  For the record, it looks good.  I liked the load_mirror macro assembler function but it did redundant work.

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PR Review: https://git.openjdk.org/jdk/pull/24114#pullrequestreview-2729165704