RFR: AArch64: 8179954: AArch64: C1 and C2 volatile accesses are not sequentially consistent

[White, Derek]

So good news - you made getstatic 5x faster. Bad news - only in the interpreter.

So this one goes out to all the static initializers!

Actual code review question:
In templateTable_aarch64.cpp:
  Line 2411: We tbz on flags.
  Line 2423: We extract into flags.
  Line 2547: We tbz on flags. 
    - Is the volatile bit still in flags? 

Thanks!

 - Derek

-----Original Message-----
From: Andrew Haley [mailto:aph at redhat.com] 
Sent: Wednesday, May 10, 2017 10:19 AM
To: White, Derek <Derek.White at cavium.com>; Aleksey Shipilev <shade at redhat.com>; hotspot-dev Source Developers <hotspot-dev at openjdk.java.net>
Subject: Re: RFR: AArch64: 8179954: AArch64: C1 and C2 volatile accesses are not sequentially consistent

So you were right.  Dammit.  :-)

This test:

    @State(Scope.Benchmark)
    public static class BenchmarkState {
        static int nn = 99;
    }
    @Benchmark
    public int testMethod(BenchmarkState state) {
        return state.nn;
    }

Interpreter-only, before my patch:

Benchmark               Mode  Cnt   Score   Error  Units
MyBenchmark.testMethod  avgt    5  92.938 ? 0.870  ns/op

After my patch, it's slower:

# Run complete. Total time: 00:00:07

Benchmark               Mode  Cnt   Score   Error  Units
MyBenchmark.testMethod  avgt    5  94.518 ? 0.562  ns/op

But if I insert conditional branches around the fences as you suggest, the result is much better:

Benchmark               Mode  Cnt   Score   Error  Units
MyBenchmark.testMethod  avgt   25  83.825 ? 0.161  ns/op

New patch at http://cr.openjdk.java.net/~aph/8179954-2/

OK?

Andrew.