RFR: 8330153: C2: dump barrier information for all Mach nodes [v2]

[Roberto Castañeda Lozano]

On Mon, 15 Apr 2024 07:04:11 GMT, Roberto Castañeda Lozano <rcastanedalo at openjdk.org> wrote:

>> This debug-only changeset ensures that GC-specific barrier information is dumped (via [`BarrierSetC2::dump_barrier_data()`](https://github.com/openjdk/jdk/blob/aebfd53e9d19f5939c81fa1a2fc75716c3355900/src/hotspot/share/gc/shared/c2/barrierSetC2.hpp#L311-L313)) for all C2 Mach nodes, not just `MachType` ones. This makes it possible to e.g. write IR tests that verify barrier properties of `CompareAndSwap`/`WeakCompareAndSwap` Mach implementations, which do not inherit from `MachTypeNode`. An example of such a test can be found [here](https://github.com/robcasloz/jdk/blob/e9b3c2a4cb5dd80d85af8320e559acea5920b2ff/test/hotspot/jtreg/compiler/gcbarriers/TestG1BarrierGeneration.java#L283-L292).
>> 
>> The [following program](https://bugs.openjdk.org/secure/attachment/108921/Example.java) illustrates the effect of the change:
>> 
>> 
>> import java.lang.invoke.VarHandle;
>> import java.lang.invoke.MethodHandles;
>> 
>> public class Example {
>>     static class Outer {
>>         Object f;
>>     }
>> 
>>     static final VarHandle fVarHandle;
>>     static {
>>         MethodHandles.Lookup l = MethodHandles.lookup();
>>         try {
>>             fVarHandle = l.findVarHandle(Outer.class, "f", Object.class);
>>         } catch (Exception e) {
>>             throw new Error(e);
>>         }
>>     }
>> 
>>     static boolean testCompareAndSwap(Outer o, Object oldVal, Object newVal) {
>>         return fVarHandle.compareAndSet(o, oldVal, newVal);
>>     }
>> 
>>     public static void main(String[] args) {
>>         for (int i = 0; i < 10_000; i++) {
>>             Outer o = new Outer();
>>             Object oldVal = new Object();
>>             o.f = oldVal;
>>             Object newVal = new Object();
>>             testCompareAndSwap(o, oldVal, newVal);
>>         }
>>     }
>> }
>> 
>> 
>> Before this changeset, issuing this command:
>> 
>> 
>> $ java -Xbatch -XX:+UseZGC -XX:+ZGenerational -XX:CompileOnly=Example::testCompareAndSwap -XX:CompileCommand=PrintIdealPhase,Example::testCompareAndSwap,FINAL_CODE Example.java | grep zCompareAndSwapP
>> 
>> 
>> gives the following dump:
>> 
>> 
>>  R10     37  zCompareAndSwapP  === 28 35 38 54 22 41  [[ 40 42 36 27 56 25 ]]  !jvms: VarHandleReferences$FieldInstanceReadWrite::compareAndSet @ bci:44 (line 180) VarHandleGuards::guard_LLL_Z @ bci:50 (line 68) Example::testCompareAndSwap @ bci:6 (line 20)
>> 
>> 
>> After this changeset, we get:
>> 
>> 
>>  R10     37  zCompareAndSwapP  === 28 35 38 54 22 41  [[ 40 42 36 27 56 25 ]]  barrier(strong )  !jvms: VarHandleRefer...
>
> Roberto Castañeda Lozano has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add example

Thanks for reviewing, Tobias!

@vnkozlov: I added a simple IR test as requested, could I get a second review? Thanks!

-------------

PR Comment: https://git.openjdk.org/jdk/pull/18754#issuecomment-2068919807