RFR: 8252505: C1/C2 compiler support for blackholes [v11]

Vladimir Ivanov vladimir.x.ivanov at oracle.com
Thu Dec 3 11:54:20 UTC 2020


I like it! Very informative.

Best regards,
Vladimir Ivanov

On 03.12.2020 14:45, Aleksey Shipilev wrote:
> On 12/2/20 6:21 PM, Vladimir Ivanov wrote:
>>
>>> So where do we go from here? Somehow recording the operands of
>>> MachCallBlackhole?
>>
>> Have you tried `PhaseRegAlloc::dump_register(const Node *n, char *buf)`
>> on argument inputs?
> 
> Yes, new commit has it. For the sample method like:
> 
>      public void test_08(Blackhole bh) {
>          bh.consume(x + y);
>          bh.consume(x + y);
>          ...
> 
> -XX:+PrintOptoAssembly finally looks like this:
> 
> 02c     movl    R11, [RSI + #16 (8-bit)]        # int ! Field: 
> org/openjdk/jmh/samples/XplusY.y
> 030     addl    R11, [RSI + #12 (8-bit)]        # int
> 034     blackhole RDX, R11
> 
> 034     movl    R11, [RSI + #16 (8-bit)]        # int ! Field: 
> org/openjdk/jmh/samples/XplusY.y
> 038     addl    R11, [RSI + #12 (8-bit)]        # int
> 03c     blackhole RDX, R11
> 
> RDX is receiver ("bh"), and R11 is "x + y".
> 


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