How to add a new intrinsic

[Aleksey Shipilev]

Hi Jaromir,

On 11/09/2014 09:53 PM, Jaromir Hamala wrote:
> I do not have ambitions to include it in OpenJDK,

Why not? Please follow the step 0 from here:
http://openjdk.java.net/contribute/ -- submit the OCA.


> but I greatly appreciate any feedback / help. I guess the next step
> for me is to include C1 and eventually C2 support - again - any
> pointers are very highly appreciated!

This may be a shortest example for simple Unsafe intrinsic handled in
interpreter, C1 and C2 (notice how much shorter the interpreter code is,
since we "just" use the native methods as interpreter handlers):
  http://hg.openjdk.java.net/jdk8/jdk8/jdk/rev/ad6097d547e1
  http://hg.openjdk.java.net/jdk8/jdk8/hotspot/rev/1e41b0bc58a0


IIRC, for C1, you would need to:

 1) Handle the intrinsic in LIRGenerator::do_Intrinsic
(c1_LIRGenerator.cpp), it should add the nodes to C1 IR, see e.g.
membar_acquire(). You will have to create a new LirOp, with 0 arguments,
in LIR_Code enum, say, "lir_pause".

 2) Lower the lir_pause to machine code in LIR_Assembler::emit_op0 (see
c1_LIRAssembler.cpp). There should be a call to macro-assembler defining
the PAUSE instruction.


For C2, you would need to:

 1) Add the intrinsic definitions and intrinsic code into
library_call.cpp/hpp. It would be easier to follow the code for some
already-existing simple intrinsic, see e.g. inline_unsafe_prefetch. Your
code should emit a new, special-named IR node, say, PauseNode.

 2) Add the matching rule for PauseNode into architecture description
file (x86_32.ad or x86_64.ad). This file matches the IR node to the
concrete machine code to emit. It is usually macroed into assembler
call. E.g. PrefetchRead node with mem argument is matched to
Assembler::prefetchr in assembler_x86.cpp. There, the exact machine code
is emitted.


I think this is enough to make a working example.

-Aleksey.