RFR: 8255553: [PPC64] Introduce and use setbc and setnbc P10 instructions

[Martin Doerr]

On Wed, 28 Oct 2020 17:00:43 GMT, Ziviani <github.com+670087+jrziviani at openjdk.org> wrote:

> - setbc RT,BI: sets RT to 1 if CR(BI) is 1, otherwise 0.
> - setnbc RT,BI: sets RT to -1 if CR(BI) is 1, otherwise 0.
> Ref: PowerISA 3.1, page 129.
> 
> These instructions are particularly interesting to improve the following
> pattern `(src1<src2)? -1: ((src1>src2)? 1: 0)`, which can be found in
> `instruct cmpL3_reg_reg_ExEx()@ppc.ad`, by removing its branches.
> 
> Long.toString, that generate such pattern in getChars, has showed a
> good performance gain by using these new instructions.
> 
> Example:
> for (int i = 0; i < 200_000; i++)
>   res = Long.toString((long)i);
> 
> java -Xcomp -XX:CompileThreshold=1 -XX:-TieredCompilation TestToString
> 
> Without setbc (average): 0.1178 seconds
> With setbc (average): 0.0396 seconds

If you just want to add C1 code, I suggest to do that in this PR.
It's up to you if you prefer a new PR for further changes. I still think cleaning up the ad file a bit and using branch free code for all Power processors would be nice. I'd also be ok with replacing the "expand" code by assembly code directly in "ins_encode". Should be good enough for modern out-of-order processors.

src/hotspot/cpu/ppc/ppc.ad line 11521:

> 11519:     __ setbc(R0, (($crx$$reg << 2) | 1) /* greater than */);
> 11520:     __ setnbc($dst$$Register, ($crx$$reg << 2) /* less than */);
> 11521:     __ or_unchecked($dst$$Register, $dst$$Register, R0);

In general, I think it'd be better to use orr which makes sure we never unintentionally emit an instruction which modifies smt priority "smt_prio_...". In this case dst != R0, so this doesn't happen.

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PR: https://git.openjdk.java.net/jdk/pull/907