RFR: 8283694: Improve several operations on x86 [v3]

[Quan Anh Mai]

> Hi, this patch improves some operations on x86_64:
> 
> - Base variable scalar shifts have bad performance implications and should be replaced by their bmi2 counterparts if possible:
>   + Bounded operands
>   + Multiple uops both in fused and unfused domains
>   + May result in flag stall since the operations have unpredictable flag output
> 
> - Flag to general-purpose registers operation currently uses `cmovcc`, which requires set up and 1 more spare register for constant, this could be replaced by set, which transforms the sequence:
> 
>         xorl dst, dst
>         sometest
>         movl tmp, 0x01
>         cmovlcc dst, tmp
> 
>         into:
> 
>         sometest
>         setbcc dst
>         movzbl dst, dst
> 
> This sequence does not need a spare register and without any drawbacks.
> (Note: `movzx` is often elided and thus has 0 latency)
> 
> - Some small improvements:
>   + Add memory variances to `tzcnt` and `lzcnt`
>   + Add memory variances to `rolx` and `rorx`
>   + Add missing `rolx` rules (note that `rolx dst, imm` is actually `rorx dst, size - imm`)
> 
> The speedup can be observed for variable shift instructions
> 
>         Before:
>         Benchmark               (size)  Mode  Cnt   Score   Error  Units
>         Integers.shiftLeft         500  avgt    5   0.836 ± 0.030  us/op
>         Integers.shiftRight        500  avgt    5   0.843 ± 0.056  us/op
>         Integers.shiftURight       500  avgt    5   0.830 ± 0.057  us/op
>         Longs.shiftLeft            500  avgt    5   0.827 ± 0.026  us/op
>         Longs.shiftRight           500  avgt    5   0.828 ± 0.018  us/op
>         Longs.shiftURight          500  avgt    5   0.829 ± 0.038  us/op
> 
>         After:
>         Benchmark               (size)  Mode  Cnt   Score   Error  Units
>         Integers.shiftLeft         500  avgt    5   0.761 ± 0.016  us/op
>         Integers.shiftRight        500  avgt    5   0.762 ± 0.071  us/op
>         Integers.shiftURight       500  avgt    5   0.765 ± 0.056  us/op
>         Longs.shiftLeft            500  avgt    5   0.755 ± 0.026  us/op
>         Longs.shiftRight           500  avgt    5   0.753 ± 0.017  us/op
>         Longs.shiftURight          500  avgt    5   0.759 ± 0.031  us/op
> 
> For `cmovcc 1, 0`, I have not been able to create a reliable microbenchmark since the benefits are mostly regarding register allocation.
> 
> Thank you very much.

Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:

  cisc

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7968/files
  - new: https://git.openjdk.java.net/jdk/pull/7968/files/e970a2a5..2e537bf2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7968&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7968&range=01-02

  Stats: 12 lines in 1 file changed: 6 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7968.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7968/head:pull/7968

PR: https://git.openjdk.java.net/jdk/pull/7968