RFR: 8282204: Use lea instructions for arithmetic operations on x86_64 [v4]

[Jie Fu]

On Thu, 24 Feb 2022 12:16:58 GMT, Quan Anh Mai <duke at openjdk.java.net> wrote:

>> Hi,
>> 
>> This patch adds several matching rules for x86_64 backend to use `lea` instructions for several fused arithmetic operations. Also, `lea`s don't kill flags and allow different `dst` and `src`, so it is preferred over `sll` if possible, too. 
>> 
>> Thank you very much.
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add benchmark

test/micro/org/openjdk/bench/vm/compiler/LeaInstruction.java line 32:

> 30: @BenchmarkMode(Mode.AverageTime)
> 31: @OutputTimeUnit(TimeUnit.NANOSECONDS)
> 32: @Fork(value = 2, jvmArgsAppend = {"-XX:LoopUnrollLimit=1"})

Why we need `-XX:LoopUnrollLimit=1`?

test/micro/org/openjdk/bench/vm/compiler/LeaInstruction.java line 43:

> 41:         int x = this.x;
> 42:         for (int i = 0; i < ITERATION; i++) {
> 43:             x = x * 4 + 10;

Do we need `bh.consume(x)` here?

test/micro/org/openjdk/bench/vm/compiler/LeaInstruction.java line 53:

> 51:             x = x + y + 10;
> 52:             y = x + y + 20;
> 53:             bh.consume(x);

I would suggest `bh.consume` to be out of the for loop.

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PR: https://git.openjdk.java.net/jdk/pull/7560