RFR: JDK-8277178: Reduce the priority of data dependent nodes when OptoScheduling enabled [v6]

[Vladimir Kozlov]

On Thu, 13 Jan 2022 09:02:06 GMT, SUN Guoyun <duke at openjdk.java.net> wrote:

>> when doing gcm/lcm, We should not only consider the height of nodes(latency), but also consider whether there is data dependency between nodes. When there is data dependency between two nodes and the delay of the previous node is large, another node without data dependency can be considered inserting between the two nodes. For example:
>> for java code
>> <pre><code class="java">
>>     public static final double fval = 2.00;
>>     public static double[] A = new double[N];
>>     public static int[] B = new int[N];
>> 
>>     public static void testP(){
>> 	for (int i=0; i<N; i++) {
>> 	   A[i] += A[i] * fval;
>> 	   B[i] += B[i]+2;
>>         }
>>     }
>> </code></pre>
>> 
>> when use `-XX:+OptoScheduling` in aarch64, the sequence is
>> <pre><code class="shell">
>> 190     B15: #	out( B15 B16 ) <- in( B14 B15 ) Loop( B15-B15 inner main of N118 strip mined) Freq: 9.9999e+11
>> 190     sxtw  R13, R15	# i2l
>> 194 +   add R14, R17, R13, LShiftL #3	# ptr
>> 198     ldrd  V16, [R14, #16]	# double
>> 19c +   fmuld   V18, V16, V17
>> 1a0 +   faddd   V16, V18, V16
>> 1a4     strd  V16, [R14, #16]	# double
>> 1a8 +   add R13, R0, R13, LShiftL #2	# ptr
>> 1ac +   ldrw  R1, [R13, #16]	# int
>> 1b0 +   addw  R14, R1, R1
>> 1b4 +   addw R1, R14, #2
>> 1b8 +   addw R15, R15, #1
>> 1bc     strw  R1, [R13, #16]	# int
>> 1c0 +   cmpw  R15, R12
>> 1c4     blt B15 	// counted loop end  P=1.000000 C=40960.000000
>> </code></pre>
>> 
>> Then a more efficient sequence should be:
>> <pre><code class="shell">
>> 190     B15: #	out( B15 B16 ) <- in( B14 B15 ) Loop( B15-B15 inner main of N118 strip mined) Freq: 9.9999e+11
>> 190     sxtw  R13, R14	# i2l
>> 194     add R15, R17, R13, LShiftL #3	# ptr
>> 198     add R13, R0, R13, LShiftL #2	# ptr
>> 19c     ldrd  V16, [R15, #16]	# double
>> 1a0     ldrw  R2, [R13, #16]	# int
>> 1a4     fmuld   V18, V16, V17
>> 1a8     addw  R1, R2, R2
>> 1ac     faddd   V16, V18, V16
>> 1b0     strd  V16, [R15, #16]	# double
>> 1b4     addw R1, R1, #2
>> 1b8     strw  R1, [R13, #16]	# int
>> 1bc     addw R14, R14, #1
>> 1c0     cmpw  R14, R12
>> 1c4     blt B15 	// counted loop end  P=1.000000 C=40960.000000
>> </code></pre>
>> 
>> This problem also exists in MIPS architecture. This is a patch to fix this problem. Please help review it.
>> Thanks
>
> SUN Guoyun has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:
> 
>   8277178: Reduce the priority of data dependent nodes when OptoScheduling enabled

I asked our performance experts and they observed before variations I saw on Aarch64. It seems they are not caused by your changes.

You did not answered by suggestion about added `C->do_scheduling()` check.

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PR: https://git.openjdk.java.net/jdk/pull/6407