RFR: 8286104: use aggressive liveness for unstable_if traps [v15]

[Vladimir Kozlov]

On Wed, 29 Jun 2022 05:23:40 GMT, Xin Liu <xliu at openjdk.org> wrote:

>> I found that some phi nodes are useful because its uses are uncommon_trap nodes. In worse case, it would hinder boxing object eliminating and scalar replacement. Test.java of JDK-8286104 reveals this issue. This patch allows c2 parser to collect liveness based on next bci for unstable_if traps.  In most cases, next bci is closer to exits, so live locals are diminishing.  It helps to reduce the number of inputs of unstable_if traps. 
>> 
>> This is not a REDO of Optimization of Box nodes in uncommon_trap(JDK-8261137). Two patches are orthogonal.  I adapt test from [TestEliminateBoxInDebugInfo.java](https://github.com/openjdk/jdk/pull/2401/files#diff-49b2e38825aa4c28ca196bdc70c3cbecc2e835c2899f4f393527df4796b177ea), so part of credit goes to the original author.  I found that Scalar replacement can take care of the object `Integer ii = Integer.valueOf(value)` in original test even it can't be removed by later inliner.  I tweak the profiling data of Integer.valueOf() to hinder scalar replacement. 
>> 
>> This patch can cover the problem discovered by JDK-8261137. I ran the microbench and got 9x speedup on x86_64. It's almost same as JDK-8261137.  Besides runtime, the codecache utilization reduces from 1648 bytes to 1192 bytes, or 27.6%
>> 
>> Before:  
>> 
>> Benchmark               Mode  Cnt   Score   Error  Units
>> MyBenchmark.testMethod  avgt   10  32.776 ± 0.075  us/op
>> 
>> Compiled method (c2)     281  636       4       MyBenchmark::testMethod (50 bytes)
>>  total in heap  [0x00007fa1e49ab510,0x00007fa1e49abb80] = 1648
>>  relocation     [0x00007fa1e49ab670,0x00007fa1e49ab6b0] = 64
>>  main code      [0x00007fa1e49ab6c0,0x00007fa1e49ab940] = 640
>>  stub code      [0x00007fa1e49ab940,0x00007fa1e49ab968] = 40
>>  oops           [0x00007fa1e49ab968,0x00007fa1e49ab978] = 16
>>  metadata       [0x00007fa1e49ab978,0x00007fa1e49ab990] = 24
>>  scopes data    [0x00007fa1e49ab990,0x00007fa1e49aba60] = 208
>>  scopes pcs     [0x00007fa1e49aba60,0x00007fa1e49abb30] = 208
>>  dependencies   [0x00007fa1e49abb30,0x00007fa1e49abb38] = 8
>>  handler table  [0x00007fa1e49abb38,0x00007fa1e49abb68] = 48
>>  nul chk table  [0x00007fa1e49abb68,0x00007fa1e49abb80] = 24
>> 
>> After: 
>> 
>> Benchmark               Mode  Cnt   Score   Error  Units
>> MyBenchmark.testMethod  avgt   10  3.656 ± 0.006  us/op
>> 
>> Compiled method (c2)     288  633       4       MyBenchmark::testMethod (50 bytes)
>>  total in heap  [0x00007f35189ab010,0x00007f35189ab4b8] = 1192
>>  relocation     [0x00007f35189ab170,0x00007f35189ab1a0] = 48
>>  main code      [0x00007f35189ab1a0,0x00007f35189ab360] = 448
>>  stub code      [0x00007f35189ab360,0x00007f35189ab388] = 40
>>  oops           [0x00007f35189ab388,0x00007f35189ab390] = 8
>>  metadata       [0x00007f35189ab390,0x00007f35189ab398] = 8
>>  scopes data    [0x00007f35189ab398,0x00007f35189ab408] = 112
>>  scopes pcs     [0x00007f35189ab408,0x00007f35189ab488] = 128
>>  dependencies   [0x00007f35189ab488,0x00007f35189ab490] = 8
>>  handler table  [0x00007f35189ab490,0x00007f35189ab4a8] = 24
>>  nul chk table  [0x00007f35189ab4a8,0x00007f35189ab4b8] = 16
>>  ```
>> 
>> Testing
>> I ran tier1 test with and without `-XX:+DeoptimizeALot`. No regression has been found yet.
>
> Xin Liu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   restore the option OptimizeUnstableIf to diagnostic.
>   
>   also update commments.

Looks good. I ran it through tier1 to make sure this last change did not break it.

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.org/jdk/pull/8545