Integrated: 8256827: C2: Avoid reallocations by pre-sizing lists in post_allocate_copy_removal

[Claes Redestad]

On Sun, 22 Nov 2020 01:05:28 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> By pre-sizing the Node_Lists created in PhaseChaitin::post_allocate_copy_removal we avoid all re-allocations. 
> 
> As lists are allocated to the size we need we might also reduce memory waste, which reduce memory used by these structures by up to 50%
> 
> Throughput wise this is also a gain and saves about 10,000 instructions per C2 compilation in SimpleRepeatCompilation.trivialMath. By using bulk clearing, avoiding redundant clearing of newly created lists and adding a shallow copy routine to Node_List we save another ~9,500 instructions per compilation in the same benchmark. This corresponds with a small but statistically significant gain:
> 
> Benchmark                                      Mode  Cnt    Score   Error  Units
> SimpleRepeatCompilation.trivialMath_repeat_c2    ss   50  355.342 ± 2.069  ms/op # baseline
> SimpleRepeatCompilation.trivialMath_repeat_c2    ss   50  350.705 ± 1.577  ms/op # patch
> 
> Testing: tier1-4

This pull request has now been integrated.

Changeset: b450e7c1
Author:    Claes Redestad <redestad at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/b450e7c1
Stats:     51 lines in 3 files changed: 13 ins; 14 del; 24 mod

8256827: C2: Avoid reallocations by pre-sizing lists in post_allocate_copy_removal

Reviewed-by: kvn, thartmann

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PR: https://git.openjdk.java.net/jdk/pull/1370